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Adaptive significance of variation in vertebral number in fishes : evidence in Gasterosteus aculeatus.. 1986

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ADAPTIVE SIGNIFICANCE OF VARIATION IN VERTEBRAL NUMBER IN FISHES: EVIDENCE IN Gasterosteus a c u l e a t u s AND M y l o c h e i l u s c a u r i n u s By DOUGLAS PAUL SWAIN B.Sc.(Hons.), The U n i v e r s i t y of Manitoba, 1975 M.Sc, The U n i v e r s i t y of Manitoba, 1979 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY in THE FACULTY OF GRADUATE STUDIES (Department of Zoology) We accept t h i s t h e s i s as conforming to the r e q u i r e d standard THE © UNIVERSITY OF BRITISH COLUMBIA November 1986 Douglas Paul Swain, 1986 In p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t of the requirements f o r an advanced degree at the U n i v e r s i t y o f B r i t i s h Columbia, I agree t h a t the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and study. I f u r t h e r agree t h a t p e r m i s s i o n f o r e x t e n s i v e copying o f t h i s t h e s i s f o r s c h o l a r l y purposes may be granted by the head o f my department or by h i s or her r e p r e s e n t a t i v e s . I t i s understood t h a t copying or p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l gain s h a l l not be allowed without my w r i t t e n p e r m i s s i o n . Department o f ? o o L O & V The U n i v e r s i t y of B r i t i s h Columbia 1956 Main Mall Vancouver, Canada V6T 1Y3 DE-6 (3/81) i i A b s t r a c t V a r i a t i o n i n v e r t e b r a l number i s widespread i n f i s h e s , and i s p a r t l y g e n e t i c i n o r i g i n . I t s a d a p t i v e s i g n i f i c a n c e was t e s t e d i n young t h r e e s p i n e s t i c k l e b a c k s Gasterosteus a c u l e a t u s by p r e d a t i o n experiments and by d i r e c t measurements of swimming performance, and i n young peamouth chub M y l o c h e i l u s c a u r i n u s by p r e d a t i o n experiments. Counts of w i l d f r y grouped by l e n g t h or age were examined for evidence of s e l e c t i o n f o r v e r t e b r a l number in the w i l d . S u r v i v a l of s t i c k l e b a c k s exposed to p r e d a t i o n by s u n f i s h Lepomis gibbosus was g r e a t e r f o r f i s h with 31 TV ( t o t a l v e r t e b r a e ) than f o r those with 32 TV at lengths of 8.1-8.3 mm (mean at end of experiments), but not at s m a l l e r (7.6 mm) or l a r g e r (8.9-11.2 mm) l e n g t h s , u s i n g f i s h from e i t h e r Holden or Kennedy Lake, B.C. Among Holden Lake s t i c k l e b a c k s , g r e a t e r s u r v i v a l of f i s h with 31 TV at small lengths (8.1-8.3 mm) was due to f i s h with a high r a t i o of 14AV/17CV (abdominal/caudal v e r t e b r a e ) . At intermediate (9.8-10.0 mm) or l a r g e (11.2 mm) l e n g t h s , s u r v i v a l was g r e a t e s t f o r f i s h with intermediate (14/18, 13/17) or low (13/18) r a t i o s , r e s p e c t i v e l y . Among Kennedy Lake s t i c k l e b a c k s , the r a t i o s at advantage d u r i n g p r e d a t i o n a l s o decreased as prey s i z e i n c r e a s e d , but higher r a t i o s were favoured at a given s i z e . S e l e c t i v e p r e d a t i o n f o r v e r t e b r a l number or r a t i o was not a t t r i b u t a b l e to s i z e s e l e c t i o n or s e l e c t i o n f o r body p r o p o r t i o n s (precaudal/caudal or abdominal/caudal l e n g t h s ) , and d i d not vary between cover (presence/absence) or temperature (15/ 20 or 25C) treatments. Burst swimming performance of Holden Lake s t i c k l e b a c k s at 15C was s u p e r i o r among f r y with a h i g h r a t i o of 14AV/17CV at s m a l l lengths (7.4-7.8 mm), among those with an i n t e r m e d i a t e r a t i o (14/18) at intermediate l e n g t h s (7.8-8.3 mm), and among those with a low r a t i o (13/18) at l a r g e lengths (8.3-9.0 mm). At even l a r g e r lengths (9.0-11.5 mm), performance was u n r e l a t e d to AV/CV. E f f e c t s of AV/CV were s i m i l a r at 25C, except that f r y with h i g h or intermediate r a t i o s were s u p e r i o r at s l i g h t l y s h o r t e r lengths at t h i s higher temperature. The e f f e c t of AV/CV on performance d i f f e r e d g r e a t l y between water and an 0.1% s o l u t i o n of m e t h y l c e l l u l o s e at 15C. E f f e c t s of AV/CV c o u l d not be a t t r i b u t e d to e f f e c t s of p r e c a u d a l / c a u d a l l e n g t h r a t i o . D i f f e r e n c e s between p r e d a t i o n and swimming performance experiments i n the lengths a t which p a r t i c u l a r r a t i o s were opt i m a l probably r e f l e c t e d growth and the c o n c e n t r a t i o n of m o r t a l i t y at s m a l l e r lengths d u r i n g p r e d a t i o n experiments. V e r t e b r a l counts of w i l d s t i c k l e b a c k f r y i n Holden Lake i n d i c a t e d s e l e c t i o n f a v o u r i n g a h i g h r a t i o (14AV/17CV) and a low t o t a l count (31) at small l e n g t h s (7.3-7.8 mm), and i n t e r m e d i a t e r a t i o s (14/18, 13/17) and a h i g h t o t a l count (32) at s l i g h t l y l a r g e r l engths (7.8-8.3 mm). S u r v i v a l of peamouth chub d u r i n g p r e d a t i o n by s u n f i s h or smallmouth bass M i c r o p t e r u s dolomieui was g r e a t e r f o r f i s h with 44 TV than f o r those with 45 TV at l e n g t h s of 10.8-11.1 mm (mean at end of experiments), but not at smaller l e n g t h s (when v e r t e b r a e of most f r y were undeveloped). S e l e c t i o n f o r v e r t e b r a l number c o u l d not be a t t r i b u t e d to s i z e s e l e c t i o n by p r e d a t o r s . i v S e l e c t i o n i n the w i l d favoured f r y with 44 TV at smal l lengths (9.3-9.9 mm), those with 45 TV at s l i g h t l y l a r g e r lengths (9.9-10.6 mm), and n e i t h e r number at even l a r g e r lengths (10.6-14.0 mm). E f f e c t s of v e r t e b r a l number on performance may i n v o l v e optimal a n t e r o p o s t e r i o r g r a d i e n t s i n f l e x i b i l i t y . E x p l a n a t i o n s are suggested f o r pleomerism and Jordan's r u l e , i n terms of s e l e c t i o n o p e r a t i n g on the l a r v a e or f r y soon a f t e r h a t c h i n g . R e s u l t s are r e l a t e d to the maintenance of v a r i a t i o n i n v e r t e b r a l number w i t h i n p o p u l a t i o n s , and to the p o s s i b l e a d a p t i v e s i g n i f i c a n c e of e n v i r o n m e n t a l l y induced v a r i a t i o n i n v e r t e b r a l number. V Table of Contents Page A b s t r a c t • i i L i s t of Tables v i i L i s t of F i g u r e s x i Acknowledgements x i v I n t r o d u c t i o n 1 Part I. P r e d a t i o n experiments with t h r e e s p i n e s t i c k l e b a c k s .. 5 M a t e r i a l and Methods 5 R e s u l t s 14 T o t a l v e r t e b r a e 14 1. Kennedy Lake experiments 14 2. Holden Lake experiments 18 3. Summary 24 Abdominal and cau d a l v e r t e b r a e 27 1. Holden Lake experiments 27 2. Kennedy Lake experiments 36 3. Summary 41 Body p r o p o r t i o n s 43 1 . Holden Lake experiments 43 2. Kennedy Lake experiments 50 3 . Summary . 56 Part I I . Burst swimming performance of t h r e e s p i n e s t i c k l e b a c k s 57 M a t e r i a l and Methods 57 R e s u l t s 61 Abdominal and cau d a l v e r t e b r a e 61 1. Performance at 15C 61 2. Performance at 25C 68 v i Table of contents c o n t i n u e d ... 3. Performance at 15C i n 0.1% m e t h y l c e l l u l o s e 74 Body p r o p o r t i o n s 81 Summary 83 Part I I I . Changes i n v e r t e b r a l count with l e n g t h i n w i l d s t i c k l e b a c k f r y 84 M a t e r i a l and Methods 84 R e s u l t s 87 Part IV. P r e d a t i o n experiments with peamouth chub 102 M a t e r i a l and Methods 102 R e s u l t s 108 Part V. Changes i n v e r t e b r a l count with l e n g t h i n w i l d peamouth chub 120 M a t e r i a l and Methods 120 R e s u l t s 122 D i s c u s s i o n 147 Experiments with G a s t e r o s t e u s 147 Experiments with M y l o c h e i l u s 154 E f f e c t of v e r t e b r a l number on b u r s t swimming performance.. 156 Genetic c o n t r o l of the r a t i o of abdominal to caudal v e r t e b r a e 164 V a r i a t i o n among p o p u l a t i o n s 169 1. Pleomerism 169 2. Jordan's r u l e 175 V a r i a t i o n w i t h i n p o p u l a t i o n s 178 Developmental noi s e 181 Phenotypic p l a s t i c i t y 186 L i t e r a t u r e c i t e d 190 v i i L i s t of Tables Table Page 1. D e s c r i p t i o n of 1982 p r e d a t i o n experiments u s i n g Kennedy Lake s t i c k l e b a c k s as prey 7 2. D e s c r i p t i o n of 1983 p r e d a t i o n experiments u s i n g Holden Lake s t i c k l e b a c k s as prey 8 3. V e r t e b r a l counts of Kennedy Lake s t i c k l e b a c k s exposed or unexposed to p r e d a t i o n by s u n f i s h 15 4. Regressions between v e r t e b r a l count and l e n g t h i n 1982 experiments u s i n g Kennedy Lake s t i c k l e b a c k s 17 5. V e r t e b r a l counts of Holden Lake s t i c k l e b a c k s exposed or unexposed to p r e d a t i o n by s u n f i s h 19 6. Regression between v e r t e b r a l number and l e n g t h i n 1983 experiments u s i n g Holden Lake s t i c k l e b a c k s .. . 22 7. V e r t e b r a l count c l a s s e s i n c o n t r o l groups of Holden Lake p r e d a t i o n experiments, based on numbers of abdominal and caudal v e r t e b r a e 28 8. R a t i o s of abdominal to caudal v e r t e b r a e i n Holden Lake s t i c k l e b a c k s exposed or unexposed to p r e d a t i o n by s u n f i s h 29 9. R e l a t i o n s h i p between v e r t e b r a l count c l a s s and l e n g t h i n c o n t r o l groups i n Holden Lake experiments 33 10. R a t i o of abdominal to caudal v e r t e b r a e i n Holden Lake s t i c k l e b a c k s exposed or unexposed to p r e d a t i o n by s u n f i s h , and the r a t i o expected i n exposed f i s h i f p r e d a t i o n i s s e l e c t i v e f o r prey s i z e but not f o r the r a t i o AV/CV 35 11. V e r t e b r a l count c l a s s e s i n c o n t r o l groups of Kennedy Lake p r e d a t i o n experiments, based on numbers of abdominal and caudal v e r t e b r a e 37 v i i i L i s t of t a b l e s c o n t i n u e d . . . 12. R a t i o s of abdominal to caudal v e r t a b r a e i n Kennedy Lake s t i c k l e b a c k s exposed or unexposed to p r e d a t i o n by s u n f i s h 38 13. R a t i o s of abdominal to caudal v e r t e b r a e i n c o n t r o l groups i n Kennedy Lake experiments, at lengths l e s s than or equal to or g r e a t e r than the mean l e n g t h 42 14. Regression of the r a t i o of abdominal to c a u d a l v e r t e b r a e on the r a t i o of precaudal to caudal l e n g t h i n c o n t r o l and experimental groups of Holden Lake experiments 44 15. Body p r o p o r t i o n s of Holden Lake s t i c k l e b a c k s exposed or unexposed to p r e d a t i o n by s u n f i s h 47 16. Change i n p r e c a u d a l / c a u d a l l e n g t h r a t i o w i t h i n v e r t e b r a l count c l a s s e s i n Holden Lake s t i c k l e b a c k s a f t e r exposure to p r e d a t i o n i n 1983 49 17. Regression of v e r t e b r a l count r a t i o on l e n g t h r a t i o s i n Kennedy Lake f i s h 52 18. Body p r o p o r t i o n s of Kennedy Lake s t i c k l e b a c k s exposed or unexposed to p r e d a t i o n by s u n f i s h 55 19. S i g n i f i c a n c e of e f f e c t s of v e r t e b r a l count c l a s s on burst swimming performance of s t i c k l e b a c k f r y w i t h i n l e n g t h c l a s s e s at 15C 64 20. Regressions of swimming performance of s t i c k l e b a c k f r y on the r a t i o of abdominal to caudal v e r t e b r a e and t o t a l l e n g t h , w i t h i n l e n g t h c l a s s e s at 15C 66 21. C o e f f i c i e n t s of r e g r e s s i o n s of swimming performance of s t i c k l e b a c k f r y on l e n g t h , w i t h i n v e r t e b r a l count c l a s s e s 67 ix L i s t of t a b l e s c o n t i n u e d . . . 22. Regressions of swimming performance on the r a t i o of abdominal to caudal v e r t e b r a e (VR), on the p r e c a u d a l / c a u d a l l e n g t h r a t i o (LR), and on VR, LR and t o t a l l e n g t h , w i t h i n small or l a r g e l e n g t h c l a s s e s at 15C 82 23. V e r t e b r a l count c l a s s f r e q u e n c i e s (%) of s t i c k l e b a c k s 8.3 mm or l e s s i n l e n g t h , c o l l e c t e d from s i t e A between May 7 and 31, or between June 4 and 11 , 1984 94 24. D e s c r i p t i o n of p r e d a t i o n experiments u s i n g peamouth chub as prey 103 25. V e r t e b r a l development and a b n o r m a l i t i e s of peamouth chub s u r v i v i n g p r e d a t i o n experiments 106 26. V e r t e b r a l counts of f r y s u r v i v i n g or not s u r v i v i n g post- experimental r e a r i n g i n two groups from experiment 2 .... 109 27. Mean l e n g t h s of peamouth chub f r y exposed or unexposed to p r e d a t i o n 111 28. Regressions between v e r t e b r a l number and l e n g t h among pea- mouth chub f r y exposed or unexposed to p r e d a t i o n 112 29. V e r t e b r a l counts of peamouth chub f r y exposed or unexposed to p r e d a t i o n 116 30. V e r t e b r a l counts of peamouth chub f r y exposed or unexposed to p r e d a t i o n at small or l a r g e l e n g t h s i n experiments 3 and 5 118 31. V e r t e b r a l counts of peamouth chub f r y c o l l e c t e d from Hemer Creek between 2200 and 2300 h, i n May and June, 1984 125 32. V e r t e b r a l counts and lengths of peamouth chub f r y c o l l e c t e d from Hemer Creek at d i f f e r e n t times on the same night ... 128 X L i s t of t a b l e s c o n t i n u e d . . . 33. Percent of peamouth chub f r y with developed v e r t e b r a e , among those c o l l e c t e d from Holden Lake at the s i z e and on the date shown 132 34. V e r t e b r a l counts of peamouth chub f r y c o l l e c t e d from Holden Lake between May 14 and 31, 1984 133 35. V e r t e b r a l counts of s m a l l or l a r g e f r y i n cohort A, i n samples c o l l e c t e d between May 23 and 31 136 36. V e r t e b r a l counts of s m a l l or l a r g e f r y i n cohort A, on May 31 or June 4 142 37. V e r t e b r a l counts i n r e p l i c a t i o n s of groups with widely v a r y i n g e x t e n t s of r e a r i n g m o r t a l i t y 144 38. Growth r a t e s r e p o r t e d f o r l a r v a e and f r y of s e v e r a l f i s h s p e c i e s , i n the l a b o r a t o r y (L) or w i l d (W) 149 39. F i t s of two models f o r the g e n e t i c c o n t r o l of the r a t i o of abdominal to caudal v e r t e b r a e to counts observed in c o n t r o l groups of Holden Lake p r e d a t i o n experiments 166 x i L i s t of F i g u r e s F i g u r e Page 1. A x i a l s k e l e t o n of a t h r e e s p i n e s t i c k l e b a c k f r y 11 2. Change i n percent frequency of v e r t e b r a l counts i n s t i c k l e b a c k s exposed to p r e d a t i o n at v a r i o u s mean le n g t h s 25 3. Change i n percent frequency d u r i n g p r e d a t i o n of v e r t e b r a l count c l a s s e s based on the r a t i o of abdominal to caudal v e r t e b r a e , i n 1983 experiments with Holden Lake s t i c k l e - backs 30 4. Change i n percent frequency d u r i n g p r e d a t i o n of v e r t e b r a l count c l a s s e s based on the r a t i o AV/CV, i n 1982 e x p e r i - ments with Kennedy Lake s t i c k l e b a c k s 39 5. R a t i o s of precaudal/caudal l e n g t h i n v e r t e b r a l count c l a s s e s VR of Holden Lake s t i c k l e b a c k s exposed or un- exposed to pr e d a t i o n by s u n f i s h 45 6. R a t i o s of abdominal/caudal l e n g t h i n v e r t e b r a l count c l a s s e s VR' of Kennedy Lake s t i c k l e b a c k s exposed or un- exposed to p r e d a t i o n by s u n f i s h 53 7. Burst swimming performance at 15C of s t i c k l e b a c k f r y 6.6 - 9.0 mm i n len g t h i n 1983 (A) and 1984 (B) 62 8. Burst swimming performance at 15C of s t i c k l e b a c k f r y 9.0 - 11.5 mm i n len g t h i n 1983 (A), 1984 (B), and 1985 (C) 69 x i i L i s t of f i g u r e s c o n t i n u e d . . . 9. Burst swimming performance at 25C of s t i c k l e b a c k f r y 6.9 - 9.0 mm i n l e n g t h 72 10. Regressions of swimming performance on l e n g t h among s t i c k l e b a c k f r y with v e r t e b r a l count r a t i o s of 0.72 or 0.82 AV/CV, at 15C i n 1983 (A), at 15C i n 1984 (B), and at 25C i n 1984 (C) 75 11. Burst swimming performance of s t i c k l e b a c k f r y 6.6 - 9.0 mm i n l e n g t h i n an 0.1% s o l u t i o n of m e t h y l c e l l u l o s e at 1 5C 77 12. Map of Holden Lake, B.C., showing sampling s i t e s 85 13. Frequencies of v e r t e b r a l count c l a s s e s i n w i l d s t i c k l e - back f r y grouped by l e n g t h 88 14. Frequencies of v e r t e b r a l count c l a s s e s i n f r y l e s s than 7.4 mm i n l e n g t h , grouped by c o l l e c t i o n date 91 15. V e r t e b r a l count r a t i o s of s t i c k l e b a c k f r y i n two 'cohorts' at s i t e B, comparing counts i n l e n g t h c l a s s i on day 36 and l e n g t h c l a s s i + 1 on day 39 96 16. Percent f r e q u e n c i e s of t o t a l v e r t e b r a l counts, i n f r y grouped by l e n g t h at s i t e A or B 99 17. Regressions between v e r t e b r a l number and l e n g t h i n c o n t r o l and experimental groups, peamouth chub p r e d a t i o n e x p e r i - ments 3 - 5 114 18. Number of peamouth chub f r y c a p t u r e d per 5 min Surber sampler s e t , at 2200-2300 h i n Hemer Creek, 1984 123 19. Lengths of peamouth chub f r y c a p t u r e d i n Hemer Creek between 2200 and 2300 h 126 x i i i L i s t of f i g u r e s c o n t i n u e d . . . 20. Length d i s t r i b u t i o n s of peamouth chub f r y c o l l e c t e d from Holden Lake between May (M) 21 and June (J) 27, 1984 ... 130 21. Frequencies of f r y with 44 v e r t e b r a e , i n l e n g t h c l a s s e s of c o l l e c t i o n s between June 4 and 27 137 22. V e r t e b r a l counts of f r y i n cohort A, among f i s h r e a r e d a f t e r c o l l e c t i o n on May 31 and those preserved upon c o l l e c t i o n between June 4 and 27 140 23. A model e x p l a i n i n g pleomerism 170 24. C o n d i t i o n s under which mixed or pure s t r a t e g i e s are opt i m a l when there i s temporal v a r i a t i o n i n s e l e c t i o n .. 183 x i v Acknowledgements I t i s a p l e a s u r e to acknowledge the advice and generous support of my s u p e r v i s o r , Dr. C. C. L i n d s e y . Laboratory, o f f i c e and computing f a c i l i t i e s were p r o v i d e d by the P a c i f i c B i o l o g i c a l S t a t i o n at Nanaimo, B.C. I thank J . Blackburn, A. Solmie, Dr. W.C. C l a r k e and Dr. D.E. Hay f o r p r o v i d i n g these f a c i l i t i e s . C. Moore and A. Pronk a s s i s t e d i n the c o l l e c t i o n of s t i c k l e b a c k s from Kennedy Lake; I thank them and Dr. K. Hyatt f o r a r r a n g i n g t h i s a s s i s t a n c e . I thank C. Armstrong f o r the shocking d e v i c e used i n swimming performance experiments, and C. Haegele and Dr. L. Gass f o r the loan of photographic equipment. I thank E. Cameron (who counted about 500,000 chub v e r t e b r a e ) , C P . A r c h i b a l d , D. M i l l e r , G. M a l l e t t , and K. S h i l l i n g t o n f o r a s s i s t a n c e i n the l a b o r a t o r y , M. Hamer, S. M c K i n n e l l and P. Neaves f o r a s s i s t a n c e on the computer, R. M a l l e t t f o r a s s i s t a n c e i n the shop, and C. J . Foote and R. L e G u e r r i e r f o r a s s i s t a n c e i n the w i l d . Above a l l , I thank my wife E l i z a b e t h M a l l e t t f o r her understanding and support d u r i n g the course of t h i s study. F i n a n c i a l support from the N a t u r a l Sciences and E n g i n e e r i n g Research C o u n c i l of Canada, i n g r a n t s to C.C. Lindsey and a s c h o l a r s h i p to myself, and from the K i l l a m T r u s t i n a p r e d o c t o r a l f e l l o w s h i p i s g r a t e f u l l y acknowledged. 1 I n t r o d u c t i o n The a d a p t i v e s i g n i f i c a n c e of v a r i a t i o n w i t h i n s p e c i e s i s a c e n t r a l problem i n e v o l u t i o n a r y b i o l o g y . Present i n t e r e s t i n t h i s problem has been s t i m u l a t e d l a r g e l y by the d i s c o v e r y of vast amounts of allozyme v a r i a t i o n i n p o p u l a t i o n s (e.g., H a r r i s 1966; Lewontin and Hubby 1966). T h i s v a r i a b i l i t y , g r e a t e r than had been expected by p o p u l a t i o n g e n e t i c i s t s , can be i n t e r p r e t e d i n two ways. I t may be s e l e c t i v e l y n e u t r a l , and p e r s i s t s simply because no s e l e c t i v e f o r c e s a c t on i t . Or, s e l e c t i v e mechanisms capable of m a i n t a i n i n g polymorphism may be more widespread than had been supposed. T h i s l a t t e r p o s s i b i l i t y has l e d to much t h e o r e t i c a l work on the c o n d i t i o n s under which d i v e r s i f y i n g s e l e c t i o n i n space or time can maintain g e n e t i c v a r i a t i o n w i t h i n p o p u l a t i o n s (Levene 1953; Dempster 1955; Haldane and Jayaker 1963; Bryant 1976; Hedrick et a l . 1976; S p i e t h 1979; Ewing 1979). An analogous and o l d e r problem e x i s t s r e g a r d i n g the maintenance of m o r p h o l o g i c a l and b e h a v i o u r a l v a r i a t i o n i n p o p u l a t i o n s . T h i s problem i s c o m p l i c a t e d by the p o s s i b i l i t y t h at such v a r i a t i o n may r e f l e c t e n v i r o n m e n t a l l y induced r a t h e r than g e n e t i c v a r i a t i o n , or may r e s u l t from i n d i r e c t s e l e c t i o n a c t i n g on g e n e t i c a l l y c o r r e l a t e d t r a i t s . The mechanisms m a i n t a i n i n g morphological v a r i a t i o n have r e c e i v e d much a t t e n t i o n i n the g a s t e r o s t e i d f i s h e s . These f i s h e s are c o n s p i c u o u s l y v a r i a b l e f o r c h a r a c t e r s r e l a t i n g to the extent of body armature (number of l a t e r a l p l a t e s , number and s i z e of 2 d o r s a l and p e l v i c s p i n e s ) . P r e d a t i o n has u s u a l l y been i m p l i c a t e d as an important f a c t o r i n s e l e c t i o n o p e r a t i n g on these c h a r a c t e r s (McPhail 1969; Hagen and G i l b e r t s o n 1972, 1973; Moodie 1972; Moodie et a l . 1973; Moodie and Reimchen 1976; B e l l and Haglund 1978; Reimchen 1980, 1983; R e i s t 1980a,b; Blouw and Hagen I984a,b). Some workers have emphasized a d i r e c t f u n c t i o n a l s i g n i f i c a n c e of the v a r i o u s c h a r a c t e r s t a t e s i n a v o i d i n g a v a r i e t y of p r e d a t o r s i n a v a r i e t y of c i r c u m s t a n c e s (e.g., Reimchen 1980, 1983). Others have suggested that the c h a r a c t e r of d i r e c t s e l e c t i v e s i g n i f i c a n c e may not be the extent of body armature i t s e l f , but r a t h e r some c o r r e l a t e d b e h a v i o u r a l c h a r a c t e r (e.g., Moodie et a l . 1973; R e i s t 1980a,b; Blouw and Hagen 1984a). V a r i a t i o n i n the number of v e r t e b r a e i s widespread w i t h i n and among f i s h p o p u l a t i o n s . T h i s v a r i a t i o n i s p a r t l y environmental i n o r i g i n (e.g., Lindsey and Arnason 1981; Swain and Lindsey I986a,b), but a l s o has a g e n e t i c component (Lindsey 1962; A l i and Lindsey 1974; Leary et a l . 1985a). The ' n e u t r a l i s t ' view has been that such v a r i a t i o n p e r s i s t s because, w i t h i n narrow l i m i t s , the p r e c i s e v e r t e b r a l count i s without s e l e c t i v e s i g n i f i c a n c e (Fowler 1970). Wide m a l l e a b i l i t y of v e r t e b r a l count i n response to environmental i n f l u e n c e s d u r i n g e a r l y development has been c o n s i d e r e d c o n s i s t e n t with a l a c k of strong s e l e c t i v e advantage to p a r t i c u l a r counts. Fowler (1970) has argued t h a t , w i t h i n l i m i t s , i t may be more a d a p t i v e to ' l e t ' the number of v e r t e b r a e vary due to random environmental changes, than to f i x the number g e n e t i c a l l y , s i n c e to do so would l i m i t a 3 f i s h ' s a b i l i t y to respond to s t r e s s e s e x e r t e d by mutation or environmental change on other developmental processes of g r e a t e r s e l e c t i v e s i g n i f i c a n c e (Bateson 1963). A c o n t r a s t i n g ' s e l e c t i o n i s t ' view i s supported by the widespread tendency among r e l a t e d forms f o r higher v e r t e b r a l number to be a s s o c i a t e d with longer maximum body le n g t h (pleomerism) and with h i g h e r l a t i t u d e or c o l d e r waters (Jordan's r u l e ) (Lindsey 1975). I t has been argued that these trends might r e f l e c t s e l e c t i o n , not f o r v e r t e b r a l number per se, but r a t h e r f o r c h a r a c t e r s such as egg s i z e or developmental r a t e , which i n c i d e n t l y i n f l u e n c e the number of v e r t e b r a e formed i n embryos (Hubbs 1926, 1928). A l t e r n a t i v e l y , a f u n c t i o n a l advantage, perhaps i n v o l v i n g locomotory a b i l i t y , may be a s s o c i a t e d with some optimum number of v e r t e b r a e (Lindsey 1975). T h i s might i n v o l v e f l e x i b i l i t y , myomere number or some other f e a t u r e of the a x i a l segmentation. I f so, pleomerism suggests that the f u n c t i o n a l l y optimum number of segments might depend on body s i z e , and Jordan's r u l e suggests that the optimum number at a given s i z e might depend on water temperature or v i s c o s i t y . In t h i s t h e s i s , I t e s t the hypotheses that some s e l e c t i v e advantage i s a s s o c i a t e d with p a r t i c u l a r numbers of v e r t e b r a e , that the number at advantage v a r i e s with body s i z e , and that the optimum number at a given s i z e depends on water temperature or v i s c o s i t y . I assume that v e r t e b r a l number i s adapted not to the maximum body l e n g t h s i n a p o p u l a t i o n , but r a t h e r to the f r y le n g t h s , when m o r t a l i t y i s high and s e l e c t i o n r e l a t e d to locomotory a b i l i t y ( to escape p r e d a t o r s ) i s l i k e l y to be most 4 s t r i n g e n t . These hypotheses are t e s t e d i n two s p e c i e s , the t h r e e s p i n e s t i c k l e b a c k G a s t e r o s t e u s a c u l e a t u s • (Linnaeus) and peamouth chub M y l o c h e i l u s c a u r i n u s (Richardson), u s i n g p r e d a t i o n experiments i n which v e r t e b r a l counts of s u r v i v o r s of p r e d a t i o n are compared to those of unexposed c o n t r o l s . I a l s o look f o r evidence of s e l e c t i o n i n the w i l d , by comparing v e r t e b r a l counts of w i l d f r y of v a r i o u s s i z e s and ages. In a d d i t i o n , I t e s t the hypothesis that locomotory performance depends on v e r t e b r a l number, by d i r e c t measurements of b u r s t swimming performance of G. a c u l e a t u s f r y of v a r i o u s s i z e s and at v a r i o u s water temperatures and v i s c o s i t i e s . F i n a l l y , r e s u l t s of these t e s t s are r e l a t e d to the maintenance of v a r i a t i o n i n v e r t e b r a l number w i t h i n and among p o p u l a t i o n s , and to the p o s s i b l e adaptive s i g n i f i c a n c e of environmental i n f l u e n c e s on v e r t e b r a l number. 5 Part I. P r e d a t i o n experiments with t h r e e s p i n e s t i c k l e b a c k s M a t e r i a l and Methods Breeding s t i c k l e b a c k s were c o l l e c t e d from e i t h e r Kennedy or Holden Lakes on Vancouver I s l a n d . Kennedy Lake i s a l a r g e o l i g o t r o p h i c lake c o n t a i n i n g a l l three l a t e r a l p l a t e morphs (Hagen and G i l b e r t s o n 1972) of G. a c u l e a t u s ; Holden Lake i s a small e u t r o p h i c lak e c o n t a i n i n g only the low p l a t e d morph. Each male was a r t i f i c i a l l y c r o s s e d to two females, and t h e i r o f f s p r i n g were reared i n the l a b o r a t o r y at about 17C. Fry were h e l d at d e n s i t i e s of about 100/L f o r the f i r s t few days a f t e r h a t c h i n g and about 30/L t h e r e a f t e r . Fry were fed n a t u r a l plankton, Artemia n a u p l i i and nematodes. For each of three experiments conducted i n 1982 using Kennedy Lake f i s h , the o f f s p r i n g of a s i n g l e c o l l e c t i o n of parents (about 50 c r o s s e s ) were mixed and d i s t r i b u t e d among s i x 190-L tanks (of green f i b e r g l a s s , approximate water dimensions 110 x 50 x 34 cm) 15-20 d a f t e r h a t c h i n g . Two tanks were de s i g n a t e d as c o n t r o l tanks and four as experimental tanks. One c o n t r o l and two experimental tanks were maintained at 15C; the remaining tanks were maintained at e i t h e r 17 or 20C. In experiment K1, f r y were f i r s t d i s t r i b u t e d i n l o t s of 10-30 f i s h a l t e r n a t e l y among the three tanks to be h e l d at 15C u n t i l each had r e c e i v e d i t s f u l l complement of f i s h , and then a l t e r n a t e l y among the three tanks to be h e l d at 20C. In experiments K2 and K3, f r y were d i s t r i b u t e d i n small l o t s a l t e r n a t e l y among a l l s i x tanks. Tanks were i l l u m i n a t e d by overhead f l u o r e s c e n t l i g h t s on 6 a photoperiod of 16.5 h l i g h t : 7.5 h dark. Water flow was 1-2L/min i n each tank. Cover was u s u a l l y p r o v i d e d by shredded p l a s t i c suspended near each end of experimental tanks, but was removed while a s s e s s i n g the extent of p r e d a t i o n and was u s u a l l y not r e p l a c e d when the estimated number of f r y eaten approached the d e s i r e d number. A f t e r about 15 h of a c c l i m a t i o n , f r y i n experimental tanks were exposed to p r e d a t i o n by 10-30 pumpkinseed s u n f i s h (Lepomis gibbosus) f o r 10-50 h u n t i l 50-60 % of the i n i t i a l number had been eaten. S u n f i s h were r e p l a c e d every 2-5 h, and removed ov e r n i g h t i n experiments l a s t i n g more than 1 d. The s u n f i s h used were c o l l e c t e d from Holden Lake, and averaged 24 mm i n standard l e n g t h (range 15-30 mm). F r y were fed each morning 1-2 h before the i n t r o d u c t i o n of s u n f i s h . F u r t h e r d e t a i l s are given i n Table 1. Three c o l l e c t i o n s of parents were made from Holden Lake i n 1983 (80-110 c r o s s e s each), and o f f s p r i n g of each used i n two experiments at d i f f e r e n t s i z e s . Experiments resembled those conducted i n 1982 except that (1) temperatures were e i t h e r 15 or 25 C, (2) cover was p r o v i d e d i n only one of the two experimental tanks at each temperature, and (3) s u n f i s h were r e p l a c e d only every day. When cover was p r o v i d e d i t remained i n p l a c e f o r the e n t i r e experiment. D e t a i l s are given i n Table 2. At the end of each experiment, f r y were k i l l e d i n a n a e s t h e t i c (MS222), preserved i n 10% b u f f e r e d f o r m a l i n , s t a i n e d with a l c i a n b lue, c l e a r e d with t r y p s i n and 0.5% KOH, and s t o r e d i n g l y c e r i n e ( f o l l o w i n g Dingerkus and Uhler (1977), except that 2 mg of a l c i a n blue per ml of s t a i n s o l u t i o n were used h e r e ) . Table 1. Description of 1982 predation experiments using Kennedy Lake sticklebacks as prey. Percent cover is percent of predator-hours (pred.-h) with cover. Pred.-h = no. predators x h present. Duration in h includes night periods without predators. Predators are sunfish c o l l e c t e d from Holden Lake. standard length of Duration No. survivors (mm) Temp. % % eaten per No. Exp. Treatment ( C) Cover h Pred.-h eaten pred. . -h surv1v1ng Mean SD K1 Control 15 0 12 0 0 0. .0 87 8 .07 0.52 20 0 22 0 0 0 .0 89 8 .55 0.72 Exptl. 15 88 12 60 62 3. . 1 106 8 .23 0.51 15 64 12 107 55 1 , .5 127 8 .26 0.59 20 57 22 104 61 1. 8 123 8 . 52 0.61 20 61 22 135 64 1 . .5 107 8 .74 0.54 K2 Control 15 0 28 0 0 0 .0 126 8 . 14 0.72 20 0 1 1 0 0 0 .0 117 8 .23 0.66 Exptl. 15 55 29 91 58 2. .2 144 8 .50 0.64 15 48 30 104 60 1 . .9 132 8 .48 0.69 20 88 10 56 51 3. .0 165 8 .43 0.68 20 74 1 1 67 51 2. 6 167 8. .58 0.75 K3 Control 15 0 50 0 0 0 .0 132 8 .91 0.82 17 0 35 0 0 0. ,0 152 8 .93 0.84 Exptl. 15 96 50 303 58 0 .75 162 9 . 17 0.54 15 0 52 329 63 0. .75 147 9 . 10 0.55 17 100 35 262 53 0. .80 187 9 .03 0.64 17 0 51 373 59 0 .59 157 9 . 10 0.50 Table 2. Description of 1983 predation experiments using Holden Lake sticklebacks as prey. Cover 1s present (Y) or absent (N) during a l l predator-hours (pred.-h). Duration 1n h includes night periods without predators. Predators are sunfish c o l l e c t e d from Holden Lake. Prey In experiments with the same parent code are of f s p r i n g of the same c o l l e c t i o n of parents. standard standard length of length of Duration predators (mm) No. survivors (mm) Exp. Parents Treatment Temp. ( C) Cover h Pred.-h Mean SD % eaten eaten per pred.-h No. surviving Mean SD H1 A Control 15 N 46 0 0 119 7. 62 0.53 25 N 23 0 0 121 7. 63 0.57 Exptl. 15 Y 52 298 23 . 13 0, .74 55 0, ,55 135 7. 97 0.52 15 N 46 298 23. .47 1 , . 19 63 0, ,63 112 7. 98 0.54 25 Y 22 119 23. , 15 1 . .00 55 1. 39 133 7. 83 0.54 25 N 22 122 23. .60 0, .81 59 1 . ,44 124 7. 78 0.49 H2 B Control 15 N 52 0 0 124 8. 27 0.49 25 N 33 0 0 125 8. 35 0.48 Exptl. 15 Y 54 496 24, .30 0, .76 56 0. 34 132 8. 65 0.55 15 N 50 419 24, .28 0, .79 62 0. ,45 1 13 8. 79 0.54 25 Y 29 165 24, . 10 0. .74 58 1. 05 127 8. 56 0.52 25 N 32 195 24. . 10 0. ,74 64 0. 98 108 8. 69 0.53 H3 C Control 15 N 25 0 0 124 8 .56 0.51 25 N 13 0 0 125 8 .50 0.63 Exptl. 15 Y 26 136 28, .07 0. .80 62 1 . ,36 1 15 8 .90 0.56 15 N 24 92 27 , 93 0. .80 58 1 . 90 126 8 .92 0.60 25 Y 12 97 28. .00 0. 82 65 2 . 03 104 8 .97 0.52 25 N 12 109 28 . OO 0. .82 70 1 . .94 89 8 .97 0.50 contd. Table 2. contd. Duration Temp. Exp. Parents Treatment ( C) Cover h Pred.-h H4 C Control 15 N 32 0 25 N 30 0 Exptl. 15 Y 32 246 15 N 31 238 25 Y 31 171 25 N 30 156 H5 A Control 15 N 71 0 25 N 56 0 Exptl. 15 Y 78 742 15 N 60 612 25 Y 56 254 25 N 36 198 H6 B Control 15 N 56 0 25 N 50 0 Exptl. 15 Y 58 608 15 N 56 507 25 Y 51 246 25 N 48 226 standard standard length of length of predators (mm) No. survivors (mm) '% . eaten per No. Mean SD eaten pred.-h surviving ' Mean SD 0 124 9 .83 0. ,63 0 123 9, .76 0. ,63 29 .50 1 .03 57 0 .69 128 10, .26 0. ,53 29 .50 1 .03 57 0 .71 128 10, .31 0. .61 29 .50 1 .08 60 1 , .04 121 10, .03 O. .63 29 .50 1 .08 58 1 . 1 1 125 10, .22 0. ,66 0 120 9, .89 0. 62 0 1 19 10. . 12 0. 66 29 .75 1 .87 56 0. ,22 133 10. ,21 0. 64 29 .50 1 .89 58 0. .28 126 10, .05 0. 62 28 .50 1 .84 59 0. ,69 124 10. ,05 0. 65 28 .90 1 .85 57 0. ,87 128 9. .66 0. 57 0 125 1 1 . . 13 0. 72 0 1 13 11 . , 19 0. 80 32, .94 1 .05 63 0. ,31 1 10 11 . ,47 0. 78 32, .97 1 .03 57 0. ,34 130 1 1 . ,67 0. 80 32 .75 1 .07 59 0. 65 113 1 1 . ,54 0. 76 32. ,80 1 . 15 58 0. 70 1 16 1 1 . ,66 0. 72 10 Counts were made of c e n t r a , e x c l u d i n g the u r o s t y l e . The l a s t centrum f r e q u e n t l y bore two n e u r a l or haemal arc h e s . Such complex v e r t e b r a e were counted as one. Vertebrae were de s i g n a t e d as 'abdominal' or 'caudal' on the b a s i s of haemal spine l e n g t h . In over 80% of f i s h a sharp d i s c o n t i n u i t y i n haemal spine l e n g t h o c c u r r e d i n the v i c i n i t y of the f i r s t a n a l b a s a l ( F i g . 