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Behavioural adaptations to stream velocity in the guppy, Poecilia reticulata Crow, Richard Thomas 1981

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BEHAVIOURAL ADAPTATIONS TO STREAM VELOCITY IN THE GUPPY, POECILIA RETICULATA by RICHARD THOMAS CROW B.Sc, The U n i v e r s i t y o f B r i t i s h C o l u m b i a , 1976 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n THE FACULTY OF GRADUATE STUDIES (Department o f Zoology) We a c c e p t t h i s t h e s i s as c o n f o r m i n g t o the r e q u i r e d s t a n d a r d THE UNIVERSITY OF BRITISH COLUMBIA J u l y , 1981 C J R i c h a r d Thomas Crow, 1981 I n 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 o f t h e r e q u i r e m e n t s f o r an advanced degree a t t h e U n i v e r s i t y o f B r i t i s h C o l u m b i a , I a g r e e t h a t t h e 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 s t u d y . 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 c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y p u r p o s e s may be g r a n t e d by t h e head o f my department o r by h i s o r h e r r e p r e s e n t a t i v e s . I t i s u n d e r s t o o d t h a t c o p y i n g o r 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 g a i n s h a l l n o t be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . Department o f Z o o l o g y  The U n i v e r s i t y o f B r i t i s h C o l u m b i a 2075 Wesbrook P l a c e V ancouver, Canada V6T 1W5 Date i i ABSTRACT P o p u l a t i o n s o f g u p p i e s l i v i n g i n d i f f e r e n t streams v a r y i n t h e i r "behaviour and morphology. Some p o p u l a t i o n s l i v e i n f a s t - f l o w i n g streams w h i l e o t h e r s occupy s l o w - f l o w i n g w a t e r . I h y p o t h e s i z e d t h a t b e h a v i o u r a l d i f f e r e n c e s between the p o p u l a t i o n s may r e p r e s e n t a d a p t a t i o n s to stream v e l o c i t y . I t e s t e d seven p r e d i c t i o n s based on t h i s h y p o t h e s i s i n two e x p e r i m e n t s . I n E x p e r i m e n t I , I. examined the b e h a v i o u r o f l a b o r a t o r y r e a r e d g u p p i e s descendant from t h r e e n a t u r a l p o p u l a t i o n s . These g u p p i e s were examined a t .03, «07, .10, and .20 m/sec stream v e l o c i t i e s . E x p e r i m e n t I I used w i l d - c a u g h t g u p p i e s from f o u r p o p u l a t i o n s . T h e i r c o u r t s h i p b e h a v i o u r was examined i n s t i l l w a t e r (.00 m/sec) and a t .08 m/sec v e l o c i t y . As p r e d i c t e d , i n E x p e r i m e n t I g u p p i e s from s l o w - f l o w i n g w a t e r showed l ) g r e a t e r c o h e s i o n , 2) l e s s a g g r e s s i v e "behaviour, and 3) a g r e a t e r p r e f e r e n c e f o r the s u r f a c e r e g i o n o f stream t a n k s t h a n f a s t w a t e r f i s h . A l s o as p r e d i c t e d , s low w a t e r males performed fewer s i g m o i d d i s p l a y s "but more t h r u s t s and g o n o p o d i a l swings t h a n f a s t w a t e r g u p p i e s . The p e r s i s t e n c e o f t h e s e b e h a v i o u r a l d i f f e r e n c e s i n l a b o r a t o r y r a i s e d d escendants o f i s o l a t e d p o p u l a t i o n s demonstrates a g e n e t i c c o n t r i b u t i o n t o the d i f f e r e n c e s . T h e r e f o r e the d i f f e r e n c e s are presumably the p r o d u c t o f n a t u r a l s e l e c t i o n and r e p r e s e n t e v o l u t i o n a r y a d a p t a t i o n s . E x p e r i m e n t I a l s o showed t h a t stream v e l o c i t y d i r e c t l y a f f e c t s the performance o f c o u r t s h i p b e h a v i o u r by males. The f r e q u e n c y o f s i g m o i d d i s p l a y s and g o n o p o d i a l swings d e c r e a s e d m a r k e d l y as stream v e l o c i t y i n c r e a s e d . As stream v e l o c i t y i n c r e a s e d , f a s t w a t e r males m a i n t a i n e d t h e i r f r e q u e n c y and d u r a t i o n o f s i g m o i d d i s p l a y s b e t t e r t h a n sl'0wr„water males, t h u s p r o v i d i n g e v i d e n c e f o r "behavioural a d a p t a t i o n to stream v e l o c i t y . The h i g h e r r a t i o o f s i g m o i d d i s p l a y s : t h r u s t s e x h i b i t e d by f a s t w a t e r f i s h may a l s o r e p r e s e n t an a d a p t a t i o n to stream v e l o c i t y . Stream v e l o c i t y had no d i r e c t e f f e c t on group c o h e s i o n and a g g r e s s i o n i n the guppy. However, i t d i r e c t l y a f f e c t e d guppy stream depth p r e f e r e n c e . Slow w a t e r f i s h c o u l d n o t m a i n t a i n p o s i t i o n a t the t o p o f the stream i n f a s t e r - f l o w i n g w a t e r , whereas f i s h b r e d from an i n t e r m e d i a t e stream v e l o c i t y p o p u l a t i o n were a b l e t o do so. F a s t w a t e r f i s h always p r e f e r r e d the bottom o f the stream bed. I n E x p e r i m e n t I I w i l d - c a u g h t f i s h from f a s t and slow-f l o w i n g streams were t e s t e d t o g e t h e r i n two stream c o n d i t i o n s . A g a i n , as p r e d i c t e d , slow w a t e r f i s h performed f e w e r s i g m o i d d i s p l a y s b u t more t h r u s t s and g o n o p o d i a l swings t h a n f a s t w a t e r f i s h . Because o f the s l o w v e l o c i t y used d u r i n g the e