1). The f i r s t v e r t e b r a b e a r i n g a long haemal spine was des i g n a t e d the f i r s t c audal v e r t e b r a ; normally t h i s was the f i r s t v e r t e b r a whose haemal spine p r o j e c t e d p o s t e r i o r to the f i r s t a n a l b a s a l . In those f i s h whose haemal spine l e n g t h i n c r e a s e d g r a d u a l l y near the f i r s t a n a l b a s a l , the f o l l o w i n g c r i t e r i a were used. In the 1983 (Holden Lake) experiments, the f i r s t v e r t e b r a b e a r i n g a haemal spine 1.5 or more times as long as i t s centrum, or at l e a s t 85% as long as the longest haemal spine i n the v i c i n i t y of the anal b a s a l s , was desig n a t e d the f i r s t caudal v e r t e b r a . In the 1982 (Kennedy Lake) experiments (recounted i n 1986), the f i r s t v e r t e b r a whose haemal spine l e n g t h was 80% or more of the maximum spine l e n g t h i n the v i c i n i t y of the a n a l b a s a l s was des i g n a t e d the f i r s t caudal v e r t e b r a . Of 332 f i s h counted u s i n g both methods, the d e s i g n a t i o n of the f i r s t c audal v e r t e b r a d i f f e r e d between methods i n only 5 f i s h ; i n 3 f i s h the f i r s t method d e s i g n a t e d one fewer caudal v e r t e b r a e , and i n 2 f i s h one more. T o t a l l e n g t h was measured from the t i p of the snout to the end of the hypural p l a t e . In Kennedy Lake f i s h , l e n g t h of the v e r t e b r a l column was a l s o measured, from the a n t e r i o r edge of the f i r s t v e r t e b r a to the p o s t e r i o r edge of the hyp u r a l p l a t e . In F i g u r e 1. A x i a l s k e l e t o n of t h r e e s p i n e s t i c k l e b a c k f r y . A. E n t i r e s k e l e t o n . B-D. D i v i s i o n between abdominal and caudal v e r t e b r a e marked by arrow (B. most common d i v i s i o n , D. most r a r e d i v i s i o n ) . S c a l e 1 mm. F i s h lengths 8.0 (A,B) or 8.1 (C,D) mm. CL i s caudal l e n g t h .  1 3 f i s h from both l a k e s , caudal l e n g t h was measured from the a n t e r i o r edge of the f i r s t v e r t e b r a whose haemal spine opposed or p r o j e c t e d p o s t e r i o r to the m i d l i n e of the f i r s t anal b a s a l , to the p o s t e r i o r edge of the hypural p l a t e ( F i g . 1). The ve r t e b r a e i n c l u d e d i n t h i s l e n g t h normally corresponded to those d e s i g n a t e d as caudal v e r t e b r a e a c c o r d i n g to the c r i t e r i a d e s c r i b e d above. However, i n some i n s t a n c e s , the f i r s t caudal v e r t e b r a was excluded from t h i s l e n g t h , or r a r e l y , the l a s t abdominal v e r t e b r a was i n c l u d e d i n i t ( F i g . 1C and 1D, r e s p e c t i v e l y ) . In these cases, i n f i s h from Holden Lake, an a d j u s t e d caudal l e n g t h was c a l c u l a t e d by adding or s u b t r a c t i n g the average l e n g t h of a v e r t e b r a i n the caudal l e n g t h of the f i s h i n q u e s t i o n . Adjusted caudal l e n g t h s c o u l d not be c a l c u l a t e d i n Kennedy Lake f i s h , s i n c e the counts of caudal v e r t e b r a e made when caudal l e n g t h s were measured d i d not employ those c r i t e r i a d e s c r i b e d above. Independence of count d i s t r i b u t i o n and treatment was assessed by c h i - s q u a r e t e s t s c a l c u l a t e d u s i n g BMDP4F (Dixon 1981). Yates' c o r r e c t i o n f o r c o n t i n u i t y was used i n a l l 2x2 comparisons with sample s i z e s of 200 or l e s s . P r o b a b i l i t i e s c a l c u l a t e d u s i n g t h i s c o r r e c t i o n may be c o n s e r v a t i v e (Sokal and Rohlf 1981; Dixon 1981). L i n e a r r e g r e s s i o n s were c a l c u l a t e d and e q u a l i t y of s l o p e s t e s t e d u s i n g BMDP1R and BMDP1V, r e s p e c t i v e l y (Dixon 1981). Analyses of v a r i a n c e and c o v a r i a n c e were performed u s i n g BMDP7D, BMDP1V or BMDP2V. 14 R e s u l t s T o t a l Vertebrae 1. Kennedy Lake experiments V e r t e b r a l count d i s t r i b u t i o n s were a p p a r e n t l y homogeneous among tanks before exposure to p r e d a t o r s . In each of the f i r s t two experiments, d i s t r i b u t i o n s i n the two c o n t r o l tanks were v i r t u a l l y i d e n t i c a l (Table 3 ). D i f f e r e n c e s between the c o n t r o l d i s t r i b u t i o n s i n the t h i r d experiment were not s t a t i s t i c a l l y s i g n i f i c a n t (p=0.14, with data grouped as f i s h with or without 31 v e r t e b r a e ) . The f i r s t two experiments p r o v i d e d s t r i k i n g evidence of s e l e c t i v e p r e d a t i o n with respect to v e r t e b r a l number (Table 3). The frequency of f i s h with 31 v e r t e b r a e was c o n s i s t e n t l y g r e a t e r i n e x p e r i m e n t a l than i n c o n t r o l tanks a f t e r p r e d a t i o n . T h i s d i f f e r e n c e i s h i g h l y s i g n i f i c a n t (p=0.00l4, grouping over both experiments; count d i s t r i b u t i o n s are homogeneous between experiments w i t h i n p r e d a t i o n treatments, p>0.20). Judging from the d i f f e r e n c e i n counts between c o n t r o l and experimental groups, the s u r v i v a l r a t e of f i s h with 31 v e r t e b r a e was about 1.7 and 1.3 times t h a t of f i s h with 32 v e r t e b r a e i n the f i r s t and second experiments, r e s p e c t i v e l y . The t h i r d experiment d i f f e r e d from the p r e v i o u s two i n average prey s i z e . Judging from the s i z e d i s t r i b u t i o n s of c o n t r o l and experimental groups, the m a j o r i t y of the f i s h eaten were about 8.5-10.5 mm long, whereas most of those eaten i n the Table 3. Vertebral counts of Kennedy Lake sticklebacks exposed (experimental) or unexposed (control) to predation by sunfish. Probabilities are from chi-square tests of independence between vertebral count and predation treatment, with fish grouped as those with or without 31 vertebrae. Mean Vertebral count (%) Temp. length No. Exp. Treatment ( C) (mm) surviving 29 30 31 32 33 Probability K1 K2 K3 Control 15 8. ,07 87 1 . , 1 41 . 4 56. 3 1 . 1 20 8 .55 89 40, .4 59. 6 176 0. 6 40, .9 58. ,0 0. 6 Exptl. 15 8 ,23 106 1 . ,9 55, .7 40. 6 1 . .9 15 8. .26 127 52 .8 44. ,9 2. 4 20 8. .52 123 1 , .6 52, ,8 44. , 7 0. 8 20 8. .74 107 0. ,9 54. .2 43. ,9 0. .9 463 1 . . 1 53, .8 43. ,6 1 . .5 Control 15 8. . 14 126 6, .3 47. .6 45, .2 0. 8 20 8. .23 1 17 5, . 1 46. .2 47 , .0 1 . ,7 243 5, .8 46, .9 46. . 1 ' 1 . 2 Exptl. 15 8 .50 144 6, .9 59, .0 33 .3 0. ,7 15 8. .48 132 0.8 8 .3 49 .2 39. .4 2. 3 20 8 .43 165 3, .0 52, .7 43, .0 1 . .2 20 8 .58 167 6 .0 52 .7 40. .7 0. .6 608 0.2 5 .9 53 .5. 39, .3 1 . 2 Control 15 8 .91 132 4, .5 48, .5 47 , .0 17 8 .93 152 4. .6 57, .2 36 . 8 1 . 3 284 4, .6 53 .2 41 . 5 0. .7 Exptl . 15 9 . 17 162 4, .3 60, .5 34, 6 0. 6 15 9 . 10 147 4, ,8 54, .4 39. .5 1 . .417 9 .03 187 2 . 1 57, .2 40, . 1 0. .5 17 9 . 10 157 1 , .9 56, . 1 38. .9 3. .2 0.004 0.085 0.26 653 3.2 57.1 38.3 1.4 16 f i r s t two experiments were about 7.0-8.5 mm long. P r e d a t i o n on these longer f i s h was not s i g n i f i c a n t l y s e l e c t i v e f o r v e r t e b r a l number; the frequency of f i s h with 31 v e r t e b r a e was only s l i g h t l y g r e a t e r i n experimental than i n c o n t r o l groups. P r e d a t i o n was a l s o s e l e c t i v e w i t h r e s p e c t to prey s i z e . The average l e n g t h of f i s h s u r v i v i n g p r e d a t i o n i n experimental groups was u s u a l l y s l i g h t l y g r e a t e r than that of f i s h unexposed to p r e d a t i o n i n the co r r e s p o n d i n g c o n t r o l groups (Table 3). V e r t e b r a l number and l e n g t h were p o s i t i v e l y c o r r e l a t e d among f i s h i n a l l groups, but t h i s r e l a t i o n s h i p was not s i g n i f i c a n t i n any c o n t r o l group (Table 4). Moreover, t h i s c o r r e l a t i o n was i n the d i r e c t i o n t h at would cause s i z e s e l e c t i v e p r e d a t i o n to c o u n t e r a c t r a t h e r than c o n t r i b u t e to the observed d i f f e r e n c e s i n v e r t e b r a l numbers. T h e r e f o r e , s e l e c t i v i t y of p r e d a t i o n with r e s p e c t to v e r t e b r a l number cannot have been due to s i z e s e l e c t i o n i n these experiments. Although s i g n i f i c a n t i n no c o n t r o l group, the c o r r e l a t i o n between v e r t e b r a l number and l e n g t h was s i g n i f i c a n t i n experimental groups i n one experiment (K2 i n Table 4 ) . T h i s i n c r e a s e i n s i g n i f i c a n c e i n experimental r e l a t i v e to c o n t r o l groups c o u l d r e s u l t from s e l e c t i o n i n favour of f i s h with 31 v e r t e b r a e only at smal l e r s i z e s w i t h i n the range exposed to p r e d a t o r s i n t h i s experiment, or may simply r e f l e c t i n c r e a s e d sample s i z e i n experimental groups. Slopes of r e g r e s s i o n s between v e r t e b r a l number and l e n g t h d i d not d i f f e r s i g n i f i c a n t l y between experimental and c o n t r o l groups i n any of the three experiments (Table 4 ) . Table 4. Regressions between vertebral count and length In 1982 experiments using offspring of Kennedy Lake sticklebacks. Data are grouped over replications within predation treatments since slopes are equal among replications (p>0.35). Probabi11ty of Exp. Treatment No. Slope Probabi11ty of zero slope equal slopes between treatments K1 Control Exptl. 176 463 0.091 0.012 0.12 0.78 0.28 K2 Control Exptl. 243 608 0.031 0.099 0.59 0.006 0.31 K3 Control Exptl. 284 653 0.056 0.032 0.22 0.43 0.69 18 No s i g n i f i c a n t e f f e c t of temperature on the extent of s e l e c t i v e p r e d a t i o n was d e t e c t e d . V e r t e b r a l counts of s u r v i v o r s i n experimental groups were v i r t u a l l y i d e n t i c a l at the two temperatures i n experiment K1. In experiments K2 and K3, f i s h w ith 32 v e r t e b r a e were s l i g h t l y more frequent i n experimental groups at the higher temperature, but d i f f e r e n c e s between temperatures were not s t a t i s t i c a l l y s i g n i f i c a n t (p=0.16 and 0.49, r e s p e c t i v e l y ) , and may simply r e f l e c t the lower percent m o r t a l i t y at the higher temperatures. 2. Holden Lake experiments S e l e c t i v e p r e d a t i o n f o r v e r t e b r a l number of Holden Lake s t i c k l e b a c k s i n 1983 resembled that seen using Kennedy Lake f i s h i n 1982. At average prey l e n g t h s of about 8.1-8.2 mm ( i . e . , among f i s h 8.5 mm or l e s s i n l e n g t h i n experiments H2 and H3), s u r v i v a l d u r i n g exposure to p r e d a t i o n was again g r e a t e r f o r f i s h w i t h 31 ver t e b r a e than f o r those with other counts (Table 5 ) . T h i s i n c r e a s e i n the frequency of f i s h with 31 v e r t e b r a e i n experimental compared to c o n t r o l groups was h i g h l y s i g n i f i c a n t (p=0.0025, combining both experiments s i n c e the frequency i n c o n t r o l groups was homogeneous between experiments (p=0.82)). The extent of s e l e c t i v e p r e d a t i o n i n these experiments was u n r e l a t e d both to temperature and to the a v a i l a b i l i t y of cover (p>0.65). P r e d a t i o n was a l s o s e l e c t i v e with r e s p e c t to prey s i z e i n these experiments. V e r t e b r a l number and l e n g t h were p o s i t i v e l y c o r r e l a t e d among f i s h i n H2 and H3 c o n t r o l groups (Table 6 ) . Since s u r v i v a l d u r i n g p r e d a t i o n was g r e a t e r f o r l a r g e r f i s h , t h i s c o r r e l a t i o n was again i n the d i r e c t i o n t h a t Table 5. Vertebral counts of Holden Lake sticklebacks exposed (experimental) or unexposed (control) to predation by sunfish. Probabilities are from chi-square tests of independence between count and predation treatment, with fish grouped as those with or without the favoured count (31 In experiments at sizes under 8.5 or over 11.0 mm; 32 in experiments at other sizes). Results of experiments H2 and H3 are shown separately for fish 8.5 mm or less in length, or over 8.5 mm In length. Vertebral count (%) Exp. Treatment H1 Temp. ( C) Cover H2 H3 Mean 1ength (mm) Control 15 N 7. 62 25 N 7. 63 Exptl. 15 Y 7. ,97 15 N 7. .98 25 Y 7. 83 25 N 7. ,78 .5 mm or less Control 15 N 8. ,02 25 N 8. . 10 Exptl . 15 Y 8. . 18 15 N 8 . 15 25 Y 8. . 13 25 N 8. . 15 .5 mm or less Control 15 N 8 . 15 25 N 8 .09 Exptl. 15 Y 8 .20 15 N 8 . 14 25 Y 8 . 19 25 N 8 .29 No. surviving <30 31 32 533 119 10. , 1 58. 8 29. 4 1 . ,7 121 12. ,4 63. 6 22. 3 1 . 7 240 11. 2 61 . 3 25. 8 1 . 7 135 13. 4 60. 7 25. 9 112 11 . ,6 68. 8 18. 8 0. 9 133 9. 0 66. 2 24. 8 124 10. ,5 63. ,7 25. 0 0. 8 504 11 . , 1 64. ,7 23. 8 0. ,4 87 8 .0 59. 8 28. ,7 3 .4 85 2. .4 52. .9 43. .5 1 , .2 172 5. .2 56. .4 36. .0 2, .3 62 6 .5 69. .4 24. ,2 36 2 .8 66, .7 30, .6 63 4, .8 65. . 1 30, .2 44 4, .5 72, .7 20, .5 2 .3 205 4, .9 68 .3 26 .3 0 .5 62 14 .5 71 .0 14 .5 75 26 .7 46 .7 26 .7 137 21 .2 57 .7 21 .2 29 17 .2 69 .0 13 .8 34 8 .8 70 .6 20 .6 21 14 .3 71 .4 14 .3 21 23 .8 66 .7 9 .5 Probabi1ity 0.36 0.017 0.058 105 15.3 69.5 15.2 contd. Table 5. contd. Mean Temp. length Exp. Treatment ( C) Cover (mm) H2 over 8.5 mm Control Exptl. H3 over 8.5 mm Control Exptl. 15 N 8 .85 25 N 8. .88 15 Y 9. .07 15 N 9. . 10 25 Y 8 .98 25 N 9 .06 15 N 8 .97 25 N 9. . 1 1 15 Y 9. . 14 15 N 9. .21 25 Y 9. . 17 25 N 9. . 18 Vertebral count (%) No. . surviving ^30 31 32 £33 Probabl1ity 37 73 .0 24 .3 2. .7 40 7 .5 62 .5 30, .0 77 3 .9 67 .5 27 .3 1 . .3 70 2 .9 62 .9 34, .3 77 2 .6 67 .5 28 .6 1 . .364 4 .7 60 .9 29 .7 4. .7 64 4 .7 57 .8 37 .5 275 3 .6 62 .5 32 .4 1 . .5 62 8 . 1 64 .5 27 .4 50 14 .0 54 .0 30, .0 2. .0 112 10 .7 59 .8 28. .6 0. .9 86 1 1 , .6 55, .8 32. .6 92 14, . 1 50, .0 35. .9 83 4, .8 59, .0 34. .9 1 . .268 10, .3 66 .2 23. .5 329 10, .3 57. . 1 32. .2 0. ,3 contd. Table 5. contd. Mean Temp. length Exp. Treatment ( C) Cover (mm) H4 Control Exptl. H5 Control Exptl. H6 Control Exptl. 15 N 9. 83 25 N 9. ,76 15 Y 10. .26 15 N 10. ,31 25 Y 10. ,03 25 N 10 .22 15 N 9 .89 25 N 10 . 12 15 Y 10, .21 15 N 10 .05 25 Y 10 .05 25 N 9 .66 15 N 11 . 13 25 N 11 . 19 15 Y 1 1 .47 15 N 11 .67 25 Y 1 1 .54 25 N 1 1 .66 Vertebral count (%) No. surviving ^30 31 32 £33 Probabi11ty 123 5. ,7 64, .2 30, . 1 122 8. ,2 68. .9 21 , .3 1 , .6 245 6 .9 66 .5 25, .7 0 .8 128 9. .4 67 .2 22 .7 0, .8 128 7. a 63 .3 28 .9 121 8. ,3 66 . 1 25, .6 125 6. .4 54 .4 38 .4 0 .8 502 8.0 62.7 28.9 0.4 120 10.8 69. 2 20 .0 119 11.8 70. .6 16 .8 0. 8 239 11.3 69. 9 18 .4 0. ,4 133 10.5 70. ,7 18, .0 0. 8 126 12.7 68. .3 19 .0 124 8.9 64. 5 25 .8 0. 8 128 13.3 64. . 1 21 .9 0. 8 511 11.4 66.9 21.1 0.6 125 8. 8 69, .6 20, .8 0, .8 113 9. .7 64. .6 23, .9 1 , .8 238 9. .2 67 .2 22, .3 1. .3 110 8. .2 72 .7 18 .2 0 .9 130 6. .9 67, ,7 23, . 1 2 .3 113 4, .4 66 .4 27, .4 1 , ,8 1 16 6. .9 75, .0 18, . 1 469 6.6 70.4 21.7 1.3 Table 6. Regressions between vertebral number and length in experiments using offspring of Holden Lake sticklebacks. Only results grouped over replications within predation treatments are shown, since slopes are equal among replications (p>0.08). Probabl11ty of Probability of equal slopes Exp. Treatment No. Slope zero slope between treatments H1 Control 240 -0.020 0 .79 0.39 Exptl. 504 0.057 0 .27 H2 Control 172 0.230 0 . 11 0.35 8̂.5mm Exptl. 205 0.056 O .65 H3 Control 137 0.724 <0 .0001 0.001 <8.5mm Exptl. 105 -0.119 0 .55 H2 Control 77 0.237 0 .37 0.24 >8.5mm Exptl. 275 -0.115 0. .31 H3 Control 112 O. 348 0. . 1 1 0.46 >8.5mm Exptl. 329 0. 194 0. 032 H4 Control 245 0.088 0. 12 0. 18 Exptl. 502 0. 183 <o. 0001 H5 Control 239 0.111 0. 046 0.47 Exptl. 511 0.061 0. 13 H6 Control 238 -0.004 O. 94 0.71 Exptl. 469 0.019 0. 59 23 would cause s i z e s e l e c t i v e p r e d a t i o n to c o u n t e r a c t r a t h e r than c o n t r i b u t e to the observed d i f f e r e n c e s i n v e r t e b r a l numbers. T h e r e f o r e , as i n the Kennedy Lake experiments, the s e l e c t i v i t y of p r e d a t i o n with r e s p e c t to v e r t e b r a l number i n these experiments cannot have been due to s i z e s e l e c t i o n . Among f i s h 8.5 mm or l e s s i n l e n g t h i n experiment H3, the c o r r e l a t i o n between v e r t e b r a l number and l e n g t h was s i g n i f i c a n t i n c o n t r o l but not i n experimental groups (Table 6). Slopes d i f f e r e d s i g n i f i c a n t l y between the two treatments (p=0.00l). T h i s d i f f e r e n c e between c o n t r o l and experimental groups c o u l d be e x p l a i n e d by stronger s e l e c t i o n i n favour of f i s h with 31 v e r t e b r a e at longer lengths below 8.5 mm. At average prey lengths below 8.0 or above 8.5 mm, p r e d a t i o n was not s i g n i f i c a n t l y s e l e c t i v e f o r t o t a l v e r t e b r a l number (Table 5). At the s m a l l e r s i z e , f i s h with 31 v e r t e b r a e were s l i g h t l y more frequent i n experimental than i n c o n t r o l groups; at the l a r g e r s i z e s , f i s h with 32 v e r t e b r a e were u s u a l l y more frequent i n experimental than i n c o n t r o l groups. None of these d i f f e r e n c e s were s i g n i f i c a n t when temperature and cover treatments were grouped together (p>0.35). However, the e f f e c t of p r e d a t i o n appeared to d i f f e r between cover treatments i n experiment H4 (p=0.0l9). In t h i s experiment, f i s h with 32 v e r t e b r a e appeared to be at an advantage over f i s h with other v e r t e b r a l counts i n the absence, but not i n the presence of cover (p=0.054 and 0.68, r e s p e c t i v e l y ) . In no other experiment d i d the s e l e c t i v i t y of p r e d a t i o n appear to depend upon the a v a i l a b i l i t y of cover (p>0.50). V e r t e b r a l numbers i n experimental groups d i d 24 not d i f f e r s i g n i f i c a n t l y between temperatures i n any experiment (p>0.lO i n a l l cases, p>0.35 i n a l l but two c a s e s ) . P r e d a t i o n was s e l e c t i v e f o r prey s i z e i n a l l experiments except H5. Among experiments at prey l e n g t h s below 8.0 or above 8.5 mm, the c o r r e l a t i o n between v e r t e b r a l number and l e n g t h was s i g n i f i c a n t i n c o n t r o l groups only i n H5 (Table 6). In other experiments at these s i z e s , t h i s c o r r e l a t i o n , though not s i g n i f i c a n t , was i n the d i r e c t i o n that would cause s i z e s e l e c t i v e p r e d a t i o n to c o n t r i b u t e to the s l i g h t d i f f e r e n c e s i n v e r t e b r a l number observed between experimental and c o n t r o l groups. 3. Summary The s e l e c t i v i t y of p r e d a t i o n f o r t o t a l v e r t e b r a l number of s t i c k l e b a c k s depends upon prey l e n g t h and i s c o n s i s t e n t between p o p u l a t i o n s ( F i g . 2 ) . In both the Kennedy and the Holden Lake p o p u l a t i o n s , f i s h with 31 ve r t e b r a e are at a s i g n i f i c a n t advantage over f i s h with other v e r t e b r a l counts when exposed to p r e d a t i o n at average l e n g t h s of 8.0-8.5 mm, but not when exposed at smaller (7.6 mm) or g r e a t e r (8.9-11.2 mm) l e n g t h s . When s e l e c t i v e p r e d a t i o n was s i g n i f i c a n t , i t s extent was u n r e l a t e d to e i t h e r temperature or the a v a i l a b i l i t y of cover. Although p r e d a t i o n was a l s o u s u a l l y s e l e c t i v e with r e s p e c t to prey s i z e , s e l e c t i v e p r e d a t i o n f o r v e r t e b r a l number c o u l d not be a t t r i b u t e d to s i z e s e l e c t i o n i n any experiment at average l e n g t h s of 8.0-8.5 mm. 25 F i g u r e 2. Change i n percent frequency of v e r t e b r a l counts i n s t i c k l e b a c k s exposed to p r e d a t i o n at v a r i o u s mean s i z e s (experimental minus c o n t r o l f i s h ) . P o i n t s below the h o r i z o n t a l a x i s are experiments i n which f i s h with 31 v e r t e b r a e are more frequent i n exposed than i n unexposed groups; those above are experiments i n which f i s h with 32 v e r t e b r a e are more frequent i n exposed groups. 26 z TD o CD ^_ 1 1 o < > Q D LU «+- r r CD CL O k_ JQ CD CD Z CD > C\J r o Q >- o LU TD CD ID k_ O ZS o LU >r r o s— u_ ra e  z _Q CD LU CL) CD > Z r o < X o 8 r 6 4 0 2 4 6 8 10 12 • HOLDEN L. o KENNEDY L o o o 8 9 A V E R A G E P R E Y 10 L E N G T H (mm) 27 Abdominal and Caudal Vertebrae 1. Holden Lake experiments Count c l a s s e s based on numbers of abdominal and caudal v e r t e b r a e are shown i n Table 7 f o r o f f s p r i n g of Holden Lake f i s h . Three c l a s s e s are common: f i s h with 14 abdominal and 17 caudal v e r t e b r a e (31 t o t a l v e r t e b r a e (TV)), those with 14 abdominal and 18 caudal v e r t e b r a e (32 TV), and those with 13 abdominal and 18 caudal v e r t e b r a e (31 TV). R e s u l t s of the p r e d a t i o n experiments i n terms of count c l a s s e s based on the r a t i o of abdominal to caudal v e r t e b r a e (AV/CV) are shown i n Table 8 and F i g . 3. Data are grouped over r e p l i c a t i o n s w i t h i n p r e d a t i o n treatments, s i n c e the frequency of f i s h with the favoured r a t i o ( s ) d i d not d i f f e r between temperatures nor between cover treatments among experimental groups i n any experiment (p>0.35). At the s m a l l e s t prey s i z e (7.6 mm), no count c l a s s was favoured d u r i n g exposure to p r e d a t i o n . However, as prey s i z e was i n c r e a s e d above t h i s v a l u e , f i s h with p r o g r e s s i v e l y lower r a t i o s AV/CV were favoured d u r i n g exposure to p r e d a t i o n . At average prey lengths of about 8.1-8.2 mm, f i s h with a h i g h r a t i o of 0.82 AV/CV were s i g n i f i c a n t l y more frequent a f t e r p r e d a t i o n i n experimental groups than i n unexposed c o n t r o l groups (p=0.006 grouping experiments H2S and H3S, s i n c e the frequency of f i s h with t h i s r a t i o d i d not d i f f e r between experiments (p=0.9l)). At average prey lengths of about 9.8-10.0 mm, f i s h with i n t e r m e d i a t e to low r a t i o s of 0.78-0.72 AV/CV were more frequent a f t e r exposure to p r e d a t i o n than i n unexposed 28 Table 7. V e r t e b r a l count c l a s s e s i n c o n t r o l groups of Holden Lake p r e d a t i o n experiments, based on numbers of abdominal and caud a l v e r t e b r a e . V e r t e b r a l number T o t a l Abdominal Caudal No. R a t i o Abd./Caud. 30 1 5 15 1 1 .00 1 4 16 68 0.88 1 3 17 68 0.76 1 2 18 5 0.67 31 1 5 16 35 0.94 1 4 1 7 701 0.82 13 18 196 0.72 32 1 5 17 52 0.88 1 4 18 290 0.78 1 3 19 24 0.68 Table 8. Ratios of abdominal to caudal vertebrae in Holden Lake sticklebacks exposed (exptl.) or unexposed (control) to predation by sunfish. Results of experiments H2 and H3 are shown separately for fish 8.5 mm or less (S) or over 8.5 mm (L) in length. Probabilities are from chi-square tests of independence between count class and predation treatment, with fish grouped as those with or without the ratio(s) favoured during exposure to predation. (In experiment H1, a ratio of 0.82 is tested). Abbreviations are total vertebral number (TV), number of abdominal vertebrae (AV), and number of caudal vertebrae (CV). Vertebral count class (%) Exp. Treatment Mean 1ength (mm) AV: TV: AV/CV: £0.88 14 31 0.82 14 32 0. 78 13 30 0.76 13 31 0.72 other No. surviving Favoured ratio(s) Probabi1Ity H1 Control 7 63 1 1 3 45. 4 19. 6 4 6 13. 8 5 5 240 (0.82) 0.87 Exptl. 7 89 1 1 9 46. 0 17. 7 5 4 16. 5 2 6 504 H2S Control 8 06 14 6 45. 3 29. 7 1 . 2 6. 4 2 9 172 0.82 0.038 Exptl. 8 15 15 2 56. 1 19. 5 2. 0 6. 3 1 0 205 H3S Control 8 12 13 2 46. 0 19. 7 10 2 10. 9 137 0.82 0.062 Exptl. 8 20 11 5 58. 1 14. 3 4. 8 10. 5 1 0 105 H2L Control 8 87 9 1 57. 1 20. 8 2. 6 9. 1 1 3 77 0.78 0.43 Exptl. 9 05 13 4 50. 5 25. 1 1 5 7. 3 2 2 275 H3L Control 9 03 10 7 44. 6 24. 1 4. 5 14. 3 1 8 112 0.78 0.46 Exptl. 9 17 10 6 41 . 9 27. 7 5. 2 13. 4 1 2 329 H4 Control 9 79 10 7 49. 8 20. 4 2 9 13. 9 2 4 245 0.78-0.72 0.066 Exptl. 10 21 8 8 45. 2 24 3 4 6 15. 3 1 8 502 H5 Control 10 01 9 2 46. 0 13. 0 5. 9 21 . 8 4 2 239 0.78-0.72 0.01 1 Exptl. 9 99 4 9 41 . 5 17. 8 7 8 24. 9 3 1 511 H6 Control 1 1 16 8 4 52. 5 17 2 5 5 1 1 . 8 4 7 238 0.72 0.006 Exptl. 11 59 5 4 49. 0 17. 9 3 4 20. 0 4 3 469 30 F i g u r e 3. Change i n percent frequency d u r i n g p r e d a t i o n of v e r t e b r a l count c l a s s e s based on the r a t i o of abdominal to caudal v e r t e b r a e (experimental minus c o n t r o l f r e q u e n c i e s ) , i n 1983 experiments with Holden Lake s t i c k l e b a c k s . S o l i d bars above h o r i z o n t a l a x i s are v e r t e b r a l count c l a s s e s i n c r e a s i n g i n frequency d u r i n g exposure to p r e d a t i o n ; open bars below a x i s are those d e c r e a s i n g d u r i n g p r e d a t i o n . Mean l e n g t h i n c o n t r o l group at end of experiment i s given i n each p a n e l . P r o b a b i l i t i e s are as i n Table 8. A b b r e v i a t i o n s TV, AV and CV are numbers of t o t a l , abdominal and caudal v e r t e b r a e , r e s p e c t i v e l y . 5 " 0 - - 5 - 1 0 5 c o 0 o v? • - 5 C L X UJ - 1 0 °̂ 1 0 Z o 5 r- < 0 Q UJ CC - 5 0, - 1 0 CD CC 5 ID Q 0 >- . - 5 U UJ 5 o UJ 0 u . - 5 5 UJ 0 AN  - 5 X o 5 0 - 5 10 5 0 - 5 H I 7 . 6 3 m m J I H 2 S 8 . 0 6 m m T Z T H 3 S 8 . 1 2 m m H 2 L 8 . 8 7 m m H 3 L 9 . 0 3 m m H 4 9 . 7 9 m m H 5 1 0 . 0 1 m m T Z Z T 1 H 6 I I . 1 6 m m i i i i i A V / C V > 0 . 8 8 0 . 8 2 0 . 7 8 - 0 . 7 6 0 . 7 2 O T H E R T V 3 0 - 3 2 31 3 2 , 3 0 31 V E R T E B R A L C O U N T 32 c o n t r o l groups (p=0.002 grouping experiments H4 and H5, s i n c e the frequency of f i s h with these r a t i o s d i d not d i f f e r between these experiments (p=0.44)). F i n a l l y , f i s h with a low r a t i o of 0.72 AV/CV were s i g n i f i c a n t l y more frequent a f t e r p r e d a t i o n at the l a r g e s t prey s i z e t e s t e d (11.2 mm). T h i s c l o s e r examination of the Holden Lake experiments r e v e a l s that s e l e c t i v e p r e d a t i o n f o r t o t a l v e r t e b r a l number i n these experiments i s e v i d e n t l y the r e s u l t of s e l e c t i o n f o r the r a t i o AV/CV. The i n c r e a s e d frequency of f i s h with 31 v e r t e b r a e a f t e r p r e d a t i o n at l e n g t h s of about 8.1-8.2 mm i s accounted f o r by the i n c r e a s e i n frequency of f i s h with a h i g h r a t i o of 0.82 AV/CV; f i s h with 31 v e r t e b r a e and a low r a t i o of 0.72 AV/CV d i d not i n c r e a s e i n frequency a f t e r p r e d a t i o n at these s i z e s . S e l e c t i v e p r e d a t i o n with r e s p e c t to the r a t i o AV/CV cannot be a t t r i b u t e d to s i z e s e l e c t i o n i n these experiments. In experiment H5, no s i z e s e l e c t i o n o c c u r r e d . In a l l other experiments, longer f i s h tended to have g r e a t e r s u r v i v a l d u r i n g exposure to p r e d a t i o n . In experiments H2S and H3S, f i s h with the favoured r a t i o of 0.82 AV/CV were s l i g h t l y (though not s i g n i f i c a n t l y ) l e s s frequent at g r e a t e r lengths i n c o n t r o l groups (Table 9). Hence, s i z e s e l e c t i o n c o u l d not have c o n t r i b u t e d to the observed i n c r e a s e i n the frequency of f i s h with t h i s r a t i o d u r i n g p r e d a t i o n i n these two experiments. In experiments H2L, H4 and H6, f i s h with the favoured r a t i o ( s ) were s l i g h t l y more frequent at g r e a t e r l e n g t h s i n c o n t r o l groups (Table 9). Hence, s i z e s e l e c t i o n may have c o n t r i b u t e d s l i g h t l y to the observed i n c r e a s e i n the frequency of f i s h with these r a t i o s d u r i n g Table 9. Relationship between vertebral count class and length 1n control groups In Holden Lake experiments. Frequencies of fish with the favoured ratio(s) are shown for lengths less than or equal to the mean (S) or greater than the mean (L). Probabilities are ch1-square tests of Independence between vertebral count and size classes, with fish grouped as those with or without the favoured ratio. Favoured Mean Frequency of Exp. rat lo AV/CV Size cl ass 1ength (mm) favoured ratio (%) No. Probabi1 H1 (0.82) S 7. . 16 43, .0 1 14 0.47 L 8 .05 47 .6 126 H2S 0.82 S 7 . 74 51 .4 72 0. 23 L 8 .29 41 .0 100 H3S 0.82 S 7, .80 46. .8 62 1 .00 L 8. .38 45, .3 75 H2L 0.78 S 8 .70 14 .6 41 0.26 L 9 .07 27 .8 36 H3L 0.78 S 8. .77 24, .2 62 1 .00 L 9. 35 24. O 50 H4 0. 78-0.72 S 9. 29 36. 9 122 0.93 L 10. ,30 37 , .4 123 H5 0. 78-0.72 S 9. 51 35. 5 124 0. 10 L 10. 54 46. , 1 1 15 H6 0. 72 S 10. 53 10. 3 1 16 0.51 L 1 1 . 76 13. 1 122 34 p r e d a t i o n i n these other experiments. However, i n no case d i d the frequency of the favoured r a t i o ( s ) d i f f e r s i g n i f i c a n t l y between f i s h below or above the mean l e n g t h i n c o n t r o l groups (Table 9). Since t h i s comparison i n v o l v e s a much gr e a t e r d i f f e r e n c e i n mean s i z e than that between c o n t r o l and experimental groups, i t i s u n l i k e l y that s e l e c t i v e p r e d a t i o n with r e s p e c t to the r a t i o AV/CV can be e x p l a i n e d by s i z e s e l e c t i o n i n any of these experiments. To f u r t h e r r u l e out t h i s p o s s i b i l i t y , I c a l c u l a t e d the counts expected i n experimental groups as a r e s u l t of s i z e s e l e c t i o n a l o n e . The expected frequency E of f i s h with the favoured r a t i o ( s ) was c a l c u l a t e d as E = (^ j Pj Nj) / Nt where Pj i s the frequency of f i s h with the favoured r a t i o ( s ) i n the j t h s i z e c l a s s i n c o n t r o l groups, Nj i s the number of f i s h i n the j t h s i z e c l a s s i n experimental groups, and Nt i s the t o t a l number of f i s h i n experimental groups. Four s i z e c l a s s e s were d i s t i n g u i s h e d : (1) L ^ X-0.68s, (2) X-0.68S < L ^ X, (3) X < L ^ X+0.68s, and (4) L > X+0.68s, where X and s are the mean l e n g t h and i t s standard d e v i a t i o n i n c o n t r o l groups. In a l l experiments i n which the frequency of f i s h with the favoured r a t i o AV/CV d i f f e r e d s i g n i f i c a n t l y between experimental and c o n t r o l groups, i t a l s o d i f f e r e d s i g n i f i c a n t l y between experimental groups and those expected as a r e s u l t of s i z e s e l e c t i o n alone (Table 10). Table 10. Ratio of abdominal to caudal vertebrae (AV/CV) In Holden Lake sticklebacks exposed (experimental) or unexposed (control) to predation by sunfish, and the ratio expected in exposed fish If predation Is selective for prey size but not for the ratio AV/CV. Frequencies of fish with the favoured ratio are shown. Probabilities are ch1-square tests comparing the observed frequency In experimental groups and that expected due to size selection alone. Probabilities are calculated assuming that the expected frequency due to size selection alone Is a sampled value, with sample size equal to that In control groups. Frequency of favoured ratio (%) Experimental Exp. Favoured rat 1o AV/CV Control Expected due to size selection Observed Probabl11ty H1 (0.82) H2S 0.82 H3S 0.82 H2L 0.78 H3L 0.78 45.4 45 . 3 46 .0 20.8 24 . 1 37.2 40.7 11.8 46.0 44 .6 46. 1 16.8 24 .8 37 .4 40.5 12.9 46.0 56. 1 58 . 1 25 . 1 27.7 44.2 50.5 20.0 0.025 0.05 0. 10 0.50 0.05 0.01 0.01 >0.90 0.05 0. 10 0.25 0.75 0. 10 0.025 0.025 H4 0.78-0.72 H5 0.78-0.72 H6 0.72 36 2. Kennedy Lake experiments The d i v i s i o n of the v e r t e b r a l column i n t o abdominal and caudal regions i n Kennedy Lake f i s h d i f f e r e d markedly from that seen i n Holden Lake f i s h (Table 11). Kennedy Lake f i s h tended to have one more abdominal v e r t e b r a than Holden Lake f i s h with the same t o t a l v e r t e b r a l count. Thus, r a t i o s of abdominal to caudal v e r t e b r a e tended to be higher i n Kennedy than i n Holden Lake f i s h . In experiments K2 and K3, r e s u l t s resembled those seen u s i n g Holden Lake f i s h , i n that the r a t i o s of abdominal to caudal v e r t e b r a e at advantage d u r i n g p r e d a t i o n appeared to decrease as prey s i z e i n c r e a s e d (Table 12 and F i g . 4). At the smaller prey s i z e i n experiment K2, f i s h with h i g h r a t i o s of 0.88-0.94 AV/CV were more frequent a f t e r p r e d a t i o n i n experimental groups than i n unexposed c o n t r o l groups (p=0.027). Conversely, at the l a r g e r prey s i z e i n experiment K3, f i s h with low r a t i o s of 0.78-0.82 AV/CV were more frequent a f t e r p r e d a t i o n (p=0.024). However, the a c t u a l r a t i o s at advantage d u r i n g p r e d a t i o n at a given s i z e d i f f e r e d between the two p o p u l a t i o n s . At average prey s i z e s of about 8.1-8.2 mm, r a t i o s of 0.88-0.94 were favoured i n Kennedy Lake f i s h , while one of 0.82 was favoured i n Holden Lake f i s h . R e s u l t s i n experiment K1 departed somewhat from the p a t t e r n d e s c r i b e d above. In t h i s experiment, f i s h w ith t o t a l v e r t e b r a l counts of 31 appeared to be at advantage d u r i n g p r e d a t i o n r e g a r d l e s s of the p r o p o r t i o n of v e r t e b r a e that were abdominal. However, r e s u l t s d i d conform to the expected p a t t e r n to the 37 Table 11. V e r t e b r a l count c l a s s e s i n c o n t r o l groups of Kennedy Lake p r e d a t i o n experiments, based on numbers of abdominal and caudal v e r t e b r a e . V e r t e b r a l number T o t a l Abdominal Caudal No. Abd./Caud. 30 1 5 15 6 1 .00 1 4 16 22 0.88 31 16 15 1 1 .07 15 16 198 0.94 1 4 1 7 138 0.82 32 1 6 16 1 2 1 .00 1 5 1 7 250 0.88 1 4 18 70 0.78 33 15 18 6 0.83 Table 12. Ratios of abdominal to caudal vertebrae 1n Kennedy Lake sticklebacks exposed (experimental) or unexposed (control) to predation by sunfish. Probabilities are from chi-square tests of Independence between vertebral count classes and predation treatments, with fish grouped as those with or without the ratios favoured during exposure to predators. In experiment KI, two ratios (0.94 or 0.82) are tested. Abbreviations are as in Table 8. Vertebral count class (%) Exp. Treatment Mean 1ength (mm) AV: TV: AV/CV: 15 31 0.94 15 32 0.88 14 31 0.82 14 32 0.78 Other No. surv1v1ng Favoured rat1os Probabl1i ty K1 Control 8.31 21.0 40.3 19.9 17.6 1 . 1 176 0.94 0.038 Exptl. 8.43 29.2 32.2 24.6 10.8 3.2 463 0.82 0.21 K2 Control 8. 18 24.7 30.5 22.2 12.3 10.3 243 0.88-0.94 0.027 Exptl. 8.50 31.3 32. 1 21.5 5.8 9.4 608 K3 Control 8.92 35.6 37 .0 17.3 3.2 7.0 284 0.78-0.82 0.024 Exptl. 9. 10 35.7 30.5 21.3 6. 1 6.4 653 39 F i g u r e 4. Change i n percent frequency dur i n g p r e d a t i o n of v e r t e b r a l count c l a s s e s based on the r a t i o AV/CV, i n 1982 experiments u s i n g Kennedy Lake s t i c k l e b a c k s . Symbols and a b b r e v i a t i o n s are as i n F i g . 3. ko 1 0 < o UJ LT CL C9 Z ) C Q ° O O ^ ^ I LU C L Z) x a LU LLI ~ 0 - i o L 1 0 0 I O L UJ CD z : < x o l O r 0 -10 AV/CV TV L l K2 8.18 mm K I 8.31 mm K 3 8.92 mm 0.94 0.88 0.82 0.78 Other 31 32 31 32 V E R T E B R A L COUNT 41 extent that t h i s i n c r e a s e i n frequency of f i s h with 31 ve r t e b r a e a f t e r p r e d a t i o n was s i g n i f i c a n t among f i s h with a high r a t i o of 0.94 AV/CV (p=0.038), but not among those with a lower r a t i o of 0.82 AV/CV (p=0.2l). S e l e c t i v e p r e d a t i o n with r e s p e c t to the r a t i o of abdominal to caudal v e r t e b r a e cannot be a t t r i b u t e d to s i z e s e l e c t i o n i n these experiments. In a l l three experiments, l a r g e r f i s h tended to have hig h e r s u r v i v a l d u r i n g p r e d a t i o n , but the frequency of f i s h with the favoured r a t i o s was lower i n l a r g e r than i n s m a l l e r f i s h b efore p r e d a t i o n i n c o n t r o l groups (Table 13). 3. Summary S e l e c t i v e p r e d a t i o n f o r t o t a l v e r t e b r a l number i n these experiments a p p a r e n t l y r e s u l t e d from s e l e c t i o n f o r the r a t i o of abdominal to c a u d a l v e r t e b r a e . In 1983 experiments with Holden Lake s t i c k l e b a c k s , s u r v i v a l at smal l prey s i z e s (8.1-8.3 mm) was g r e a t e s t among f r y with a hi g h r a t i o of 0.82 AV/CV. At int e r m e d i a t e (9.8-10.0 mm) or l a r g e (11.2 mm) prey s i z e s , s u r v i v a l was g r e a t e s t f o r f r y with i n t e r m e d i a t e to low (0.78-0.72) or low (0.72) r a t i o s , r e s p e c t i v e l y . In 1982 experiments w i t h Kennedy Lake s t i c k l e b a c k s , the r a t i o s at advantage d u r i n g exposure to p r e d a t i o n a l s o tended to decrease as prey s i z e i n c r e a s e d . However, r a t i o s tended to be higher i n Kennedy than i n Holden Lake f i s h , and higher r a t i o s were favoured at a gi v e n prey s i z e i n the Kennedy lake f i s h . S e l e c t i v e p r e d a t i o n f o r v e r t e b r a l count r a t i o was not a t t r i b u t a b l e to s i z e s e l e c t i o n . Table 13. Ratios of abdominal to caudal vertebrae In control groups in Kennedy Lake experiments, at lengths less than or equal to (S) or greater than (L) the mean length. Probabilities are from chi- square tests of independence between vertebral count and length classes, with fish grouped as those with or without the ratios favoured during predation. In experiment K1, two ratios (0.94 or 0.82) are tested. Abbreviations are as 1n Table 8. Vertebral count class (%) AV: 15 15 14 14 Size TV: 31 32 31 32 Favoured Exp. cl ass AV/CV: 0.94 0.88 0.82 0.78 Other No. ratios Probabi11ty K1 S 21.3 36.3 23.8 17.5 1.3 80 0.94 1.00 L 20.8 43.8 16.7 17.7 1 .0 96 0.82 0.33 K2 S 29.2 27.5 23. 1 9.2 10.8 120 0.88-0.94 0.64 L 20.3 33.3 21.1 15.4 9.8 123 K3 S 32.5 35.8 20.3 4. 1 7.3 123 0.78-0.82 0. 15 L 37.9 37 .9 14.9 2.5 6.8 161 4=>. K> 43 Body P r o p o r t i o n s 1. Holden Lake experiments S e l e c t i o n with r e s p e c t to the r a t i o of abdominal to caudal v e r t e b r a e c o u l d r e s u l t from s e l e c t i o n with respect to body p r o p o r t i o n s . To t e s t t h i s p o s s i b i l i t y , I c o n s i d e r e d the p r e c a u d a l / c a u d a l l e n g t h r a t i o , where p r e c a u d a l l e n g t h i s the t o t a l minus the caudal l e n g t h . As might be expected, the r a t i o of abdominal to caudal v e r t e b r a e and t h i s l e n g t h r a t i o were d i r e c t l y and h i g h l y s i g n i f i c a n t l y (p<0.000l) r e l a t e d (Table 14). However, onl y about 30-65% of the o v e r a l l v a r i a t i o n i n v e r t e b r a l count r a t i o (VR) i s e x p l a i n e d by v a r i a t i o n i n l e n g t h r a t i o (LR). (I use the a d j u s t e d (see M a t e r i a l and Methods) caudal l e n g t h i n these a n a l y s e s s i n c e l e n g t h r a t i o s c a l c u l a t e d with t h i s adjustment e x p l a i n over twice as much of the v a r i a t i o n i n VR as do those c a l c u l a t e d without i t ) . W i t h i n a v e r t e b r a l count c l a s s , v a r i a t i o n i n LR i s c o n s i d e r a b l e ( F i g . 5). T h i s v a r i a t i o n w i t h i n v e r t e b r a l count c l a s s e s may r e s u l t p a r t l y from v a r i a t i o n i n r e l a t i v e head l e n g t h s , and p a r t l y from v a r i a t i o n i n the spacing of v e r t e b r a e ( i . e . , i n the number of abdominal or caudal v e r t e b r a e per u n i t of abdominal or caudal body l e n g t h ) . In most experiments, the r e g r e s s i o n of VR on LR d i f f e r s s i g n i f i c a n t l y between c o n t r o l and experimental groups i n slope or i n t e r c e p t , i n d i c a t i n g s e l e c t i v e p r e d a t i o n f o r VR, LR or both. LR decreased d u r i n g exposure to p r e d a t i o n i n experiments H1, H2S and H5, and i n c r e a s e d d u r i n g p r e d a t i o n i n experiment H6 (Table 15). LR and t o t a l l e n g t h were i n v e r s e l y r e l a t e d (p<0.05) in a l l four T a b l e 14. R e g r e s s i o n of the r a t i o of abdominal to caudal v e r t e b r a e (VR) on the r a t i o of precauda to c a u d a l l e n g t h (LR) i n c o n t r o l and experimental groups o f - H o l d e n Lake experiments. P r o b a b i 1 i t y VR vs LR e q u a l i t y of z e r o s l o p e s and e q u a l i t y 2 Exp. Treatment No. I n t e r c e p t Slope s i ope I n t e r c e p t s of s l o p e s r H1 C o n t r o l 240 0. .1514 0 .4683 <0. .0001 0.0005 0.009 0.40 E x p t l . 504 0. .3215 0 .3518 <0. .0001 0. 32 H2 C o n t r o l 249 0. . 1806 0. .4572 <0 .0001 0.0001 0.038 0.44 E x p t l . 480 0. .0710 0. .5446 <0. .0001 0.47 H3 C o n t r o l 249 0. , 1 136 0, .4971 <0. .0001 0.60 0.78 0.53 E x p t l . 434 9 . 1310 0 .4863 <0. .0001 0.48 H4 C o n t r o l 245 0 .0746 0 .5341 <0 .0001 0.026 0.007 0.48 E x p t l . 502 -0. .0740 0. .6430 <0. .0001 0.61 H5 C o n t r o l 239 -0. .0398 0. .5965 <0. .0001 0.0006 0. 13 0.66 E x p t l . 511 -0. . 1042 0 .6494 <0. .0001 0.63 H6 C o n t r o l 238 0. .0273 0. .5657 <0. .0001 <0.0001 0.085 0.54 E x p t l . 469 -0. .0800 0. .6308 <0. .0001 0.66 45 F i g u r e 5. R a t i o s of p r e c a u d a l / c a u d a l l e n g t h (LR) i n v e r t e b r a l count c l a s s e s VR of Holden Lake s t i c k l e b a c k s exposed (experimental, open bars) or unexposed ( c o n t r o l , b l a c k bars) to p r e d a t i o n by s u n f i s h . VR i s the r a t i o of abdominal to caudal v e r t e b r a e . R e s u l t s are shown f o r three c a s e s : A. H1, p r e d a t i o n s e l e c t i v e f o r LR but not VR; B. H2S, s e l e c t i o n f a v o u r i n g low LR but h i g h VR; and C. H6, s e l e c t i o n f a v o u r i n g h i g h LR but low VR.  Table 15. Body proportions of Holden Lake sticklebacks exposed (exptl.) or unexposed (control) to predation by sunfish. Body proportions are the pre-caudal length divided by the caudal length. When length ratios are related (p<0.05) to total length, adjusted ratios are also shown. When slopes of this relationship differ (p<0.05) between predation treatments, slopes within treatments are also shown. Methods of adjustment are : (A) no adjustment made. (B) ratios adjusted to grand mean length (standard analysis of covariance), (C) ratios in control group adjusted to mean length in experimental group, or (D) ratios In experimental group adjusted to mean length in control group. Regression between length ratio and total length Probability of Precaudal/caudal length ratio Probability zero equal of zero Adjusted Adjustment Probability of Exp. SI ope s 1 ope slopes Treatment Slope si ope No. Mean SE mean method equal means H1 -0.00229 <0.001 0.42 Control 240 1 .3832 0 .00433 1 .3782 B 0.029 Exptl. — -- 504 1 . 3642 0 .00297 1 .3666 H2S -0.00176 0.039 0.023 Control -0.003G7 0.004 172 1 . 3830 0 .00497 1 .3788 C 0.079 Exptl. 0.00181 0.87 205 1 .3671 0. .00455 1 .3671 H3S -0.00487 <0.001 0.56 Control -- -- 137 1 .3928 0 .00526 1 .3907 B 0.41 Exptl . -- 105 1 .3946 0 .00601 1 .3973 H2L 0.00113 0.20 0.41 Control -- 77 1 .3673 0 .00719 -- A 0.66 Exptl. — -- 275 1 .3639 0 .00374 H3L -0.00188 0.007 0.015 Control 0.00136 0.41 1 12 1 .3830 0. .00646 1 . 3829 D 0.71 Exptl. -0.00278 0.0003 329 1 . 3753 0, .00374 1 .3802 H4 -0.00090 0.002 0.54 Control -- -- 245 1 .3635 0. .00402 1 .3604 B 0.64 Exptl. -- 502 1 . 3566 0. .00276 1 .3581 H5 -0.00117 <0.001 0.66 Control -- 239 1 .3951 0, ,00417 1 .3952 B <0.001 Exptl. — -- 511 1 .3687 0. .00285 1 .3686 HG -0.00055 0.033 0.56 Control -- 238 1 .3695 0. ,00432 1 .3676 B 0.005 Exptl. -- -- 469 1 .3817 0. .00304 1 .3827 Note: Regressions are calculated with length In ocular micrometer units: 1 unit = 0.082083 mm. SE = standard error. 48 experiments, but s e l e c t i v e p r e d a t i o n with res p e c t to LR cannot be a t t r i b u t e d to s i z e s e l e c t i o n a l o n e . In experiment H1, a s i g n i f i c a n t decrease i n LR d u r i n g p r e d a t i o n p e r s i s t s a f t e r adjustment of c o n t r o l and experimental groups to a common t o t a l l e n g t h . In experiment H2S, the mean LR of experimental groups remains lower than that of c o n t r o l groups a f t e r adjustment, although the d i f f e r e n c e between groups only approaches s i g n i f i c a n c e (p=0.08). In experiment H5, the mean LR of experimental groups was lower than that of c o n t r o l groups even though no s i z e s e l e c t i o n o c c u r r e d . In experiment H6, s i z e s e l e c t i o n c o u n t e r a c t e d s e l e c t i o n with r e s p e c t to LR. In summary, low LR was sometimes favoured d u r i n g p r e d a t i o n at small (H1,H2S) or medium (H5) prey s i z e s , while h i g h LR was favoured a t l a r g e prey s i z e (H6). R e s u l t s are shown s e p a r a t e l y f o r each v e r t e b r a l count c l a s s i n T able 16 and F i g . 5. In a l l experiments with s i g n i f i c a n t o v e r a l l s e l e c t i o n f o r LR, i t i s i n the same d i r e c t i o n i n a l l count c l a s s e s . However, s i g n i f i c a n t i n t e r a c t i o n does occur between v e r t e b r a l count c l a s s and p r e d a t i o n treatment i n experiment H5, and p o s s i b l y i n experiments H3L and H4. In experiment H5, the decrease i n LR d u r i n g p r e d a t i o n i s g r e a t e s t i n the count c l a s s with the h i g h e s t mean LR (VR^0.88). In experiment H2S, s e l e c t i o n f o r low LR was a p p a r e n t l y p a r t l y obscured by s e l e c t i o n f o r hi g h (0.82) VR. A f t e r a d j u s t i n g to a common t o t a l l e n g t h i n t h i s experiment, the decrease i n LR du r i n g p r e d a t i o n only approached s i g n i f i c a n c e combining v e r t e b r a l count c l a s s e s (Table 15), but was h i g h l y s i g n i f i c a n t w i t h i n v e r t e b r a l Table 16. Change in precaudal/caudal length ratio (LR) within vertebral count classes in Holden Lake sticklebacks after exposure to predation in 1983. Data are the mean in experimental groups minus that in control groups. Unadjusted data and data adjusted to a common total length (TL) are shown. Adjustment A employs standard analysis of covariance; tests of zero slope and equality of slopes among groups are shown for the regression of'LR on TL. Groups with slopes differing (p<0.05) from the slope of other groups combined are noted. A second adjustment B is shown when slopes are heterogeneous among groups. PT is the probability that mean LR does not differ between predation treatments, and PT x CT the probability of no interaction between predation treatment and count class. Abbreviations: C = control, E = experimental, C72 = control with 0.72 abd./caud. vertebrae. Ratio abdominal/caudal vertebrae Probability Probability Probability Groups Qf z e r o 0 f equal differing Exp. Method 50.88 0.82 0.77 0.72 PT PT x CT slopes slopes from rest H1 Unadjusted -0 .018 -0. .017 Adjusted A -0 .015 -0. .012 Adjusted B -0 .010 -0. .008 H2S Unadjusted -0 .040 -0. .017 Adjusted A -0 .037 -0. .015 Adjusted B -0 .035 -0. .016 H3S Unadjusted -0. .024 0. ,009 Adjusted A -0. .019 0. ,01 1 Adjusted B -O .031 0. ,010 H2L Unadj usted 0. .008 -0. ,009 Adjusted A 0 .002 -0. .013 H3L Unadjusted -0. .025 0. ,008 Adjusted A -0. .025 0. ,009 Adjusted B -0. .028 0. ,010 H4 Unadjusted -0. .002 -0. 001 Adjusted A -0. .002 0. ,002 Adjusted B -0. .002 -0. ,001 H5 Unadjusted -0. .058 -0. ,016 Adjusted A -0. .057 -0. ,016 H6 Unadjusted 0. .018 0. 025 Adjusted A 0. .021 0. 027 Adjusted B 0 ,024 0. 027 0. .027 -0, .030 <0. .0001 0, .44 0. .020 -0 .021 0. .0002 0, .79. 0 .018 -0 .018 0, .0025 0, . 73 0, .004 -0, .033 0. .0004 0. . 13 0. .004 -0, .032 0. .0009 0, . 17 0. .004 -0 .032 0. .0010 0, .22 •0, .002 -0, .023 0. . 17 0, .21 0, .001 -0, .022 0. ,27 0. . 19 0. .001 -0. .023 0. . 12 0, .076 0. .010 0. .014 0. ,93 0. .62 0. ,014 0 ,010 0. ,64 0. ,67 0. ,014 0. ,015 0. 53 0. ,069 0. ,013 0. .019 0. 68 0. ,054 0. .012 0. .020 0. .65 0. ,034 0. .002 -0. ,013 0. ,24 0. ,60 0. .0003 -0, ,01 1 0. ,49 0. .61 0. ,016 -0. .013 0. ,94 0. .044 0.020 -0.018 <0.0001 0.012 0.020 -0.018 <0.0001 0.012 0, ,028 0, .007 0. ,0011 0. 49 0. .030 0, .009 <0. ,0001 0. ,25 0. ,030 0, .009 <0. .0001 0. 26 <0.0001 0.007 C72, E77 0.005 0.09 C88 0.0004 0.18 E88 0.013 0.93 0.15 0.17 C88 0.033 <0.001 C77 0.010 0.18 0.015 0.15 E88 Note: Adjustment B: (1) H1: slopes homogeneous among control groups; LR In control groups adjusted to mean TL in experimental groups. (2) H2S, 3S, 3L, and 6: slopes homogeneous among groups omitting the group noted in table; LR is adjusted to the mean TL of all groups combined, using either the slope in the differing group or that in all other groups combined. (3) H4: slope Is significant In C77 only; LR in C77 adjusted to mean TL in E77. vo 50 count c l a s s e s (Table 16). S e l e c t i o n with r e s p e c t to LR cannot account f o r s e l e c t i o n f o r the r a t i o of abdominal to cau d a l vertebrae (VR). In experiment H1, s e l e c t i o n was s i g n i f i c a n t f o r LR but not f o r VR. In experiment H2S, s e l e c t i o n favoured h i g h (0.82) VR but low LR. In experiments H3S and H4, s e l e c t i o n approached s i g n i f i c a n c e f o r VR (p=0.06-0.07) but not f o r LR (p=0.40-0.60). In experiment H6, s e l e c t i o n favoured low (0.72) VR but hig h LR. Thus, i n some experiments (H1, H3S, and H4) s e l e c t i o n was s i g n i f i c a n t f o r one but not the other prey a t t r i b u t e , w h ile i n other experiments (H2S and H6) s e l e c t i o n f o r one a t t r i b u t e c o u n t e r a c t e d s e l e c t i o n f o r the o t h e r . 2. Kennedy Lake experiments Body p r o p o r t i o n measurements were made i n experiments K1 and K2 o n l y . Two l e n g t h r a t i o s were c o n s i d e r e d : abdominal/caudal l e n g t h (LR1) and pr e c a u d a l / c a u d a l l e n g t h (LR2) (abdominal l e n g t h = t o t a l - head - caudal l e n g t h ; p r e c a u d a l l e n g t h = head l e n g t h + abdominal l e n g t h ) . The two l e n g t h r a t i o s were h i g h l y c o r r e l a t e d (p<0.000l); 80 and 86% of the v a r i a t i o n i n the pr e c a u d a l / c a u d a l r a t i o was e x p l a i n e d by v a r i a t i o n i n the abdominal/caudal r a t i o i n experiments K1 and K2, r e s p e c t i v e l y . These l e n g t h r a t i o s c o u l d not be compared among c l a s s e s of the u s u a l v e r t e b r a l count r a t i o VR, s i n c e the c r i t e r i a f i n a l l y employed to d i s t i n g u i s h abdominal from caudal vertebrae were not those used when these l e n g t h measurements were made. Instead, a r a t i o VR', based on the numbers of ve r t e b r a e a n t e r i o r to or 51 opposed and p o s t e r i o r to the f i r s t a n a l b a s a l , w i l l be used here. VR and VR' were e q u i v a l e n t i n 89% of f i s h i n experiments K1 and K2. In the remainder, the d i v i s i o n used i n VR' d i f f e r e d by one v e r t e b r a from that used i n VR. Both l e n g t h r a t i o s showed a h i g h l y s i g n i f i c a n t c o r r e l a t i o n w i t h VR' (Table 17). However, v a r i a t i o n i n l e n g t h r a t i o i s c o n s i d e r a b l e w i t h i n any one v e r t e b r a l count c l a s s , even f o r the abdominal/caudal r a t i o ( F i g . 6). In the case of t h i s l a t t e r l e n g t h r a t i o , most v a r i a t i o n w i t h i n count c l a s s e s must be due to v a r i a t i o n i n the spacing of v e r t e b r a e . R e l a t i o n s h i p s between LR and t o t a l l e n g t h or VR (or VR') d i f f e r e d somewhat between Kennedy and Holden Lake f i s h . LR was i n v e r s e l y r e l a t e d to t o t a l l e n g t h i n Holden Lake f i s h (Table 15), but d i r e c t l y r e l a t e d to t o t a l l e n g t h i n Kennedy Lake f i s h (Table 18). More of the v a r i a t i o n i n VR was e x p l a i n e d by v a r i a t i o n i n LR i n Holden than i n Kennedy Lake f i s h (Tables 14 and 17). T h i s o c c u r s d e s p i t e the i n c l u s i o n of head l e n g t h i n the LR used i n the Holden Lake comparison, but not i n LR1 i n the Kennedy Lake comparison. F i n a l l y , r e g r e s s i o n s of VR on LR u s u a l l y d i f f e r e d between c o n t r o l and experimental groups i n the Holden Lake experiments (Table 14), but not i n the Kennedy Lake experiments (Table 17). Some of these d i f f e r e n c e s might r e s u l t from the use of more a p p r o p r i a t e c r i t e r i a to d i s t i n g u i s h abdominal from caudal v e r t e b r a e i n the LR a n a l y s i s of Holden Lake experiments. Table 17. Regression of vertebral count ratio VR' on length ratios LR in Kennedy Lake fish. VR' is the number of vertebrae anterior to the firs t anal basal divided by the number opposing or posterior to i t . LR1 is the length from the fi r s t vertebra to the fi r s t one opposing or posterior to the f i r s t anal basal divided by the length from the latter point to the end of the hypural plate. LR2 resembles LR1, but includes the head length in the numerator. Regressions are shown separately for control and experimental groups, and equality of slopes and intercepts tested between the two. Probabi1i ty equal Exp . LR Treatment No. Intercept S1 ope zero slope slopes and 1 ntercepts equal s1 opes 2 r K1 1 Control 17S 0. 3778 0. .4912 <0. .0001 0.36 0. 19 0. 19 Exptl. 460 0. 4882 0. . 3765 <0. .0001 0. 15 2 Control 176 0. 4252 0. , 2555 <0. .0001 0.72 0. 54 0. 13 Exptl. 460 0. 4824 0. . 2205 <0. .0001 0. 12 K2 1 Control 232 0. 3349 0. .5465 <0. .0001 0.052 0.86 0. 28 Exptl. 460 0. 3314 0. .5592 <0. ,0001 0. 24 2 Control 232 0. 2535 0. .3667 <0. .0001 0.25 0.63 0. 27 Exptl. 605 0. 2997 0. , 3430 <0. ,0001 0. 20 F i g u r e 6. R a t i o s of abdominal/caudal l e n g t h i n v e r t e b r a l count c l a s s e s VR' of Kennedy Lake s t i c k l e b a c k s exposed (experimental, open bars) or unexposed ( c o n t r o l , b l a c k bars) to p r e d a t i o n by s u n f i s h . VR' i s the number of vert e b r a e a n t e r i o r to the f i r s t a n a l b a s a l d i v i d e d by the number opposing and p o s t e r i o r to i t . 5h 1.0 1.2 1.0 1.2 L R 2 = A B D 0 M I N A L / C A U D A L L E N G T H Table 18. Body proportions of Kennedy Lake sticklebacks exposed (exptl.) or unexposed (control) to predation by sunfish. Body proportions LR1 and LR2 are as defined 1n Table 17. When LR is significantly (p<0.05) related to total length TL, adjusted LR is also shown. When slopes of regressions of LR on TL differ significantly between predation treatments, slopes within treatments are also shown. Adjustment methods are as in Table 15, except that in D control and experimental groups are adjusted to the grand mean TL using the separate slopes within each group. Probabi11ty Probabi1i ty zero equal of zero Adjusted Adjustment Probability of Exp. LR S1 ope s 1 ope slopes Treatment SI ope slope Mean SE mean method equal means K1 1 -0.00OO1 0.96 0.53 Control Exptl. -- — 0 0 .9827 .9946 0. 0. .00430 .00265 -- A 0.018 2 0.00121 0.008 0.28 Control Exptl. -- -- 1 1 .7039 . 7246 0. 0. .00655 .00404 1.7052 1 .7241 B 0.015 K2 1 0.00034 0. 10 0.004 Control Exptl. 0.00129 -0.00004 0.003 0.85 0 0 .9870 .9797 0. 0, .00332 .00207 0.9919 0.9797 C 0.002 2 0.00133 <0.001 0.015 Control Exptl. 0.00250 0.00086 0.0001 0.012 1 1 .6920 .6900 0. 0, .00486 .00304 1.6967 1 .6879 D 0.12 56 S e l e c t i v e p r e d a t i o n with r e s p e c t to LR d i f f e r e d between the two experiments (Table 18). During exposure to p r e d a t i o n , mean LR i n c r e a s e d i n experiment K1, but decreased i n experiment K2 ( a f t e r adjustment of c o n t r o l and experimental groups to a common t o t a l l e n g t h ) . Thus, s e l e c t i o n with respect to LR may have c o n t r i b u t e d to s e l e c t i o n f o r the r a t i o of abdominal to caudal v e r t e b r a e i n experiment K1, but c o u n t e r a c t e d s e l e c t i o n f o r t h i s r a t i o i n experiment K2. T h e r e f o r e , i n these experiments as i n the Holden Lake experiments, s e l e c t i o n with respect to v e r t e b r a l count r a t i o s cannot i n g e n e r a l be a t t r i b u t e d s o l e l y to s e l e c t i o n with respect to l e n g t h r a t i o s . 3. Summary In 1983 experiments u s i n g Holden Lake f i s h , low LR was sometimes favoured d u r i n g p r e d a t i o n at small or medium f r y s i z e s , while high LR was favoured at l a r g e f r y s i z e s . S i m i l a r l y , i n 1982 experiments with Kennedy Lake f i s h , low LR was favoured a t the s m a l l e r f r y s i z e i n experiment K2, and high LR at the l a r g e r f r y s i z e i n experiment K1. S e l e c t i v e p r e d a t i o n f o r v e r t e b r a l count r a t i o was not a t t r i b u t a b l e to t h i s s e l e c t i o n f o r LR. In some experiments, s e l e c t i o n was s i g n i f i c a n t f o r one but not f o r the other prey a t t r i b u t e , while i n other experiments s e l e c t i o n f o r one a t t r i b u t e c o u n t e r a c t e d s e l e c t i o n f o r the ot h e r . 57 Part I I . Burst swimming performance of t h r e e s p i n e s t i c k l e b a c k s M a t e r i a l s and Methods F i s h . used were l a b o r a t o r y - r e a r e d o f f s p r i n g of breeding s t i c k l e b a c k s c o l l e c t e d from Holden Lake i n August 1983, June - August 1984, and June 1985. In 1983, 113 c r o s s e s were made from a s i n g l e c o l l e c t i o n of paren t s , and the embryos produced reared together at about 17C i n the same 75 L tank. In 1984, between 1 and 15 c r o s s e s were made from each of 8 c o l l e c t i o n s of pa r e n t s , and embryos reared at temperatures between 14 and 23C. A f t e r h a t c h i n g , f r y from a s i n g l e r e a r i n g temperature and c o l l e c t i o n of parents were mixed t o g e t h e r , and h e l d at 15C u n t i l use. In 1985, 5 c r o s s e s were made from a s i n g l e c o l l e c t i o n of p a r e n t s , and embryos reared at. 14C, or at 22C u n t i l 46h a f t e r f e r t i l i z a t i o n and 14C t h e r e a f t e r . A f t e r h a t c h i n g i n a l l y e a r s , f r y were fed Artemia n a u p l i i twice d a i l y . I l l u m i n a t i o n was a r t i f i c i a l , but simulated the n a t u r a l p h o t o p e r i o d . Burst swimming performance was measured of f r y about 7-11.5 mm i n l e n g t h i n 1983 and 1984, and of f r y 9.4-11.5 mm i n l e n g t h i n 1985. Performance was measured i n a tank 1 m square i n 1983, or 0.6 m square i n 1984 and 1985. Water depth was 3 cm. S i n g l e f r y were i n t r o d u c e d i n t o a 3x3 cm c o n t a i n e r i n t h i s tank. A 250W f l o o d l i g h t was switched on, a s l i d i n g door i n the c o n t a i n e r opened, and f r y allowed to emerge from the c o n t a i n e r . Burst swimming was i n i t i a t e d u s i n g an a.c. e l e c t r i c shock s t i m u l u s a p p l i e d through two s t a i n l e s s s t e e l g r i d s 15 cm a p a r t . In 1983, 58 swimming was i n a 2V/cm e l e c t r i c f i e l d ; i n 1984 and 1985, swimming fo l l o w e d a 32 msec sti m u l u s of 8V/cm (with the exception noted below). Swimming was f i l m e d through a m i r r o r mounted overhead at a 45 degree angle, on 16 mm c i n e - f i l m at 64 frames/sec. In 1983, water temperature v a r i e d between 15 and 17C; i n 1984 and 1985, the f i l m i n g arena was immersed i n a water bath which maintained temperatures u s u a l l y w i t h i n 0.5C of e i t h e r 14.5 or 24.5C i n 1984, or 15.OC i n 1985. Temperature treatments w i l l be r e f e r r e d to as 15C or 25C. In 1984, some f r y were a l s o f i l m e d at 15C i n a v i s c o u s s o l u t i o n of 0.1% m e t h y l c e l l u l o s e ( v i s c o s i t y about 0.021 p o i s e , measured with an Ostwald v i s c o m e t e r ) . Some f r y f i l m e d i n t h i s s o l u t i o n experienced a stimulus of 48 msec d u r a t i o n ; performance was s i m i l a r whether stimulus d u r a t i o n was 32 or 48 msec. In summary, performance was measured under two temperature treatments (15 or 25C) and three v i s c o s i t y treatments: about 0.009 poise ( i n 25C water), 0.011 p o i s e ( i n 15C water) or 0.021 p o i s e ( i n 15C m e t h y l c e l l u l o s e s o l u t i o n ) . Fry were a c c l i m a t e d to the experimental temperature and v i s c o s i t y f o r at l e a s t 8 h, and f a s t e d f o r 8-24 h before use. A f t e r f i l m i n g , f r y were k i l l e d i n a n a e s t h e t i c , p r e s e r v e d i n 10% b u f f e r e d f o r m a l i n i n i n d i v i d u a l l y numbered v i a l s , and c l e a r e d and s t a i n e d as d e s c r i b e d above. Counts were made of c e n t r a e x c l u d i n g the u r o s t y l e . The l a s t v e r t e b r a was o f t e n complex; such v e r t e b r a e were counted as one. F i s h with other v e r t e b r a l i r r e g u l a r i t i e s were omitted from a n a l y s e s . Abdominal and caudal v e r t e b r a e were d i s t i n g u i s h e d on the b a s i s of haemal spine l e n g t h . The f i r s t v e r t e b r a whose haemal spine l e n g t h was 80% or more of 59 the maximum spine l e n g t h i n the v i c i n i t y of the a n a l b a s a l s was designated the f i r s t caudal v e r t e b r a . T o t a l l e n g t h was measured to the p o s t e r i o r edge of the hypural p l a t e . Caudal l e n g t h was measured from the a n t e r i o r end of the f i r s t caudal v e r t e b r a . F i l m records were a n a l y s e d frame by frame. The g r e a t e s t d i s t a n c e t r a v e l l e d i n 4 frame i n t e r v a l s (0.0625 s) at 15C, or i n 3 frame i n t e r v a l s (0.047 s) at 25C, was c a l c u l a t e d f o r each f i s h . The s h o r t e r time i n t e r v a l was used at 25C because b u r s t s of swimming tended to be of s h o r t e r d u r a t i o n at t h i s higher temperature. The recorded b u r s t s of swimming were s u b j e c t i v e l y scored f o r response q u a l i t y before v e r t e b r a l counts were known. Three c r i t e r i a were c o n s i d e r e d : (1) an i n d i c a t i o n of c o n v u l s i o n or p a r a l y s i s b e f o r e , d u r i n g or a f t e r b u r s t s , (2) a f a i l u r e to respond with a s u s t a i n e d b u r s t of swimming, and (3) a.change i n depth d u r i n g b u r s t s . The f i r s t f a c t o r was the most frequent problem i n responses to the extreme sti m u l u s used i n 1983; the frequency of t h i s problem i n c r e a s e d as f r y s i z e i n c r e a s e d . T h i s problem was avoided i n 1984 and 1985 by u s i n g a b r i e f e l e c t r i c pulse as a s t i m u l u s . However, f i s h more o f t e n f a i l e d to respond with a s u s t a i n e d b u r s t of swimming to t h i s more m i l d s t i m u l u s . F a i l u r e to respond e n t h u s i a s t i c a l l y was most frequent i n the 15C, 0.011 p o i s e treatment, and was a p p a r e n t l y u n r e l a t e d to s i z e . I attempted to o b j e c t i v e l y s e l e c t responses f o r a n a l y s i s as f o l l o w s . In each s i z e c l a s s i n each experiment, I c a l c u l a t e d the percentage of responses s u b j e c t i v e l y scored as good. Using a s l i g h t l y lower percentage X, I then s e l e c t e d the f a s t e s t X% of responses w i t h i n each count c l a s s of a given s i z e c l a s s . The 60 percentages used were: (1) 15C, 1983: 70% f o r the l e n g t h c l a s s 7.4-7.8 mm, 60% f o r lengths of 7.8-8.3 mm, 55% f o r lengths of 8.3-9.0 mm, and 40% f o r l e n g t h c l a s s e s 9.0-9.8 and 9.8-11.4 mm; (2) 15C, 1984: 70% f o r a l l l e n g t h c l a s s e s ; (3) 15C, 1985: 60% f o r a l l l e n g t h c l a s s e s ; (4) 25C, 1984: 80% f o r a l l l e n g t h c l a s s e s ; and, (5) 15C, 0.1% m e t h y l c e l l u l o s e : 80% f o r a l l l e n g t h c l a s s e s . R e s u l t s were a l s o examined using responses s e l e c t e d on the b a s i s of s u b j e c t i v e s c o r e s of response q u a l i t y . Both s e l e c t i o n procedures r e v e a l e d the same p a t t e r n i n r e s u l t s , so onl y those r e s u l t s obtained u s i n g the o b j e c t i v e procedure are d e s c r i b e d here. In most a n a l y s e s d e s c r i b e d below, f i s h are grouped i n l e n g t h c l a s s e s . Length c l a s s e s were d e f i n e d i n o c u l a r micrometer u n i t s (1 unit= 0.0816667 mm). The l e n g t h c l a s s e s u s u a l l y used were: 81-90, 91-95, 96-101, 102-110, 111-120, and 121 or more. These c l a s s e s w i l l be r e f e r r e d to as: 6.6-7.4 mm, 7.4-7.8 mm, 7.8-8.3 mm, 8.3-9.0 mm, 9.0-9.8 mm, and >9.8mm. E f f e c t s of v e r t e b r a l count on swimming performance, and i n t e r a c t i o n s between l e n g t h and the e f f e c t of count, were t e s t e d by one- or two-way an a l y s e s of v a r i a n c e (ANOVA), and by r e g r e s s i o n a n a l y s e s . ANOVA was computed using BMDP7D (Dixon 1981). Homogeneity of v a r i a n c e s among groups was t e s t e d u s i n g 61 Levene's t e s t (Brown and Forsythe 1974a). V a r i a n c e s d i f f e r e d s i g n i f i c a n t l y among groups i n only two t e s t s : (1) the e f f e c t of count at s i z e s over 9.8 mm at 15C i n 1983, and (2) t h i s e f f e c t i n the 7.4-7.8 mm l e n g t h c l a s s at 15C i n 0.1% m e t h y l c e l l u l o s e . In these two cases, e q u a l i t y of means was t e s t e d u s i n g the Welch s t a t i s t i c (Brown and Forsythe 1974b). Regression l i n e s were c a l c u l a t e d u sing BMDP1R, and e q u a l i t y of s l o p e s t e s t e d u s i n g BMDP1V. The s i g n i f i c a n c e of r e g r e s s i o n s of sl o p e on v e r t e b r a l count r a t i o was t e s t e d as d e s c r i b e d by Sokal and Rohlf (1981, p.503-505). The t h i r d order i n t e r a c t i o n between v i s c o s i t y treatment, l e n g t h c l a s s and count c l a s s was t e s t e d u s i n g BMDP4V. R e s u l t s Abdominal and caudal v e r t e b r a e 1. Performance at 15C The same p a t t e r n i n swimming performance was seen both i n 1983 and 1984 among f i s h f i l m e d a t 15C at le n g t h s of 7.4-9.0 mm ( F i g . 7 ) . Performance depended not on the a b s o l u t e number of ve r t e b r a e , but on the r a t i o of abdominal to caud a l v e r t e b r a e . Performance was best among f i s h with a high r a t i o of 0.82 AV/CV (abdominal/caudal v e r t e b r a e ) at small s i z e s (7.4-7.8 mm), among those with an in t e r m e d i a t e r a t i o (0.78) at i n t e r m e d i a t e s i z e s (7.8-8.3 mm), and among those with a low r a t i o (0.72) at l a r g e s i z e s (8.3-9.0 mm). T h i s i n t e r a c t i o n between l e n g t h and optimum v e r t e b r a l count r a t i o was s i g n i f i c a n t i n both years (Table 19). With i n l e n g t h c l a s s e s , the e f f e c t of v e r t e b r a l count r a t i o on performance was s i g n i f i c a n t a c c o r d i n g to ANOVA at sm a l l and l a r g e F i g u r e 7. Burst swimming performance at 15C of s t i c k l e b a c k f r y 6.6-9.0 mm i n l e n g t h i n 1983 (A) and 1984 (B). Fry are grouped by l e n g t h and by the r a t i o of abdominal to caudal v e r t e b r a e (AV/CV), and p l o t t e d at the mean le n g t h i n each group. Symbol areas are p r o p o r t i o n a l to sample s i z e s . 63 2 2 r to i n C\J CD O O* E E >- 2 0 18 16 A . 1 9 8 3 o I5°C © • o • • S A M P L E - S I Z E © o 5 O 10 - O 2 0 - o 1 O 4 0 < i — 2 2 o > 3 2 0 - X < 18 16 B 1 9 8 4 I5°C o o A V C V A V / C V • 14 16 0 . 8 8 • 14 17 0 . 8 2 © 14 18 0 . 7 8 3 13 17 0 . 7 6 O 13 18 0 . 7 2 i 7 . 0 8 . 0 L E N G T H ( m m ) 9 .0 Table 19. Significance of effects of vertebral count class on burst swimming performance of stickleback fry within length classes at 15C. Vertebral count classes are based on the ratio of abdominal to caudal vertebrae. To avoid small sample sizes, fish with ratios above 0.82 are omitted, and those with intermediate ratios of 0.7G and 0.78 grouped together. Probabilities are for the effect of count class In one- or two-way analyses of variance. Variances are homogeneous among groups 1n a l l comparisons. The maximum and minimum sample sizes are given in parentheses for each comparison. Data are shown In F1g. 7. Length class (mm) Interaction Year * 6.6-7.4 7.4-7.8 7.8-8.3 8.3-9.0 Count x Length 1983 — 0. .098 0. .62 0 . 13 0 .042 (6 - 24) (5 -• 15) (7 • - 24) (5 • - 24) 1984 0.095 0. 020 0. 27 0. .017 0. ,001 (10 - 31) (10 - 40) (17 - 45) (28 - 43) ( 10 - 45) Both -- 0. 003 0. 23 0. ,006 65 s i z e s i n 1984, but not i n 1983 (when sample s i z e s tended to be s m a l l , Table 19). Combining both years i n a two-way a n a l y s i s , e f f e c t s of v e r t e b r a l count r a t i o were h i g h l y s i g n i f i c a n t at small and l a r g e s i z e s (Table 19). At these s m a l l and l a r g e s i z e s , performance tended to show a l i n e a r r e l a t i o n s h i p to v e r t e b r a l count r a t i o between 0.72 and 0.82. At the small s i z e , t h i s r e l a t i o n s h i p was p o s i t i v e and s i g n i f i c a n t i n both y e a r s ; at the l a r g e s i z e , i t was negative and s i g n i f i c a n t i n both years (Table 20) . Regressions of swimming performance on l e n g t h w i t h i n v e r t e b r a l count c l a s s e s are shown i n Table 21. At 15C, s l o p e s d i f f e r s i g n i f i c a n t l y among v e r t e b r a l count c l a s s e s i n both y e a r s . In both y e a r s , s l o p e s i n c r e a s e d as v e r t e b r a l count r a t i o decreased between 0.82 and 0.72. T h i s l i n e a r r e g r e s s i o n of slope on v e r t e b r a l count r a t i o was s i g n i f i c a n t i n 1984 (p<0.025), but not i n 1983 (p>0.25; however, degrees of freedom were minimal (1,1) i n the 1983 c a l c u l a t i o n ) . R e s u l t s are a v a i l a b l e only i n 1984 f o r l e n g t h s l e s s than 7.4 mm. The t r e n d seen between l e n g t h s of 7.4 and 9.0 mm d i d not extend to these s m a l l e r s i z e s at 15C; performance was not best among f i s h with a high v e r t e b r a l count r a t i o of 0.82 or 0.88 ( F i g . 7B). F i s h with an i n t e r m e d i a t e r a t i o appeared to perform best, but e f f e c t s of v e r t e b r a l count r a t i o on performance were not s i g n i f i c a n t at these s i z e s under 7.4 mm (Table 19). Table 20. Regressions of swimming performance of stickleback fry on the ratio of abdominal to caudal vertebrae (VR) and total length (TL), within length classes at 15C. Only ratios between 0.82 and 0.72 inclusive are included. Abbreviations are b (partial regression coefficient), n (sample size) and P(b) (probability that the coefficient Is zero). Length class (mm) Year Varlable 6.6-7.4 7.4-7.8 7.8-8.3 8.3-9.0 1983 n -- 38 32 47 VR b P(b) -- 15.5628 0.032 -4.5185 0.53 -13.4940 0.038 TL b P(b) — -0.6021 0.81 - 1 .6979 0.39 1.0022 0.33 1984 n 50 61 87 104 VR b P(b) 0.3896 0.92 12.9016 0.006 -2.3170 0.50 -12 . 1149 0.0007 TL b P(b) 1 .8036 0.019 2.0705 0. 16 0.2000 0.83 2.0114 0.003 Table 21. Coefficients of regressions of swimming performance of stickleback fry on length, within vertebral count classes VR. VR Is the ratio of abdominal to caudal vertebrae. Regressions are over the length interval - 6.9 - 9.0 mm in the 25C treatment, and 7.4 - 9.0 in the 15C treatments. Abbrevatlons are MC, 0.1% methylcellulose; P(b), probability that slope Is zero; P(equal b), probability that slopes are equal among vertebral count classes; n, sample size. Treatment VR n Intercept slope P(b) P(equal 15C 1983 0.82 63 7 .4261 1 .4271 0 .0008 0. 78 36 5 . 1687 1 .7478 0 .0027 0.014 0.72 18 -14 .6921 4 . 1631 0 .0003 15C 1984 0.88 14 0 .6901 2 .2721 O .018 0.82 128 12 .3298 0 .8845 0 .0027 0. 78 26 10 .5446 1, . 1402 0 . 10 0.001 0.76 43 0. .7743 2 .3191 <0 .0001 0.72 55 -4 . 6274 2 .9851 <0 .0001 25C 0.88 34 1 . .9724 2. .2709 • 0, .0010 0.82 183 9. 1220 1 . .3815 <0. .0001 0.086 0. .76-0.78 30 5. .7740 1 . .8084 0. .022 0.72 47 -4. 0622 3. ,0621 <o. ,0001 15C MC 0. 88-0.94 26 -12. 1075 3. 7128 O. OOOI 0.82 1 10 -7 . 9750 3. 2144 <0. 0001 0.097 O. 76-0.78 26 5. 0943 1 . 6003 0. 035 0. 72 52 -6. 7205 3. 0609 <0. 0001 68 Swimming performance was measured at 15C at lengths over 9.0 mm i n three years ( F i g . 