x p e r i m e n t , no e f f e c t o f a f a s t stream v e l o c i t y on c o u r t s h i p b e h a v i o u r was o b t a i n e d . D u r i n g the experiment males g e n e r a l l y p r e f e r r e d t o c o u r t f e m a l e s from t h e i r own p o p u l a t i o n . These p r e f e r e n c e s may r e p r e s e n t p a r t i a l i s o l a t i n g mechanisms. I c o n c l u d e d t h a t d i f f e r e n c e s between guppy p o p u l a t i o n s i n c o u r t s h i p b e h a v i o u r and stream depth p r e f e r e n c e r e p r e s e n t a d a p t a t i o n s t o d i f f e r e n t stream v e l o c i t i e s . Stream v e l o c i t y i s t h e r e f o r e presumed t o have been one o f s e v e r a l e n v i r o n m e n t a l f a c t o r s t h a t i n t e r a c t e d t o shape the guppy's p r e s e n t b e h a v i o u r . i v TABLE OF CONTENTS Page A b s t r a c t - ; i i L i s t o f T a b l e s v i L i s t o f F i g u r e s v i i i Acknowledgements • i x C h a p t e r I . I n t r o d u c t i o n 1 I I . Guppy C o u r t s h i p B e h a v i o u r and N a t u r a l Environment . 8 R e p r o d u c t i v e B i o l o g y and C o u r t s h i p B e h a v i o u r i n the Guppy. 8 The E n v i r o n m e n t o f the Guppy 10 I I I . S t o c k C o l l e c t i n g , F i e l d O b s e r v a t i o n s , and G e n e r a l Methods lk C o l l e c t i n g S t o c k s 1> F i e l d O b s e r v a t i o n s 16 M a i n t a i n i n g S t o c k s 17 The Stream Tanks 18 R e c o r d i n g o f O b s e r v a t i o n s 20 IV. E x p e r i m e n t I : The S o c i a l B e h a v i o u r o f P. r e t i c u l a t a P o p u l a t i o n s a t D i f f e r e n t Water V e l o c i t i e s . . . . 21 I n t r o d u c t i o n 21 M a t e r i a l s and Methods 22 S t a t i s t i c a l Treatment o f D a t a 2k R e s u l t s and D i s c u s s i o n 25 Stream Depth L o c a t i o n 25 I n d e x o f C o h e s i o n . - 30 Male A g g r e s s i o n 33 Page C o u r t s h i p B e h a v i o u r P a t t e r n s 3^ T h r u s t s and S i g m o i d D i s p l a y s 36 G o n o p o d i a l Swings. k6 C o p u l a t i o n A t t e m p t s 50 Summary o f R e s u l t s 52 V. E x p e r i m e n t I I : Male P. r e t i c u l a t a C o u r t s h i p B e h a v i o u r and Mate P r e f e r e n c e i n S t i l l and F l o w i n g Water C o n d i t i o n s 55 I n t r o d u c t i o n 55 M a t e r i a l s and Methods 57 S t a t i s t i c a l Treatment o f the Dat a 60 R e s u l t s and D i s c u s s i o n 6 l T h r u s t s and Si g m o i d D i s p l a y s .61 G o n o p o d i a l Swings . . . . . . . . . . . . . . . 67 S i d e - s w i t c h e s , L e a p s , C o p u l a t i o n A t t e m p t s , and C o p u l a t i o n s 69 C o u r t s h i p B o u t s and the Number o f B e h a v i o u r P a t t e r n s p e r C o u r t s h i p Bout 71 Mate P r e f e r e n c e o f Males 7^4-Summary o f R e s u l t s 77 V I . G e n e r a l D i s c u s s i o n 79 The E v o l u t i o n o:f B e h a v i o u r and Morphology i n P. r e t i c u l a t a 79 L i t e r a t u r e C i t e d . . . . . . $k Appendix 98 C o r r e l a t i o n s between Male S i z e and C o u r t s h i p B e h a v i o u r P a t t e r n s 98 C o r r e l a t i o n s between C o u r t s h i p B e h a v i o u r P a t t e r n s 103 v i LIST OF TABLES T a b l e Page I. C l a s s i f i c a t i o n and p h y s i c a l f e a t u r e s o f streams i n T r i n i d a d . .« 12 I I . Comparison o f "group depth" f o r each s t o c k a t d i f f e r e n t stream v e l o c i t i e s 27 I I I . Comparison o f "group depth" between s t o c k s a t d i f f e r e n t stream v e l o c i t i e s 29 IV. Comparison o f "Index o f C o h e s i o n " between, s t o c k s a t d i f f e r e n t stream v e l o c i t i e s . . . . 32 V. Comparison o f Male A g g r e s s i o n a t d i f f e r e n t s t r e a m v e l o c i t i e s 35 V I . Comparison o f number o f T h r u s t s , S i g m o i d D i s p l a y s , and the r a t i o o f S i g m o i d D i s p l a y s : T h r u s t s f o r each s t o c k a t d i f f e r e n t stream v e l o c i t i e s . 38 V I I . Comparison o f number o f T h r u s t s , S i g m o i d D i s p l a y s and the r a t i o o f S i g m o i d D i s p l a y s : T h r u s t s between s t o c k s a t d i f f e r e n t v e l o c i t i e s . 39 V I I I . Mean number and d u r a t i o n o f S i g m o i d D i s p l a y s a t f o u r stream v e l o c i t i e s ^5 IX. Comparison o f number o f G o n o p o d i a l Swings performed a t d i f f e r e n t stream v e l o c i t i e s f o r each s t o c k . ^-8 X. Comparison o f number o f G o n o p o d i a l Swings between s t o c k s a t d i f f e r e n t stream v e l o c i t i e s . ^ 9 X I . Mean number o f C o p u l a t i o n A t t e m p t s and ;,p p e r c e n t a g e o f S i g m o i d D i s p l a y s f o l l o w e d by C o p u l a t i o n A t t e m p t s . . . . 51 X I I . Mean number and per c e n t a g e o f S i g m o i d D i s p l a y s w i t h o r f o l l o w e d by S i d e - s w i t c h e s , L eaps, and C o p u l a t i o n A t t e m p t s f o r males from f o u r s t o c k s i n two stream c o n d i t i o n s . , 70 X I I I . Mean number o f c o u r t s h i p b o u t s p e r male f o r each s t o c k i n two stream c o n d i t i o n s 72 XIV. P e r c e n t a g e o f s i g m o i d d i s p l a y s and t h r u s t s p e r f ormed by males t o f e m a l e s o f t h e i r own o r a n o t h e r s t o c k 75 v i i - ' T a b l e Page ^XV. Spearman rank c o r r e l a t i o n c o e f f i c i e n t s between male s i z e and c o u r t s h i p b e h a v i o u r p a t t e r n s and between v a r i o u s c o u r t s h i p b e h a v i o u r p a t t e r n s . Experiment,;.!