8). The ra n k i n g of v e r t e b r a l count c l a s s e s with r e s p e c t to performance d i f f e r e d among y e a r s . At leng t h s of 9.0-9.8 mm, f i s h with an i n t e r m e d i a t e r a t i o of 0.78 appeared to perform p o o r l y and those with other r a t i o s to perform e q u a l l y w e l l i n 1983 and 1984. However, i n 1985, performance i n t h i s l e n g t h c l a s s appeared to be i n v e r s e l y r e l a t e d to v e r t e b r a l count r a t i o , as had been seen at s l i g h t l y s m a l l e r s i z e s (8.3-9.0 mm) i n both p r e v i o u s y e a r s . At lengths of 9.8-11.5 mm, f i s h with a r a t i o of 0.78 again appeared to perform r e l a t i v e l y p o o r l y i n 1983, while performance appeared to be s i m i l a r among a l l v e r t e b r a l count c l a s s e s i n 1985. None of these d i f f e r e n c e s i n performance among v e r t e b r a l count c l a s s e s was s i g n i f i c a n t (p=0.10-0.63), e i t h e r w i t h i n years or grouping over years i n two-way an a l y s e s of v a r i a n c e . Nor was the i n t e r a c t i o n between year and the e f f e c t of count c l a s s s i g n i f i c a n t at e i t h e r s i z e (p=0.l9 at l e n g t h s of 9.0-9.8 mm, p=0.28 a t len g t h s of 9.8-11.5 mm). Swimming performance i s a p p a r e n t l y u n r e l a t e d to v e r t e b r a l count r a t i o at 15C at len g t h s between 9.0 and 11.5 mm (or, the optimum r a t i o at these l a r g e s i z e s i s not among those t e s t e d , i . e . not between 0.72 and 0.88 AV/CV). 2. Performance at 25C E f f e c t s of v e r t e b r a l count r a t i o on swimming performance between le n g t h s of 6.9 and 9.0 mm at 25C resembled those seen between le n g t h s of 7.4 and 9.0 mm at 15C. Performance was best among f i s h with a hig h r a t i o at small s i z e s , among those with an int e r m e d i a t e r a t i o at an int e r m e d i a t e s i z e , and among those with 69 F i g u r e 8. Burst swimming performance at 15C of s t i c k l e b a c k f r y 9.0 - 11.5 mm i n l e n g t h i n 1983 (A), 1984 (B) and 1985 ( C ) . Symbols and sample s i z e s are as i n F i g . 7 legends, except as noted. M A X I M U M V E L O C I T Y (mm/0 .0625 s ) ro O ro ro ro ro CD - 1 — o b cn co o co o O J m z. ^ H X o 3 b o O cn co o co CD O b o CO c n O m > CO X CO > o _ s m Id _„ I -U m P CO m 3 cn co ° co o cn OL 71 a low r a t i o at l a r g e s i z e s ( F i g . 9). However, the s i z e s at which performance was best among f i s h with h i g h or int e r m e d i a t e r a t i o s appeared to be s h i f t e d to s l i g h t l y s h o r t e r l e n g t h s at 25C compared to 15C. Performance was best among f i s h with a high r a t i o of 0.82 AV/CV at lengths of 7.4-7.8 mm at 15C, but at leng t h s of 6.9-7.4 mm at 25C. S i m i l a r l y , performance appeared to be best among f i s h with i n t e r m e d i a t e r a t i o s of 0.76-0.78 at 7.8-8.3 mm at 15C, but at 7.4-7.8 mm at 25C. T h i s i n t e r a c t i o n between temperature treatment and the e f f e c t of v e r t e b r a l count r a t i o on performance was s i g n i f i c a n t i n the 7.4-7.8 mm l e n g t h c l a s s (p=0.05l), but not i n other l e n g t h c l a s s e s (p>0.20, but sample s i z e s are small i n the sm a l l e r l e n g t h c l a s s ) . ( P r o b a b i l i t i e s are from two-way ANOVAs w i t h i n l e n g t h c l a s s e s with temperature (1984 15C or 25C) and v e r t e b r a l count r a t i o s (0.82, 0.72 and i n a l l but the s m a l l e s t l e n g t h c l a s s 0.76-0.78) as t r e a t m e n t s ) . E f f e c t s of v e r t e b r a l count r a t i o on performance were not s i g n i f i c a n t at 25C w i t h i n any l e n g t h c l a s s (p>0.20), but sample s i z e s tended to be small f o r a l l r a t i o s but 0.82 ( u s u a l l y l e s s than 10, sometimes l e s s than 5 w i t h i n a l e n g t h c l a s s ) . However, the r e g r e s s i o n of performance on v e r t e b r a l count r a t i o was s i g n i f i c a n t over the range 0.72-0.82 i n the 8.3-9.0 mm l e n g t h c l a s s at 25C (b=-12.1080 f p=0.054). Slopes of r e g r e s s i o n s of swimming performance on l e n g t h showed the same p a t t e r n among v e r t e b r a l count c l a s s e s at 25C as was seen a t 15C (Table 21). At both temperatures, slopes i n c r e a s e d as v e r t e b r a l count r a t i o decreased from 0.82 to 0.72. At 25C, d i f f e r e n c e s i n slope among v e r t e b r a l count c l a s s e s were 72 F i g u r e 9. Burst swimming performance at 25C of s t i c k l e b a c k f r y 6.9 - 9.0 mm i n l e n g t h . Symbols and sample s i z e s are as i n F i g . 7 legends, except as noted. 73 IS- o b E JE >- ( - o o > X < 2 2 2 0 8 25 °C O • - • S A M P L E S I Z E S A N D • S Y M B O L S A S IN Q F I G . 7 E X C E P T : O N = 7 0 i i 9 A V / C V = 0 . 7 6 - 0 . 7 8 1 i i 7.0 8 .0 L E N G T H ( m m ) 9 .0 74 s i g n i f i c a n t over t h i s range of r a t i o s (p=0.053), but only approached s i g n i f i c a n c e i n c l u d i n g the more extreme r a t i o of 0.88 (p=0.086). D i f f e r e n c e s i n s l o p e between the r a t i o s that performed best at small or l a r g e s i z e s (0.82 and 0.72, r e s p e c t i v e l y ) were h i g h l y s i g n i f i c a n t (p=0.0l5). Regressions of swimming performance on l e n g t h are shown i n F i g . 10 f o r f i s h with v e r t e b r a l count r a t i o s of 0.72 or 0.82 at each of the two temperatures. The s i m i l a r i t i e s and d i f f e r e n c e s between e f f e c t s of v e r t e b r a l count r a t i o on performance at the two temperatures are c l e a r l y seen i n t h i s f i g u r e . At both temperatures, s l o p e s of t h i s r e g r e s s i o n are g r e a t e r among f i s h with the low r a t i o than among those with the high r a t i o . At both temperatures, f i s h with the h i g h r a t i o are s u p e r i o r at small s i z e s , while those with the low r a t i o are s u p e r i o r at l a r g e s i z e s . In both r e p l i c a t i o n s at 15C, the two r e g r e s s i o n l i n e s i n t e r s e c t at the same l e n g t h (8.07-8.08 mm). However, at 25C, the l i n e s i n t e r s e c t at a s m a l l e r s i z e (7.85 mm). Regression l i n e s were c a l c u l a t e d over the l e n g t h ranges 7.4-9.0 mm at 15C, and 6.9-9.0 mm at 25C. However, the s h i f t i n i n t e r s e c t i o n p o i n t between temperatures i s not a r e s u l t of t h i s change i n range. Regression l i n e s c a l c u l a t e d over the range 7.4-9.0 mm at 25C a l s o i n t e r s e c t at 7.85 mm. 3. Performance at 15C i n 0.1% m e t h y l c e l l u l o s e Swimming performance i n an 0.1% s o l u t i o n of m e t h y l c e l l u l o s e at 15C i s shown i n F i g . 11 f o r l e n g t h s between 6.6 and 9.0 mm. O v e r a l l performance was not g r e a t l y a f f e c t e d by the high 75 F i g u r e 10. Regressions of swimming performance on l e n g t h among s t i c k l e b a c k f r y with v e r t e b r a l count r a t i o s of 0.72 or 0.82 AV/CV, at 15C i n 1983 (A), at 15C i n 1984 (B), and at 25C i n 1984 (C). The p r o b a b i l i t y of equal s l o p e s between v e r t e b r a l count r a t i o s i s given by 'p'. The i n t e r s e c t i o n p o i n t between the two l i n e s i s shown on the l e n g t h a x i s i n each p a n e l . 7 6 CO i n v_ C\J ^ CD J — o o ° o _ l LU > E E 22" 20H 1984 15 C 0.72 p=0.004 0 . 8 2 8.08 0.72 p<0.00l 0.82 18- B x < CO O d E E 2 4 i 2 2 2 0 18 1984 25 C 8.07 -0.72 P=0.0I5 0.82 16 7.0 8.0 7 .85 L E N G T H ( m m ) 9.0 F i g u r e 11. Burst swimming performance of s t i c k l e b a c k 6.6 - 9.0 mm i n l e n g t h i n an 0.1% s o l u t i o n of m e t h y l c e l l u l o s e at 15C. Symbols and sample s i z e s are as i n F i g . 7 legends, except as noted. 78 2 0 x < 18 LU > 16 14 M E T H Y L C E L L U L O S E # • I 5 ° C • • S A M P L E S I Z E A N D S Y M B O L S A S IN F I G . 9 E X C E P T O N = 5 0 1 1 • A V / C V = 0 B 8 - 0 . 9 4 - — i 1 i _ 7.0 8.0 9 .0 L E N G T H ( m m ) 79 v i s c o s i t y of t h i s s o l u t i o n . W i thin a l e n g t h and count c l a s s , performance i n t h i s s o l u t i o n averaged 92% (range 80-101%) of that i n water at 15C. (These comparisons are with the best 80% of responses w i t h i n a l e n g t h and count c l a s s i n the 1984 15C treatment; that below i s with the best 70% of responses as shown i n F i g . 7B). However, the e f f e c t of v e r t e b r a l count r a t i o on performance d i f f e r e d g r e a t l y between t h i s and the p r e v i o u s treatments. Performances of f i s h with high or low r a t i o s of 0.82 or 0.72 AV/CV were s i m i l a r i n t h i s v i s c o u s s o l u t i o n w i t h i n a l l l e n g t h c l a s s e s between 6.6 and 9.0 mm. E f f e c t s of v e r t e b r a l count r a t i o on performance were not s i g n i f i c a n t w i t h i n any l e n g t h c l a s s a c c o r d i n g to ANOVA (p=0.16 - 0.98). But the i n t e r a c t i o n between l e n g t h and the e f f e c t of v e r t e b r a l count r a t i o on performance was s i g n i f i c a n t over the range 7.4-9.0 mm (p=0.028). T h i s i n t e r a c t i o n presumably r e f l e c t s the s u p e r i o r performance of f i s h with intermediate r a t i o s (0.76-0.78) at small s i z e s and t h e i r i n f e r i o r performance at l a r g e s i z e s ( F i g . 11). Comparing performance i n water or t h i s v i s c o u s s o l u t i o n at 15C, the i n t e r a c t i o n between l e n g t h and the e f f e c t of v e r t e b r a l count r a t i o d i f f e r e d s i g n i f i c a n t l y between v i s c o s i t y treatments (p=0.004, f o r the t h i r d order i n t e r a c t i o n i n the ANOVA t e s t i n g e f f e c t s of count r a t i o (0.72, 0.76-0.78, 0.82), l e n g t h c l a s s (as grouped i n F i g . 11) and v i s c o s i t y (1984 15C: water or 0.1% m e t h y l c e l l u l o s e ) ) . S i m i l a r c o n c l u s i o n s are reached comparing the slopes of r e g r e s s i o n s of performance on l e n g t h among v e r t e b r a l count c l a s s e s (Table 21). The i n v e r s e r e l a t i o n s h i p between slope and 8 0 v e r t e b r a l count r a t i o seen i n the p r e v i o u s treatments f o r r a t i o s between 0.72 and 0.82 i s absent i n the m e t h y l c e l l u l o s e treatment. Instead, s l o p e s i n t h i s treatment are s i m i l a r l y h i g h among f i s h with h i g h or low r a t i o s , and low among those with i n t e r m e d i a t e r a t i o s . D i f f e r e n c e s i n s l o p e are not s i g n i f i c a n t o v e r a l l (p=0.097), but are h i g h l y s i g n i f i c a n t i f f i s h are grouped as those with intermediate (0.76-0.78) or with other r a t i o s (P=0.017). In summary, the e f f e c t of v e r t e b r a l count r a t i o on swimming performance d i f f e r e d g r e a t l y between water and 0.1% m e t h y l c e l l u l o s e at 15C. The s i g n i f i c a n c e of t h i s d i f f e r e n c e i s d i f f i c u l t to a s s e s s . I t does not seem to be due to a t o x i c e f f e c t of m e t h y l c e l l u l o s e , s i n c e performance was not g r e a t l y d i m i n i s h e d i n the 0.1% s o l u t i o n of i t . (Even long term exposure to 0.1% m e t h y l c e l l u l o s e i s r e l a t i v e l y innocuous. F i s h were rea r e d f o r a month i n water or t h i s s o l u t i o n ; s u r v i v a l i n m e t h y l c e l l u l o s e was s l i g h t l y b e t t e r than i n water). A s m a l l decrease i n v i s c o s i t y (about 0.002 poise) from 15C to 25C appeared to s h i f t the s i z e s at which f i s h with high or i n t e r m e d i a t e v e r t e b r a l count r a t i o s were s u p e r i o r to s l i g h t l y s m a l l e r s i z e s . Perhaps the l a r g e i n c r e a s e i n v i s c o s i t y (about 0.010 p o i s e ) from water to 0.1% m e t h y l c e l l u l o s e at 15C produced a l a r g e s h i f t i n the other d i r e c t i o n , so that the e f f e c t s seen i n water at 15C would be seen i n 0.1% m e t h y l c e l l u l o s e at s i z e s l a r g e r than those examined. A l t e r n a t i v e l y , the e f f e c t s of such l a r g e changes i n v i s c o s i t y may d i f f e r q u a l i t a t i v e l y from those of the s m a l l changes normally e x p e r i e n c e d i n nature. 81 Body P r o p o r t i o n s E f f e c t s of the r a t i o of abdominal to caudal v e r t e b r a e on swimming performance c o u l d r e s u l t from e f f e c t s of body p r o p o r t i o n s on performance. To t e s t t h i s p o s s i b i l i t y , I c o n s i d e r e d the p r e c a u d a l / c a u d a l l e n g t h r a t i o (where p r e c a u d a l l e n g t h i s t o t a l minus caudal l e n g t h ) . The c o r r e l a t i o n between v e r t e b r a l count r a t i o (VR) and t h i s l e n g t h r a t i o (LR) was h i g h l y s i g n i f i c a n t (p<0.000O among f i s h f i l m e d at 15C both i n 1983 and 1984. V a r i a t i o n i n LR e x p l a i n e d 57% of the v a r i a t i o n i n VR among 1984 f i s h , but only 25% of t h i s v a r i a t i o n among 1983 f i s h . E f f e c t s of VR and LR on performance were compared by examining the simple l i n e a r r e g r e s s i o n s of performance on each and the p a r t i a l r e g r e s s i o n c o e f f i c i e n t s of each i n m u l t i p l e l i n e a r r e g r e s s i o n s (Table 22). Regressions were c a l c u l a t e d s e p a r a t e l y w i t h i n the l e n g t h c l a s s e s 7.4-7.8 mm and 8.3-9.0 mm, among f i s h f i l m e d at 15C i n e i t h e r 1983 or 1984. Simple l i n e a r r e g r e s s i o n s of performance on VR were s i g n i f i c a n t (p<0.05) i n a l l four cases, while those on LR were s i g n i f i c a n t i n onl y one case and approached s i g n i f i c a n c e (p=0.063) i n only one o t h e r . P a r t i a l r e g r e s s i o n c o e f f i c i e n t s on VR were s i g n i f i c a n t i n a l l but one case, while those on LR were s i g n i f i c a n t i n no ca s e s . In a l l but one case, s i g n s of the p a r t i a l c o e f f i c i e n t s on LR were o p p o s i t e to those on VR and to those of the simple c o e f f i c i e n t s on both VR and LR. Thus, e f f e c t s of VR on swimming performance are c l e a r l y not a t t r i b u t a b l e to e f f e c t s of LR on performance. Table 22. Regressions of swimming performance on the ratio of abdominal to caudal vertebrae (VR), on the precaudal/caudal length ratio (LR), and on VR, LR and TL (total length), within small or large length classes at 15C. Only fish with VR between 0.72 and 0.82 inclusive are included. Abbreviations are as In Table 20. Length class (mm) Independent Year variables Statistic 7.4 - 7.8 8.3 - 9.0 1983 n 38 47 VR b 15.417 -13.247 P(b) 0.031 0.041 LR b 1.157 -7.864 P(b) 0.81 0.044 VR.LR.TL VR b 17.075 -9.608 P(b) 0.032 0.21 LR b -2.625 -4.384 P(b) 0.58 0.34 TL b -0.685 0.824 P(b) 0.79 0.43 1984 n 61 104 VR b 13.028 -10.488 P ( b ) 0.006 0.004 LR b 6.184 -3.964 P(b) 0.063 0.13 VR.LR.TL VR b 15.003 -14.250 P(b) 0.032 0.007 LR b -1.971 2.048 P(b) 0.68 0.58 TL b 2.180 1.960 P(b) O.15 0.004 83 Summary Swimming performance depended not on the a b s o l u t e number of v e r t e b r a e , but on the r a t i o of abdominal to caudal v e r t e b r a e . At 15C, performance was s u p e r i o r among f r y with a high r a t i o of 0.82 AV/CV at small s i z e s (7.4-7.8 mm), among those with an i n t e r m e d i a t e r a t i o (0.78) at intermediate s i z e s (7.8-8.3 mm), and among those with a low r a t i o (0.72) at l a r g e s i z e s (8.3-9.0 mm). Performance at even s m a l l e r or l a r g e r s i z e s d i d not d i f f e r s i g n i f i c a n t l y among the r a t i o s t e s t e d . A s i m i l a r e f f e c t of v e r t e b r a l count r a t i o on performance was seen at 25C, except that performance of f r y with h i g h or intermediate r a t i o s was s u p e r i o r at s l i g h t l y s m a l l e r s i z e s a t t h i s higher temperature. The e f f e c t of v e r t e b r a l count r a t i o on performance d i f f e r e d g r e a t l y between water and 0.1% m e t h y l c e l l u l o s e . Fry with h i g h (0.82) or low (0.72) r a t i o s performed e q u a l l y w e l l i n the v i s c o u s s o l u t i o n w i t h i n a l l l e n g t h c l a s s e s between 6.6 and 9.0 mm. E f f e c t s of v e r t e b r a l count r a t i o on swimming performance were not a t t r i b u t a b l e to an e f f e c t of precaudal/caudal l e n g t h on performance. 84 Part I I I . Changes i n v e r t e b r a l count with l e n g t h i n w i l d s t i c k l e b a c k f r y . M a t e r i a l and Methods S t i c k l e b a c k f r y were captured by d i p net (25 x 17 cm gape) from Holden Lake, B.C. C o l l e c t i o n s were made at four s i t e s , from a canoe f l o a t i n g near shore ( F i g . 12). Fry were c o l l e c t e d from s i t e s A1, A3 and A4 between May 7 and June 11, 1984, and from s i t e B between June 4 and 14, 1984. S i t e s were between 5 x 5 m and 8 x 12 m i n a r e a . S i t e s A3 and A4 were a d j o i n i n g ; s i t e A1 was separated from A3 by about 20 m, and s i t e B from A1 by about 200 m. A f t e r c o l l e c t i o n , f r y were k i l l e d i n a n a e s t h e t i c , p r e s e r v e d i n 10% b u f f e r e d f o r m a l i n , and c l e a r e d and s t a i n e d as d e s c r i b e d i n Part I. Centra were counted, t o t a l lengths measured and abdominal and caudal v e r t e b r a e d i s t i n g u i s h e d as d e s c r i b e d i n Part I I . The l a s t v e r t e b r a o f t e n bore two n e u r a l and/or haemal arches; such v e r t e b r a e were counted as one. Counts were e q u i v o c a l i n about 1.5% of f i s h due to other i r r e g u l a r i t i e s ; these e q u i v o c a l counts were excluded from a n a l y s e s . V e r t e b r a l development was i n s u f f i c i e n t to o b t a i n counts from 12% of f i s h 6.1-6.6 mm i n l e n g t h , 0.5% of f i s h 6.7-7.2 mm i n l e n g t h , and 0.1% of f i s h 7.3-7.7 mm i n l e n g t h , among f i s h c o l l e c t e d from A s i t e s . Development was s u f f i c i e n t to o b t a i n counts from a l l f i s h c o l l e c t e d from s i t e B. 85 F i g u r e 12. Map of Holden Lake, B.C., showing sampling s i t e s . HEMER CR 5 0 0 m 87 Fry were grouped f o r a n a l y s i s a c c o r d i n g to the r a t i o of abdominal to cau d a l v e r t e b r a e (AV/CV). Four groups were d i s t i n g u i s h e d : (1) 0.82 AV/CV (14 AV/ 17 CV), (2) 0.78-0.76 AV/CV (14/18, 13/17), (3) 0.72 AV/CV (13/18), and (4) other r a t i o s (mostly 0.88 or more). P r o b a b i l i t i e s are from c h i - s q u a r e t e s t s , c a l c u l a t e d u s i n g BMDP4F (Dixon 1981). R e s u l t s D i f f e r e n c e s i n v e r t e b r a l counts of r e c r u i t s were t e s t e d among s i t e s by comparing counts of f r y under 7.4 mm i n l e n g t h . Frequencies of the four v e r t e b r a l count c l a s s e s d i d not d i f f e r among s i t e s A1, A3 and A4 (p=0.l8), but d i d d i f f e r between these s i t e s and s i t e B (p=0.0085). Hence, f i s h from s i t e s A and B are anal y s e d s e p a r a t e l y below. V e r t e b r a l count r a t i o s of f r y grouped by l e n g t h are shown i n F i g . 13, p o o l i n g c o l l e c t i o n s from d i f f e r e n t d a t e s . At s i t e B, f r y with a hig h r a t i o of 0.82 AV/CV i n c r e a s e d i n frequency, and those with i n t e r m e d i a t e r a t i o s of 0.76-0.78 decreased i n frequency, as mean l e n g t h i n c r e a s e d from about 6.9 to 7.5 mm (p=0.020). As mean l e n g t h i n c r e a s e d f u r t h e r to about 8.0 mm, the rev e r s e change i n frequency o c c u r r e d (p=0.024). No s i g n i f i c a n t changes i n frequency o c c u r r e d with f u r t h e r i n c r e a s e s i n f r y l e n g t h (p=0.80). Among f r y c o l l e c t e d from s i t e A, no s i g n i f i c a n t changes i n frequency o c c u r r e d between mean lengths of 6.9 and 7.5 mm (p=0.l3). However, the same decrease i n frequency of f i s h with the h i g h r a t i o and i n c r e a s e i n frequency of those with the F i g u r e 13. Frequencies of v e r t e b r a l count c l a s s e s i n wi s t i c k l e b a c k f r y grouped by l e n g t h . Count c l a s s e s are based on the r a t i o of abdominal to caudal v e r t e b r a e . A. Fry c o l l e c t e d from s i t e A; B. Fry c o l l e c t e d from s i t e B. Symbols as i n F i g . 14. 40 SAMPLE SIZE O 535 O 700 SAMPLE SIZE O 115 J J X 1 I I • I • I 7 8 9 10 I LENGTH (mm) 90 intermediate r a t i o s was seen as mean l e n g t h i n c r e a s e d f u r t h e r from 7.5 to 8.0 mm (p=0.040). Again, no s i g n i f i c a n t changes i n frequency o c c u r r e d with even f u r t h e r i n c r e a s e s i n f r y l e n g t h (p=0.51>. These, changes i n frequency c o u l d r e f l e c t s e l e c t i o n f a v o u r i n g f r y with a high r a t i o of 0.82 AV/CV at lengths of about 7.3-7.7 mm at s i t e B, and those with i n t e r m e d i a t e r a t i o s of 0.76-0.78 at lengths of about 7.8-8.3 mm at both s i t e s A and B. A l t e r n a t e e x p l a n a t i o n s would be that one (though probably not both) of the changes i n frequency between s u c c e s s i v e l e n g t h c l a s s e s might r e f l e c t changes i n the v e r t e b r a l counts of r e c r u i t s to the p o p u l a t i o n over time, or an i n i t i a l c o r r e l a t i o n between count and l e n g t h i n r e c r u i t s . V e r t e b r a l count f r e q u e n c i e s of r e c r u i t s ( i . e . f r y under 7.4 mm i n length) to the two s i t e s are shown over time i n F i g . 14. With data grouped as shown i n the f i g u r e , f r e q u e n c i e s of the four v e r t e b r a l count c l a s s e s i n r e c r u i t s d i d not d i f f e r s i g n i f i c a n t l y among days, e i t h e r at s i t e B (p=0.46) or at s i t e A (p=0.l8). No t r e n d i n the frequency of the most common v e r t e b r a l count r a t i o (0.82) i s seen over the extended sampling p e r i o d at s i t e A ( F i g . 14A). However, f r e q u e n c i e s of the i n t e r m e d i a t e and 'other' c l a s s e s do tend to d i f f e r between r e c r u i t s c o l l e c t e d before or a f t e r day 23. D i f f e r e n c e s i n count f r e q u e n c i e s between samples grouped as those c o l l e c t e d at s i t e A before or a f t e r t h i s date are s i g n i f i c a n t (p=0.006). However, the i n c r e a s e i n frequency of f r y with i n t e r m e d i a t e r a t i o s between mean len g t h s of 7.5 and 8.0 mm at s i t e A i s not e x p l a i n e d by t h i s i n c r e a s e i n frequency between e a r l y and l a t e r e c r u i t s . The two 91 F i g u r e 14. Frequencies of v e r t e b r a l count c l a s s e s i n f r y l e s s than 7.4 mm i n l e n g t h , grouped by c o l l e c t i o n date. Count c l a s s e s are the r a t i o of abdominal to caudal v e r t e b r a e (AV/CV). Samples from s u c c e s s i v e days grouped to g i v e minimum sample s i z e s of 50 f o r s i t e A (panel A) and 35 f o r s i t e B (panel B). A 92 6 0 4 0 >- o LU ZD O LU CC Li_ h- ~ZL LU O DT LU CL 2 0 6 0 4 0 2 0 7 M a y 7 L E G E N D B S A M P L E S I Z E o 3 5 o 5 0 - 9 0 O 1 1 0 - 1 7 5 A V / C V • 0 . 8 2 © 0 . 7 6 - 0 . 7 8 o 0 . 7 2 • O T H E R M a y 7 1 0 J u n e 14 2 0 D A Y 3 0 [ 4 0 J u n e 14 93 l e n g t h c l a s s e s c o n t a i n e d the same p r o p o r t i o n of f r y c o l l e c t e d l a t e i n the sampling p e r i o d (47.6 and 47.5 % of f r y i n the l e n g t h c l a s s e s 7.3-7.7 and 7.8-8.3 mm, r e s p e c t i v e l y , were c o l l e c t e d a f t e r day 25 (the l a t e r date i s used to allow f o r the growth of f r y i n t o these l e n g t h c l a s s e s ) ) . Furthermore, the same changes in v e r t e b r a l count are seen as mean f r y l e n g t h i n c r e a s e s from 7.5 to 8.0 mm i n both e a r l y and l a t e c o l l e c t i o n s (Table 23), though these changes i n frequency are s i g n i f i c a n t i n n e i t h e r subsample alone (p=0.086 and 0.21, r e s p e c t i v e l y ) . The a l t e r n a t e e x p l a n a t i o n invoking an i n i t i a l c o r r e l a t i o n between count and l e n g t h i n r e c r u i t s can be s i m i l a r l y d i s c r e d i t e d . Most f r y were a p p a r e n t l y r e c r u i t e d at l e n g t h s below 7.8 mm. Thus, the g r e a t e s t e f f e c t of a c o r r e l a t i o n between count and r e c r u i t m e n t l e n g t h should be seen between the two s m a l l e s t l e n g t h c l a s s e s , i . e . between .mean lengths of 6.9 and 7.5 mm. However, no s i g n i f i c a n t d i f f e r e n c e i n v e r t e b r a l count o c c u r r e d between these l e n g t h s at s i t e A. A c o r r e l a t i o n between v e r t e b r a l number and h a t c h i n g l e n g t h might be expected i n view of the developmental p r o c e s s e s thought to be i n v o l v e d i n d e t e r m i n i n g v e r t e b r a l number (Lindsey and Arnason 1981). I f so, a p o s i t i v e c o r r e l a t i o n i s expected, and an i n c r e a s e i n the frequency of f r y with an i n t e r m e d i a t e r a t i o of 0.78 AV/CV ( i . e . , 32 t o t a l v e r t e b r a e ) i s p r e d i c t e d between mean lengths of 6.9 and 7.5 mm. When changes i n v e r t e b r a l count are seen between these l e n g t h s , they are o p p o s i t e to these p r e d i c t e d changes. Thus, an i n i t i a l c o r r e l a t i o n between v e r t e b r a l count and l e n g t h i n r e c r u i t s may c o u n t e r a c t r a t h e r than c o n t r i b u t e to the changes i n v e r t e b r a l Table 23. Vertebral count class frequencies (%) of sticklebacks 8.3 mm or less In length, collected from site A between May 7 and 31, or between June 4 and 11, 1984. Vertebral count classes based on the ratio of abdominal to caudal vertebrae. Date Length cl ass (mm) Mean 1ength (mm) Vertebral count 0.82 0.76-0.78 class 0.72 (%) Other Sample s ize May 7-31 6.1-7. 2 6.86 58.3 13.0 10.0 18.6 408 7.3-7. 7 7.46 59.9 14.8 7.4 17.9 364 7.8-8. 3 7.99 55.2 21.2 4.9 18.7 364 June 4-11 6.1-7. 2 6.94 60.5 16.7 10.5 12.2 294 7.3-7. 7 7.46 63. 1 19.6 7.6 9.7 331 7.8-8. 3 8.00 55.0 24.3 9. 1 11.6 329 95 count observed between mean lengths of 6.9 and 7.5 mm. Fry were c o l l e c t e d from s i t e A over an extended p e r i o d , and were grouped over time i n comparisons among l e n g t h c l a s s e s . E f f e c t s of any change i n the counts of r e c r u i t s over time, or of any c o r r e l a t i o n between count and l e n g t h among newly hatched f r y , would be mostly c a n c e l l e d by t h i s grouping over time. However, f r y from s i t e B were c o l l e c t e d over o n l y a b r i e f p e r i o d , so comparisons among l e n g t h c l a s s e s of these f r y are more l i k e l y to be confounded by such e f f e c t s . These problems can be e l i m i n a t e d by r e s t r i c t i n g comparisons to a s i n g l e c o h o r t of f r y . Such an a n a l y s i s can be attempted f o r s i t e B i f i t i s assumed that f r y grow from one l e n g t h c l a s s to the next between s u c c e s s i v e c o l l e c t i o n d a t e s . Judging from the peaks i n l e n g t h d i s t r i b u t i o n s of f r y i n s u c c e s s i v e c o l l e c t i o n s , growth r a t e s of f r y . were at l e a s t about 0.2 mm/d. Successive mean l e n g t h s d i f f e r by 0.6 and 0.5 mm r e s p e c t i v e l y f o r the f i r s t three l e n g t h c l a s s e s , so t h i s assumption may be v a l i d f o r c o l l e c t i o n s 3d a p a r t . Large numbers of f r y were c o l l e c t e d from s i t e B on days 36 and 39 only. Counts of f r y i n one l e n g t h c l a s s on day 36 are compared with those of f r y i n the next l e n g t h c l a s s on day 39 i n F i g . 15. The same changes i n frequency are seen i n these comparisons as were seen i n the comparisons grouped over a l l c o l l e c t i o n dates, though l e v e l s of s i g n i f i c a n c e are reduced. Thus, i t seems l i k e l y that the changes i n v e r t e b r a l count seen among l e n g t h c l a s s e s r e f l e c t s e l e c t i o n f o r v e r t e b r a l count i n those l e n g t h c l a s s e s . 96 F i g u r e 15. V e r t e b r a l count - r a t i o s of s t i c k l e b a c k f r y i n two 'cohorts' at s i t e B, comparing counts i n l e n g t h c l a s s i on day 36 and l e n g t h c l a s s i+1 on day 39. Symbols as i n F i g . 14. A. i= 6.1-7.2 mm; B. i= 7.3-7.7 mm. 97 / CM / L O / o r - / o O / C L X / o / CJ 4 CD E CT) e 1 ' r o LO > o o ro < . II * — ' E c o E ̂  r o ̂  r o < i " Q K ) Z oo o d II Q . I CD £ — r o CD >_ ^ < r 1 " Q f O ^ CD c _ ^ ^ L O < i II Q —. Z CD — O 0 0 o CD O O CO A 3 N 3 n 0 3 c d d ! N 3 3 c J 3 d 98 T o t a l v e r t e b r a l counts of f r y i n the v a r i o u s l e n g t h c l a s s e s are shown i n F i g 16. Changes i n frequency are those expected given the apparent s e l e c t i o n f o r the r a t i o of abdominal to caudal v e r t e b r a e seen i n F i g . 13. The only s i g n i f i c a n t change seen at s i t e A was an i n c r e a s e i n frequency of f r y with 32 v e r t e b r a e , and a c o r r e s p o n d i n g decrease i n frequency of those with 31, as mean l e n g t h i n c r e a s e d to 8 mm. Most of t h i s change o c c u r r e d between mean len g t h s of 7.5 and 8 mm. On the other hand, the most s i g n i f i c a n t change seen at s i t e B was an i n c r e a s e i n frequency of f r y with 31 v e r t e b r a e and decrease i n frequency of those with 32, as mean l e n g t h i n c r e a s e d from 6.9 to 7.5 mm. As at s i t e A, the reverse change i n f r e q u e n c i e s o c c u r r e d as mean l e n g t h i n c r e a s e d f u r t h e r to 8 mm, but t h i s second change only approached s i g n i f i c a n c e at s i t e B. At n e i t h e r s i t e d i d s i g n i f i c a n t changes in frequency occur as mean l e n g t h i n c r e a s e d above 8 mm. In summary, changes i n the r e l a t i v e f r e q u e n c i e s of v e r t e b r a l counts w i t h l e n g t h among w i l d s t i c k l e b a c k f r y i n Holden Lake are c o n s i s t e n t with s e l e c t i o n f a v o u r i n g a high r a t i o of 0.82 AV/CV and a low t o t a l count of 31 at small s i z e s of 7.3-7.7 mm, and in t e r m e d i a t e r a t i o s of 0.76-0.78 AV/CV and a high t o t a l count of 32 at s l i g h t l y l a r g e r s i z e s of 7.8-8.3 mm. E f f e c t s of changes i n the v e r t e b r a l counts of r e c r u i t s over time, or of an i n i t i a l c o r r e l a t i o n between count and l e n g t h i n r e c r u i t s , cannot be completely e l i m i n a t e d , but are probably not the main causes of these changes i n r e l a t i v e frequency with l e n g t h . These changes p e r s i s t when c o l l e c t i o n s from d i f f e r e n t dates are pooled (so that l e n g t h and recruitment date or s i z e w i l l not be s t r o n g l y 99 F i g u r e 16. Percent f r e q u e n c i e s of t o t a l v e r t e b r a l counts, i n f r y grouped by l e n g t h at s i t e A (panel A) or B (panel B). Only counts between 30 and 32 (>98% of a l l counts) are shown. K - p = 0.006-H p = 0.39 31 p=O.I7 p=0.023 J i P = 0 - 0 2 0 - t p=0.65 p=0.0035 H H p=0.076 20h B 8 9 LENGTH (mm) 10 101 confounded), and when fry in one length class of a given collection are compared with those in the next length class of the next collection. 1 02 P a r t IV. P r e d a t i o n experiments with peamouth chub. M a t e r i a l and Methods Ripe peamouth chub M y l o c h e i l u s c a u r i n u s were c o l l e c t e d from Holden Lake on A p r i l 28 and May 11, 1983, and 7 (PM1) or 27 (PM8) c r o s s e s r e s p e c t i v e l y made i n the l a b o r a t o r y (each between a s i n g l e male and female). Embryos from each set of c r o s s e s were incubated i n separate 20 L tanks at 14C. A f t e r h a t c h i n g , f r y were f e d Artemia n a u p l i i twice d a i l y , with o c c a s i o n a l supplements of nematodes and n a t u r a l p l a n k t o n . C o n d i t i o n s were crowded, and growth and development slow compared to those of f r y i n the w i l d (see below). Between 22 and 56 d a f t e r h a t c h i n g , f r y were d i s t r i b u t e d among two c o n t r o l and four experimental tanks, and those i n e x p e r i m e n t a l tanks exposed to p r e d a t i o n by s u n f i s h or smallmouth bass M i c r o p t e r u s dolomieui u n t i l 50-60% of the i n i t i a l number had been eaten. In each of f i v e experiments, f r y were exposed at two temperatures (15 or 25C, +/- 1C) and two cover treatments (cover p r e s e n t or a b s e n t ) . Experimental design and procedure were the same as those d e s c r i b e d i n d e t a i l above f o r the 1983 experiments w i t h s t i c k l e b a c k s , except that p r e d a t o r s were not removed o v e r n i g h t i n these experiments. D e t a i l s of each experiment are given i n Table 24. In a l l but experiment 5, some f r y were below the s i z e at which v e r t e b r a e are s u f f i c i e n t l y formed to be c o u n t a b l e . Experiments were done at these small s i z e s s i n c e s e l e c t i o n with r e s p e c t to v e r t e b r a l number c o u l d r e f l e c t s e l e c t i o n f o r myomere Table 24. Description of predation experiments using peamouth chub as prey. Predators are sunfish (S) or bass (B) Predator-hours (pred-h) are calculated using lighted periods only. Exp. Par. Temp. Tmt. (C) Cover Durat ion h Pred-h Predators Length (mm) Type Mean SD , NO. eaten % per eaten pred-h No. surv i v i ng Pres . Reared Rear i ng mortal 1ty (%) Length (mm) of preserved survivors Mean SD PM8 PM1 PM8 Con 15 N 28 0 - - - 0 - 60 155 5 .8 8 .84 0 .37 25 N 27 0 - - - 0 - 49 161 23 .0 9. .02 0. .40 Exp 15 Y 26 203 S 31.2 2.6 55 1 .35 70 155 10 . 3 8 .95 0. .32 15 N 22 154 s 30.4 2. 1 52 1 . .7.1 62 186 37 . 1 8 .86 0. 30 25 Y 23 140 s 29.4 2.4 61 2. .34 37 168 19 .6 9 .05 0. 29 25 N 24 148 s 30.0 2.6 66 2, .42 54 131 12 . 2 9 .06 0. 33 Con 15 N 78 0 _ _ _ 0 _ 53 149 20 .8 9. .89 0. 38 25 N 54 0 - - - 0 - 53 149 0 .0 10. . 13 0. 58 Exp 15 Y 98 2208 B 14.8 1 .7 48 0. . 12 75 201 1 . .0 10. .03 0. .49 15 N 96 2082 B 14.5 2. 1 51 0. . 13 61 196 17 . 9 9. .85 0. 55 25 Y 52 830 B 16.7 2.3 64 0. 40 34 153 0. .0 10. 23 0. 57 25 N 54 868 B 16.6 2. 1 64 0. 38 4 1 146 0 O 10. . 18 0. 59 Con 15 N 49 0 _ 0 _ 58 142 7. ,0 10. . 14 0. 53 25 N 29 0 - - - 0 - 48 152 5. , 3 10. .38 0. 47 Exp 15 Y 48 614 B 22.8 4.3 61 0. 50 52 142 3. .5 10. 42 0. 48 15 N 46 589 B 21.8 4.0 68 0. 58 45 1 16 15. .5 10. .67 0. 48 25 Y 28 192 B 23.8 4.8 60 1 . 56 57 143 1 . . 4 10. 56 0. 46 25 N 30 214 B 23.3 5.5 57 1 . 33 50 163 7 . 0 10. 47 0. 41 contd. Table 24. contd. Predators Length (mm) No. No. of preserved Duration Length (mm) eaten surviving Rearing survivors Temp. % per mortality Exp. Par. Tmt. (C) Cover h Pred-h Type Mean SD eaten pred-h Pres. Reared (%) Mean SD PM1 PM8 Con 15 N 73 0 - 0 - 48 215 0.0 10. 81 0. ,74 25 N 49 0 - 0 - 43 162 0.0 10. 86 0. ,67 Exp 15 Y 70 1599 B 17, .8 2, .8 49 0. , 15 86 167 0.0 10. ,77 0. ,71 15 N 74 1751 B 17, .5 2. .0 49 0. 14 74 187 0.0 10. .91 0. .74 25 Y 47 610 B 19, .0 0. .8 55 0. 44 54 167 0.0 11. 12 0. ,72 25 N 48 623 B 19, .0 2. .8 57 0. ,46 47 163 0.0 11. . 14 0. ,85 Con 15 N 31 0 _ 0 _ 109 0 _ 1-1, .60 0, .62 25 N 27 0 - 0 - 1 10 0 - 11, .84 0, .73 Exp 15 Y 30 377 B 23 .5 4, .8 58 0. ,43 1 14 0 - 12, .25 0, .89 15 N 30 359 B 23 .6 5, .2 58 0. ,44 1 16 0 - 12 . 11 0. .85 25 Y 26 150 B 25 .7 5, .5 60 1 . . 10 1 1 1 0 - 12, . 19 0, .81 25 N 26 152 B 25 .7 6, .0 60 1 . 09 1 10 0 - 12 .26 0, .82 Abbreviations: Par = parental crosses Tmt = predation treatment: control (con) or experimental (exp) Pres = preserved at end of experiment without further rearing Other abbreviations as in Table 2. 