* 101 XVI. Spearman r a n k c o r r e l a t i o n c o e f f i c i e n t s between male s i z e and c o u r t s h i p b e h a v i o u r p a t t e r n s and between v a r i o u s c o u r t s h i p b e h a v i o u r p a t t e r n s . E x p e r i m e n t I I lQk v i i i LIST OF FIGURES F i g u r e Page 1. Map o f the n o r t h e r n h a l f o f T r i n i d a d , showing the major r i v e r systems. . • ' • 1 5 2. Schematic diagram o f stream tank, 19 3. "Group depth" i n r e l a t i o n t o stream v e l o c i t y . . 26 k. Index o f C o h e s i o n i n r e l a t i o n t o stream • •• ' , v e l o c i t y . . . . 31 5. Male a g g r e s s i o n i n r e l a t i o n t o stream v e l o c i t y . 3^ 6. Number o f t h r u s t s i n r e l a t i o n t o stream v e l o c i t y 37 7» Number o f s i g m o i d d i s p l a y s i n r e l a t i o n t o st r e a m v e l o c i t y 4-0 8. R a t i o o f s i g m o i d d i s p l a y s : t h r u s t s i n r e l a t i o n t o stream v e l o c i t y . . . . . . . . •. kl 9. Number o f g o n o p o d i a l swings i n r e l a t i o n t o stream v e l o c i t y -^7 10. Number o f t h r u s t s i n r e l a t i o n t o stream v e l o c i t y • . . . 62 11. Number o f s i g m o i d d i s p l a y s i n r e l a t i o n t o stream v e l o c i t y 63 12. R a t i o o f s i g m o i d d i s p l a y s : t h r u s t s i n r e l a t i o n t o stream v e l o c i t y 65 13• Number o f g o n o p o d i a l swings i n r e l a t i o n t o s t r e a m v e l o c i t y . . . . . . 68 1^. P r o p o r t i o n o f c o u r t s h i p b o u t s w i t h one, two, and t h r e e o r more b e h a v i o u r p a t t e r n s p e r c o u r t s h i p bout 73 15« T o t a l l e n g t h o f males t e s t e d i n E x p e r i m e n t I . 99 16. T o t a l l e n g t h o f males t e s t e d f o r each s t o c k . . 102 ACKNOWLEDGEMENTS i x I s i n c e r e l y thank ray. s u p e r v i s o r , Dr. N.R. L i l e y , f o r p r o v i d i n g me the o p p o r t u n i t y t o work on t h i s p r o j e c t . I thank him and my r e s e a r c h committee, Dr. J.N.M. Smith and Dr. J.D. M c P h a i l , f o r comments and d i s c u s s i o n on my r e s e a r c h p r o p o s a l . I am a l s o g r a t e f u l t o Dr. L i l e y and Dr. Smith f o r c r i t i c a l l y r e a d i n g the m a n u s c r i p t . I thank Dr. J.S. Kenny f o r h o s p i t a l i t y i n the Department o f B i o l o g i c a l S c i e n c e s , U n i v e r s i t y o f the West I n d i e s , T r i n i d a d , and S e n a t o r J . S t o l l m e y e r f o r p e r m i s s i o n t o c o l l e c t f i s h on h i s e s t a t e . I am i n d e b t e d t o Dr. L i l e y , MrsikHenktLuytenf,''. and Mr. I a n Dube f o r t h e i r h e l p i n c o l l e c t i n g f i s h . F i n a l l y , I thank Ms. Lynda H i n d f o r h e l p i n g t o compile raw d a t a and f o r h e r c o n s t a n t encouragement t h r o u g h o u t the st u d y . T h i s work was s u p p o r t e d by a N a t i o n a l R e s e a r c h C o u n c i l o f Canada O p e r a t i n g G r a n t t o Dr. L i l e y and a U n i v e r s i t y o f B r i t i s h C o l u m b i a Graduate F e l l o w s h i p t o m y s e l f . 1 CHAPTER I INTRODUCTION W i t h i n a s p e c i e s , i n d i v i d u a l s v a r y i n t h e i r b e h a v i o u r and a b i l i t y t o s u r v i v e and r e p r o d u c e . Those i n d i v i d u a l s b e s t adapted t o t h e i r p a r t i c u l a r environment c o n t r i b u t e more o f t h e i r genes t o s u b s e q u e n t e g e n e r a t i o n s . Thus, n a t u r a l s e l e c t i o n may l i n k s p e c i f i c b e h a v i o u r p a t t e r n s t o c e r t a i n e c o l o g i c a l f a c t o r s . I n t h i s t h e s i s I examine whether i n d i v i d u a l ; ' ^ i s h d e r i v e d from d i f f e r e n t n a t u r a l p o p u l a t i o n s are adapted to a s p e c i f i c e c o l o g i c a l f a c t o r , namely stream v e l o c i t y . To demonstrate the a d a p t i v e ( o r s u r v i v a l ) v a l u e o f a s t r u c t u r e o r b e h a v i o u r , i t i s n e c e s s a r y t o demonstrate t h a t i t c o n t r i b u t e s t o r e p r o d u c t i v e s u c c e s s . S t r i c t l y s p e a k i n g , t h i s r e q u i r e s a s s e s s i n g r e p r o d u c t i v e s u c c e s s w i t h and w i t h o u t the c h a r a c t e r . T h i s i s seldom done s i n c e 1) i t i s u s u a l l y i m p o s s i b l e t o f i n d two p o p u l a t i o n s d i f f e r i n g i n o n l y one . c h a r a c t e r and 2) i t i s r a r e l y p o s s i b l e t o measure r e p r o d u c t i v e s u c c e s s under n a t u r a l c o n d i t i o n s . However, the combined use o f c o m p a r a t i v e and e x p e r i m e n t a l methods can determine the a d a p t i v e v a l u e o f b e h a v i o u r (see Hinde, 1975)- I n t h i s a pproach, c o r r e l a t i o n s are made between p o p u l a t i o n d i f f e r e n c e s : and e c o l o g i c a l v a r i a b l e s i n the environment. These c o r r e l a t i o n s g e n e r a t e h y potheses on the observ e d r e l a t i o n s h i p s and the hy p o t h e s e s may be t e s t e d by f u r t h e r comparisons o r by ex p e r i m e n t s i n the f i e l d and l a b o r a t o r y . 2 N a t u r a l populations of the guppy, P o e c i l i a r e t i c u l a t a ( P e t e r s ) , d i s p l a y considerable v a r i a t i o n i n t h e i r morphology and behaviour. This f a c t , along w i t h the guppy*s short generation p e r i o d and easy maintenance i n the l a b o r a t o r y , makes i t i d e a l f o r studying the adaptive value of behaviour. D i f f e r e n t populations of the guppy were f i r s t s t u d i e d i n d e t a i l i n t h e i r n a t u r a l environment by ( C P . ) Haskins, (E.F.) Haskins, McLaughlin, and Hewitt (1961). They found that populations of guppies occupying d i f f e r e n t streams v a r i e d g e n e t i c a l l y i n t h e i r c olour p a t t e r n s . Since t h i s study, considerable i n t e r e s t has been shown i n these n a t u r a l populations. I n t e r - p o p u l a t i o n v a r i a t i o n has been found i n guppy s i z e , sex r a t i o , s c h o o l i n g , a n t i p r e d a t o r behaviour, male c o u r t s h i p behaviour, and male aggression (Seghers, 1973, 197^a, 197^h; B a l l i n , 1973; L i l e y and Seghers, 1975; F a r r , 1975; and Snyder, 1978). Studies on the v a r i a t i o n i n male colour p a t t e r n s have also continued (Endler, 1978, 1980). I n most of these s t u d i e s the i n v e s t i g a t o r s suggest t h a t morphological and behavioural d i f f e r e n c e s between populations of guppies are adaptations to d i f f e r e n t p r edation pressures. L i l e y and Seghers (1975)f however, suggest that many other f e a t u r e s of the environment l i k e l y . r e s u l t i n s e l e c t i o n pressures which compete and i n t e r a c t w i t h those due to predation. Some populations of guppies occur i n f a s t - f l o w i n g mountain streams while others occupy slow-flowing or stagnant water. This f a c t l e d me to hypothesize that d i f f e r e n t populations may be adapted to p a r t i c u l a r stream v e l o c i t i e s and, consequently, that stream v e l o c i t y may have acted i n the past as a s e l e c t i o n 3 p r e s s u r e , p a r t l y m o u l d i n g the s p e c i e s * p r e s e n t b e h a v i o u r . To t e s t t h i s h y p o t h e s i s , I examine the r e l a t i o n s h i p "between s o c i a l b e h a v i o u r and w a t e r v e l o c i t y . 3?hus, u n l i k e p r e v i o u s s t u d i e s , I examine the e f f e c t o f a p h y s i c a l f a c t o r on the b e h a v i o u r o f d i f f e r e n t guppy p o p u l a t i o n s r a t h e r t h a n the e f f e c t o f p r e d a t i o n . Water v e l o c i t y i s c l o s e l y c o r r e l a t e d w i t h t u r b i d i t y : f a s t - f l o w i n g w a t e r s are a l m o s t i n v a r i a b l y c l e a r , s l o w - f l o w i n g w a t e r s are g e n e r a l l y t u r b i d (see C h a p t e r I I I ) . D u r i n g my e x p e r i m e n t s , t u r b i d i t y was k e p t c o n s t a n t and stream v e l o c i t y was m a n i p u l a t e d . I t i s i m p o r t a n t t o r e c o g n i z e , however, t h a t the s o c i a l b e h a v i o u r o b s e r v e d i s a l m o s t c e r t a i n l y coadapted t o b o t h p r e v a i l i n g f l o w and t u r b i d i t y c o n d i t i o n s ( a s w e l l as b i o t i c f a c t o r s such as p r e d a t i o n ) . Male c o u r t s h i p b e h a v i o u r was chosen as a s o c i a l b e h a v i o u r on w h i c h t o c o n c e n t r a t e d d u r i n g t h i s s t u d y s i n c e f a c t o r s t h a t a f f e c t c o u r t s h i p b e h a v i o u r may a l s o d i r e c t l y a f f e c t r e p r o d u c t i v e s u c c e s s . The h y p o t h e s i s t h a t guppy p o p u l a t i o n s are adapted t o d i f f e r e n t stream v e l o c i t y and t u r b i d i t y c o n d i t i o n s l e d t o the f o l l o w i n g p r e d i c t i o n s : 1) Guppies d e r i v e d from s l o w - f l o w i n g t u r b i d w a t e r s h o u l d show g r e a t e r c o h e s i o n ( s c h o o l i n g ) t h a n f i s h from f a s t - f l o w i n g c l e a r streams. 2) Slow w a t e r g u p p i e s s h o u l d be l e s s a g g r e s s i v e t h a n f a s t w a t e r g u p p i e s . 3) Guppies from s l o w - f l o w i n g t u r b i d w a t e r s h o u l d use the top o f the w a t e r column ( s u r f a c e q r e g i o n ) , whereas f i s h from f a s t - f l o w i n g w a t e r s h o u l d r e m a i n n e a r the bottom o f the stream. k) Male g u p p i e s from t u r b i d s l o w - f l o w i n g w a t e r s h o u l d p e r f o r m s i g m o i d d i s p l a y s l e s s f r e q u e n t l y b u t t h r u s t s and g o n o p o d i a l swings more f r e q u e n t l y t h a n males from f a s t - f l o w i n g streams. ( F o r a d e s c r i p t i o n o f these b e h a v i o u r p a t t e r n s see C h a p t e r I I . ) 5 ) F o r a l l guppy p o p u l a t i o n s the f r e q u e n c y o f c o u r t s h i p b e h a v i o u r ( s i g m o i d d i s p l a y s , t h r u s t s , and g o n o p o d i a l swings) s h o u l d d ecrease w i t h i n c r e a s i n g stream v e l o c i t y and the f r e q u e n c y o f s i g m o i d d i s p l a y s s h o u l d decrease more t h a n the f r e q u e n c y o f t h r u s t s . 