105 number or some other f e a t u r e of the a x i a l segmentation, and might thus occur before v e r t e b r a l development i s complete. At the end of a l l but experiment 5, f r y i n each tank were d i v i d e d i n t o q u a r t e r s u s i n g a 'plankton s p l i t t e r ' . One-quarter of the f r y were pr e s e r v e d f o r l e n g t h measurements, and the remainder reared to a l a r g e r s i z e . A l l f r y were preserved at the end of experiment 5. Fry were k i l l e d i n a n a e s t h e t i c , preserved i n 10% b u f f e r e d f o r m a l i n , and c l e a r e d and s t a i n e d as d e s c r i b e d above. Length was measured from the t i p of the snout t o the p o s t e r i o r edge of the hypural ' p l a t e ' . Counts were made of c e n t r a , e x c l u d i n g the u r o s t y l e and i n c l u d i n g the members of the Weberian complex. The l a s t or second l a s t v e r t e b r a f r e q u e n t l y bore two n e u r a l and o c c a s i o n a l l y two haemal ar c h e s . Such complex v e r t e b r a e were counted as one. F i s h with other v e r t e b r a l i r r e g u l a r i t i e s were ra r e (Table 25) and were excluded from a n a l y s e s . Counts r e p o r t e d f o r experiments 1 and 2 are of r e a r e d f r y only, s i n c e v e r t e b r a e of a l l or most f r y p r e s e r v e d without f u r t h e r r e a r i n g were undeveloped i n these experiments. In experiments 3 and 4, most f r y p r eserved without p o s t - e x p e r i m e n t a l r e a r i n g had countable v e r t e b r a e . In both experiments, counts of reared f r y and of f r y without p o s t - e x p e r i m e n t a l r e a r i n g but with developed v e r t e b r a e d i f f e r e d by l e s s than 1% over a l l treatments. A c c o r d i n g l y , counts r e p o r t e d f o r experiments 3 and 4 are of both reared and non-reared f r y . Counts r e p o r t e d f o r experiment 5 are e n t i r e l y of f r y without p o s t - e x p e r i m e n t a l r e a r i n g . Table 25. Vertebral development and abnormalities of peamouth chub surviving predation experiments. Abnormalities not including complex vertebrae In the last or second last positions. Length 1s the mean in controls at the end of experiments. Undeveloped vertebrae (%) Abnormalities (%) Length Without After Non- :xP. (mm) rearIng rearing reared Reared 1 8.9 100.0 0.0 - 2 . 1 2 10.0 57.5 0.7 6.9 2.0 3 10. 2 25.8 1 .3 0.0 0.6 4 10.8 13.6 1 .2 1.7 1 .3 5 11.7- O.O - 0.4 - 1 07 Abdominal and caudal v e r t e b r a e c o u l d not be d i s t i n g u i s h e d . At the smal l e r s i z e s examined, haemal arches and spines were undeveloped or rudimentary. The d e s i g n a t i o n of the abdominal/caudal d i v i s i o n was s t r o n g l y s i z e dependent, u s i n g e i t h e r c l o s u r e of the haemal a r c h (when developed) or p o s i t i o n r e l a t i v e to other s t r u c t u r e s such as the a n a l f i n b a s a l s as c r i t e r i a . The use of r e l a t i v e haemal spine l e n g t h as a c r i t e r i o n was not p r a c t i c a l , s i n c e changes i n l e n g t h near the abdominal/caudal d i v i s i o n were not d i s c o n t i n u o u s as d e s c r i b e d above f o r G a s t e r o s t e u s . In the a n a l y s i s of experiments 3 and 5, v e r t e b r a l counts are compared between p r e d a t i o n treatments among f i s h above or below a c e r t a i n l e n g t h at the end of experiments (10.35 mm i n experiment 3, 11.5 mm i n experiment 5). In experiment 3, reared f i s h were a s s i g n e d to the small or l a r g e s i z e c l a s s as f o l l o w s . F i r s t , the percentage of f r y below 10.35 mm at the end of the experiment (say X%) was determined f o r each of the s i x groups u s i n g the samples preserved without post-experimental r e a r i n g . Then, the s m a l l e s t X% of f r y i n the corres p o n d i n g reared group were a s s i g n e d to the small s i z e c l a s s , and the remainder to the l a r g e s i z e c l a s s . Lengths were compared by ANOVA, c a l c u l a t e d using BMDP7D. Va r i a n c e s were t e s t e d f o r h e t e r o g e n e i t y u s i n g Levene's t e s t (Brown and Forsythe 1974a), and means compared u s i n g the Brown-Forsythe t e s t (Brown and Forsythe 1974b) when v a r i a n c e s were s i g n i f i c a n t l y (p<0.05) heterogeneous. Count d i s t r i b u t i o n s were compared by c h i - s q u a r e t e s t s , c a l c u l a t e d u s i n g BMDP4F. To 108 a v o i d c l a s s e s with small expected v a l u e s , counts were grouped as 44, 45 and 'other' (Table 29), or as 44 and 'other' when sample s i z e s were small (Tables 26 and 30). Yates c o r r e c t i o n f o r c o n t i n u i t y was used i n 2x2 comparisons with sample s i z e s under 200. L i n e a r r e g r e s s i o n s were c a l c u l a t e d u s i n g BMDP1R, and e q u a l i t y of slop e s t e s t e d u s i n g BMDP1V. R e s u l t s Rearing m o r t a l i t i e s were hig h i n some groups i n experiments 1, 2 and 3 (Table 24). M o r t a l i t y was l a r g e l y due to i n f e c t i o n by f u n g i , b a c t e r i a or p a r a s i t i c f l u k e s , and i s not expected to be s t r o n g l y s e l e c t i v e f o r v e r t e b r a l number at the stages of development reared here (Lindsey 1962). V e r t e b r a l counts of f r y dying d u r i n g p o s t - e x p e r i m e n t a l r e a r i n g were ob t a i n e d f o r two groups i n experiment 2. Counts of these f r y (Table 26) d i d not d i f f e r s i g n i f i c a n t l y from those of s u r v i v o r s of pos t - e x p e r i m e n t a l r e a r i n g i n these groups (p=0.38 combining the two groups s i n c e counts do not d i f f e r between groups w i t h i n m o r t a l i t y treatments, p>0.40). Sample s i z e was, however, small f o r f i s h dying d u r i n g r e a r i n g . I f r e a r i n g m o r t a l i t y was s e l e c t i v e , the data suggest that i t was lower f o r f i s h with 44 v e r t e b r a e . Given such s e l e c t i v e m o r t a l i t y , f i s h with 44 vert e b r a e would be expected to be more frequent i n r e p l i c a t i o n s with high m o r t a l i t y than i n those with low m o r t a l i t y . T h i s r e l a t i o n s h i p was not seen. In experiments 1 and 2, r e a r i n g m o r t a l i t y was high i n one c o n t r o l group and low i n the other (Table 24). In both experiments, f r y with 44 ve r t e b r a e were a c t u a l l y l e s s frequent among s u r v i v o r s i n the group with h i g h m o r t a l i t y . Thus, the a v a i l a b l e evidence Table 26. Vertebral counts of fry surviving (Surv) or not surviving (Mort) post-experimental rearing in two groups from experiment 2. Vertebral number (%) Group £43 44 45 546 No. 1. Control 15C Mort - 50.0 50.0 - 20 Surv 0.9 56.6 41.6 0.9 113 2. Exptl 15C No cover Mort 5.0 55.0 40.0 - 20 Surv 1 .9 62.3 35. 1 0.6 . 154 110 suggests that r e a r i n g m o r t a l i t y was not s t r o n g l y s e l e c t i v e f o r v e r t e b r a l number i n these experiments. The mean l e n g t h of s u r v i v o r s of p r e d a t i o n i n experimental groups tended to be s l i g h t l y g r e a t e r than that of f r y i n c o n t r o l groups at the end of a l l experiments (Table 27). However, s i z e s e l e c t i o n was s t a t i s t i c a l l y s i g n i f i c a n t i n only experiments 3 and 5. Rates of p r e d a t i o n i n these two experiments were i n t e r m e d i a t e to those i n the experiments without s i g n i f i c a n t s i z e s e l e c t i o n (Table 24). Regressions between v e r t e b r a l number and l e n g t h are shown i n Table 28. Data are grouped over r e p l i c a t i o n s w i t h i n p r e d a t i o n treatments s i n c e s l o p e s d i d not d i f f e r among such r e p l i c a t i o n s i n any experiment (p>0.l8). The s i g n s of slo p e s i n c o n t r o l groups d i f f e r e d between the two s e t s of c r o s s e s : s l o p e s were n e g a t i v e before p r e d a t i o n among o f f s p r i n g of PM1 parents (experiments 2 and 4), but p o s i t i v e among those of PM8 parents (experiments 1, 3 and 5 ). In experiments 1 and 2, s l o p e s d i f f e r e d s i g n i f i c a n t l y from zero i n n e i t h e r c o n t r o l nor experimental groups. Among f r y with p o s t - e x p e r i m e n t a l r e a r i n g i n experiments 3 and 4, s l o p e s d i f f e r e d s i g n i f i c a n t l y from zero i n c o n t r o l but not i n experimental groups. In experiment 5, slope d i f f e r e d s i g n i f i c a n t l y from zero i n the experimental but not i n the c o n t r o l group. D i f f e r e n c e s i n s i g n i f i c a n c e between c o n t r o l and experimental groups might be e x p l a i n e d by the d i f f e r e n c e i n sample s i z e between the two groups i n experiment 5, but not i n experiments 3 and 4. In the l a t t e r experiments, r e g r e s s i o n s were s i g n i f i c a n t i n the group with the s m a l l e r sample s i z e . Mean Table 27. Mean lengths of peamouth chub fry exposed (exptl.) or unexposed (control) to predation. Means are the unweighted averages of the means within temperature treatments. Means within temperature treatments are also shown when the interaction (INT) between predation (PT) and temperature (TMP) treatments 1s significant. Mean length (mm) Probability Exp. Temp. Control Exptl. E--C PT TMP INT 1 Both 8 .93 8. .98 0 .05 0.26* 0 .0001 0.72 2 Both" 10. .01 10. .08 0. .07 0.31 0 .0001* 0.88 3 Both 10. 26 10. .53 0. 27 <0.0001 0. .052 0.026 15C 10. , 14 10. ,54 0. 40 <0.0001 25C 10. 38 10. 52 0. 14 0.081 4 Both 10. 84 10. 98 0. , 14 0. 1 1 0. .061 0. 17 5 Both 11 . 72 12. 20 0. 48 <0.0001* 0. ,028 0. 1 1 * Variances heterogeneous (p<0.05). Brown-Forsythe test used. Table 28. Regressions between vertebral number and length among peamouth chub fry exposed (exptl.) or unexposed (control) to predation. Fry were either preserved at the end of experiments (Pres) or reared to a larger size (Rear). Predation Probability Exp. Type treatment No. Intercept Slope of zero slope 1 Rear Control 266 Exptl. 494 2 Rear Control 258 Exptl. 634 3 Pres Control 60 Exptl. 170 Rear Control 268 Exptl. 500 4 Pres Control 82 Exptl. 216 Rear Control 358 Exptl. 675 5 Pres Control 219 Exptl. 451 43.8435 0.0405 0.13 44.3808 -0.0015 0.93 44.8603 -0.0439 0.73 44.3083 0.0015 0.92 42.1349 0.2083 0.24 45.4714 -0.0953 0.41 43.1562 0.1147 0.002 43.9449 0.0398 0.20 45.1025 -0.0708 0.41 43.9354 0.0330 0.48 45.0395 -0.0605 0.035 44.5598 -0.0217 0.27 44.2292 0.0194 0.72 43.6556 0.0635 0.043 1 1 3 lengths v a r i e d more among r e p l i c a t i o n s of reared experimental groups than between r e p l i c a t i o n s of reared c o n t r o l groups i n experiments 3 and 4. But r e g r e s s i o n s were a l s o s i g n i f i c a n t w i t h i n r e p l i c a t i o n s of c o n t r o l groups but not w i t h i n those of experimental groups i n these experiments. Thus, the d i f f e r e n c e s i n s i g n i f i c a n c e between c o n t r o l and experimental groups are not e x p l a i n e d by grouping over a wider range of mean lengths i n the l a t t e r . D i f f e r e n c e s i n the s i g n i f i c a n c e of r e g r e s s i o n s between c o n t r o l and experimental groups c o u l d r e s u l t from s e l e c t i v e p r e d a t i o n f o r v e r t e b r a l number. These observed changes i n s i g n i f i c a n c e between groups exposed or unexposed to p r e d a t i o n are c o n s i s t e n t with s e l e c t i o n f a v o u r i n g f r y with 44 v e r t e b r a e at l a r g e r s i z e s i n the range 9.2-11.2 mm (mean +/- 2 SD) i n experiment 3, and at s m a l l e r s i z e s i n the ranges 9.4-12.3 mm i n experiment 4 and 10.4-13.1 mm i n experiment 5 ( F i g . 17). V e r t e b r a l counts of f r y exposed or unexposed to p r e d a t i o n are shown i n Table 29. Data are grouped over temperature and cover treatments, • s i n c e counts d i d not d i f f e r s i g n i f i c a n t l y between l e v e l s of these treatments i n experimental groups i n any experiment (p>0.13) and s i n c e the n o n - s i g n i f i c a n t v a r i a t i o n s i n count between l e v e l s d i d not show any p a t t e r n c o n s i s t e n t over experiments. Counts of f r y exposed to p r e d a t i o n d i d not d i f f e r from those of unexposed c o n t r o l s i n any experiment. In experiment 1, a decrease i n the frequency of f r y with extreme v e r t e b r a l counts a f t e r exposure to p r e d a t i o n approached s i g n i f i c a n c e (p=0.065). The g r e a t e s t change i n frequency seen i n the f i v e experiments was an i n c r e a s e i n the frequency of f r y with 1 1 4 F i g u r e 17. Regressions between v e r t e b r a l number and l e n g t h i n c o n t r o l (C) and experimental (E) groups, peamouth chub p r e d a t i o n experiments 3-5. Length shown on lower h o r i z o n t a l a x i s i s at the end of experiments ( f o r exp. 3 and 4, r e g r e s s i o n s are among f i s h with p o s t - e x p e r i m e n t a l r e a r i n g , but l i n e s are transposed to the estimated l e n g t h s before r e a r i n g ; s c a l e s of reared l e n g t h s are a l s o shown). A s t e r i s k s i n d i c a t e s l o p e s s i g n i f i c a n t l y d i f f e r e n t from zero (p<0.05). L i n e s drawn over the range X +/- 1.5 SD. 115 R E A R E D L E N G T H ( m m ) 4 4 . 6 n 4 4 . 4 i 4 4 . 2 4 4 . 6 - , 4 4 . 4 ^ C Exp. 5 4 4 . 2 - 10 II 12 LENGTH (mm) 13 Table 29. Vertebral counts of peamouth chub fry exposed (exptl.) or unexposed (control) to predation. P is the probability that count distributions do not differ between predation treatments. Vertebral number (%) Exp. Predat ion treatment < 43 44 45 :>46 No. P 1 Control 4 . 1 59. 9 33 .3 2 .6 267 0 .065 Exptl. 2, .4 60. ,4 36 .4 0 .8 503 2 Control 0 .7 64 . 4 34 . 5 0. .4 278 0 . 19 Exptl. 2 .9 61 . 6 35. .3 0, .2 654 3 Control 1 . 5 57. 7 38. ,7 2. , 1 333 0. 31 Exptl . 2. 9 55. 8 38. ,4 2. 9 683 4 • Control 2. 7 62. 3 34. 1 0. 9 440 0. 18 Expt1. 1 . 8 67. 2 30. 1 O. 9 891 5 Control O. 9 54. 3 42. 9 1 . 8 219 0. 76 Exptl. 1 . 6 55. 9 40. 6 2. O 451 1 17 44 v e r t e b r a e a f t e r exposure to p r e d a t i o n i n experiment 4 (by about 5%, p=0.l8). In experiments 3 and 5, s e l e c t i o n i n favour of f r y with 44 v e r t e b r a e c o u l d have been obscured by s i z e s e l e c t i o n . Counts are compared w i t h i n small or l a r g e s i z e c l a s s e s i n these two experiments i n Table 30. In experiment 3, f r y with 44 v e r t e b r a e are s l i g t h l y more common a f t e r than before exposure to p r e d a t i o n at lengths over 10.35 mm, but the i n c r e a s e in frequency (5.5%) i s not s i g n i f i c a n t (p=0.23). Conversely, at the smaller lengths i n t h i s experiment, f r y with 44 v e r t e b r a e are l e s s frequent a f t e r exposure to p r e d a t i o n , but t h i s d i f f e r e n c e again l a c k s s i g n i f i c a n c e (p=0.l0) and c o u l d i n any event be a t t r i b u t e d at l e a s t p a r t l y to s i z e s e l e c t i o n . In experiment 5, f r y with 44 v e r t e b r a e are s i g n i f i c a n t l y more common a f t e r than before exposure to p r e d a t i o n at lengths under 11.5 mm (p=0.031), but not at g r e a t e r l e n g t h s . T h i s d i f f e r e n c e at the s h o r t e r lengths cannot be a t t r i b u t e d to s i z e s e l e c t i o n . In summary, these experiments p r o v i d e some evidence of s e l e c t i o n i n favour of f r y with 44 v e r t e b r a e at l e n g t h s between about 10.3 and 11.5 mm, but not at s m a l l e r l e n g t h s . Evidence f o r s e l e c t i v e p r e d a t i o n with r e s p e c t to v e r t e b r a l number i s str o n g i n the experiment at the l a r g e s t prey s i z e ( 5 ) , but o n l y weak and c i r c u m s t a n t i a l i n the experiments at in t e r m e d i a t e prey s i z e s (3 and 4 ) i In experiments at smal l e r s i z e s (1 and 2), p r e d a t i o n was s e l e c t i v e with r e s p e c t to n e i t h e r v e r t e b r a l number nor s i z e , and c o r r e l a t i o n s between v e r t e b r a l number and l e n g t h were s i g n i f i c a n t n e i t h e r before nor a f t e r p r e d a t i o n . One p o s s i b i l i t y , suggested by the absence of s i z e s e l e c t i o n i n these experiments, i s that Table 30. Vertebral counts of peamouth chub fry exposed or unexposed to predation at small or large lengths in experiments 3 and 5. Abbreviations as 1n Table 29. Length Mean Vertebral number (%) class length Predation Exp. (mm) (mm) treatment £43 44 45 £46 No. P 3 <10.35 9 .94 Control 1 .7 64 .4 33 .3 0. 6 174 0. 10 10 .06 Exptl. 4. .2 56. . 1 36 .9 2. 8 214 >10.35 10. . 76 Control 1 . .3 50. .0 44 .9 3. 8 158 0.23 10. 80 Exptl. 2. .4 55. .5 39 .4 2. 8 465 5 <1 1 .5 1 1 . 13 Control 1 . O 53. 6 43. .3 2. 1 97 0.031 11 . 16 Exptl. 69. 9 29. .0 1 . 1 93 > 1 1 . 5 12. 18 Control 0. 8 54. 9 42. .6 1 . 6 122 0.61 12. 47 Expt1. 2. 0 52. 2 43. 6 2. 2 358 119 h i g h predator e f f i c i e n c y overshadowed d i f f e r e n c e s i n performance r e l a t e d to v e r t e b r a l number or s i z e of prey at these small s i z e s . T h i s p o s s i b i l i t y i s d i s c o u n t e d by a very low p r e d a t i o n r a t e i n experiment 2. Ap p a r e n t l y , f r y which w i l l develop 44 or 45 v e r t e b r a e perform e q u a l l y w e l l at these small s i z e s . 120 Part V. Changes i n v e r t e b r a l number with l e n g t h i n w i l d peamouth chub f r y M a t e r i a l and Methods Fry were c o l l e c t e d from Holden Lake and from i t s main i n l e t stream, Hemer Creek, i n 1984. Spawning of peamouth chub appeared to be c o n f i n e d to the creek, and o c c u r r e d on s e v e r a l n i g h t s between l a t e A p r i l and e a r l y June. A f t e r h a t c h i n g , f r y migrated i n t o the lake at n i g h t , beginning at dusk. In 1984, the f i r s t f r y m i g r a t i o n i n t o the lake o c c u r r e d on the evening of May 12 or 13. F ry m i g r a t i n g i n t o the lake were c o l l e c t e d between May 14 and J u l y 1, us i n g a Surber sampler set about 15 m upstream of the la k e . Sets were of 5 or r a r e l y 15 min d u r a t i o n between 2200 and 2300 h, and sampled the e n t i r e water column. A d d i t i o n a l s e t s were made at e a r l i e r or l a t e r times on two o c c a s i o n s . C o l l e c t i o n s were made every day or two. Fry were a l s o c o l l e c t e d from the lake between May 14 and June 27 at A s i t e s , and between May 31 and June 27 at s i t e B ( F i g . 12). Lake c o l l e c t i o n s were made by d i p net (25 x 17 cm gape), from a canoe f l o a t i n g near shore. Vertebrae were undeveloped i n f r y c o l l e c t e d from the creek, i n most f r y c o l l e c t e d from the lake i n May, and i n smaller f r y c o l l e c t e d from the lake i n June. F ry c o l l e c t i o n s from the creek were d i v i d e d i n t o h a l v e s or q u a r t e r s u s i n g a plankton s p l i t t e r . One-half or -q u a r t e r were reared i n the l a b o r a t o r y to a l a r g e r s i z e , and the remainder k i l l e d i n a n a e s t h e t i c and preserved i n 10% b u f f e r e d f o r m a l i n . Fry c o l l e c t i o n s from the lake were 121 t r e a t e d i n one of three ways: (1) A l l f r y c o l l e c t e d on May 14 and 18 were reared to a l a r g e r s i z e , s i n c e sample s i z e s were r e l a t i v e l y s m a l l . (2) F r y c o l l e c t e d between May 20 and June 18, and on June 27, were d i v i d e d i n t o two groups u s i n g a plankton s p l i t t e r . One group was k i l l e d i n a n a e s t h e t i c and p r e s e r v e d i n 10% b u f f e r e d f o r m a l i n . Before June 11 or 14 (depending on c o l l e c t i o n s i t e ) , the second group was reared to a l a r g e r s i z e . A f t e r these dates, f r y i n the second group were a n a e s t h e t i s e d and d i v i d e d i n t o s i z e groups. F r y i n the smaller groups were re a r e d to a l a r g e r s i z e , and those i n the l a r g e r group pr e s e r v e d i n 10% b u f f e r e d f o r m a l i n . (3) F r y c o l l e c t e d on June 22 were a n a e s t h e t i s e d and d i v i d e d i n t o s m a l l (<9.5 mm) or l a r g e (> 9.5 mm) s i z e c l a s s e s . Those i n the small s i z e c l a s s were reared to a l a r g e r s i z e , and those i n the l a r g e c l a s s preserved i n f o r m a l i n . F r y r e a r e d to a l a r g e r s i z e and those p r e s e r v e d upon c o l l e c t i o n from the lake were c l e a r e d and s t a i n e d as d e s c r i b e d i n Part I. T o t a l l e n g t h was measured, and c e n t r a counted as d e s c r i b e d i n Part IV. V e r t e b r a l a b n o r m a l i t i e s (other than a c c e s s o r y arches on the l a s t or second l a s t v e r t e b r a ) o c c u r r e d i n 1.3% of f r y reared a f t e r c o l l e c t i o n from the creek, i n 1.7% of those r e a r e d a f t e r c o l l e c t i o n from the l a k e , and i n 0.8% of those p r e s e r v e d upon c o l l e c t i o n from the l a k e . These abnormal f r y were excluded from a n a l y s e s . Fry preserved upon c o l l e c t i o n from the creek were not c l e a r e d and s t a i n e d , but were measured. Lengths of these f r y cannot be compared d i r e c t l y to those of c l e a r e d and 1 22 s t a i n e d f r y . C l e a r i n g and s t a i n i n g appeared to reduce f r y l e n g t h by about 0.5 - 0.7 mm. L i n e a r r e g r e s s i o n was c a l c u l a t e d u s i n g BMDP1R. Mean lengths were compared by ANOVA, c a l c u l a t e d u s i n g BMDP7D. Other p r o b a b i l i t i e s are from c h i - s q u a r e t e s t s , c a l c u l a t e d using BMDP4F. V e r t e b r a l counts were u s u a l l y grouped as 44, 45 or 'other' i n order to a v o i d small expected v a l u e s i n chi - s q u a r e t e s t s . R e s u l t s Fry m i g r a t i o n i n t o the lake was g r e a t e s t before May 21, and u s u a l l y s l i g h t t h e r e a f t e r ( F i g . 18). Peak mi g r a t i o n s o c c u r r e d on the evenings of May 15 and May 18 or 19. Lesser peaks o c c u r r e d on June 1 and 19. About 95% of f r y e n t e r i n g the lake between 2200 and 2300 h had 44 or 45 ve r t e b r a e (Table 31). V e r t e b r a l counts d i f f e r e d markedly between f r y e n t e r i n g the lake before or a f t e r May 17 (p<0.000l). Counts of 44 ve r t e b r a e o c c u r r e d i n only about 45% of f r y e n t e r i n g before t h i s date, but in over 70% of those e n t e r i n g t h e r e a f t e r . Average l e n g t h of f r y e n t e r i n g the lake a l s o v a r i e d over the m i g r a t i o n p e r i o d , d e c r e a s i n g from e a r l y to l a t e m i g r a t i o n dates (p<0.000l a c c o r d i n g to l i n e a r r e g r e s s i o n a n a l y s i s , F i g . 19). Wit h i n an evening, f r y m i g r a t i o n s were a p p a r e n t l y homogeneous over time with r e s p e c t to v e r t e b r a l number, but not with r e s p e c t to l e n g t h (Table 32). Hence, v e r t e b r a l counts of f r y e n t e r i n g the lake between 2200-2300 h on a given evening (Table 31) are app a r e n t l y r e p r e s e n t a t i v e of those e n t e r i n g the lake over the e n t i r e 1 23 F i g u r e 18. Number of peamouth chub f r y captured per 5 min Surber sampler s e t , at 2200-2300 h i n Hemer Creek, 1984.  Table 31. Vertebral counts of peamouth chub fry collected from Hemer Creek between 2200 and 2300 h. In May and June, 1984. Rearing Vertebral count (%) mortal 1 ty No. Date (%) £43 44 45 46 counted May 14 12 . 1 1 .4 46, . 1 50, . 1 2. .4 423 15 21 . 3 1 , .8 46, .2 49. .9 2, .0 941 16 15, .5 4 , .3 44, .3 49. .3 2. . 1 140 19 10 .7 2 .2 71 , .7 25. .6 0. ,6 180 28 2 O 6 .3 70. ,8 22. .9 0. O 48 June 1 9. .6 4. .7 80. .0 15. 3 0. ,0 170 9 0. .0 6. .9 58. ,6 34 . 5 O. 0 58 13 10. 2 5. 4 73. ,0 21 . 3 0. 0 296 19 2. , 4 7. 9 78 . ,7 13. 4 0. 0 202 1 26 F i g u r e 19. Lengths of peamouth chub f r y ca p t u r e d i n Hemer Creek between 2200 and 2300 h. V e r t i c a l bars are standard e r r o r s . Regression l i n e between l e n g t h and c o l l e c t i o n day i s shown. P i s the p r o b a b i l i t y t h a t the slope of t h i s l i n e i s zero . 127 9.0 e E 8.8 o L U 1 < 8.6 L U 8.4 S A M P L E S I Z E o 5-10 o 2 4 - 3 6 O 4 8 0 9 6 p < 0 . 0 0 0 l May 14 D A Y July 5 T a b l e 32. V e r t e b r a l counts and l e n g t h s of peamouth chub f r y c o l l e c t e d from Hemer Creek at d i f f e r e n t times on the same n i g h t . P ( l ) and P(v) a r e the p r o b a b i l i t i e s that l e n g t h s and counts, r e s p e c t i v e l y , do not d i f f e r among c o l l e c t i o n times. Date T i me Length (mm) No. per 5 min Rear i ng mortal 1ty (%) V e r t e b r a l number (%) No. counted P(v) Mean SD No. P (D 43 44 45 46 May 15 2215-2230 8.87 0.33 48 0.0064 807 21.3 1 .8 46.2 49.9 2.0 941 0.81 16 0115-0130 9.05 0.29 48 58 27.3 5.6 44.2 50.0 0.0 54 May 16 2115-2120 9. 15 0.21 11 59 16.7 5.0 47.5 47 .5 0.0 40 2145-2150 9.02 0.27 48 0.39 338 18.3 2.8 51.1 45.4 0.7 141 0.72 2215-2200 9.02 0.31 48 378 15.5 4.3 44.3 49.3 2. 1 142 1 29 evening. Length d i s t r i b u t i o n s of f r y c o l l e c t e d from the lake between May 21 and June 27 are shown i n F i g . 20. L i t t l e growth of f r y was apparent i n the lake before about May 28. Average f r y l e n g t h a c t u a l l y decreased from May 21 to 23. Vertebrae were undeveloped i n a l l f r y c o l l e c t e d before May 28 (Table 33). Between May 25 and June 8, the p r o p o r t i o n of f r y with developed v e r t e b r a e i n c r e a s e d at a l l l e n g t h s . By June 4, v e r t e b r a e were developed i n most f r y 9.3 mm or more in l e n g t h . V e r t e b r a l counts of f r y c o l l e c t e d from the lake between May 14 and 31 are shown i n Table 34. Because v e r t e b r a e were undeveloped i n most f r y c o l l e c t e d on these dates, counts are of f r y r e a r e d i n the l a b o r a t o r y a f t e r c o l l e c t i o n . F ry are grouped over a l l four c o l l e c t i o n s i t e s , s i n c e v e r t e b r a l counts d i f f e r e d n e i t h e r among A s i t e s (p=0.85) nor between s i t e s A and B (p=0.59). V e r t e b r a l counts d i f f e r e d among c o l l e c t i o n dates (p<0.000l). The frequency of f r y with 44 v e r t e b r a e i n c r e a s e d between May 14-18 and May 21 (p<0.000l), and decreased between May 21 and l a t e r c o l l e c t i o n s (p=0.0l3). The i n c r e a s e i n frequency of f r y with 44 v e r t e b r a e between May 18 and 21 i n the lake presumably r e s u l t s from the i n c r e a s e d frequency of t h i s v e r t e b r a l count among f r y m i g r a t i n g i n t o the lake on May 19 (Table 31). The decreased frequency of t h i s v e r t e b r a l count between f r y c o l l e c t e d from the lake on May 21 and 23 might r e f l e c t g r e a t e r m o r t a l i t y among newly a r r i v e d f r y i n the l a k e . At any r a t e , v e r t e b r a l count d i s t r i b u t i o n s were r e l a t i v e l y homogeneous among c o l l e c t i o n s made a f t e r May 21. In p a r t i c u l a r , 130 F i g u r e 20. Length d i s t r i b u t i o n s of peamouth chub f r y c o l l e c t e d from Holden Lake between May(M) 21 and June(J) 27, 1984. The broken and s o l i d l i n e s connect the estimated median and s m a l l e s t l e n g t h s , r e s p e c t i v e l y , of f r y i n cohort A (see t e x t ) . Only f r y over about 9 mm i n l e n g t h are shown f o r June 22. 131 L E N G T H (ocular micrometer units) 5 0 6 0 70 8 0 >- o z LU ZD O LU or •z. LU U rr LU 0_ 20 r L E N G T H ( m m ) Table 33. Percent of peamouth chub fry with developed vertebrae, among those collected from Holden Lake at the size and on the date shown. Empty cells indicate fewer than 5 fry preserved without laboratory rearing. Length class Collection date omu mm M21 M23 M25 M28 M31 04 08 J1 1 J14 J18 <54 <8.87 0.0 0.0 0.0 0.0 0.0 0.7 4 . 2 4.5 5.9 2.9 55 9 .03 0.0 0.0 0.0 0.0 7.8 34 .8 36.8 50.0 66.7 50.0 56 9. 19 12.5 16.9 45.2 72.2 70.0 50.0 100.0 57 9.36 18.2 40.6 82.4 94 . 7 73.3 93.3 100.0 58 9.52 42.9 53.3 90.2 100.0 100.0 100.0 100.0 59 9.69 63.9 96.4 100.0 100.0 100.0 100.0 60 9.85 76 .0 98.6 •98 . 1 100.0 100.0 100.0 61 10.01 70.0 100.0 100.0 100.0 100.0 100.0 62 10. 18 97.7 100.0 100.0 100.0 100.0 >63 >10.34 100.0 100.0 100.0 100.0 100.0 omu=ocular micrometer unit; 1 omu = 0.1641667 mm. M = May, J = June. Table 34. Vertebral counts of peamouth chub fry collected from Holden Lake between May 14 and 31, 1984. Fry were reared to a countable size In the laboratory. Rearing Vertebral count (%) mortal Ity No. Date (%) <:43 44 45 46 counted May 14 16 .0 3 .0 50 .9 44 .2 1 .8 165 18 24 .3 3, . 1 43, .0 53 .4 0, .4 223 21 30 .0 3 .5 68 .2 27 .5 0. 9 349 23 7 . 8 6. .0 60, .3 32 .8 0. 9 232 25 9 .6 1 .0 61 . 1 37 .6 0. 3 306 28 10, .7 2. ,5 62. 6 33, ,2 1 . 6 364 31 1 1 , .8 2. 8 59. .6 36. .8 0. 8 497 1 34 the frequency of f r y with 44 v e r t e b r a e v a r i e d l i t t l e over the p e r i o d May 23-31 (p=0.83). In the f o l l o w i n g a n a l y s e s , t h r e e 'cohorts' of f r y are d i s t i n g u i s h e d . F r y e n t e r i n g the lake before May 22 comprise cohort A; those e n t e r i n g the lake about June 1, cohort B; and those e n t e r i n g June 19-21, cohort C. An attempt to d e l i m i t cohort A i s shown i n F i g . 20. In t h i s f i g u r e , the broken l i n e connects the estimated median l e n g t h of f r y of t h i s cohort i n each c o l l e c t i o n from the l a k e , and the s o l i d l i n e shows the approximate lower s i z e l i m i t of t h i s cohort i n each c o l l e c t i o n . The s o l i d l i n e i s drawn assuming t h a t f r y of the s m a l l e s t and median lengths have s i m i l a r growth r a t e s . Since s m a l l e r f r y may have lower growth r a t e s , t h i s l i n e may be drawn c o n s e r v a t i v e l y h i g h and exclude a small p r o p o r t i o n of f r y a c t u a l l y i n . c o h o r t A. However, t h i s c o n s e r v a t i v e procedure should a l s o ensure that those f r y as s i g n e d to cohort A do not i n c l u d e a s i g n i f i c a n t p r o p o r t i o n of f r y e n t e r i n g the lake a f t e r May 21. No attempt i s made to d e l i m i t c o h o r t s B and C i n F i g . 20. Cohort B can be f i r s t d i s t i n g u i s h e d as the mode a t small s i z e s i n the June 4 sample, and cohort C as that i n the June 27 sample. Cohort C was a l s o present i n the June 22 sample, but i s not shown i n F i g . 20 on t h i s date because most f r y below 9 mm i n len g t h i n t h i s sample were re a r e d to a l a r g e r s i z e a f t e r c o l l e c t i o n (see M a t e r i a l and Methods). 1 35 A p o s i t i v e c o r r e l a t i o n between v e r t e b r a l number and l e n g t h might be expected i n cohort A, s i n c e f r y e n t e r i n g the lake l a t e i n the p e r i o d May 14-21 had fewer v e r t e b r a e than d i d those e n t e r i n g e a r l y i n t h i s p e r i o d . However, such an a s s o c i a t i o n was not seen in any c o l l e c t i o n between May 23 and 31 (Table 35). The absence of such an a s s o c i a t i o n can be e x p l a i n e d by the apparent l a c k of growth among f r y i n the lake before May 24. V e r t e b r a l counts of f r y p r e s e r v e d upon c o l l e c t i o n i n June are shown i n F i g . 21, grouped by l e n g t h c l a s s and c o l l e c t i o n d a te. Fry below 9.3 mm i n l e n g t h are omitted from the f i g u r e , due to a high frequency of undeveloped v e r t e b r a e at these s i z e s (Table 33). In most c o l l e c t i o n s , the frequency of f r y with 44 v e r t e b r a e tended to decrease as l e n g t h i n c r e a s e d . Within c o l l e c t i o n s obtained l a t e r than about June 8, t h i s tendency c o u l d be at l e a s t p a r t l y e x p l a i n e d by confounding between l e n g t h and c o h o r t , s i n c e f r y with 44 v e r t e b r a e were more common in c o h o r t s e n t e r i n g the lake l a t e i n the season than i n those e n t e r i n g e a r l y . However, the s i g n i f i c a n t d i f f e r e n c e among l e n g t h c l a s s e s on June 4 cannot be so e x p l a i n e d . Nor i s i t l i k e l y that such confounding can e x p l a i n the s i g n i f i c a n t d i f f e r e n c e seen among l e n g t h c l a s s e s when f r y c o l l e c t e d between June 4 and 22 are grouped together. In the former case, a l l f r y compared are of the same cohort; i n the l a t t e r case, most confounding between l e n g t h and cohort has been e l i m i n a t e d by grouping over time, at l e a s t f o r lengths under about 12 mm. These changes i n l e n g t h c o u l d r e f l e c t s e l e c t i o n i n favour of f r y with 45 v e r t e b r a e at l e n g t h s of about 9.9-10.6 mm. Table 35. Vertebral counts of small or large fry In cohort A, in samples collected between May 23 and 31. Length class (mm) After Before Vertebral count (%) rearing rearing Date (estimated) £43 44 45 46 No. P May 23 <10.6 <8 .4 7 .6 60 .6 31 .8 0. .0 132 0. >10.6 >8.4 4 .0 60 .0 34 .0 2. .0 100 May 25 9.6-10. .9 7.8-8, ,4 1 .9 59. .6 37 .9 0. .6 161 0. >10.9 >8.4 0 .0 61 .7 38 .3 0. .0 141 May 28 9.6-10. 6 8.1-8. .7 2 .9 64. .5 30. 2 2 . 3 172 0. >10.6 >8 .7 2 .2 61 .0 35. .7 1 . 1 182 May 31 10.1-10. 9 8.6-9. 3 4 , .0 55. 6 39. .9 0. 5 198 0. >10.9 >9.3 2 .0 60. 2 36. 6 1 . 2 246 F i g u r e 21. Frequencies of f r y with 44 v e r t e b r a e , i n l e n g t h c l a s s e s of c o l l e c t i o n s between June 4 and 27. P r o b a b i l i t i e s are from c h i - s q u a r e t e s t s with counts grouped as 44 or o t h e r . L E N G T H (mm) 1 39 No sample a p p r o p r i a t e f o r comparison with f r y grouped over c o h o r t s i s a v a i l a b l e to t e s t f o r s e l e c t i o n at s m a l l e r l e n g t h s . Such samples are a v a i l a b l e o n l y f o r cohort A a l o n e . V e r t e b r a l counts of f r y i n cohort A are shown i n F i g . 22, both f o r f r y c o l l e c t e d on May 31 when v e r t e b r a e were mostly undeveloped and f o r those c o l l e c t e d i n June when ve r t e b r a e were mostly developed. Counts are of reared f i s h f o r the May sample, and of f i s h p r e s erved upon c o l l e c t i o n f o r the June samples. Fry below 9.3 mm i n l e n g t h are again omitted from the June samples. The same r e l a t i o n s h i p between v e r t e b r a l number and l e n g t h i s seen i n the June samples of cohort A alone as was seen i n these samples grouped over c o h o r t s . F r y with 44 v e r t e b r a e decreased i n frequency, and those with 45 v e r t e b r a e i n c r e a s e d i n frequency, between the 9.3-9.9 and 9.9-10.6 mm l e n g t h c l a s s e s (p=0.022). Since v e r t e b r a l number and l e n g t h were u n r e l a t e d i n May samples (Table 35), t h i s change i n frequency i n d i c a t e s s e l e c t i o n f a v o u r i n g f r y with 45 v e r t e b r a e at the l a r g e r s i z e . A s i m i l a r (though n o n - s i g n i f i c a n t ) r e s u l t can be seen comparing only the l a r g e r f r y i n the May 31 and June 4 samples (Table 36). On the other hand, f r y with 44 v e r t e b r a e were more frequent, and those with 45 v e r t e b r a e l e s s f r e q u e n t , i n June samples at lengths of 9.3-9.9 mm than i n the May sample. T h i s comparison i s v a l i d s i n c e v e r t e b r a l number and l e n g t h were u n r e l a t e d i n May samples, and suggests s e l e c t i o n f a v o u r i n g f r y with 44 v e r t e b r a e at lengths below 9.9 mm. T h i s r e s u l t i s confirmed comparing counts of s m a l l e r f r y i n the May 31 and June 4 samples (Table 36). F i n a l l y , v e r t e b r a l counts vary l i t t l e with l e n g t h between 10.6 and 14.0 mm, suggesting t h a t s e l e c t i o n favours n e i t h e r f r y with 1 40 F i g u r e 22. V e r t e b r a l counts of f r y i n cohort A, among f i s h r e a r e d a f t e r c o l l e c t i o n on May 31 and among those p r e s e r v e d upon c o l l e c t i o n between June 4 and 22. Fry c o l l e c t e d i n June grouped by l e n g t h . p=0.010 VERTEBRAE SAMPLE SIZE • 44 QIOO 0 325 0 45 • OTHER O 175-250 O 4 0 ° " 4 5 0 - _ a • • p=0.022 a. May 31 10 II June 4-22 BY L E N G T H (mm) 12 13 14 i Table 36. Vertebral counts of small or large fry In cohort A, on May 31 or June 4. Counts are of fry preserved upon collection on June 4, or reared after collection on May 31. Lengths of reared fry are the estimated lengths before rearing. Vertebral number (%) Group £43 44 45 46 No. P May 31 8.8-9. June 4 9.3-9. , 3 mm . 9 mm 3.0 2.5 55.4 69.3 41.1 28. 