6) Mal e s from s l o w - f l o w i n g w a t e r s h o u l d be l e s s a b l e t o m a i n t a i n t h e i r c o u r t s h i p b e h a v i o u r and stream p o s i t i o n a t h i g h v e l o c i t i e s t h a n f i s h from f a s t - f l o w i n g streams. Slow w a t e r f i s h s h o u l d t h e r e f o r e show a g r e a t e r decrease t h a n f a s t w a t e r f i s h i n t h e i r f r e q u e n c y o f c o u r t s h i p b e h a v i o u r as stream v e l o c i t y i n c r e a s e s . 7) A t f a s t v e l o c i t i e s the s i g m o i d d i s p l a y s performed by males from t u r b i d s l o w - f l o w i n g w a t e r s h o u l d be o f s h o r t e r d u r a t i o n t h a n the d i s p l a y s o f males from f a s t - f l o w i n g w a t e r . These p r e d i c t i o n s were t e s t e d i n two e x p e r i m e n t s . The f i r s t e x p e r i m e n t t e s t e d a l l o f the p r e d i c t i o n s , u s i n g t h r e e s t o c k s o f g u p p i e s c o n t a i n i n g a t l e a s t f i f t h g e n e r a t i o n descendants o f w i l d - c a u g h t g u p p i e s . These s t o c k s , each b r e d from a d i f f e r e n t n a t u r a l stream p o p u l a t i o n , were c u l t u r e d under s i m i l a r s t i l l w a t e r c o n d i t i o n s b e f o r e b e i n g t e s t e d i n f o u r stream v e l o c i t i e s . T h e r e f o r e , b e h a v i o u r a l d i f f e r e n c e s found between s t o c k s s h o u l d n o t be due t o p r i o r exposure t o d i f f e r e n t e n v i r o n m e n t a l f a c t o r s b u t i n s t e a d r e p r e s e n t g e n e t i c 5 d i f f e r e n c e s "between s t o c k s . I n the second e x p e r i m e n t s e v e r a l p o p u l a t i o n s o f w i l d - c a u g h t g u p p i e s were used t o t e s t p r e d i c t i o n s k, 5 » and 6 under two stream c o n d i t i o n s . I n a d d i t i o n , t h i s e x periment examined male mate p r e f e r e n c e s f o r fem a l e s from d i f f e r e n t p o p u l a t i o n s . The p r e d i c t i o n s were i n p a r t based on p r e v i o u s s t u d i e s . I now g i v e a more d e t a i l e d r a t i o n a l e f o r each. P r e d i c t i o n 1 assumes t h a t i n t u r b i d w a t e r one might e x p e c t f i s h t o keep c l o s e t o g e t h e r f o r communication o r t o p r o v i d e p r o t e c t i o n from p r e d a t o r s ( a s su g g e s t e d by Seghers, 1973. 197kh)• I t f o l l o w s t h a t p o p u l a t i o n s w i t h a tendency t o s c h o o l s h o u l d be l e s s a g g r e s s i v e t h a n those w h i c h are more spaced out ( P r e d i c t i o n 2). Thus, stream v e l o c i t y and t u r b i d i t y s h o u l d i n d i r e c t l y a f f e c t a g g r e s s i o n i n g u p p i e s by a f f e c t i n g s c h o o l i n g b e h a v i o u r . The t h i r d p r e d i c t i o n ( t h a t f a s t w a t e r f i s h s h o u l d r e m a i n n e a r the bottom o f the stream) i s based on the as s u m p t i o n t h a t f a s t w a t e r f i s h may need t o r e t a i n v i s u a l c o n t a c t w i t h the stream bed t o h o l d t h e i r p o s i t i o n and make use o f the d e c e l e r a t i o n o f wa t e r c l o s e t o the s u b s t r a t e . On the o t h e r hand, by m a i n t a i n i n g a p o s i t i o n i n the w e l l - l i t s u r f a c e l a y e r , s l ow w a t e r f i s h s h o u l d be a s s i s t e d i n s c h o o l i n g and f i n d each o t h e r more e a s i l y . M ales from c l e a r f a s t - f l o w i n g w a t e r are p r e d i c t e d t o s i g m o i d d i s p l a y more b u t t h r u s t and g o n o p o d i a l swing l e s s t h a n males from t u r b i d s l o w - f l o w i n g w a t e r ( P r e d i c t i o n k). B a l l i n (1973) and Snyder (1978) found t h a t p o p u l a t i o n s o f g u p p i e s demonstrated these d i f f e r e n c e s i n c o u r t s h i p when obser v e d i n s t i l l w a t e r . B a l l i n s p e c u l a t e d t h a t males from t u r b i d w a t e r s 6 may d i s p l a y l e s s f r e q u e n t l y and t h r u s t more f r e q u e n t l y t h a n those from f a s t - f l o w i n g c l e a r streams p a r t l y as a response t o stream t u r b i d i t y . I n h i s v i e w , female g u p p i e s are l e s s a b l e to see the d i s p l a y s o f males i n t u r b i d water. T h e r e f o r e , i n t u r b i d w a t e r males s h o u l d b e n e f i t l e s s from d i s p l a y i n g and more from a t t e m p t i n g c o p u l a t i o n s by p e r f o r m i n g t h r u s t s . ( T h r u s t s r e p r e s e n t i n s e m i n a t i o n a t t e m p t s w i t h o u t the c o o p e r a t i o n o f f e m a l e s , whereas d i s p l a y s o c c a s i o n a l l y e l i c i t female c o o p e r a t i o n and t h e r e f o r e r e s u l t i n s u c c e s s f u l i n s e m i n a t i o n more o f t e n t h a n t h r u s t s (Kadow, 1 9 5 ^ ; L i l e y , 1966).) As stream v e l o c i t y i n c r e a s e s , more energy s h o u l d be r e q u i r e d by f i s h t o m a i n t a i n p o s i t i o n i n the stream and t o p e r f o r m c o u r t s h i p . S i g m o i d d i s p l a y s , which i n v o l v e f i n s p r e a d i n g by males and the maintenance o f a p o s i t i o n p e r p e n d i c u l a r to f e m a l e s (and t h u s t o the d i r e c t i o n o f stream f l o w ) , s h o u l d be p a r t i c u l a r l y d i f f i c u l t t o m a i n t a i n as stream v e l o c i t y i n c r e a s e s ( P r e d i c t i o n 5 ) • P r e d i c t i o n s 6 and 7 are o f p a r t i c u l a r importance t o