1 0.6 0.0 168 199 0.022 May 31 >9.3 mm 2.0 60.2 36.6 1.2 246 0.56 June 4 >9.9 mm 3.0 54.8 40.7 1.5 135 143 44 nor those with 45 ver t e b r a e at these g r e a t e r l e n g t h s . Since counts are compared here of reared and non-reared f r y , and s i n c e r e a r i n g m o r t a l i t y v a r i e s s u b s t a n t i a l l y among groups, the p o s s i b i l i t y t h a t r e a r i n g m o r t a l i t y may be s e l e c t i v e with resp e c t to v e r t e b r a l number must be c o n s i d e r e d . In the p r e v i o u s s e c t i o n (Part I V ) , i t appeared that r e a r i n g m o r t a l i t y was not s i g n i f i c a n t l y s e l e c t i v e f o r v e r t e b r a l number. R e s u l t s i n t h i s s e c t i o n l i k e w i s e show no i n d i c a t i o n of s e l e c t i v e r e a r i n g m o r t a l i t y . No c o n s i s t e n t p a t t e r n i s seen between v e r t e b r a l number and extent of r e a r i n g m o r t a l i t y i n Tables 31 and 34. In Table 37, r e p l i c a t i o n s with s u b s t a n t i a l l y d i f f e r e n t r e a r i n g m o r t a l i t i e s are shown f o r four groups. The f i r s t group c o n s i s t s of f r y c o l l e c t e d from Hemer Creek between 2250 and 2315 on June 13. The second and t h i r d r e p l i c a t i o n s of t h i s group are subsamples from the same Surber sampler s e t , separated u s i n g a plankton s p l i t t e r . Each of the remaining three groups c o n s i s t of samples from d i f f e r e n t A s i t e s , c o l l e c t e d on the same da t e . In no case do v e r t e b r a l counts d i f f e r s i g n i f i c a n t l y among r e p l i c a t i o n s , d e s p i t e wide v a r i a t i o n i n the extent of r e a r i n g m o r t a l i t y . Nor i s any c o n s i s t e n t p a t t e r n seen among r e p l i c a t i o n s between v e r t e b r a l number and the extent of r e a r i n g m o r t a l i t y . I t i s u n l i k e l y that the s i g n i f i c a n t d i f f e r e n c e s seen above among reared groups, or between reared and non-reared groups, r e s u l t from v a r y i n g e x t e n t s of r e a r i n g m o r t a l i t y . Table 37. Vertebral counts In replications of groups with widely varying extents of rearing mortality. Rearing Vertebral number (%) mortal 1ty Group Repl . (%) £43 44 45 46 No. P Hemer Cr., June 13 1 15. 7 7. 0 69. 8 23. 3 0. .0 43 2 24. 1 6. 3 77. 8 15. 9 0. ,0 63 0.81 3 2 . 9 5. 3 72. 1 22. 6 O. .0 190 Holden L., May 14 A1 21 . 2 3. 2 52. 4 41 . 3 3. 2 63 0.70 A3 12. 5 2. 9 50. 0 46. 1 1 . .0 102 May 18 A1 34. 7 3. 1 50. 0 46. 9 0. .0 32 A3 24. 1 3. 3 45. 8 51 . 0 0. .0 153 0.24 A4 14 . 6 2. 6 26. 3 68. 4 2. 6 38 May 21 A1 25. 1 2 . 1 68. 4 28. 4 1 . . 1 190 A3 58 . 0 2 . 1 70. 2 27. 7 0. .0 47 0.49 A4 18. 0 5 . 4 67. 0 25. 9 0. ,9 1 12 1 45 Vertebrae were undeveloped i n some of the sm a l l e r non-reared f r y but i n few of the r e a r e d or l a r g e r non-reared f r y . However, t h i s d i f f e r e n c e can be d i s c o u n t e d as a major cause of d i f f e r e n c e s i n v e r t e b r a l number among groups. Among f r y used i n p r e d a t i o n experiments (Part IV), v e r t e b r a l number and degree of development were a p p a r e n t l y u n r e l a t e d . Reared and non-reared subsamples, d i f f e r i n g by 12-24% i n the numbers of f r y with undeveloped (uncountable) v e r t e b r a e , d i f f e r e d by l e s s than 1% i n v e r t e b r a l numbers. Even i f the degree of v e r t e b r a l development d i d d i f f e r among v e r t e b r a l numbers, the small d i f f e r e n c e s between groups i n the p r o p o r t i o n s of f r y with countable v e r t e b r a e c o u l d not produce the l a r g e d i f f e r e n c e s i n v e r t e b r a l number seen i n some comparisons. For example, i n cohort A, v e r t e b r a e were undeveloped i n about 4% of non-reared f r y i n the 9.3-9.9 mm l e n g t h c l a s s i n June samples, and i n no reared f r y of the May samples or non-reared f r y i n the 9.9-10.6 mm l e n g t h c l a s s of June samples. However, the number of f r y with 44 v e r t e b r a e i n the f i r s t sample d i f f e r e d by 10% or more from the numbers i n the l a t t e r two samples. In summary, changes i n the v e r t e b r a l counts of f r y i n Holden Lake among May samples, i n which v e r t e b r a e of most f r y were undeveloped and uncountable, probably r e f l e c t changes i n the v e r t e b r a l counts of r e c r u i t s i n t o the l a k e , or g r e a t e r m o r t a l i t y of new r e c r u i t s , r a t h e r than s e l e c t i o n f o r v e r t e b r a l number per se. On the other hand, changes i n the v e r t e b r a l counts of f r y i n the lake between May and June samples, and between l e n g t h c l a s s e s of June samples, i n d i c a t e s e l e c t i o n f a v o u r i n g f r y with 44 146 vert e b r a e at lengths below 9.9 mm, and those with 45 v e r t e b r a e at lengths between 9.9 and 10.6 mm. At g r e a t e r l e n g t h s (between 10.6 and 14.0 mm), s e l e c t i o n appears to favour n e i t h e r number. S e l e c t i o n f o r v e r t e b r a l number at the s m a l l e r s i z e s appears to occur only a f t e r v e r t e b r a e are s u f f i c i e n t l y developed to be cou n t a b l e . 147 D i s c u s s i o n Experiments with Gasterosteus The experiments with Gasterosteus have demonstrated d i f f e r e n c e s i n swimming performance of f r y with d i f f e r e n t v e r t e b r a l counts, s e l e c t i v e p r e d a t i o n with r e s p e c t to v e r t e b r a l number of f r y and changes i n mean v e r t e b r a l number of w i l d f r y with l e n g t h . The same p a t t e r n i n r e l a t i v e performance was seen both i n p r e d a t i o n and i n swimming performance experiments using s t i c k l e b a c k s from Holden Lake. Swimming performance was best, and s u r v i v a l d u r i n g exposure to p r e d a t i o n g r e a t e s t , among f r y with a high r a t i o of 0.82 AV/CV at smal l s i z e s , among those with i n t e r m e d i a t e r a t i o s at intermediate s i z e s , and among those with a low r a t i o at l a r g e s i z e s . Changes i n v e r t e b r a l count with l e n g t h among w i l d f r y a l s o conformed to t h i s p a t t e r n , i n that f r y with the h i g h r a t i o sometimes i n c r e a s e d i n frequency at smal l s i z e s , as d i d those with the intermediate r a t i o s at s l i g h t l y l a r g e r s i z e s . T h i s s i m i l a r i t y i n p a t t e r n among experiments suggests that the s e l e c t i v e m o r t a l i t y seen i n p r e d a t i o n experiments i n the l a b o r a t o r y , and a p p a r e n t l y seen among f r y i n the w i l d , may r e s u l t from d i f f e r e n c e s i n the swimming performance of f r y with d i f f e r e n t v e r t e b r a l numbers. The changes i n v e r t e b r a l count seen among w i l d f r y are p r e c i s e l y those expected i f t h i s were so. Fry with the hig h r a t i o of 0.82 AV/CV i n c r e a s e d i n frequency i n the w i l d at j u s t those s i z e s when burst swimming performance i s best among such f r y , as d i d f r y with the in t e r m e d i a t e r a t i o s of 148 0.78-0.76. However, r e s u l t s of the p r e d a t i o n experiments d i f f e r e d from those of the swimming performance experiments i n two important r e s p e c t s . F i r s t , the two experiments appeared to d i f f e r i n the e f f e c t of temperature. R e s u l t s appeared s i m i l a r between temperatures i n p r e d a t i o n experiments, but the s i z e s at which r e l a t i v e swimming performance was best s h i f t e d s l i g h t l y between temperatures f o r f r y with h i g h or intermediate v e r t e b r a l count r a t i o s . T h i s apparent d i f f e r e n c e may simply r e f l e c t the r e l a t i v e l y wide range of s i z e s exposed to p r e d a t i o n i n any one experiment, and the r e l a t i v e l y s l i g h t s h i f t between temperatures i n the s i z e at which f r y with p a r t i c u l a r v e r t e b r a l count r a t i o s perform the best. Second, p a r t i c u l a r v e r t e b r a l count r a t i o s appeared to be favoured at somewhat l a r g e r s i z e s i n p r e d a t i o n than i n swimming performance experiments. D i s c r e p a n c i e s between mean lengths i n the two types of experiments were about 0.5-0.8 mm at the sm a l l e r s i z e s , 1.5-2 mm at the intermediate s i z e s , and 2.5 mm at the l a r g e s i z e s . S ince l e n g t h s i n p r e d a t i o n experiments are those at the end of experiments, these d i s c r e p a n c i e s c o u l d be due to growth d u r i n g p r e d a t i o n experiments. T h i s e x p l a n a t i o n would r e q u i r e growth r a t e s of 0.2-0.5 mm/d at 15C and 0.6-1.5 mm/d at 25C i n p r e d a t i o n experiments at small s i z e s (experiments H1-3), and 0.5-1.1 mm/d at 15C and 0.9-1.4 mm/d at 25C i n those at l a r g e r s i z e s (experiments H4-6). These r a t e s are mostly w i t h i n the range r e p o r t e d f o r l a r v a e and f r y of other s p e c i e s , e s p e c i a l l y at the higher temperature (Table 38). They are, however, hi g h i n t h i s range, and are i n most cases c o n s i d e r a b l y Table 38. Growth rates reported for larvae and fry of several fish species, 1n the laboratory (L) or wild (W). Length Growth rate Spec i es Type (mm) (mm/d) Comments Source Pungitius pungitius L 7-13 0 .5 12C Griswold and Smith 1972 Mlcropterus salmoldes L 8-14 1 .2 25-30C Strawn 1961 W >7-10 0.6 • - 1.4 Kramer and Smith 1960 Etheostoma spectabile L 9-16 1 .0 26C West 1966 Perca flavescens L 7-9 0. .2 17-18C. 500/4L Hinshaw 1985 Morone saxatills L 6-7.5 0, .4 18C, 3 % sal1n1ty, 100/8L Eldridge et al. 1981 8-9 0, .2 W <10 0. .2 Dey 1981 >10 0. .8 Harengula pensacola L 4.5-20 0.3 - 1 .0 22-33.5C, G = 0.054 T - 0.85 Saksena et al. 1972 Anchoa mltchi11i L 3-12 0 .6 29C Saksena et al. 1972 Clupea harengus (L) >10 0. . 1 1n 120L tank 8-14C Geffen 1982 0, .2 in 500L tank 8-14C 0. .3 in Loch Ewe bags 8-14C 0. .4 in Norway pond 8-14C Bel one belone L 12-35 0.7- -1.8 13-24C. G = 0.093 T - 0.43 Fonds et a l . 1974 G = growth rate (mm/d) T = temperature ( C) 150 g r e a t e r than rough estimates of growth r a t e s of w i l d f r y i n Holden Lake (0.2 or 0.4 mm/d f o r w i l d f r y under or over 8.2 mm i n l e n g t h , r e s p e c t i v e l y ) . But the estimated growth r a t e s of w i l d f r y are minimum estimates, judged from the d i s t a n c e between adjacent peaks i n l e n g t h d i s t r i b u t i o n s of f r y i n s u c c e s s i v e c o l l e c t i o n s . In any case, growth r a t e s d u r i n g p r e d a t i o n experiments may have been g r e a t e r than those of s i m i l a r l y s i z e d f r y i n the w i l d , due e i t h e r to h i g h food d e n s i t i e s i n the l a b o r a t o r y or to the change from crowded to uncrowded c o n d i t i o n s d u r i n g experiments. Growth i s t y p i c a l l y slow at the s m a l l e s t f r y s i z e s when f e e d i n g i s f i r s t i n i t i a t e d , and i n c r e a s e s r a p i d l y at l a r g e r s i z e s when feed i n g i s w e l l e s t a b l i s h e d (e.g., Kramer and Smith 1960; Dey 1981; West 1966; G r i s w o l d and Smith 1972). Feeding was w e l l e s t a b l i s h e d i n f r y used i n p r e d a t i o n experiments, though s i z e s were smal l due to crowded h o l d i n g c o n d i t i o n s . Perhaps growth r a t e s of these f r y when t r a n s f e r r e d to the uncrowded experimental c o n d i t i o n s were s i m i l a r to those of l a r g e r f r y with w e l l e s t a b l i s h e d f e e d i n g . A l s o , growth r a t e s of the s u r v i v o r s of p r e d a t i o n i n these experiments may have been g r e a t e r than the average r a t e s i n the p o p u l a t i o n , i f s e l e c t i o n favoured the more vigorous and f a s t e r growing i n d i v i d u a l s . In any case, the l e n g t h d i s c r e p a n c i e s between the two types of experiments can a l s o be e x p l a i n e d even given slower growth r a t e s , i f m o r t a l i t y i n p r e d a t i o n experiments was c o n c e n t r a t e d at the s m a l l e r s i z e s . Such was the case i n most experiments, s i n c e p r e d a t i o n was u s u a l l y s i z e s e l e c t i v e , f a v o u r i n g l a r g e r prey. 151 In the above view, as f r y grew d u r i n g p r e d a t i o n experiments (except H 6 ) , they experienced s e l e c t i o n f o r f i r s t one and then a second v e r t e b r a l count. The r e s u l t observed at the end of each experiment i s thus the net r e s u l t of s e l e c t i o n over these v a r i o u s i n t e r v a l s . Hence, s e l e c t i o n w i t h i n any one i n t e r v a l may have been much more inte n s e than that judged on the b a s i s of net changes i n frequency between c o n t r o l and experimental groups. S e l e c t i o n at the l a r g e r s i z e s near the end of experiments would not be expected to completely c a n c e l e f f e c t s of s e l e c t i o n at the small s i z e s near the s t a r t of experiments, because p r e d a t i o n r a t e s were probably g r e a t e s t e a r l y i n experiments when p r e d a t o r s were most hungry, n i l d u r i n g night p e r i o d s l a t e r i n experiments when p r e d a t o r s were absent and low d u r i n g day p e r i o d s l a t e r i n experiments when predator numbers were g e n e r a l l y much reduced. An a l t e r n a t e view i s that the s e l e c t i v e p r e d a t i o n seen i n the l a b o r a t o r y i s not the r e s u l t of d i f f e r e n c e s i n the b u r s t swimming performance of f r y with d i f f e r e n t v e r t e b r a l numbers. F a s t - s t a r t performance may be more important i n a v o i d i n g p r e d a t o r s than bu r s t swimming performance, but c o u l d not be measured at the a v a i l a b l e framing r a t e s . Perhaps i t too depends on v e r t e b r a l count, but p a r t i c u l a r counts perform the best at somewhat l a r g e r s i z e s i n f a s t - s t a r t s than i n bu r s t swimming. Or the observed s e l e c t i v e p r e d a t i o n might have r e s u l t e d from a c o r r e l a t i o n between v e r t e b r a l number and some other m o r p h o l o g i c a l or b e h a v i o u r a l c h a r a c t e r of importance i n a v o i d i n g p r e d a t o r s . At the s i z e s used here, few other m o r p h o l o g i c a l c h a r a c t e r s l i k e l y to be of importance i n a v o i d i n g p r e d a t o r s are yet expressed: 1 52 l a t e r a l p l a t e s are not yet formed, spines are rudimentary or undeveloped, and f i n rays are not f u l l y formed. B e h a v i o u r a l d i f f e r e n c e s r e l a t e d to v u l n e r a b i l i t y to p r e d a t i o n have been found between d i f f e r e n t l a t e r a l p l a t e phenotypes i n s t i c k l e b a c k s (Moodie et a l . 1973) but there the d i f f e r e n t phenotypes were from d i f f e r e n t p o p u l a t i o n s . The s t i c k l e b a c k s used here were from a s i n g l e p o p u l a t i o n , so such a s s o c i a t i o n s between t r a i t s are l e s s l i k e l y . However, the changes i n v e r t e b r a l count f r e q u e n c i e s seen i n w i l d f r y argue a g a i n s t t h i s a l t e r n a t e view. Fry with h i g h or i n t e r m e d i a t e v e r t e b r a l count r a t i o s i n c r e a s e d i n frequency i n the w i l d a t j u s t those s i z e s when t h e i r b u r s t swimming performance was the b e s t . At the s i z e s recorded at the end of p r e d a t i o n experiments, changes i n v e r t e b r a l count f r e q u e n c i e s e i t h e r were absent i n the w i l d (experiments H4-6) or were not those p r e d i c t e d from experiment (H1-3). Thus, i t seems l i k e l y that the s e l e c t i v e p r e d a t i o n seen i n the l a b o r a t o r y r e s u l t e d from an e f f e c t of v e r t e b r a l number on swimming performance, and that the l e n g t h d i s c r e p a n c i e s seen between p r e d a t i o n and swimming performance experiments r e s u l t e d from growth d u r i n g p r e d a t i o n experiments and the c o n c e n t r a t i o n of m o r t a l i t y at the sm a l l e r s i z e s i n these experiments. Changes i n v e r t e b r a l count f r e q u e n c i e s of w i l d f r y d i f f e r e d from those p r e d i c t e d from swimming performance experiments i n one r e s p e c t . Fry with the low r a t i o of 0.72 AV/CV d i d not s i g n i f i c a n t l y i n c r e a s e i n frequency at any s i z e i n the w i l d . However, f r y with t h i s r a t i o were r a r e i n the w i l d , so s e l e c t i o n 153 i n t h e i r favour over a b r i e f p e r i o d may not have produced d e t e c t a b l e changes i n frequency. In l a b o r a t o r y experiments, these f r y were favoured at l a r g e r s i z e s than were those with h i g h or i n t e r m e d i a t e r a t i o s . Growth r a t e s at these l a r g e r s i z e s appeared to be g r e a t e r i n the w i l d than those at the s m a l l e r s i z e s , so f r y with the low r a t i o s may have been favoured d u r i n g even b r i e f e r p e r i o d s i n the w i l d than were those with high or i n t e r m e d i a t e r a t i o s . R e s u l t s a l s o d i f f e r e d somewhat between s i t e s . F ry with the h i g h r a t i o of 0.82 AV/CV i n c r e a s e d i n frequency at small s i z e s at s i t e B but not at s i t e A. T h i s d i f f e r e n c e c o u l d r e f l e c t temporal r a t h e r than s p a t i a l v a r i a t i o n . Fry from s i t e A were mostly c o l l e c t e d on e a r l i e r dates and may have experienced lower temperatures as embryos, than f r y from s i t e B. S i z e at h a t c h i n g o f t e n i n c r e a s e s as i n c u b a t i o n temperature decreases (see below). The apparent d i f f e r e n c e i n s e l e c t i o n between s i t e s A and B c o u l d be e x p l a i n e d by r e c r u i t m e n t of l a r g e r f r y to s i t e A. Or i t might r e f l e c t temporal or s p a t i a l d i f f e r e n c e s i n the s i z e or type of p r e d a t o r s . P r e d a t i o n experiments were r e p l i c a t e d u sing f i s h from two p o p u l a t i o n s , from e c o l o g i c a l l y d i s s i m i l a r lakes with a wide geographic s e p a r a t i o n . F i s h from the two p o p u l a t i o n s d i f f e r e d c o n s i d e r a b l y i n morphology (e.g., i n l a t e r a l p l a t e number). Yet, r e s u l t s were s i m i l a r between p o p u l a t i o n s , i n that f r y with h i g h r a t i o s of abdominal to caudal v e r t e b r a e were favoured at small s i z e s , and those with low r a t i o s at l a r g e r s i z e s . However, v e r t e b r a l count r a t i o s d i f f e r e d markedly between p o p u l a t i o n s , and 1 54 d i f f e r e n t a c t u a l r a t i o s were favoured at the same f r y s i z e i n the two p o p u l a t i o n s . Perhaps the optimum v e r t e b r a l count r a t i o depends not j u s t on f r y l e n g t h , but a l s o on other dimensions such as width or depth (Lindsey 1975; Lindsey and L a v i n 1986) which may have v a r i e d between the two p o p u l a t i o n s . In these experiments, the c h a r a c t e r of f u n c t i o n a l importance was a p p a r e n t l y not t o t a l v e r t e b r a l number, but r a t h e r the r a t i o of abdominal to caudal v e r t e b r a e . However, the two c h a r a c t e r s were r e l a t e d . Fry with low t o t a l numbers tended to have h i g h r a t i o s . A c c o r d i n g l y , s e l e c t i o n f o r the r a t i o r e s u l t e d i n s e l e c t i o n f o r t o t a l number, both i n l a b o r a t o r y experiments (K1, K2, H2, H3) and i n the w i l d . F ry with low numbers (31) were favoured at small s i z e s , those with high numbers (32) at s l i g h t l y l a r g e r s i z e s . Experiments with M y l o c h e i l u s R e s u l t s u s i n g M y l o c h e i l u s resembled those u s i n g G a s t e r o s t e u s . S e l e c t i o n a c t i n g on w i l d f r y appeared to favour low v e r t e b r a l numbers (44) at smal l lengths (9.3-9.9 mm), h i g h v e r t e b r a l numbers (45) at s l i g h t l y g r e a t e r lengths (9.9-10.6 mm), and n e i t h e r number at even g r e a t e r lengths (10.6-14.0 mm). As with G a s t e r o s t e u s , s e l e c t i o n appeared to occur at s l i g h t l y l a r g e r s i z e s i n p r e d a t i o n experiments than i n the w i l d . Again, l e n g t h s r e p o r t e d f o r p r e d a t i o n experiments were those at the end of experiments, so t h i s d i s c r e p a n c y c o u l d be due to growth d u r i n g experiments, or to the c o n c e n t r a t i o n of m o r t a l i t y at the s m a l l e r s i z e s i n experiments. Of course, d i f f e r e n c e s between r e s u l t s i n 1 55 the l a b o r a t o r y and i n the w i l d c o u l d a l s o be due to p h y s i o l o g i c a l , m orphological or b e h a v i o u r a l d i f f e r e n c e s between l a b o r a t o r y - r e a r e d and w i l d f r y , i n the case of M y l o c h e i l u s . However, t h i s p o s s i b l e e x p l a n a t i o n does not h o l d f o r G a s t e r o s t e u s , s i n c e r e s u l t s were s i m i l a r between w i l d f r y and l a b o r a t o r y - r e a r e d f r y i n swimming performance experiments. Evidence from p r e d a t i o n experiments was l e s s c o n c l u s i v e u s i n g M y l o c h e i l u s than u s i n g G a s t e r o s t e u s . Most of the experiments u s i n g M y l o c h e i l u s were ap p a r e n t l y conducted at l e a s t p a r t l y at s i z e s below those to which v e r t e b r a l numbers were adapted, or at s i z e s where s e l e c t i o n i s absent because v e r t e b r a e are undeveloped. (Note that v e r t e b r a l development l i s t e d i n T a b l e 25 i s among f r y at the end of experiments; development may have been l e s s advanced at the s t a r t of experiments). In a l l experiments but 5, sampling e r r o r may have been i n c r e a s e d r e l a t i v e to that i n experiments with G a s t e r o s t e u s , due to subsampling f o r f r y to be r e a r e d to a l a r g e r s i z e . The n e c e s s i t y of r e a r i n g f r y . a f t e r a l l but experiment 5 a l s o probably i n t r o d u c e d e r r o r to the p a r t i t i o n i n g of r e s u l t s by f r y s i z e . F i n a l l y , as i n G a s t e r o s t e u s , the c h a r a c t e r of f u n c t i o n a l importance i n M y l o c h e i l u s may have a c t u a l l y been the r a t i o of abdominal to caudal v e r t e b r a e , even though t h i s r a t i o c o u l d not be p r a c t i c a l l y d i s t i n g u i s h e d . V a r i a t i o n i n t h i s r a t i o among l a b o r a t o r y - r e a r e d f r y with the same t o t a l number of v e r t e b r a e may have reduced s e l e c t i o n f o r t o t a l number in the l a b o r a t o r y . 1 56 Both i n l a b o r a t o r y experiments and i n the w i l d , s e l e c t i o n f o r f r y with low v e r t e b r a l numbers (44) f i r s t o c c u r r e d at j u s t those s i z e s when v e r t e b r a e were f i r s t developed. T h i s c o i n c i d e n c e suggests that the s t r u c t u r e s d i r e c t l y i n v o l v e d i n t h i s s e l e c t i o n may be the v e r t e b r a l c e n t r a themselves, r a t h e r than some r e l a t e d f e a t u r e of the a x i a l segmentation such as myomeres or nerves. A l s o because of t h i s c o i n c i d e n c e , i t i s not p o s s i b l e to determine from these r e s u l t s the lower l i m i t of the s i z e range over which f r y with 44 v e r t e b r a e are favoured. I f vert e b r a e were developed at s m a l l e r s i z e s , as may occur at higher temperatures, s e l e c t i o n might favour f r y with 44 v e r t e b r a e at yet smal l e r s i z e s than those seen here, or i t might favour f r y with yet lower v e r t e b r a l numbers at these smaller s i z e s . E f f e c t of v e r t e b r a l number on bur s t swimming performance Burst swimming was i n i t i a t e d i n t h i s study u s i n g an e l e c t r i c shock s t i m u l u s . While t h i s i s not a n a t u r a l s t i m u l u s , responses to e l e c t r i c shocks are a p p a r e n t l y comparable to those to more t y p i c a l s t i m u l i ( c f . Webb and C o r o l l a 1981). For example, mean burst speeds of northern anchovy l a r v a e , E n g r a u l i s mordax, are s i m i l a r whether s t i m u l a t e d by an e l e c t r i c shock (Webb and C o r o l l a 1981) or by p u r s u i t by a predator (Webb 1981). Maximum v e l o c i t i e s o b t a i n e d i n t h i s study were about 38 and 54 BL/s (body l e n g t h s / s e c ) at 15 and 25C, r e s p e c t i v e l y ( f o r f r y with a mean l e n g t h of 8.5 mm). These val u e s are comparable to those o b t a i n e d by Fuiman (1986) f o r zebra danio Danio r e r i o l a r v a e (50-65 BL/s at.21-30C), but higher than those o b t a i n e d by 1 57 Webb and C o r o l l a (1981) f o r anchovy l a r v a e (about 25 BL/s at 17C) and by Ryland (1963) f o r p l a i c e P leuronectes p l a t e s s a l a r v a e (11-16 BL/s at 6.5C). (Values were obtained by Ryland (1963) us i n g a stopwatch and measurement g r i d , and so were probably underestimates (Fuiman 1986)). The Q(10) f o r maximum v e l o c i t y i n t h i s study was 1.4 between 15 and 25C. Fuiman (1986) obtained the same value f o r maximum v e l o c i t y of zebra danio l a r v a e between 21 and 30C. Webb (1978) obt a i n e d a value of 1.7 f o r subadult rainbow t r o u t Salmo g a i r d n e r i between 5 and 15C, but found that maximum v e l o c i t y was independent of temperature i n t h i s s p e c i e s at higher temperatures (15-25C). Spouge and L a r k i n (1979) developed a model r e l a t i n g t h r u s t to v e r t e b r a l number based on hydrodynamic c o n s i d e r a t i o n s . T h e i r model i n d i c a t e d an e f f e c t of the abs o l u t e number of locomotor v e r t e b r a e on performance, r a t h e r than of the r a t i o of abdominal to caudal v e r t e b r a e as demonstrated here. A r e l a t i o n s h i p between optimum v e r t e b r a l number and l e n g t h was p r e d i c t e d by t h e i r model, but t h i s r e l a t i o n s h i p conformed to the observed i n c r e a s e i n v e r t e b r a l number with l e n g t h (Lindsey 1975) only at lengths over about 10 cm. Thus, pleomerism i s e x p l a i n e d by t h e i r model on l y i f s e l e c t i o n i s c o n c e n t r a t e d at l a r g e lengths near the maximum recorded f o r a p o p u l a t i o n . I f s e l e c t i o n f o r v e r t e b r a l number i s most i n t e n s e at l a r v a l and f r y lengths (and these are p o s i t i v e l y c o r r e l a t e d with a d u l t l e n g t h ) , t h e i r model p r e d i c t s a decrease i n v e r t e b r a l number with maximum l e n g t h , a r e l a t i o n s h i p o p p o s i t e to the observed t r e n d . Spouge and L a r k i n ' s model a l s o c o n t a i n e d 1 58 f a c t o r s dependent on temperature ( v i s c o s i t y and power per u n i t of muscle volume), but tended to i n d i c a t e that v e r t e b r a l number would decrease i n c o l d e r waters. T h i s i s i n disagreement with Jordan's r u l e , though Spouge and L a r k i n suggested t h a t t h i s r u l e might s t i l l be e x p l a i n e d by systematic v a r i a t i o n with temperature of other v a r i a b l e s i n t h e i r model (hydrodynamic e f f i c i e n c y , body p r o p o r t i o n s or v e r t e b r a l morphology). P r e d i c t i o n s of the Spouge and L a r k i n model thus conform n e i t h e r to the e f f e c t s of v e r t e b r a l number on performance observed in t h i s study, nor to the trends between v e r t e b r a l number and l e n g t h (pleomerism) or water temperature (Jordan's r u l e ) observed among f i s h p o p u l a t i o n s ( i f s e l e c t i o n i s assumed to be c o n c e n t r a t e d at s m a l l s i z e s ) . The model was d e r i v e d using L i g h t h i l l ' s (1970) 'elongated-body' theory f o r locomotion with u n d u l a t i o n s of small amplitude. Since amplitude i s not small d u r i n g b u r s t swimming, the use of L i g h t h i l l ' s (1971) large-amplitude theory might have been more a p p r o p r i a t e . L i g h t h i l l (1970) assumed that the wave of bending passed along a swimming f i s h ' s body was a sine-wave of constant amplitude and v e l o c i t y . T h i s assumption i s c e r t a i n l y not v a l i d over a l a r g e change i n p o s i t i o n along a f i s h ' s body (e.g., B a t t y 1981), but may be reasonable when the change i n p o s i t i o n i s s m a l l . In d e r i v i n g some equations i n t h e i r model, Spouge and L a r k i n assumed the l e n g t h of the caudalmost v e r t e b r a to be i n f i n i t e s i m a l l y s m a l l , an assumption of q u e s t i o n a b l e v a l i d i t y . A c r i t i c a l assumption made by Spouge and L a r k i n was that the l a t e r a l v e l o c i t y of the caudalmost v e r t e b r a r e l a t i v e to the p r e c e d i n g one 159 depends only upon the r a t e of c o n t r a c t i o n of the preceding myotome. T h i s assumption ignores the e f f e c t s of bending moments t r a n s m i t t e d from more a n t e r i o r segments and of water r e s i s t a n c e a c t i n g on a body of v a r i a b l e f l e x i b i l i t y . I t i s based on the view that the waves of bending seen on a swimming f i s h r e s u l t from c o i n c i d e n t waves of c o n t r a c t i o n , a view r e c e n t l y d i s c r e d i t e d by B l i g h t (1976, 1977) . The idea t h a t the waves of bending seen p a s s i n g down the body of a swimming f i s h are caused by c o i n c i d e n t waves of muscular c o n t r a c t i o n was suggested i n e a r l y s t u d i e s of f i s h locomotion (Breder 1926; Gray 1933a), and has p e r s i s t e d to the present (e.g., Wardle and V i d e l e r 1980). However, B l i g h t (1977) questioned t h i s view, suggesting that waves of bending w i l l be generated even when a l l muscle segments c o n t r a c t s i m u l t a n e o u s l y on a s i d e , so long as the f i s h body i s of v a r i a b l e f l e x i b i l i t y , r e l a t i v e l y s t i f f at the a n t e r i o r end and f l e x i b l e at the caudal end. The importance of t h i s g r a d i e n t i n f l e x i b i l i t y i n gen e r a t i n g waves of bending was f i r s t demonstrated by Gray (1933b), who showed that these waves were t r a n s m i t t e d along the body of a swimming w h i t i n g Gadus merlangus only when the caudal f i n was i n t a c t . Electromyograms of swimming a c t i v i t y i n amphibians and f i s h a l s o support B l i g h t ' s a l t e r n a t e view. A l l myotomes on a s i d e are seen to c o n t r a c t s i m u l t a n e o u s l y d u r i n g b u r s t swimming, both i n l a r v a e of the newt T r i t u r u s h e l v e t i c u s ( B l i g h t 1976) and i n a d u l t c a r p Cyprinus c a r p i o (Kashin et a l . 1979). During slower steady swimming, a l o n g i t u d i n a l d e l a y i n myotomal c o n t r a c t i o n i s seen, but the waves of muscular 160 a c t i v a t i o n do not c o i n c i d e with the waves of bending ( B l i g h t 1976; Kashin et a l . 