the h y p o t h e s i s t h a t guppy c o u r t s h i p b e h a v i o u r i s adapted t o stream v e l o c i t y . I f f a s t w a t e r males are b e t t e r a b l e t o m a i n t a i n t h e i r c o u r t s h i p a t h i g h v e l o c i t i e s t h a n males from s l o w -f l o w i n g w a t e r i t f o l l o w s t h a t t h e y are b e t t e r adapted t o the f a s t - f l o w i n g w a t e r environment. B e f o r e p r e s e n t i n g the two e x p e r i m e n t s t h a t t e s t t h e s e p r e d i c t i o n s , i n C h a p t e r I I I d e s c r i b e the c o u r t s h i p b e h a v i o u r p a t t e r n s s t u d i e d d u r i n g the e x p e r i m e n t s and p r o v i d e background m a t e r i a l on the n a t u r a l environment o f the' guppy. C h a p t e r I I I d e t a i l s the c o l l e c t i o n o f s t o c k s , f i e l d o b s e r v a t i o n s , and 7 g e n e r a l methods r e l e v a n t t o b o t h e x p e r i m e n t s . E x p e r i m e n t I ( C h a p t e r IV) and E x p e r i m e n t I I ( C h a p t e r V) are f o l l o w e d by a g e n e r a l d i s c u s s i o n on the e v o l u t i o n o S f morphology and b e h a v i o u r i n the guppy ( C h a p t e r V I ) . 8 CHAPTER I I GUPPY COURTSHIP BEHAVIOUR AND NATURAL ENVIRONMENT Reproductive Biology and Courtship Behaviour i n the Guppy The reproductive biology of the guppy i s s i m i l a r to that of other P o e c i l i i d fishes (Breder and Rosen, 1966). Sexual dimorphism i s quite marked, the male i s considerably smaller and more co l o u r f u l than the female. P. r e t i c u l a t a i s ovoviviparous and p r o l i f i c ; i t has a generation period of about three months, with females undergoing a well defined cycle of brood production. Male courtship behaviour consists of orientation to the female, display behaviour and physical contacts. I measured male courtship byhrecording the frequency and duration of several courtship behaviour patterns. The following b r i e f descriptions of these behaviour patterns are based on the detailed account i n L i l e y (1966): Gonopodial Swing: The gonopodium, a modified anal f i n , i s brought forward to one side of the mid-line. The organ then returns to the rest p o s i t i o n , the entire action taking only one or two seconds. Gonopodial swinging may be performed at p r a c t i c a l l y any stage during courtship and while the male i s i n any orient-ation with respect to the female. In t h i s work I recorded a l l gonopodial swings i n which the gonopodium was swung h$ degrees or more. Sigmoid Display: The male takes up a p o s i t i o n i n front of or to the side of the female, twists h i s body into a sigmoid or S-shape i n the horizontal plane, and vibrates the whole body f o r several seconds. During the display the caudal and dorsal f i n s may or may not be f u l l y spread. 9 Leap: F o l l o w i n g a s i g m o i d d i s p l a y the male may p e r f o r m a l e a p i n w h i c h he s h o o t s away from the female a l o n g a s t r a i g h t o r c u r v e d p a t h . T h r u s t : The male approaches t h e female from "below and "behind, swings the gonopodium f o r w a r d , and d i r e c t s i t v i g o r o u s l y towards the femal e ' s g e n i t a l p o r e . The gonopodium may o r may n o t make momentary c o n t a c t w i t h the f e m a l e ' s opening. C o p u l a t i o n Attempt: The c o p u l a t i o n attempt i s d i s t i n g u i s h -ed from the t h r u s t c h i e f l y by the f a c t t h a t i t i s d i r e c t l y p r e c e d ed by a s i g m o i d d i s p l a y . I n making a c o p u l a t i o n attempt the male moves, s t i l l d i s p l a y i n g , i n t o a p o s i t i o n p a r a l l e l t o one s i d e and j u s t below the f e m a l e . From t h i s p o s i t i o n the-male t h r u s t s upwards and f o r w a r d s as i n t h r u s t i n g . C o p u l a t i o n : I f , d u r i n g a c o p u l a t i o n ••attempt c o n t a c t i s made between the gonopodium and the f e m a l e ' s g e n i t a l pore t h e n i t i s m a i n t a i n e d f o r a f r a c t i o n o f a second. The male t h e n jumps away and per f o r m s a s e r i e s o f j e r k s . J e r k s : J e r k s may f o l l o w e i t h e r t h r u s t s o r c o p u l a t i o n s and are s h o r t , s h a r p , f o r w a r d and upward movements i n v o l v i n g t he whole body. I n P. r e t i c u l a t a i n s e m i n a t i o n o c c u r s a l m o s t e n t i r e l y d u r i n g t h e r e c o g n i z a b l e a c t s o f c o p u l a t i o n w h i c h a re preceded by s i g m o i d d i s p l a y s . V e r y o c c a s i o n a l l y , however, the more commonly o b s e r v e d t h r u s t s may a l s o r e s u l t i n i n s e m i n a t i o n (Kadow, 195 ;^ L i l e y , 1966). F o r most s u c c e s s f u l m a t i n g s the female p l a y s an a c t i v e r o l e w h i c h i n v o l v e s s e v e r a l r e c e p t i v e b e h a v i o u r p a t t e r n s . D u r i n g my e x p e r i m e n t s female c o u r t s h i p b e h a v i o u r was n o t r e c o r d e d s i n c e f e m a l e s are o n l y r a r e l y o b s e r v e d d u r i n g t h e i r r e c e p t i v e p e r i o d s . L i l e y (1966) d e s c r i b e s the c y c l e o f r e c e p t i v i t y i n fe m a l e s and d e t a i l s t h e i r b e h a v i o u r p a t t e r n s . A g g r e s s i o n o r a g o n i s t i c b e h a v i o u r o c c a s