1979). For example, i n steady swimming of the a d u l t tench Tinea t i n e a , the onset of muscular a c t i v i t y i s delayed and the b u r s t s of a c t i v i t y become s h o r t e r , toward the caudal end of the animal ( B l i g h t 1976). T h i s r e s u l t s i n a p e r i o d of simultaneous a c t i v i t y of most of the myotomes on a s i d e , c o i n c i d i n g with the 'S' p o s i t i o n of the body (when such simultaneous a c t i v i t y i s l e a s t expected a c c o r d i n g to c o n v e n t i o n a l t h e o r y ) . B l i g h t (1976,1977) suggests that the f u n c t i o n of t h i s l o n g i t u d i n a l d e l a y i n muscle a c t i v i t y i s not the propagation of waves of bending, but r a t h e r the r e d u c t i o n of l a t e r a l o s c i l l a t i o n of the head and the adjustment of t a i l f l e x i b i l i t y f o r wave conduction at d i f f e r e n t f r e q u e n c i e s . F i n a l l y , B l i g h t ' s theory i s a l s o supported by kinematic a n a l y s i s of f a s t swimming in the s a i t h e P o l l a c h i u s v i r e n s (Hess and V i d e l e r 1984). T h i s a n a l y s i s i n d i c a t e s that the bending moment does not t r a v e l as a running wave from head to t a i l as the l a t e r a l body c u r v a t u r e does, but r a t h e r behaves as a s t a n d i n g wave. That i s , l e f t and r i g h t s i d e s produce a l t e r n a t e c o n t r a c t i o n s s i m u l t a n e o u s l y over the whole body l e n g t h . The importance of a g r a d i e n t i n f l e x i b i l i t y i n g e n e r a t i n g the running waves of bending c h a r a c t e r i s t i c of f i s h locomotion suggests an e x p l a n a t i o n f o r the e f f e c t of v e r t e b r a l count r a t i o on swimming performance. Much of the d i f f e r e n c e i n f l e x i b i l i t y between abdominal and caudal regions of a f i s h r e s u l t s from d i f f e r e n c e s i n g i r t h . However, f l e x i b i l i t y should a l s o be i n f l u e n c e d by the number of segments ( i . e . , hinges) per u n i t 161 l e n g t h , e s p e c i a l l y i n l a r v a l f i s h whose abdominal f l e x i b i l i t y i s not so r e s t r i c t e d by wide g i r t h as i s that of a d u l t s . F i s h with a h i g h r a t i o of abdominal to caudal v e r t e b r a e w i l l have a r e l a t i v e l y low g r a d i e n t i n f l e x i b i l i t y between abdominal and caudal r e g i o n s ; those with a low r a t i o , a r e l a t i v e l y high g r a d i e n t . Thus, s e l e c t i o n f o r the r a t i o of abdominal to caudal v e r t e b r a e may r e f l e c t s e l e c t i o n f o r some optimum g r a d i e n t i n f l e x i b i l i t y between abdominal and caudal r e g i o n s . The s e l e c t i o n f o r body p r o p o r t i o n s seen i n p r e d a t i o n experiments using Holden Lake s t i c k l e b a c k s i s a l s o c o n s i s t e n t with t h i s s u g g e s t i o n . S e l e c t i o n favoured a high r a t i o of abdominal to caudal v e r t e b r a e at small s i z e s , and a low r a t i o at l a r g e s i z e s . Conversely, s e l e c t i o n favoured a low r a t i o of precaudal to caud a l l e n g t h at small s i z e s , and a hig h r a t i o at l a r g e s i z e s . Thus, s e l e c t i o n for both c h a r a c t e r s favoured a low g r a d i e n t i n f l e x i b i l i t y at small s i z e s , and a hig h g r a d i e n t at l a r g e s i z e s . Changes i n the optimum g r a d i e n t i n f l e x i b i l i t y with l e n g t h might r e s u l t from kinematic changes with l e n g t h . Webb (1976) observed t h a t f a s t - s t a r t kinematic p a t t e r n was s i z e dependent i n rainbow t r o u t 10 to 40 cm i n l e n g t h . Webb et a l . (1984) found that d u r i n g steady swimming the wavelength and amplitude of body waves were r e l a t i v e l y s m a l l e r i n l a r g e r rainbow t r o u t between lengths of 5 and 56 cm. However, these r e l a t i o n s h i p s , observed i n r e l a t i v e l y l a r g e f i s h , may not extend to f r y s i z e s . Batty (1981) found t h a t wavelength and amplitude were r e l a t i v e l y s i m i l a r i n 7 and 10 mm p l a i c e l a r v a e at c r u i s i n g speed. But Batty (1981) d i d f i n d t h a t maximum t a i l beat frequency decreased 1 62 g r e a t l y as s i z e i n c r e a s e d , a change that might favour r e l a t i v e l y s t i f f e r c audal regions at smal l e r s i z e s ( B l i g h t 1977). Hunter (1972) r e p o r t e d r e l a t i v e l y l a r g e r t a i l beat amplitudes i n l a r g e r anchovy l a r v a e , and Batty (1984) observed a change i n swimming s t y l e between 11 and 22 mm h e r r i n g l a r v a e . The amplitude of l a t e r a l o s c i l l a t i o n and maximum angle of the body to the d i r e c t i o n of motion i n c r e a s e d l i n e a r l y towards the t a i l i n 11 mm l a r v a e , and more r a p i d l y than l i n e a r l y towards the t a i l i n 22 mm l a r v a e . These l a t t e r changes with l e n g t h might favour more f l e x i b l e c a u d a l regions at l a r g e r s i z e s . Batty (1984) suggested that the changes i n swimming s t y l e seen as h e r r i n g l a r v a e grow may r e f l e c t an i n c r e a s e i n Reynolds number (R) d u r i n g growth. At low R (<20), r e s i s t i v e ( v i s c o u s ) f o r c e s are of predominant importance i n g e n e r a t i n g t h r u s t , while at h i g h R (>200), r e a c t i v e ( i n e r t i a l ) f o r c e s dominate c o n t r i b u t i o n s to t h r u s t (Webb and Weihs 1986). Batty (1984) proposed that the swimming s t y l e of small l a r v a e , i n which amplitude i s l a r g e over most of the body, r e l i e s mainly on r e s i s t i v e f o r c e s f o r p r o p u l s i o n , w hile t h a t of l a r g e l a r v a e , i n which amplitude i n c r e a s e s r a p i d l y towards the t a i l , r e l i e s mainly on r e a c t i v e f o r c e s f o r p r o p u l s i o n . While these arguments may apply to the r o u t i n e a c t i v i t i e s of f i s h l a r v a e , they are not l i k e l y to be r e l e v e n t to burs t swimming a c t i v i t i e s , s i n c e even the s m a l l e s t l a r v a e can a c c e l e r a t e to speeds high enough to generate v a l u e s of R >> 200 (Webb and Weihs 1986). The r a p i d changes i n morphology seen d u r i n g l a r v a l development (e.g., Webb and Weihs 1986) may be more important causes of the concommitant 1 63 changes i n swimming s t y l e and optimum v e r t e b r a l count r a t i o with l e n g t h d u r i n g these stages. The optimum v e r t e b r a l count r a t i o at a given s i z e appeared to depend on water temperature, at l e a s t at small s i z e s . T h i s dependency might be e x p l a i n e d by changes i n water v i s c o s i t y (as suggested by the experiments with m e t h y l c e l l u l o s e ) . As water temperature i n c r e a s e s , v i s c o s i t y d e creases. The r e s u l t a n t decrease i n water r e s i s t a n c e might favour a r e l a t i v e l y g r e a t e r g r a d i e n t i n f l e x i b i l i t y at a g i v e n s i z e i n order to maintain the same kinematic form at higher temperature. J u s t such a r e s u l t was seen i n these experiments at s m a l l e r s i z e s (compare r e s u l t s i n the 7.4-7.8 mm l e n g t h c l a s s a t 15 and 25C). A l t e r n a t i v e l y , the arguments of the p r e v i o u s paragraph notwithstanding, the e f f e c t of temperature might r e f l e c t an e f f e c t on Reynolds number. As water temperature i n c r e a s e s , v i s c o s i t y decreases and v e l o c i t y at a g i v e n s i z e i n c r e a s e s . Both changes i n c r e a s e Reynolds number. If the change i n optimum v e r t e b r a l count r a t i o between small and l a r g e f r y lengths r e s u l t s from an i n c r e a s e i n Reynolds number and a s h i f t i n the r e l a t i v e importance of r e s i s t i v e and r e a c t i v e f o r c e s i n p r o p u l s i o n , t h i s s h i f t would occur at a sma l l e r s i z e a t higher temperature. However, as noted above, the h i g h Reynolds number a s s o c i a t e d with bu r s t speeds of even the s m a l l e s t l a r v a e argues a g a i n s t t h i s a l t e r n a t i v e e x p l a n a t i o n . V e r t e b r a l count r a t i o appeared to a f f e c t performance only over a narrow range of f r y l e n g t h s . Perhaps the changes i n a n t e r o p o s t e r i o r f l e x i b i l i t y a s s o c i a t e d with changes i n v e r t e b r a l count r a t i o are important o n l y over a narrow range of Reynolds 1 64 number. Or, the r a t i o s optimal at s m a l l e r or l a r g e r s i z e s may have been absent from the p o p u l a t i o n s s t u d i e d (because s e l e c t i o n i s never c o n c e n t r a t e d at these more extreme s i z e s i n these p o p u l a t i o n s ) . A l t e r n a t i v e l y , f a c t o r s other than v e r t e b r a l count r a t i o (e.g., l o n g i t u d i n a l v a r i a t i o n i n g i r t h ) may be of predominant importance i n determining l o n g i t u d i n a l g r a d i e n t s i n f l e x i b i l i t y at the more extreme ( e s p e c i a l l y l a r g e r ) s i z e s . The r e s u l t s o b t a i n e d i n t h i s study i n d i c a t e that the r a t i o of abdominal to caudal v e r t e b r a e i s of fundamental importance i n determining swimming performance over a narrow range of f r y s i z e s . At these s i z e s , swimming occurs at Reynolds numbers near, though somewhat higher than, those a s s o c i a t e d with a t r a n s i t i o n between the predominance of r e s i s t i v e or r e a c t i v e f o r c e s i n p r o p u l s i o n . The e x p l a n a t i o n s suggested above f o r t h i s e f f e c t of v e r t e b r a l count r a t i o on performance, and f o r the dependency of the optimum r a t i o on f r y l e n g t h and water temperature, are o b v i o u s l y h i g h l y s p e c u l a t i v e . Kinematic analyses at burst speeds of f r y of v a r i o u s l e n g t h s and v e r t e b r a l numbers are needed before more d e f i n i t i v e e x p l a n a t i o n s can be suggested. Genetic c o n t r o l of the r a t i o of abdominal to caudal v e r t e b r a e The v e r t e b r a l c h a r a c t e r of s e l e c t i v e importance appears to be not the a b s o l u t e number of v e r t e b r a e , but ra t h e r the r a t i o of abdominal to caudal v e r t e b r a e . Two simple models can be suggested f o r the g e n e t i c c o n t r o l of t h i s c h a r a c t e r . The number of abdominal and the number of cau d a l v e r t e b r a e may each be 1 65 c o n t r o l l e d by separate genes. Assuming no p l e i o t r o p y or l i n k a g e d i s e q u i l i b r i u m , the expected frequency of any v e r t e b r a l count c l a s s i n a randomly mating p o p u l a t i o n i s then simply the product of the f r e q u e n c i e s of the c o r r e s p o n d i n g numbers of abdominal and c a u d a l v e r t e b r a e : p(a+c)=p(a)p(c) (model 1). A l t e r n a t i v e l y , the t o t a l number of v e r t e b r a e and the r a t i o of abdominal to caudal v e r t e b r a e may be determined by separate genes. Then, the expected frequency of a given count c l a s s ( r a t i o ) i s the product of the frequency of the c o r r e s p o n d i n g t o t a l number and the frequency of the count c l a s s given the t o t a l number: p(a+c)=p(t)p(a+c|t) where t=a+c (model 2). The two models are f i t t e d to the counts i n c o n t r o l groups of the Holden Lake p r e d a t i o n experiments In Table 39. In model 2, the r a t i o of abdominal to c a u d a l v e r t e b r a e i s assumed to be a t h r e s h o l d c h a r a c t e r . L i a b i l i t y i s assumed to be normally d i s t r i b u t e d with the same mean and standard d e v i a t i o n i n a l l t o t a l v e r t e b r a l count c l a s s e s . Thresholds of l i a b i l i t y a re assumed to be the mid-points between the observed r a t i o s of abdominal to caudal v e r t e b r a e . For example, among f i s h with 31 t o t a l v e r t e b r a e , three c l a s s e s are seen: 15/16=0.9375 AV/CV, 14/17=0.8235 AV/CV, and 13/18=0.7222 AV/CV. Thresholds between these c l a s s e s are assumed to be 0.8805 and 0.7729. Assumed t h r e s h o l d s thus d i f f e r among t o t a l v e r t e b r a l count c l a s s e s . Model 2 i s f i t t e d only to t o t a l count c l a s s e s with three or more Table 39. Fits of two models for the genetic control of the ratio of abdominal to caudal vertebrae to Counts observed in control groups of Holden Lake predation experiments. Contributions to chi-square are shown Including only classes to which both models are fitted. All chi-square probabilities are less than 0.05 . Parental Group A B C All Observed - Expected: M1: TV=30 14/16 1 .4 -9. .6 0 .5 -8 . 1 13/17 -44 .2 -22 .8 -26 .9 -95 .8 Other 2 . 3 1 .3 2 .6 TV = 31 15/16 8 . 2 13. .6 6 .9 28 . 4 14/17 44 .9 26. 8 26 .2 99 .2 13/18 40 .5 23 . 7 32 .6 97. .2 TV=32 15/17 -o .7 -2. . 1 1 . .8 -0, .4 14/18 -34. .0 -15. .4 -23 .7 -73 . 1 13/19 1 1 .8 2. .9 1 . .9 17 . 4 M2: TV=30 14/16 13/17 Other N/A -1.5 -2.2 3.6 10.2 •10.5 0.3 16.0 -20. 2 4.2 TV = 31 TV = 32 15/16 14/17 13/18 15/17 14/18 13/19 2.7 13.3 •16.0 •10.2 1 .4 8.8 4.2 8.6 •12.8 •16.4 16.3 O. 2 0. -0. -0. •14. 15. -0. 3.3 44 .0 -47 .4 -49.6 36.6 13.0 Ch1-square M1 M2 123 .6 18.6 134 .3 14.5 80.2 18. 1 354.2 73 .6 Abd/Caud TV = 30 31 32 0.7995 0.7747 0.7929+ 0.8149 0.7975 0.8233 0.8050 0.7948 0.8180 0.8113 0.7884 Abbreviations: M1=Model 1, M2=Model 2, TV=Total vertebrae. Abd/Caud=abdom1nal to caudal ratio In continuous units of l i a b i l i t y , estimated separately for each TV. + N<50 167 r a t i o s AV/CV. Weighted averages of the means and standard d e v i a t i o n s i n l i a b i l i t y c a l c u l a t e d f o r each t o t a l count c l a s s are used i n model 2. P r e d i c t i o n s of both models depart s i g n i f i c a n t l y from the observed count f r e q u e n c i e s i n a l l c o n t r o l groups. In a l l cases, p r e d i c t i o n s of model 1 depart much more widely from the observed counts than do those of model 2. Most departures of model 1 from o b s e r v a t i o n are e x p l a i n e d by an observed excess of f i s h with 31 v e r t e b r a e and d e f i c i t of those with more extreme counts. These departures cannot be e x p l a i n e d by any simple hypothesis i n v o l v i n g p l e i o t r o p y or l i n k a g e d i s e q u i l i b r i u m . On the other hand, most departures of model 2 from o b s e r v a t i o n can be so e x p l a i n e d . These departures i n d i c a t e a n e g a t i v e c o r r e l a t i o n between t o t a l v e r t e b r a l number and mean abdominal/caudal r a t i o ( i n continuous u n i t s of l i a b i l i t y ) (Table 39). Among f i s h with 31 or 32 v e r t e b r a e , t h i s c o r r e l a t i o n r e s u l t s i n an i n c r e a s e i n the f r e q u e n c i e s of abdominal / c a u d a l r a t i o s of 14/17 and/or 14/18, compared to those expected i f the two t r a i t s were independent. These r a t i o s are the two t h a t are sometimes s e l e c t e d f o r i n the w i l d i n t h i s p o p u l a t i o n (Part I I I ) . Thus, s e l e c t i o n would be expected to favour the observed c o r r e l a t i o n between t o t a l v e r t e b r a l number and abdominal / c a u d a l r a t i o . Since the f i s h used i n t h i s a n a l y s i s were r e a r e d i n a common l a b o r a t o r y environment, t h i s c o r r e l a t i o n presumably r e f l e c t s a g e n e t i c c o r r e l a t i o n ( i . e . , p l e i o t r o p y or l i n k a g e d i s e q u i l i b r i u m ) r a t h e r than an environmental one. 168 V a r i a t i o n a l s o appears to occur among p a r e n t a l groups i n which count c l a s s (14/17 or 14/18) i s more frequent than expected i f t o t a l v e r t e b r a l number and abdominal /caudal r a t i o were independent. T h i s v a r i a t i o n may represent seasonal v a r i a t i o n (A p a r ents were c o l l e c t e d J u l y 24, B parents August 4-5, and C p a r ents August 10). Seasonal v a r i a t i o n c o u l d r e f l e c t g e n e t i c v a r i a t i o n among p a r e n t a l groups, or an e f f e c t of s easonal v a r i a t i o n i n the p r e f e r t i l i z a t i o n environment or age of p a rents (Swain and Lindsey 1986a,b). Since there may a l s o be s easonal v a r i a t i o n i n which count i s most favoured by s e l e c t i o n , t h i s v a r i a t i o n c o u l d be a d a p t i v e . Most work on g e n e t i c c o r r e l a t i o n s among t r a i t s has been d i r e c t e d towards an examination of c o r r e l a t e d responses to s e l e c t i o n (Falconer 1981; A t c h l e y et a l . 1982). However, ge n e t i c c o r r e l a t i o n s may themselves be responses to s e l e c t i o n . Cheverud (1982) suggested that developmentally and f u n c t i o n a l l y r e l a t e d t r a i t s should be r e l a t i v e l y h i g h l y i n t e g r a t e d with r e s p e c t to g e n e t i c f a c t o r s , but f a i l e d to f i n d such an a s s o c i a t i o n among macaque c r a n i a l t r a i t s . He suggested t h a t t h i s f a i l u r e might r e f l e c t the e v o l u t i o n of g e n e t i c c o r r e l a t i o n s among developmentally and f u n c t i o n a l l y independent t r a i t s through s t o c h a s t i c p r o c e s s e s . Although the r e s u l t s r e p o r t e d here are o n l y p r e l i m i n a r y , they are c o n s i s t e n t with a g e n e t i c i n t e g r a t i o n of f u n c t i o n a l l y r e l a t e d v e r t e b r a l t r a i t s i n response to s e l e c t i o n . A q u a n t i t a t i v e g e n e t i c a n a l y s i s i s needed to e s t i m a t e the g e n e t i c c o r r e l a t i o n between these t r a i t s , and to look f o r an environmental c o r r e l a t i o n between them. F u r t h e r work i s a l s o 169 needed to examine the e x i s t e n c e , b a s i s and p o s s i b l e adaptive s i g n i f i c a n c e of any seasonal v a r i a t i o n i n the c o r r e l a t i o n between these t r a i t s . V a r i a t i o n among p o p u l a t i o n s 1. Pleomerism R e s u l t s d e s c r i b e d here suggest an e x p l a n a t i o n f o r pleomerism. In both G. a c u l e a t u s and M. c a u r i n u s , s e l e c t i o n appeared to favour f r y with a low v e r t e b r a l count at small s i z e s , and those with a higher v e r t e b r a l count at s l i g h t l y l a r g e r s i z e s . In f i s h e s , l a r g e females tend to produce l a r g e eggs (Fowler 1972; G a l i 1974; Kazakov 1981), and l a r g e eggs tend to produce l a r g e f r y , both at h a t c h i n g and at complete yolk a b s o r p t i o n (Fowler 1972; G a l l 1974; Wallace and A a s j o r d 1984; Beacham et a l . 1985). Thus, o f f s p r i n g of l a r g e females might face l e s s exposure to s e l e c t i o n at s i z e s when low counts are favoured than would those of small females ( F i g . 23). I f so, higher counts would tend to be favoured i n o f f s p r i n g of l a r g e females, lower counts i n those of small females. T h i s e x p l a n a t i o n r e q u i r e s o v e r l a p between the s i z e s at which s e l e c t i o n operates on v e r t e b r a l number and those at which o f f s p r i n g of l a r g e and sm a l l females are f i r s t p o t e n t i a l l y exposed to s e l e c t i o n ( r e f e r r e d to here as ' r e c r u i t e d ' ) . For example, i t cannot e x p l a i n pleomerism i f a l l o f f s p r i n g of both l a r g e and small females are r e c r u i t e d at s i z e s below those at which s e l e c t i o n favours lower v e r t e b r a l numbers. However, the r e q u i r e d o v e r l a p appears to occur i n both the s p e c i e s s t u d i e d 1 70 F i g u r e 23. A model e x p l a i n i n g pleomerism. Recruitment s i z e i s the s i z e when f r y are f i r s t p o t e n t i a l l y exposed to s e l e c t i v e p r e d a t i o n , i . e . when f r y are free-swimming and ve r t e b r a e are developed. V,, and are f r y wit h N or N+1 v e r t e b r a e . L E N G T H 172 here. The s m a l l e s t modes i n s i z e d i s t r i b u t i o n s of s t i c k l e b a c k f r y c o l l e c t e d from Holden Lake overlapped with the s i z e s at which s e l e c t i o n favoured low v e r t e b r a l numbers (31) i n these f r y . S i m i l a r l y , s e l e c t i o n appeared to favour a low v e r t e b r a l count (44) i n peamouth chub f r y at j u s t those s i z e s when v e r t e b r a e were f i r s t developed i n these f r y . S e l e c t i o n o p e r a t i n g on the f r y might r e s u l t i n pleomerism even i f o f f s p r i n g of both l a r g e and small females are r e c r u i t e d at s i z e s below those at which s e l e c t i o n favours low v e r t e b r a l numbers. Large eggs may produce more r a p i d l y growing f r y than small eggs (Wallace and A a s j o r d 1984). I f d i f f e r e n c e s i n l e n g t h - s p e c i f i c growth between f r y produced from s m a l l or l a r g e eggs decrease as l e n g t h i n c r e a s e s , higher v e r t e b r a l numbers w i l l tend to be favoured i n f r y produced from l a r g e eggs than i n those produced from small eggs. If pleomerism does r e s u l t from s e l e c t i o n o p e r a t i n g on the f r y soon a f t e r h a t c h i n g , the evidence i n G. a c u l e a t u s i s that i t i s r e l a t e d not to s e l e c t i o n o p e r a t i n g d i r e c t l y on the t o t a l number of v e r t e b r a e , but r a t h e r to s e l e c t i o n o p e r a t i n g on the r a t i o of abdominal to caudal v e r t e b r a e . In G. a c u l e a t u s , the optimum r a t i o decreased as f r y l e n g t h i n c r e a s e d . I f t h i s r e s u l t i s a general one, pleomerism i s expected only when the r a t i o and the t o t a l number of v e r t e b r a e are i n v e r s e l y c o r r e l a t e d . Such a c o r r e l a t i o n was seen i n both the s t i c k l e b a c k p o p u l a t i o n s s t u d i e d here, but few other data are a v a i l a b l e to t e s t i t s g e n e r a l i t y . An i n v e r s e c o r r e l a t i o n between the r a t i o and the t o t a l number w i l l occur i f most v a r i a t i o n i n the t o t a l number i s produced by 1 73 v a r i a t i o n i n the caudal number. T h i s p a t t e r n of v a r i a t i o n has been observed i n the p a r a d i s e f i s h Macropodus o p e r c u l a r i s (Lindsey 1954), i n the medaka O r y z i a s l a t i p e s ( A l i and Lindsey 1974), and i n R i v u l u s marmoratus (Swain 1979). In the p o p u l a t i o n of G. a c u l e a t u s s t u d i e d by Lindsey (1962), most en v i r o n m e n t a l l y induced v a r i a t i o n o c c u r r e d i n the abdominal re g i o n ( i . e . , a n t e r i o r to the a n a l s p i n e ) , while i n h e r i t e d v a r i a t i o n appeared most markedly i n the caudal r e g i o n . Thus, the p a t t e r n of v a r i a t i o n expected to produce pleomerism i s i n f a c t seen i n most of the few cases examined. I f pleomerism does r e s u l t from s e l e c t i o n f o r the r a t i o of abdominal to caudal v e r t e b r a e , the c o r r e l a t i o n with maximum a d u l t s i z e should be stronger f o r t h i s r a t i o than f o r the t o t a l number, and the degree to which a group e x h i b i t s pleomerism should depend p a r t l y on the s t r e n g t h of the i n v e r s e c o r r e l a t i o n between the r a t i o and the t o t a l number. Perhaps some groups that f a i l to e x h i b i t pleomerism do so because the t o t a l number does not show a s t r o n g i n v e r s e c o r r e l a t i o n w i t h the r a t i o AV/CV i n these groups. Lindsey (1975) noted that i n a few i n s t a n c e s pleomerism occurs between the sexes. He c i t e d three examples. In b l e n n i e s of the genus E c s e n i u s , males reach l a r g e r l e n g t h s and have more ver t e b r a e than do females. In the shark Etmopterus spinax, females are l a r g e r and have more ve r t e b r a e than males. F i n a l l y , males of the c a p e l i n M a l l o t u s v i l l o s u s tend to be l a r g e r than females; males tend to have more v e r t e b r a e than females i n B r i t i s h Columbia and Murmansk, but fewer than females i n Newfoundland. I can o f f e r two e x p l a n a t i o n s f o r d i f f e r e n c e s i n 174 v e r t e b r a l number between the sexes. F i r s t , s e l e c t i o n f o r greater e g g - c a r r y i n g c a p a c i t y might favour a high p r o p o r t i o n of abdominal to caudal v e r t e b r a e i n females. In the s t i c k l e b a c k p o p u l a t i o n s s t u d i e d here, such s e l e c t i o n would favour a lower v e r t e b r a l count i n females ( s i n c e the p r o p o r t i o n and the t o t a l number are i n v e r s e l y c o r r e l a t e d ) . Second, i n some f i s h e s , sex d e t e r m i n a t i o n i s temperature-dependent ( H a r r i n g t o n 1968,1971; Conover 1984; S u l l i v a n and S c h u l t z 1986). When spawning i s over a p r o t r a c t e d p e r i o d of r i s i n g or f a l l i n g temperatures, t h i s temperature dependency may produce a d i f f e r e n c e both i n s i z e and i n v e r t e b r a l number between the sexes. For example, i n the A t l a n t i c s i l v e r s i d e Menidia menidia, a higher p r o p o r t i o n of females are produced among l a r v a e incubated at lower temperatures; females tend to be l a r g e r than males because most are produced e a r l i e r i n the spawning season and thus experience a longer growing season (Conover 1984). Since the number of v e r t e b r a e produced i n embryos i s a l s o a f f e c t e d by i n c u b a t i o n temperature, d i f f e r e n c e s i n v e r t e b r a l number w i l l a l s o be expected between the sexes. I f low i n c u b a t i o n temperature tends to produce h i g h v e r t e b r a l counts i n embryos, the l a r g e r sex w i l l tend to have the higher mean v e r t e b r a l number. T h i s tendency might be r e i n f o r c e d by seasonal v a r i a t i o n i n s e l e c t i o n f o r v e r t e b r a l number (see below). In summary, s e l e c t i o n o p e r a t i n g on l a r v a e or f r y soon a f t e r h a t c h i n g may p r o v i d e a s u f f i c i e n t e x p l a n a t i o n f o r most instances of pleomerism. A d d i t i o n a l f a c t o r s , such as temperature-dependent sex d e t e r m i n a t i o n or s e l e c t i o n f o r a high p r o p o r t i o n of abdominal to caudal v e r t e b r a e i n females, may be r e q u i r e d to e x p l a i n 175 i n s t a n c e s of pleomerism between the sexes. S e l e c t i o n may a l s o operate on v e r t e b r a l number at a d u l t s i z e s , but such s e l e c t i o n need not be hypothesized to e x p l a i n pleomerism. In f a c t , the f a i l u r e of some groups to e x h i b i t pleomerism might r e f l e c t a poor c o r r e l a t i o n between l a r v a l and maximum a d u l t s i z e s . 2. Jordan's r u l e A f u n c t i o n a l e x p l a n a t i o n may a l s o be sought f o r Jordan's r u l e . , Body s i z e tends to be l a r g e r i n c o l d e r waters, both w i t h i n s p e c i e s (Ray 1960) and w i t h i n f a m i l i e s (Lindsey 1966) of p o i k i l o t h e r m v e r t e b r a t e s . Since higher mean v e r t e b r a l numbers are a s s o c i a t e d with g r e a t e r maximum body le n g t h s (pleomerism), l a t i t u d i n a l c l i n e s i n v e r t e b r a l number might be p u r e l y a r e f l e c t i o n of these l a t i t u d i n a l c l i n e s i n body s i z e . However, Lindsey (1975) showed that Jordan's r u l e cannot be a t t r i b u t e d s o l e l y to l a t i t u d i n a l c l i n e s i n maximum body l e n g t h . The most s t r i k i n g demonstration of t h i s was pr o v i d e d by the wrasse f a m i l y L a b r i d a e . These f i s h e s showed a marked l a t i t u d i n a l c l i n e i n v e r t e b r a l number, but no l a t i t u d i n a l c l i n e i n maximum body l e n g t h . However, Jordan's r u l e might be a t t r i b u t a b l e to l a t i t u d i n a l c l i n e s i n egg and l a r v a l s i z e s , r a t h e r than to those i n maximum a d u l t s i z e s . L i k e a d u l t s i z e s , egg and l a r v a l s i z e s tend to be l a r g e r i n c o l d e r waters (e.g., M a r s h a l l 1953). These c l i n e s are presumably at l e a s t p a r t l y g e n e t i c , but may a l s o be p a r t l y a t t r i b u t a b l e to a d i r e c t m o d i f i c a t i o n of egg and l a r v a l s i z e s by water temperatures d u r i n g development. For example, i n the 176 p u p f i s h Cyprinodon n. nevadensis, l a r g e r eggs are produced by females h e l d i n c o l d e r water (Shrode and Gerking 1977). S i m i l a r l y , c o l d e r i n c u b a t i o n temperatures produce l a r g e r l a r v a e at h a t c h i n g i n a v a r i e t y of s p e c i e s (Salmo t r u t t a , Gray 1929; Gadus macrocephalus, A l d e r d i c e and F o r r e s t e r 1971; Clupea p a l l a s i , A l d e r d i c e and V e l s e n 1971; Belone belone, Fonds et a l . 1974; Salmo s a l a r , Hamor and G a r s i d e 1977, Peterson et a l . 1977; Oncorhynchus tshawytscha, Heming 1982; but see Beacham and Murray (1986) f o r an e x c e p t i o n to t h i s t r e n d ) . Thus, higher v e r t e b r a l numbers may be favoured by s e l e c t i o n i n c o l d e r waters because the l a r g e r l a r v a e produced i n these waters face l e s s exposure to s e l e c t i o n at s i z e s when low v e r t e b r a l numbers are favoured, than do the s m a l l e r l a r v a e produced i n warmer waters. Again t h i s e x p l a n a t i o n r e q u i r e s an o v e r l a p between the s i z e s at which s e l e c t i o n operates on v e r t e b r a l number and those at which l a r v a e produced i n warm or c o l d waters are r e c r u i t e d to the p o p u l a t i o n p o t e n t i a l l y exposed to s e l e c t i o n . Examination of l a t i t u d i n a l v a r i a t i o n i n l a r v a l s i z e s i n the wrasses would p r o v i d e a t e s t of t h i s h y p o t h e s i s . Jordan's r u l e might a l s o be p a r t l y a t t r i b u t a b l e to l a t i t u d i n a l c l i n e s i n the body s i z e of p r e d a t o r s . The extent to which p r e d a t i o n i s s e l e c t i v e depends both on prey and predator s i z e s . P r e d ators that are very l a r g e compared to prey w i l l be r e l a t i v e l y u n s e l e c t i v e with r e s p e c t to the escape performance of prey. Thus, the prey s i z e upon which s e l e c t i o n operates most s t r i n g e n t l y may be l a r g e r i n c o l d e r waters, due to the l a r g e r s i z e of p r e d a t o r s i n these waters. 177 Water temperature a l s o i n f l u e n c e s a v a r i e t y of other f a c t o r s which may a f f e c t the extent or d i r e c t i o n of s e l e c t i o n f o r v e r t e b r a l number. For example, both growth r a t e s and p r e d a t i o n r a t e s are expected to i n c r e a s e with i n c r e a s i n g water temperature. Changes i n these r a t e s , i f uniform over a l l s i z e s , w i l l not a f f e c t the net d i r e c t i o n of s e l e c t i o n f o r v e r t e b r a l number, but they w i l l i n f l u e n c e the extent of t h i s s e l e c t i o n . A c c e l e r a t i o n of growth or p r e d a t i o n r a t e s would be expected to reduce or i n c r e a s e s e l e c t i o n f o r v e r t e b r a l number, r e s p e c t i v e l y . Water temperature or v i s c o s i t y a l s o a p p a r e n t l y a f f e c t s the s i z e range over which a p a r t i c u l a r v e r t e b r a l number i s favoured by s e l e c t i o n . As temperature i n c r e a s e s (or v i s c o s i t y d e c r e a s e s ) , p a r t i c u l a r counts appear to be favoured at s l i g h t l y s m a l l e r s i z e s (at l e a s t f o r hi g h and intermediate v e r t e b r a l count r a t i o s ) . The e f f e c t of t h i s s h i f t on the extent and net d i r e c t i o n of s e l e c t i o n depends on: (1) whether the s h i f t i s g r e a t e r f o r higher r a t i o s , as i s suggested i n the r e s u l t s r e p o r t e d here; (2) how o v e r a l l m o r t a l i t y r a t e s and the p r o p o r t i o n of m o r t a l i t y that i s p o t e n t i a l l y s e l e c t i v e vary with s i z e and temperature; and, (3) re c r u i t m e n t s i z e , and how much i t decreases as temperature i n c r e a s e s . Depending on how these f a c t o r s i n t e r a c t , a decrease i n the s i z e s at which p a r t i c u l a r counts are favoured due to an i n c r e a s e i n temperature (or decrease i n v i s c o s i t y ) c o u l d favour e i t h e r h i g h e r or lower v e r t e b r a l numbers, or whichever number was otherwise a t net advantage. 1 78 In summary, l a t i t u d i n a l c l i n e s i n v e r t e b r a l number might be a t t r i b u t a b l e to l a t i t u d i n a l c l i n e s i n egg and l a r v a l s i z e s , and i n the s i z e d i s t r i b u t i o n s of p r e d a t o r s . Water temperature and v i s c o s i t y a l s o a f f e c t a v a r i e t y of other f a c t o r s that may i n f l u e n c e s e l e c t i o n f o r v e r t e b r a l number, but the net e f f e c t of these v a r i o u s f a c t o r s i s u n c e r t a i n . V a r i a t i o n w i t h i n p o p u l a t i o n s P o p u l a t i o n s of g a s t e r o s t e i d f i s h e s are o f t e n c o n s p i c u o u s l y polymorphic f o r a v a r i e t y of m o r p h o l o g i c a l c h a r a c t e r s i n a d d i t i o n to v e r t e b r a l number (e.g., numbers of l a t e r a l p l a t e s or d o r s a l s p i n e s , presence or absence of p e l v i c s p i n e s ) . The f a c t o r s important i n m a i n t a i n i n g v a r i a t i o n i n v e r t e b r a l number w i t h i n p o p u l a t i o n s d i f f e r from those suggested f o r these other polymorphisms i n some r e s p e c t s . P a r t i c u l a r v e r t e b r a l numbers appear to be optimum at p a r t i c u l a r f r y s i z e s because of a f u n c t i o n a l advantage i n v o l v i n g swimming performance. In c o n t r a s t , no obvious f u n c t i o n a l advantage i s a s s o c i a t e d with v a r i a t i o n i n such c h a r a c t e r s as the number of l a t e r a l p l a t e s i n G. a c u l e a t u s (Moodie 1972; Hagen and G i l b e r t s o n 1973) or the number of d o r s a l spines i n A p e l t e s quadracus (Blouw and Hagen 1984a,b). S e l e c t i o n i s o f t e n presumed to a c t i n d i r e c t l y on these other c h a r a c t e r s , v i a s e l e c t i o n on g e n e t i c a l l y c o r r e l a t e d b e h a v i o u r a l t r a i t s (Moodie et a l . 1973; Kynard 1979; H u n t i n g f o r d 1981; Blouw and Hagen 1984a,b). Secondly, i n these other polymorphisms, each phenotype i s g e n e r a l l y supposed to be most f i t i n a d i f f e r e n t circumstance, or s e l e c t i o n i n favour of one phenotype i s supposed to be opposed by i n d i r e c t s e l e c t i o n i n 179 favour of the o t her. For example, the presence of p e l v i c s p i n e s may be of advantage in a v o i d i n g v e r t e b r a t e p r e d a t i o n , while t h e i r absence may be advantageous i n a v o i d i n g i n v e r t e b r a t e p r e d a t i o n (Reimchen 1980; R e i s t 1980,a,b). Or, the m o r p h o l o g i c a l advantage of p e l v i c spines i n a v o i d i n g v e r t e b r a t e p r e d a t i o n may be opposed by a b e h a v i o u r a l advantage c o r r e l a t e d with the absence of s p i n e s ( R e i s t 1980a). In the case of v e r t e b r a l number, opposing s e l e c t i v e f o r c e s r e s u l t , not from e x t r i n s i c d i f f e r e n c e s i n the circumstances of s e l e c t i o n (e.g., type of p r e d a t o r ) or from a balance between d i r e c t and i n d i r e c t s e l e c t i o n , but r a t h e r from an i n t r i n s i c e f f e c t of f r y s i z e on the optimum number. These opposing s e l e c t i o n p r e s s u r e s cannot of themselves m a i n t a i n a s t a b l e polymorphism, except i n the u n l i k e l y event t h a t s e l e c t i o n at one s i z e i s e x a c t l y balanced by s e l e c t i o n at another. More probably, s e l e c t i o n w i l l operate most s t r i n g e n t l y at one s i z e , and o v e r a l l f i t n e s s w i l l be g r e a t e s t f o r the v e r t e b r a l number that i s o p t i m a l at that s i z e . Even so, v a r i a t i o n might s t i l l be maintained by s p a t i a l , s e asonal or annual v a r i a t i o n i n the s i z e on which s e l e c t i o n operates most s t r i n g e n t l y . Such v a r i a t i o n c o u l d r e s u l t from v a r i a t i o n i n the s i z e d i s t r i b u t i o n of p r e d a t o r s , or from v a r i a t i o n i n water temperature (which w i l l i n f l u e n c e h a t c h i n g s i z e , the s i z e at which a p a r t i c u l a r number i s o p t i m a l , growth r a t e s and p r e d a t i o n r a t e s ) . That such s p a t i a l or seasonal v a r i a t i o n i n s e l e c t i o n c o e f f i c i e n t s occurs i s suggested by the apparent d i f f e r e n c e s i n s e l e c t i o n f o r v e r t e b r a l number of s t i c k l e b a c k f r y between s i t e s i n Holden Lake. S e l e c t i o n i n favour of f r y with h i g h counts of 180 32 was most s i g n i f i c a n t among f r y c o l l e c t e d e a r l y i n the season from s i t e A, while s e l e c t i o n i n favour of those with low counts of 31 was most s i g n i f i c a n t among those c o l l e c t e d l a t e r i n the season from s i t e B. C o n d i t i o n s under which such s p a t i a l or temporal h e t e r o g e n e i t y i n s e l e c t i o n c o e f f i c i e n t s can maintain g e n e t i c v a r i a t i o n i n p o p u l a t i o n s have r e c e i v e d much t h e o r e t i c a l c o n s i d e r a t i o n (e.g., Levene 1953; Dempster 1955; Haldane and Jayaker 1963; Hedrick et a l . 1976; Ewing 1979). About 14% of f r y c o l l e c t e d from Holden Lake had only 30 v e r t e b r a e . About a t h i r d of these had an int e r m e d i a t e r a t i o of abdominal to caudal v e r t e b r a e (0.76), and are expected to be favoured by s e l e c t i o n at about the same ' l a r g e ' s i z e s as are most f r y with 32 v e r t e b r a e . However, the m a j o r i t y of f r y with 30 ve r t e b r a e had an e x c e p t i o n a l l y h i g h r a t i o of abdominal to caudal v e r t e b r a e (0.88). An advantage to t h i s high r a t i o might be expected at very small s i z e s ( s m a l l e r than those when a r a t i o of 0.82 (31 t o t a l v e r t e b r a e ) was o p t i m a l ) , but such an advantage was not seen i n the ad m i t t e d l y sparse data at these small s i z e s . Perhaps development of these s m a l l f r y was i n s u f f i c i e n t f o r a p o t e n t i a l advantage to be expressed. On the other hand, s e l e c t i o n may favour f r y with t h i s h i g h r a t i o , not because of g r e a t e r s u r v i v a l at some s i z e , but rather because of g r e a t e r f e c u n d i t y due to a hig h abdominal to caudal r a t i o i n body p r o p o r t i o n s . Thus, a d d i t i o n a l v a r i a t i o n i n v e r t e b r a l number may be maintained i n p o p u l a t i o n s because of s p a t i a l and temporal v a r i a t i o n i n the net e f f e c t of d i f f e r e n t i a l s u r v i v a l and f e c u n d i t y among the v a r i o u s phenotypes. 181 Developmental noi s e A s i n g l e genotype d e v e l o p i n g i n a s i n g l e e x t e r n a l environment may produce two or more d i f f e r e n t v e r t e b r a l numbers i n embryos. T h i s i s c l e a r l y demonstrated w i t h i n c l o n e s of the s e l f - f e r t i l i z i n g c yprinodont f i s h R i v u l u s marmoratus (Lindsey and H a r r i n g t o n 1972; H a r r i n g t o n and Crossman 1976; Swain and L i n d s e y I986a,b), and presumably a l s o occurs i n outbreeding s p e c i e s . T h i s v a r i a t i o n must r e s u l t from random ' a c c i d e n t s ' of development or developmental noi s e (Waddington 1957). Genotypes whose phenotypic e x p r e s s i o n i s l e a s t a f f e c t e d by such developmental noi s e ( i . e . , those with g r e a t e s t developmental s t a b i l i t y ) are o f t e n c o n s i d e r e d to be the most f i t . T h i s i s the r a t i o n a l e behind the many recent s t u d i e s of e f f e c t s of l e v e l s of h e t e r o z y g o s i t y or genomic c o a d a p t a t i o n on developmental s t a b i l i t y (e.g., Angus and S c h u l t z 1983; Leary et a l . 