i o n a l l y o c c u r s between males d u r i n g c o u r t s h i p and has been d e s c r i b e d i n some d e t a i l by L i l e y (1966). P o p u l a t i o n d i f f e r e n c e s i n male a g g r e s s i o n were s t u d i e d i n E x p e r i m e n t I ( C h a p t e r I V ) . I r e c o r d e d a l l i n t e r - m a l e a t t a c k s . An a t t a c k c o n s i s t s o f a charge towards the f l a n k s o f a n o t h e r male. There i s no evi d e n c e t h a t b i t i n g o r n i b b l i n g o c c u r s and i n many cases the male f a i l s t o make c o n t a c t . The Environment o f the GUTOTJV P o e c i l i a r e t i c u l a t a i s r e s t r i c t e d i n i t s n a t u r a l d i s t r i b u -t i o n t o c o a s t a l a r e a s o f n o r t h e a s t e r n South A m e r i c a and a few of the C a r i b b e a n i s l a n d s (Rosen and B a i l e y , I963)• W i t h i n t h i s r e g i o n , however, i t i s found i n l a r g e numbers and i n a wide range o f stream e n v i r o n m e n t s . Among the many s t u d i e s on t h i s s p e c i e s o n l y those o f H a s k i n s e t a l . (1961) , Seghers ( l 9 7 3 ) i L i l e y and Seghers (1975) . F a r r (1975) , and E n d l e r (1978) d e a l w i t h the b i o l o g y o f the a n i m a l i n i t s n a t u r a l environment. A l l of these i n v e s t i g a t o r s s t u d i e d the guppy on the i s l a n d o f T r i n i d a d , as d i d I . A mountainous c h a i n extends a l o n g n o r t h e r n T r i n i d a d . The n o r t h - f a c i n g s l o p e s o f thes e mountains are d i v i d e d by s e v e r a l r o u g h l y p a r a l l e l streams emptying i n d i v i d u a l l y i n t o the C a r i b b e a n Sea w i t h no f r e s h - w a t e r c o n n e c t i o n s between them. The s o u t h - f a c i n g s l o p e s c o n t a i n a p p r o x i m a t e l y p a r a l l e l streams t h a t are co n n e c t e d i n the l o w l a n d s by d r a i n i n g i n t o the w e s t w a r d - f l o w i n g C a r o n i R i v e r . Most o f thes e streams c o n t a i n p o p u l a t i o n s o f g u p p i e s . S i n c e g u p p i e s r a r e l y o c c u r i n the open sea , ''•• p o p u l a t i o n s i n the n o r t h w a r d - f l o w i n g streams a r e v i r t u a l l y i s o l a t e d from each o t h e r . P o p u l a t i o n s i n the upper r e g i o n s o f the s o u t h w a r d - f l o w i n g streams a re p r o b a b l y a l s o g e n e t i c a l l y i s o l a t e d s i n c e l ) the upper c o u r s e s o f these streams f l o w i n deep v a l l e y s and are w e l l s e p a r a t e d a t a l l sea s o n s , 2) s e v e r a l o f t h e s e streams c o n t a i n w a t e r f a l l s w hich l i k e l y a c t as e f f e c t i v e b a r r i e r s t o upward m i g r a t i o n o f f i s h ( L i l e y and Segh e r s , 1975)» and 3) g u p p i e s r e m a i n f i x e d i n t h e i r stream l o c a t i o n s o v e r p e r i o d s o f months o r y e a r s ( H a s k i n s e t a l . , 196l)• I n c o n t r a s t t o thes e p o p u l a t i o n s , those i n the l o w l a n d r i v e r s are p r o b a b l y n o t as g e n e t i c a l l y i s o l a t e d . I examine f i s h from the upper r e g i o n s o f n o r t h w a r d and s o u t h w a r d - f l o w i n g streams as w e l l as from l o w l a n d r i v e r s . The p o p u l a t i o n s s t u d i e d r e p r e s e n t i s o l a t e d p o p u l a t i o n s from the f u l l range o f e c o l o g i c a l c o n d i t i o n s i n w h i c h g u p p i e s l i v e . S eghers (1973) made q u a n t i t a t i v e e c o l o g i c a l measures o f T r i n i d a d streams. Based on p h y s i c a l f e a t u r e s , h i s streams were c l a s s i f i e d i n t o f o u r c a t e g o r i e s : s p r i n g s , headstreams, midstreams, and l o w l a n d r i v e r s . G o i n g from s p r i n g s t o l o w l a n d r i v e r s the streams become w i d e r , deeper, warmer, and more t u r b i d . Stream v e l o c i t y g e n e r a l l y i n c r e a s e s from s p r i n g s t h r o u g h headstreams and midstreams b u t d e c r e a s e s c o n s i d e r a b l y i n the l o w l a n d r i v e r s ( T a b l e I ) . A d d i t i o n a l i n f o r m a t i o n - on the c h e m i c a l c o m p o s i t i o n o f such w a t e r s i s g i v e n i n H a s k i n s e t a l . (I96I) and on stream s u b s t r a t e s i n E n d l e r (1978). I n a d d i t i o n t o d i f f e r e n c e s i n the p h y s i c a l f e a t u r e s o f T r i n i d a d s t r e a m s , t h e r e are a l s o s t r i k i n g d i f f e r e n c e s between t h e f a u n a s o f t h e streams. The s p r i n g s and i s o l a t e d headstreams commonly c o n t a i n o n l y P. r e t i c u l a t a and a s m a l l c y p r i n o d o n t i d , R i v u l u s h a r t i i , .a p r e d a t o r o f the guppy. I n c o n t r a s t , the T a b l e I . C l a s s i f i c a t i o n and p h y s i c a l f e a t u r e s o f streams i n T r i n i d a d . M o d i f i e d from Seghers (1973)-Stream type Number o f Streams S t u d i e d W i d t h (m) Depth (m) V e l o c i t y (m/sec) Volume o f Elow (m / s e c ) Temp. Shade a s : ' T u r b i d i t y b S p r i n g 4 0.50-1.0 0.05-0.15 0.11-0.29 0.0085-0.0128 24.3-26.2 3-4 0 Headstream 7 1.20-5.0 0.06-0.15 0 . 3 2 -0.67 0.028-0.267 24 . 