1984, 1985a,b; Graham and F e l l e y 1985). However, when there i s environmental h e t e r o g e n e i t y i n s e l e c t i o n c o e f f i c i e n t s , the o p p o s i t e may be t r u e : genotypes producing two or more phenotypes i n a g i v e n environment may be more f i t than those producing a s i n g l e phenotype. Consider the f o l l o w i n g simple ( h a p l o i d ) model. Genotypes A, B and C produce phenotypes P and Q i n p r o p o r t i o n s (1,0), (p, 1-p) and (0,1), r e s p e c t i v e l y . Genotypes A and C represent 'pure' s t r a t e g i e s , each producing a s i n g l e phenotype, while B r e p r e s e n t s a 'mixed' s t r a t e g y . Environments 1 and 2 occur with f r e q u e n c i e s v and 1-v. In environment 1, the f i t n e s s e s of phenotypes P and Q 182 are F and 1, r e s p e c t i v e l y ; i n environment 2, they are 1 and G, r e s p e c t i v e l y (F>1, G>1). The r e s p e c t i v e f i t n e s s e s of genotypes A, B and C are F, pF+1-p, and 1 i n environment 1, and 1, p+G-pG, and G i n environment 2. I f environmental h e t e r o g e n e i t y i s temporal, the most f i t genotype i s the one with g r e a t e s t geometric mean f i t n e s s (Haldane and Jayaker 1963, G i l l e s p i e 1977). Geometric mean f i t n e s s e s of the three genotypes a r e : A: F v B: (pF+1-p) V (p+G-pG)'"^ C: G" V The c o n d i t i o n s under which each of the genotypes i s the most f i t are shown i n F i g . 24, f o r v a r i o u s l e v e l s of v and p. The mixed s t r a t e g i s t tends to be the most f i t when d i f f e r e n c e s i n f i t n e s s between the phenotypes are great i n both environments, e s p e c i a l l y when environmental u n p r e d i c t a b i l i t y i s hig h ( i . e . , v i s near 0.5). L e v i n s (1962) reached a s i m i l a r c o n c l u s i o n with resp e c t to the f i t n e s s of p o p u l a t i o n s (as opposed to the f i t n e s s of genotypes c o n s i d e r e d h e r e ) , using a q u a l i t a t i v e geometric a n a l y s i s . Random v a r i a t i o n may a l s o occur between c l u t c h e s . Kaplan and Cooper (1982) have shown that i n t h i s case a l s o the mixed s t r a t e g i s t i s most f i t ( i n a h a p l o i d model) when f i t n e s s d i f f e r s g r e a t l y between phenotypes i n a given environment and environmental u n p r e d i c t a b i l i t y i s hi g h . (They c o n s i d e r e d only t h i s one case, analogous to the case F=G=6, v=0.5 i n the model 183 F i g u r e 24. C o n d i t i o n s under which mixed or pure s t r a t e g i e s are optimal when there i s temporal v a r i a t i o n i n s e l e c t i o n . The mixed s t r a t e g i s t i s the most f i t under c o n d i t i o n s between the curves f o r a given p, the pure s t r a t e g i s t A below the lower curve, and the pure s t r a t e g i s t C l e f t of the upper curve. D e t a i l s i n t e x t . 181+ F 185 d e s c r i b e d h e r e ) . There i s no evidence f o r t h i s s o r t of random v a r i a t i o n i n the phenotypic e x p r e s s i o n of v e r t e b r a l number, though data to t e s t f o r i t s e x i s t e n c e are sparse (but see A l i and Lindsey 1974, p.961). In a .population of i n t e r b r e e d i n g i n d i v i d u a l s , the r e l e v a n t q u e s t i o n i s which s t r a t e g i e s w i l l be maintained i n the p o p u l a t i o n by s e l e c t i o n . The c o n d i t i o n s under which a s t r a t e g y w i l l be maintained i n an i n t e r b r e e d i n g p o p u l a t i o n are l i k e l y to be l e s s s t r i n g e n t than those under which i t i s optimal i n a h a p l o i d one, but i t i s beyond the scope of t h i s d i s c u s s i o n to c a l c u l a t e these c o n d i t i o n s . The important p o i n t here i s that under some c o n d i t i o n s of environmental h e t e r o g e n e i t y , genotypes wi t h lower developmental s t a b i l i t y w i l l be favoured by s e l e c t i o n over those with higher s t a b i l i t y . Thus, i n s t a n c e s of r e l a t i v e l y low developmental s t a b i l i t y may not i n d i c a t e developmental c o n s t r a i n t s on a d a p t a t i o n , but r a t h e r represent an op t i m a l a d a p t a t i o n to environmental u n p r e d i c t a b i l i t y . S p a t i a l and temporal h e t e r o g e n e i t y i n s e l e c t i o n c o e f f i c i e n t s f o r v e r t e b r a l number has been suggested above. The developmental noi s e observed i n the e x p r e s s i o n of v e r t e b r a l number may be an ad a p t a t i o n to t h i s h e t e r o g e n e i t y . F i n a l l y , d i s t i n c t i o n should be made with r e s p e c t to l e v e l of phenotypic e x p r e s s i o n . V e r t e b r a l number i s u s u a l l y thought of as a t h r e s h o l d t r a i t . Such t r a i t s have an u n d e r l y i n g c o n t i n u i t y with t h r e s h o l d s that impose d i s c o n t i n u i t i e s on t h e i r v i s i b l e e x p r e s s i o n . The u n d e r l y i n g continuous v a r i a b l e , termed the l i a b i l i t y , i s both g e n e t i c and environmental i n o r i g i n , and c o u l d 186 i n p r i n c i p l e be s t u d i e d as a metric c h a r a c t e r ( F a l c o n e r 1981). In the case of v e r t e b r a l number, l i a b i l i t y c o u l d r e f e r to r a t e s of embryonic growth and d i f f e r e n t i a t i o n , or numbers of c e l l s a v a i l a b l e f o r i n c o r p o r a t i o n i n t o somites (Lindsey and Arnason 1981). Developmental n o i s e at the l e v e l of observed v e r t e b r a l number i s r e l e v a n t to the d i s c u s s i o n above, while n o i s e at the l e v e l of u n d e r l y i n g l i a b i l i t y i s the more r e l e v a n t to q u e s t i o n s of e f f e c t s of h e t e r o z y g o s i t y or genomic c o a d a p t a t i o n on developmental s t a b i l i t y . D i f f e r e n c e s i n n o i s e at the l e v e l of observed v e r t e b r a l number do not n e c e s s a r i l y i n d i c a t e d i f f e r e n c e s i n the n o i s i n e s s of the u n d e r l y i n g l i a b i l i t y ; i n s t e a d they may simply r e f l e c t s h i f t s i n the mean l i a b i l i t y between t h r e s h o l d s of l i a b i l i t y ( i . e . , s h i f t s i n the mean v e r t e b r a l number between whole values) (Swain 1987). Phenotypic p l a s t i c i t y Phenotypic p l a s t i c i t y may be d e f i n e d as the extent to which the phenotype produced by a genotype depends on the developmental environment. Phenotypic p l a s t i c i t y may be favoured by n a t u r a l s e l e c t i o n when (1) the r e l a t i v e f i t n e s s of phenotypes depends s t r o n g l y on environmental c o n d i t i o n s , (2) the environment experienced by i n d i v i d u a l s cannot be chosen, and (3) the developmental environment i s c o r r e l a t e d with those environmental f a c t o r s that determine which phenotype i s the most f i t (L e v i n s 1963, 1968). The p o s s i b l e adaptive s i g n i f i c a n c e of phenotypic p l a s t i c i t y has long been emphasized i n p l a n t s (Bradshaw 1965), and i s now r e c e i v i n g c o n s i d e r a b l e a t t e n t i o n i n animals. Recent examples i n c l u d e s t u d i e s of phenotypic p l a s t i c i t y of l i f e h i s t o r y 187 t r a i t s i n the s n a i l Lymnaea elodes (Brown 1985), temperature-dependent sex d e t e r m i n a t i o n i n the f i s h Menidia menidia (Conover 1984), and the e f f e c t of temperature on egg s i z e i n the f i s h e s Cyprinodon n_. nevadensis (Shrode and Gerking 1977) and Etheostoma s p e c t a b i l e (Marsh 1984). The number of v e r t e b r a e produced i n f i s h embryos depends on water temperature. P a t t e r n s of response of v e r t e b r a l number to developmental temperature are u s u a l l y e i t h e r d e c l i v o u s or U-shaped (Fowler 1970). T h i s p l a s t i c i t y may be a d a p t i v e , s i n c e the r e l a t i v e f i t n e s s of d i f f e r e n t v e r t e b r a l numbers a l s o depends on water temperatures d u r i n g embryo development and the e a r l y free-swimming l a r v a l s t a g e s . Females h e l d i n r e l a t i v e l y c o l d water may produce r e l a t i v e l y l a r g e eggs (Shrode and Gerking 1977), and embryos d e v e l o p i n g i n r e l a t i v e l y c o l d water u s u a l l y produce r e l a t i v e l y l a r g e l a r v a e at h a t c h i n g (see r e f e r e n c e s above). As a r e s u l t of these e f f e c t s , s e l e c t i o n s hould tend to favour genotypes that produce a d e c l i v o u s response of v e r t e b r a l number to developmental temperature. However, water temperature (or v i s c o s i t y ) a l s o a p p a r e n t l y a f f e c t s the s i z e range over which a p a r t i c u l a r v e r t e b r a l number i s o p t i m a l . T h i s l a t t e r e f f e c t c o u l d favour e i t h e r higher or lower v e r t e b r a l numbers at c o l d e r temperatures, depending on a v a r i e t y of f a c t o r s (see above). The p a t t e r n of response of v e r t e b r a l number to developmental temperature a c t u a l l y favoured by s e l e c t i o n would depend on these f a c t o r s and on the r e l a t i v e magnitude of t h i s l a t t e r e f f e c t and the e f f e c t of water temperature on h a t c h i n g s i z e . The u b i q u i t y of d e c l i v o u s and U-shaped responses suggests that s e l e c t i o n 188 normally favours one of these two p a t t e r n s . The v a r i a b l e p a t t e r n of response to i n c u b a t i o n temperature w i t h i n p o p u l a t i o n s ( d e c l i v o u s or U-shaped) i s i n c o n t r a s t to the t y p i c a l l y i n v e r s e r e l a t i o n between v e r t e b r a l number and water temperature among p o p u l a t i o n s (Jordan's r u l e ) . Perhaps d i f f e r e n c e s among p o p u l a t i o n s i n h a t c h i n g s i z e due to a combination of g e n e t i c and environmental i n f l u e n c e s t y p i c a l l y overshadow d i f f e r e n c e s i n the s i z e ranges when p a r t i c u l a r v e r t e b r a l numbers are optimum due to environmental i n f l u e n c e s a l o n e . A l t e r n a t i v e l y , U-shaped p a t t e r n s of response w i t h i n p o p u l a t i o n s may be a r t i f a c t s of experimental c o n d i t i o n s . P a r e n t a l h o l d i n g temperature before f e r t i l i z a t i o n a f f e c t s the number of v e r t e b r a e produced i n o f f s p r i n g (Dentry and Lindsey 1978; Swain and L i n d s e y 1986a). When parents are h e l d at one temperature and t h e i r o f f s p r i n g r eared at a v a r i e t y of temperatures, an apparent U-shaped response to r e a r i n g temperature might be produced even though a d e c l i v o u s response would r e s u l t i f p a r e n t s were h e l d at the r e a r i n g temperature of t h e i r o f f s p r i n g (C.C. Lindsey, p e r s . comm.). Ju s t as Jordan's r u l e has an analogue i n the e f f e c t of developmental temperature on v e r t e b r a l number, pleomerism may have an analogue i n an e f f e c t of p a r e n t a l s i z e or age on the number of v e r t e b r a e produced i n o f f s p r i n g . In R. marmoratus, o f f s p r i n g produced long a f t e r the onset of breeding tend to have more v e r t e b r a e than do those produced soon a f t e r the onset of breeding (Swain and Lindsey 1986b). S i m i l a r l y , i n a p o p u l a t i o n of G. a c u l e a t u s , l a r g e females tend to produce o f f s p r i n g with 189 more v e r t e b r a e than do small females (unpublished d a t a ) . T h i s e f f e c t i s presumably non-genetic, s i n c e l a r g e females do not themselves appear to have more v e r t e b r a e i n t h i s p o p u l a t i o n . Large females o f t e n tend to produce l a r g e eggs i n f i s h e s (see above), but r e l a t i o n s h i p s between female age or s i z e and o f f s p r i n g v e r t e b r a l number are not l i k e l y to be proximate e f f e c t s of d i f f e r e n c e s i n egg s i z e (Lindsey and A l i 1971). Instead, they probably r e s u l t from b i o c h e m i c a l d i f f e r e n c e s between the eggs of small or l a r g e (or young or old) females. However, they may be u l t i m a t e e f f e c t s of d i f f e r e n c e s i n egg s i z e . S i n c e l a r g e females tend to produce l a r g e eggs and thus l a r g e o f f s p r i n g , higher v e r t e b r a l counts should be favoured by s e l e c t i o n i n o f f s p r i n g of l a r g e (or o l d ) females. Thus, the observed e f f e c t of female age or s i z e on o f f s p r i n g v e r t e b r a l number may be an a d a p t a t i o n to d i f f e r i n g s e l e c t i o n p r e s s u r e s o p e r a t i n g on o f f s p r i n g of parents of d i f f e r e n t ages or s i z e s . 190 L i t e r a t u r e c i t e d A l d e r d i c e , D. F., and C. R. F o r r e s t e r . 1971. E f f e c t s of s a l i n i t y , temperature and d i s s o l v e d oxygen on e a r l y development of the P a c i f i c cod (Gadus macrocephalus). J . F i s h . Res. Board Can. 28: 883-902. A l d e r d i c e , D. F., and F. P. J . V e l s e n . 1971. Some e f f e c t s of s a l i n i t y and temperature on e a r l y development of P a c i f i c h e r r i n g (Clupea p a l l a s i ) . J . F i s h . Res. Board Can. 28: 1545-1562. A l i , M. Y., and C. C. L i n d s e y . 1974. H e r i t a b l e and temperature- induced m e r i s t i c v a r i a t i o n i n the medaka, O r y z i a s l a t i p e s . Can. J . Z o o l . 52: 959-976. Angus, R. A., and R. J . S c h u l t z . 1983. M e r i s t i c v a r i a t i o n i n homozygous and heterozygous f i s h . Copeia 1983: 287-299. A t c h l e y , W. R., J . J . Rutledge, and D. E. Cowley. 1982. A m u l t i v a r i a t e s t a t i s t i c a l a n a l y s i s of d i r e c t and c o r r e l a t e d response to s e l e c t i o n i n the r a t . E v o l u t i o n 36: 677-698. Bateson, G. 1963. The r o l e of somatic change i n e v o l u t i o n . E v o l u t i o n , 17: 529-539. Ba t t y , R. S. 1981. Locomotion of p l a i c e l a r v a e . Symp. z o o l . Soc. Lond. 48: 53-69. 1984. Development of swimming movements and musculature of l a r v a l h e r r i n g (Clupea harengus). J . exp. B i o l . 110: 217- 229. Beacham, T. D., and C. B. Murray. 1986. Comparative developmental b i o l o g y of pink salmon, Oncorhynchus gorbuscha, i n southern B r i t i s h Columbia. J . F i s h B i o l . 28: 233-246. Beacham, T. D., F. C. W i t h l e r , and R. B. Morley. 1985. E f f e c t of egg s i z e on i n c u b a t i o n time and a l e v i n and f r y s i z e i n chum salmon (Oncorhynchus keta) and coho salmon (Oncorhynchus k i s u t c h ) . Can. J . Z o o l . 63: 847-850. B e l l , M. A., and T. R. Haglund. 1978. S e l e c t i v e p r e d a t i o n of t h r e e s p i n e s t i c k l e b a c k s ( Gasterosteus a c u l e a t u s ) by garder snakes. E v o l u t i o n 32: 304-319. B l i g h t , A. R. 1976. Undulatory swimming with and without waves of c o n t r a c t i o n . Nature 264: 352-354. 1977. The muscular c o n t r o l of v e r t e b r a t e swimming movements. B i o l . Rev. 52: 181-218. Blouw, D. M., and D. W. Hagen. 1984a. The a d a p t i v e s i g n i f i c a n c e of d o r s a l spine v a r i a t i o n i n the f o u r s p i n e s t i c k l e b a c k , 191 Ape l t e s quadracus. I I I . C o r r e l a t e d t r a i t s and experimental evidence on p r e d a t i o n . H e r e d i t y 53: 371-382. 1984b. The adap t i v e s i g n i f i c a n c e of d o r s a l spine v a r i a t i o n i n the f o u r s p i n e s t i c k l e b a c k , A p e l t e s quadracus. IV. Phenotypic c o v a r i a t i o n with c l o s e l y r e l a t e d s p e c i e s . H e r e d i t y 53: 383-396. Bradshaw, A. D. 1965. E v o l u t i o n a r y s i g n i f i c a n c e of phenotypic p l a s t i c i t y i n p l a n t s . Adv. Genet. 13: 115-155. Breder, C A . 1926. The locomotion of f i s h e s . Z o o l o g i c a 4: 159-297. Brown, K. M. 1985. I n t r a s p e c i f i c l i f e h i s t o r y v a r i a t i o n i n a pond s n a i l : the r o l e s of p o p u l a t i o n divergence and phenotypic p l a s t i c i t y . E v o l u t i o n 39: 387-395. Brown, M.B., and A.B. F o r s y t h e . 1974a. Robust t e s t s f o r the e q u a l i t y of v a r i a n c e s . J . Amer. S t a t i s t . Assoc. 69: 364-367. 1974b. The small sample behavior of some s t a t i s t i c s which t e s t the e q u a l i t y of s e v e r a l means. Technometrics 16: 129-132. Bryant, E. H. 1976. A comment on the r o l e of environmental v a r i a t i o n i n m a i n t a i n i n g polymorphisms i n n a t u r a l p o p u l a t i o n s . E v o l u t i o n 30: 188-190. Cheverud, J.M. 1982. Phenotypic, g e n e t i c and environmental morpho- l o g i c a l i n t e g r a t i o n i n the cranium. E v o l u t i o n 36: 499-516. Conover, D.O. 1984. Adaptive s i g n i f i c a n c e of temperature-dependent sex d e t e r m i n a t i o n i n a f i s h . Am. Nat. 123: 297-313. Dempster, E. R. 1955. Maintenance of g e n e t i c h e t e r o g e n e i t y . C o l d S p r i n g Harbor Symp. Quant. B i o l . 20: 25-32. Dey, W.P. 1981. M o r t a l i t y and growth of young-of-the-year s t r i p e d bass i n the Hudson R i v e r e s t u a r y . Trans. Am. F i s h . Soc. 110: 151-157. Dentry, W., and C. C. L i n d s e y . 1978. V e r t e b r a l v a r i a t i o n i n ze b r a - f i s h (Brachydanio r e r i o ) r e l a t e d to the p r e f e r t i l i z a t i o n temp- e r a t u r e h i s t o r y of t h e i r p a r e n t s . Can. J . Zo o l . 56: 280-283. Dingerkus, G., and L. D. U h l e r . 1977. Enzyme c l e a r i n g of a l c i a n blue s t a i n e d whole small v e r t e b r a t e s f o r demonstration of c a r t i l a g e . S t a i n Technology 52: 229-232. Dixon, W. J . 1981. BMDP s t a t i s t i c a l software 1981. Univ. of C a l i f o r n i a P ress, B e r k e l e y . 726 pp. E l d r i d g e , M. B., J . A. Whipple, D. Eng, M. J . Bowers, and B. M. J a r v i s . 1981. E f f e c t s of food and fee d i n g f a c t o r s on 192 l a b o r a t o r y - r e a r e d s t r i p e d bass l a r v a e . Trans. Am. F i s h . Soc. 110: 111-120. Ewing, E. P. 1979. Genetic v a r i a t i o n i n a heterogeneous e n v i r o n - ment V I I . Temporal and s p a t i a l h e t e r o g e n e i t y i n i n f i n i t e p o p u l a t i o n s . Am. Nat. 114: 197-212. F a l c o n e r , D. S. 1981. I n t r o d u c t i o n to q u a n t i t a t i v e g e n e t i c s . Longman, New York. 340 pp. Fonds, M., H. Rosenthal, and D. F. A l d e r d i c e . 1974. I n f l u e n c e of temperature and s a l i n i t y on embryonic development, l a r v a l growth and number of v e r t e b r a e of the g a r f i s h , Belone belone. p. 509-526. In: J . H. S. B l a x t e r (ed.). The e a r l y l i f e h i s t o r y of f i s h . S p r i n g e r - V e r l a g , N.Y. 765 pp. Fowler, L. G. 1972. Growth and m o r t a l i t y of f i n g e r l i n g chinook salmon as a f f e c t e d by egg s i z e . Prog. F i s h - C u l t . 34: 66-69. Fowler, J . A. 1970. C o n t r o l of v e r t e b r a l number i n t e l e o s t s - an e m b r y o l o g i c a l problem. Q. Rev. B i o l . 45: 148-167. Fuiman, L. A. 1986. Burst-swimming performance of l a r v a l zebra danios and e f f e c t s of d i e l temperature f l u c t u a t i o n s . Trans. Am. F i s h . Soc. 115: 143-148. G a l l , G. A. E. 1974. I n f l u e n c e of s i z e of eggs and age of female on h a t c h a b i l i t y and growth i n rainbow t r o u t . C a l i f . F i s h Game 60: 26-35. Ge f f e n , A. J . 1982. O t o l i t h r i n g d e p o s i t i o n i n r e l a t i o n to growth r a t e i n h e r r i n g (Clupea harengus) and t u r b o t (Scophthalmus maximus) l a r v a e . Mar. B i o l . 71: 317-326. G i l l e s p i e , J . H. 1977. N a t u r a l s e l e c t i o n f o r v a r i a n c e i n o f f - s p r i n g numbers: a new e v o l u t i o n a r y p r i n c i p l e . Am. Nat. 111: 1010-1014. Graham, J . H., and J . D. F e l l e y . 1985. Genomic c o a d a p t a t i o n and developmental s t a b i l i t y w i t h i n i n t r o g r e s s e d p o p u l a t i o n s of Enneacanthus g l o r i o s u s and E. obesus ( P i s c e s , C e n t r a r c h i d a e ) . E v o l u t i o n 39: 104-114. Gray, J . 1929. The growth of f i s h . I I I . The e f f e c t of temp- e r a t u r e on the development of the eggs of Salmo f a r i o . Br. J . Exp. B i o l . 6: 125-130. 1933a. S t u d i e s i n animal locomotion. I I . The r e l a t i o n - s h i p between waves of muscular c o n t r a c t i o n and the p r o p u l s i v e mechanism of the e e l . J . exp. B i o l . 10: 386-390. 1933b. S t u d i e s i n animal locomotion. I I I . The pro- p u l s i v e mechanism of the w h i t i n g (Gadus merlangus). J . exp. B i o l . 10: 391-400. 193 G r i s w old, B. L., and L. L. Smith, J r . 1972. E a r l y s u r v i v a l and growth of the n i n e s p i n e s t i c k l e b a c k , P u n g i t i u s p u n g i t i u s . Trans. Am. F i s h . Soc. 101: 350-352. Hagen, D. W., and L. G. G i l b e r t s o n . 1972. Geographic v a r i a t i o n and environmental s e l e c t i o n i n G a sterosteus a c u l e a t u s L. i n the P a c i f i c northwest, America. E v o l u t i o n 26: 32-51. 1973. S e l e c t i v e p r e d a t i o n and the i n t e n s i t y of s e l e c t i o n a c t i n g upon the l a t e r a l p l a t e s of t h r e e s p i n e s t i c k l e b a c k s . H e r e d i t y 30: 272-287. Haldane, J . B. S., and S. D. Jayakar. 1963. Polymorphism due to s e l e c t i o n of v a r y i n g d i r e c t i o n . J . Genet. 58: 237-242. Hamor, T., and E. T. G a r s i d e . 1977. S i z e r e l a t i o n s and y o l k u t i l i z a t i o n i n embryonated ova and a l e v i n s of A t l a n t i c salmon Salmo s a l a r L. i n v a r i o u s combinations of temperature and d i s s o l v e d oxygen. Can. J . Z o o l . 55: 1892-1898. H a r r i n g t o n , R. W., J r . 1968. D e l i m i t a t i o n of the t h e r m o l a b i l e p h e n o c r i t i c a l p e r i o d of sex d e t e r m i n a t i o n and d i f f e r e n t i a t i o n i n the ontogeny of the normally hermaphroditic f i s h , R i v u l u s marmoratus Poey. P h y s i o l . Z o o l . 41: 447-460. 1971. How e c o l o g i c a l and g e n e t i c f a c t o r s i n t e r a c t to determine when s e l f - f e r t i l i z i n g hermaphrodites of R i v u l u s marmoratus change i n t o f u n c t i o n a l secondary males, with a r e a p p r a i s a l of the modes of i n t e r s e x u a l i t y among f i s h e s . Copeia 1971: 389-432. H a r r i n g t o n , R. W., J r . , and R. A. Crossman. 1976. Temperature- induced m e r i s t i c v a r i a t i o n among three homozygous genotypes (clones) of the s e l f - f e r t i l i z i n g f i s h R i v u l u s marmoratus. Can. J . Z o o l . 54: 1143-1155. H a r r i s , H. 1966. Enzyme polymorphisms i n man. Proc. Roy. Soc. B 164: 298-310. Hedrick, P. W., M. E. Ginevan, and E. P. Ewing. 1976. G e n e t i c polymorphism i n heterogeneous environments. Annu. Rev. E c o l . S y s t . 7: 1-32. Heming, T. A. 1982. E f f e c t s of temperature on u t i l i z a t i o n of yolk by chinook salmon (Oncorhynchus tshawytscha) eggs and a l e v i n s . Can. J . F i s h . Aquat. S c i . 39: 184-190. Hess, F., and J . J . V i d e l e r . 1984. Fast continuous swimming of s a i t h e ( P o l l a c h i u s v i r e n s ) : a dynamic a n a l y s i s of bending moments and muscle power. J . exp. B i o l . 109: 229-251. Hinshaw, J . M. 1985. E f f e c t s of i l l u m i n a t i o n and prey c o n t r a s t on s u r v i v a l and growth of l a r v a l yellow perch Perca f l a v e s c e n s . Trans. Am. F i s h . Soc. 114: 540-545. 1 94 Hubbs, C. L. 1926. The s t r u c t u r a l consequences of m o d i f i c a t i o n s of the developmental r a t e i n f i s h e s , c o n s i d e r e d i n r e f e r e n c e to c e r t a i n problems i n e v o l u t i o n . Am. Nat. 60: 57-81. 1928. An hy p o t h e s i s on the o r i g i n of graded s e r i e s of l o c a l races i n f i s h e s . Anat. Rec. 41: 49. Hunter, J . R. 1972. Swimming and f e e d i n g behaviour of l a r v a l anchovy E n g r a u l i s mordax. F i s h . B u l l . 70: 821-838. H u n t i n g f o r d , F. A. 1981. Furt h e r evidence f o r an a s s o c i a t i o n between l a t e r a l scute number and a g g r e s s i v e n e s s i n the t h r e e s p i n e s t i c k l e b a c k , Gasterosteus a c u l e a t u s . Copeia 1981: 717-720. Kaplan, R. H., and W. S. Cooper. 1984. The e v o l u t i o n of develop- mental p l a s t i c i t y i n r e p r o d u c t i v e c h a r a c t e r i s t i c s : an a p p l i c a t i o n of the 'adaptive c o i n - f l i p p i n g ' p r i n c i p l e . Am. Nat. 123: 393-410. Kashin, S. M., A. G. Feldman, and G. N. O r l o v s k y . 1979. D i f f e r e n t modes of swimming of the carp, Cyprinus c a r p i o L. J . F i s h B i o l . 14: 403-405. Kazakov, R. V. 1981. The e f f e c t of the s i z e of A t l a n t i c salmon, Salmo s a l a r L., eggs on embryos and a l e v i n s . J . F i s h B i o l . 19: 353-360. Kramer, R. H., and L. L. Smith, J r . 1960. F i r s t - y e a r growth of largemouth bass, M i c r o p t e r u s salmoides (Lacepede), and some r e l a t e d e c o l o g i c a l f a c t o r s . Trans. Am. F i s h . Soc. 89: 222-233. Kynard, B. E. 1979. Nest h a b i t a t p r e f e r e n c e of low p l a t e number morphs i n t h r e e s p i n e s t i c k l e b a c k s (Gasterosteus a c u l e a t u s ) . Copeia 1979: 525-528. Leary, R. F., F. W. A l l e n d o r f , and K. L. Knudsen. 1984. Superior developmental s t a b i l i t y of heterozygotes at enzyme l o c i i n salmonid f i s h e s . Am. Nat. 124: 540-551. 1985a. I n h e r i t a n c e of m e r i s t i c v a r i a t i o n and the e v o l u t i o n of developmental s t a b i l i t y i n rainbow t r o u t . E v o l u t i o n 39: 308-314. 1985b. Developmental i n s t a b i l i t y and hi g h m e r i s t i c counts i n i n t e r s p e c i f i c h y b r i d s of salmonid f i s h e s . E v o l u t i o n 39: 1318-1325. Levene, H. 1953. Ge n e t i c e q u i l i b r i u m when more than one e c o l o g i c a l niche i s a v a i l a b l e . Am. Nat. 87: 331-333. L e v i n s , R. 1962. Theory of f i t n e s s i n a heterogeneous environment. I. The f i t n e s s s et and adaptive f u n c t i o n . Am. Nat. 96: 361-378. 195 1963. Theory of f i t n e s s i n a heterogeneous environment. I I . Developmental f l e x i b i l i t y and niche s e l e c t i o n . Am. Nat. 97: 75-90. 1968. E v o l u t i o n i n changing environments. P r i n c e t o n Univ. Press, P r i n c e t o n . 120 pp. Lewontin, R.C., and J.L. Hubby. 1966. A molecular approach to the study of genie h e t e r o z y g o s i t y i n n a t u r a l p o p u l a t i o n s . I I . Amount of v a r i a t i o n and degree of h e t e r o z y g o s i t y i n n a t u r a l p o p u l a t i o n s of D r o s o p h i l a pseudoobscura. G e n e t i c s 54: 595-609. L i g h t h i l l , M. J . 1970. Aquatic animal p r o p u l s i o n of h i g h hydro- mechanical e f f i c i e n c y . J . F l u i d Mech. 44: 265-301. 1971. Large-amplitude elongated-body theory of f i s h locomotion. Proc. Roy. Soc. Lond. B 179: 125-138. Lindsey, C. C. 1954. T e m p e r a t u r e - c o n t r o l l e d m e r i s t i c v a r i a t i o n i n the p a r a d i s e f i s h Macropodus o p e r c u l a r i s ( L . ) . Can. J . Z o o l . 32: 87-98. • 1962. Experimental study of m e r i s t i c v a r i a t i o n i n a p o p u l a t i o n of t h r e e s p i n e s t i c k l e b a c k s , G a s t e r o s t e u s a c u l e a t u s . Can. J . Z o o l . 40: 271-312. 1966. Body s i z e s of p o i k i l o t h e r m v e r t e b r a t e s at d i f f e r e n t l a t i t u d e s . E v o l u t i o n 20: 456-465. ; 1975. Pleomerism, the widespread tendency f o r v e r t e b r a l number to be c o r r e l a t e d with maximum body l e n g t h . J . F i s h . Res. Board Can. 32: 2453-2469. Lindsey, C. C , and M. Y. A l i . 1971. An experiment with medaka, O r y z i a s l a t i p e s , and a c r i t i q u e of the h y p o t h e s i s that t e l e o s t egg s i z e c o n t r o l s v e r t e b r a l count. J . F i s h . Res. Board Can. 28: 1235-1240. Lindsey, C. C , and A. N. Arnason. 1981. A model f o r responses of v e r t e b r a l numbers i n f i s h to environmental i n f l u e n c e s d u r i n g development. Can. J . F i s h . Aquat. S c i . 38: 334-347. Lindsey, C. C , and R. W. H a r r i n g t o n , J r . 1972. Extreme v e r t e - b r a l v a r i a t i o n induced by temperature i n a homozygous cl o n e of the s e l f - f e r t i l i z i n g c y p r i n o d o n t i d f i s h R i v u l u s marmoratus. Can. J . Z o o l . 50: 733-744. Lindsey, C. C , and P. A. L a v i n . 1986. Why do s l e n d e r f i s h have more segments? A b s t r a c t s , 66th Ann. Meeting Amer. SOc. I c h t h . Herp., V i c t o r i a , B.C. Marsh, E. 1984. Egg s i z e v a r i a t i o n i n c e n t r a l Texas p o p u l a t i o n s of Etheostoma s p e c t a b i l e ( P i s c e s : P e r c i d a e ) . Copeia 1984: 291-301. 196 M a r s h a l l , N. B. 1953. Egg s i z e i n a r c t i c , a n t a r c t i c , and deep- sea f i s h e s . E v o l u t i o n 7: 328-341. McP h a i l , J . D. 1969. P r e d a t i o n and the e v o l u t i o n of a s t i c k l e - back ( G a s t e r o s t e u s ) . J . F i s h . Res. Board Can. 26: 3183-3208. Moodie, G.E.E. 1972. P r e d a t i o n , n a t u r a l s e l e c t i o n and a d a p t a t i o n i n an unusual t h r e e s p i n e s t i c k l e b a c k . H e r e d i t y 28: 155-167. Moodie, G.E.E., J.D. McPhail, and D.W. Hagen. 1973. Experimental demonstration of s e l e c t i v e p r e d a t i o n on G a s t e r o s t e u s a c u l e a t u s . Behaviour 47: 95-105. Moodie, G.E.E., and T.E. Reimchen. 1976. Phenetic v a r i a t i o n and h a b i t a t d i f f e r e n c e s i n Gasterosteus p o p u l a t i o n s of the Queen C h a r l o t t e I s l a n d s . Syst. Z o o l . 25: 49-61. Peterson, R.H., H.C.E. Spinney, and A. Sreedharan. 1977. Develop- ment of A t l a n t i c salmon (Salmo s a l a r ) eggs and a l e v i n s under v a r i e d temperature regimes. J . F i s h . Res. Board Can. 34: 31-43. Ray, C. 1960. The a p p l i c a t i o n of Bergmann's and A l l e n ' s r u l e s to the p o i k i l o t h e r m s . J . Morph. 106: 85-108. Reimchen, T. E. 1980. Spine d e f i c i e n c y and polymorphism in a p o p u l a t i o n of Gasterosteus a c u l e a t u s : an a d a p t a t i o n to p r e d a t o r s ? Can. J . Z o o l . 58: 1232-1244. 1983. S t r u c t u r a l r e l a t i o n s h i p s between s p i n e s and l a t e r a l p l a t e s i n t h r e e s p i n e s t i c k l e b a c k (Gasterosteus a c u l e a t u s ) . E v o l u t i o n 37: 931-946. R e i s t , J . D. 1980a. S e l e c t i v e p r e d a t i o n upon p e l v i c phenotypes of brook s t i c k l e b a c k , Culaea inconstans, by northern p i k e , Esox l u c i u s . Can. J . Z o o l . 58: 1245-1252. 1980b. P r e d a t i o n upon p e l v i c phenotypes of brook s t i c k l e b a c k , Culaea inconstans, by s e l e c t e d i n v e r t e b r a t e s . Can. J . Z o o l . 58: 1253-1258. Ryland, J . S. 1963. The swimming speeds of p l a i c e l a r v a e . J . exp. B i o l . 40: 285-299. Saksena, V.P., C. Steinmetz, J r . , and E.D. Houde. 1972. E f f e c t s of temperature on growth and s u r v i v a l of l a b o r a t o r y - r e a r e d l a r v a e of the s c a l e d s a r d i n e , Harengula pensacolae Goode and Bean. Trans. Am. F i s h . Soc. 101: 691-695. Shrode, J . B., and S. D. Gerking. 1977. E f f e c t s of constant and f l u c t u a t i n g temperatures on r e p r o d u c t i v e performance of a d e s e r t p u p f i s h , Cyprinodon n. nevadensis. P h y s i o l . Z o o l . 50: 1-10. 1 97 S o k a l , R.R., and F . J . R o h l f . 1981. Biometry. 2nd ed. W.H. Freeman and Co., San F r a n c i s c o . 859 pp. S p i e t h , P. T. 1979. Environmental h e t e r o g e n e i t y : a problem of c o n t r a d i c t o r y s e l e c t i o n p r e s s u r e s , gene flow, and l o c a l p o l y - morphism. Am. Nat. 113: 247-260. Spouge, J . L., and P. A. L a r k i n . 1979. A reason f o r pleomerism. J . F i s h . Res. Board Can. 36: 255-269. Strawn, K. 1961. Growth of largemouth bass f r y at v a r i o u s temper- a t u r e s . Trans. Am. F i s h . Soc. 90: 334-335. Swain, D. P. 1979. E f f e c t s of p a r e n t a l and i n c u b a t i o n e n v i r o n - ments on m e r i s t i c v a r i a t i o n i n R i v u l u s marmoratus. M.Sc. t h e s i s , U n i v e r s i t y of Manitoba, Winnipeg, Manitoba. 1987. A problem with the use of m e r i s t i c c h a r a c t e r s to estimate developmental s t a b i l i t y . Am. Nat. ( i n p r e s s ) . Swain, D. P., and C. C. L i n d s e y . 1986a. M e r i s t i c v a r i a t i o n i n a c l o n e of the cyprinodont f i s h R i v u l u s marmoratus r e l a t e d to temperature h i s t o r y of the parents and of the embryos. Can. J . Z o o l . 64: 1444-1455. 1986b. I n f l u e n c e of r e p r o d u c t i v e h i s t o r y of parents on m e r i s t i c v a r i a t i o n i n o f f s p r i n g i n the cyprinodont f i s h R i v u l u s marmoratus. Can. J . Z o o l . 64: 1456-1459. Waddington, C. H. 1957. The s t r a t e g y of the genes. A l l e n and Unwin, London. Wallace, J . C , and D. A a s j o r d . 1984. An i n v e s t i g a t i o n of the consequences of egg s i z e f o r the c u l t u r e of A r c t i c c h a r r , S a l v e l i n u s a l p i n u s - ( L . ) . J . F i s h B i o l . 24: 427-435. Wardle, C. S., and J . J . V i d e l e r . 1980. F i s h swimming, p.125-150. In: Aspects of Animal Locomotion. H. Y. E l d e r and E. R. Trueman ( e d s . ) . Cambridge Univ. P r e s s , Cambridge. 250 pp. Webb, P. W. 1976. The e f f e c t of s i z e on the f a s t - s t a r t perform- ance of rainbow t r o u t Salmo g a i r d n e r i , and a c o n s i d e r a t i o n of p i s c i v o r o u s p r e d a t o r - p r e y i n t e r a c t i o n s . J . exp. B i o l . 65: 157-177. 1978. Temperature e f f e c t s on a c c e l e r a t i o n of rainbow t r o u t , Salmo g a i r d n e r i . J . F i s h . Res. Board Can. 35: 1417- 1 422. 1981. Responses of northern anchovy, E n g r a u l i s mordax, l a r v a e to p r e d a t i o n by a b i t i n g p l a n k t i v o r e , Amphiprion p e r c u l a . F i s h . B u l l . U.S. 79: 727-735. 198 Webb, P. W., and R. T. C o r o l l a . 1981. Burst swimming perform- ance of northern anchovy, E n g r a u l i s mordax, l a r v a e . F i s h . B u l l . U.S. 79: 143-150. Webb, P. W., P. T. K o s t e c k i , and E. D. Stevens. 1984. The e f f e c t of s i z e and swimming speed on locomotor kinematics of rainbow t r o u t . J . exp. B i o l . 109: 77-95. Webb, P.W., and D. Weihs. 1986. F u n c t i o n a l locomotor morphology of e a r l y l i f e h i s t o r y stages of f i s h e s . Trans. Am. F i s h . Soc. 115: 115-127. West, B. W. 1966. Growth r a t e s at v a r i o u s temperatures of the orangethroat d a r t e r Etheostoma s p e c t a b i l e ( A g a s s i z ) . Proc. Ark. Acad. S c i . 20: 50-53. PUBLICATIONS S w a i n , D . P . 1 9 8 7 . A p r o b l e m w i t h t h e u s e o f m e r i s t i c c h a r a c t e r s t o e s t i m a t e d e v e l o p m e n t a l s t a b i l i t y . Am. N a t . ( i n p r e s s ) . S w a i n , D . P . , a n d C C . L i n d s e y . 1 9 8 6 . M e r i s t i c v a r i a t i o n i n a c l o n e o f t h e c y p r i n o d o n t f i s h R i v u l u s m a r m o r a t u s r e l a t e d t o t e m p e r a t u r e h i s t o r y o f t h e p a r e n t s a n d o f t h e e m b r y o s . C a n . J . Z o o l . 6 4 : 1 4 4 4 - 1 4 5 5 . S w a i n , D . P . , a n d C C . L i n d s e y . 1 9 8 6 . I n f l u e n c e o f r e p r o d u c t i v e h i s t o r y o f p a r e n t s o n m e r i s t i c v a r i a t i o n i n o f f s p r i n g i n t h e c y p r i n o d o n t f i s h R i v u l u s m a r m o r a t u s . C a n . J . Z o o l . 6 4 : 1 4 5 6 - 1 4 5 9 . S w a i n , D . P . , a n d C C . L i n d s e y . 1 9 8 4 . S e l e c t i v e p r e d a t i o n f o r v e r t e b r a l number o f y o u n g s t i c k l e b a c k s , G a s t e r o s t e u s a c u l e a t u s . C a n . J . F i s h . A q u a t . S c i . 4 1 : 1 2 3 1 - 1 2 3 3 . L i n d s e y , C C , A . M . B r e t t , D . P . S w a i n , a n d A . N . A r n a s o n . 1 9 8 4 . R e s p o n s e s o f v e r t e b r a l numbers i n r a i n b o w t r o u t t o t e m p e r a t u r e c h a n g e s d u r i n g d e v e l o p m e n t . C a n . J . Z o o l . 6 2 : 3 9 1 - 3 9 6 .

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