6 -27.4 2-3 • 0-1 Mi d s t r e a m 5 3.0-8.0 0.13-0.20 0.42-1.18 0.150-1.129 24.3-30.0 2 1 Lowland R. 3 2.0-25.0 1 .5-3.0 0.33-0.40 0 .563-22 .50 26.9-29.1 0-1 2 0 - no shade 0 - always c l e a r "1 - s m a l l amount o f shade r e s t r i c t e d m a i n l y t o streambank 1 - t u r b i d o n l y a f t e r 2 - medium shade (50% c o v e r ) . heavy r a i n s 3 - medium to dense (75% c o v e r w i t h few exposed p a r t s ) 2 - t u r b i d t h r o u g h o u t 4 - v e r y dense c o v e r w i t h v i r t u a l l y complete s h a d i n g y e a r midstreams and l o w l a n d r i v e r s have as many as s i x t e e n s p e c i e s o f f i s h , i n c l u d i n g s e v e r a l l a r g e guppy p r e d a t o r s ( e g . H o p l i a s  malabar.icus. C r e n i c i c h l a a l t a , Aequidens p u l c h e r . A s t v a n a x  b i m a c u l a t u s and Hemibrycon s p . ) . F o r d e t a i l s see Boeseman (I960, 196^), Seghers (1973), and L i l e y and Seghers (1975). Guppy p o p u l a t i o n s i n t h e s e d i f f e r e n t e n v i ronments e x h i b i t c o n s i d e r a b l e v a r i a t i o n i n morphology and b e h a v i o u r . As summarized by L i l e y and Seghers (1975), g u p p i e s from s p r i n g s and i s o l a t e d headstreams a r e g e n e r a l l y l a r g e r ' , the males more b r i g h t l y coloured', and the f e m a l e s outnumber males by as much as f o u r t o one. They show r e l a t i v e l y p o o r l y d e v e l o p e d s c h o o l i n g b e h a v i o u r and avoi d a n c e r e s p o n s e s . These c h a r a c t e r i s t i c s are a s s o c i a t e d w i t h c l e a r , f a s t - f l o w i n g w a t e r , r e l a t i v e l y low tem p e r a t u r e s , * and a v i r t u a l absence o f a q u a t i c p r e d a t o r s o t h e r t h a n R i v u l u s . I n c o n t r a s t , i n the l o w l a n d r i v e r s , g u p p i e s a r e small,- the males l e s s b r i g h t l y c o l o u r e d and sex r a t i o s are n e a r one t o one. These g u p p i e s show v i g o r o u s avoidance r e s p o n s e s and o f t e n o c c u r i n s m a l l s c h o o l s a l o n g the edge o f a stream o r r i v e r . Here, g u p p i e s o c c u r i n s l o w - f l o w i n g t u r b i d w a t e r , h i g h t e m p e r a t u r e s , an absence o f shade, and the presence o f numerous p r e d a t o r s . The e v o l u t i o n a r y s i g n i f i c a n c e o f c o r r e l a t i o n s between t h e s e d i f f e r e n t p h y s i c a l and b i o t i c f a c t o r s and the o b s e r v e d v a r i a t i o n i n guppy morphology and b e h a v i o u r w i l l be c o n s i d e r e d a t the end o f t h i s t h e s i s ( C h a p t e r V I ) . CHAPTER I I I STOCK COLLECTING, FIELD OBSERVATIONS, AND GENERAL METHODS C o l l e c t i n g S t o c k s The s t o c k s o f f i s h were c o l l e c t e d i n T r i n i d a d from f i v e s i t e s (see map, F i g . 1). F i s h were c o l l e c t e d from the n o r t h w a r d -f l o w i n g P a r i a stream a t a p o i n t above a w a t e r f a l l b a r r i e r , 10-14- meters high'; from two o f the s o u t h w a r d - f l o w i n g streams: the s m a l l P e t i t e Curucaye strea m , a t a p o i n t c l o s e t o i t s s o u r c e , and from the Upper A r i p o (= Naranjo) stre a m , above a s e r i e s o f f a l l s 3 - 5 meters h i g h . F i s h were a l s o c o l l e c t e d f r om the Caparo and Guayamare r i v e r s . These r i v e r s l i e i n the sugar-cane p l a n t e d l o w l a n d r e g i o n . They are "both r e l a t i v e l y l a r g e streams and f l o w westward, emptying i n t o the G u l f o f P a r i a a t the C a r o n i Swamp. D e t a i l e d i n f o r m a t i o n on each c o l l e c t i o n s i t e can be found i n Seghers (1973)• The s t o c k s were c o l l e c t e d d u r i n g two d i f f e r e n t f i e l d e x p e d i t i o n s and t r a n s p o r t e d by a i r t o the l a b o r a t o r y i n Vancouver. F i s h i n E x p e r i m e n t I were b r e d from p o p u l a t i o n s c o l l e c t e d "by N. R. L i l e y and m y s e l f i n J u n e , 1976. E x p e r i m e n t I I u s ed w i l d - c a u g h t f i s h c o l l e c t e d by L i l e y and P. H. L u y t e n d u r i n g May and J u n e , 1978. The g u p p i e s were c o l l e c t e d w i t h f i n e - m e s h c i r c u l a r d i p n e t s . Lowland p o p u l a t i o n s were c o l l e c t e d by n e t t i n g from s m a l l s c h o o l s a l o n g the edges o f r i v e r s , w h i l e headstfeam and s p r i n g p o p u l a t i o n s were c o l l e c t e d f r om p o i n t s a c r o s s the stream beds. F i g u r e 1. Map o f the n o r t h e r n h a l f o f T r i n i d a d , showing the major r i v e r systems. I n s e t map i n d i c a t e s the p o s i t i o n o f the i s l a n d o f f the n o r t h e a s t c o a s t o f V e n e z u e l a . 1,6 F i e l d O b s e r v a t i o n s I n a d d i t i o n t o c o l l e c t i n g s t o c k s i n Jun e , 1976, L i l e y and I obs e r v e d the .guppies i n t h e i r n a t u r a l s t r e ams, n o t i n g t h e i r d i s t r i b u t i o n and m e a s u r i n g stream v e l o c i t y . Stream v e l o c i t y i n the f a s t e s t s e c t i o n o f each stream was found t o be w i t h i n the range g i v e n f o r the stream by Seghers (1973» and T a b l e I ) , e x c e p t f o r the l o w l a n d r i v e r s where i t was lower', s i n c e we d i d n o t measure i t f o l l o w i n g a heavy r a i n as d i d Seghers. The two headstreams, the P a r i a and Upper A r i p o , c o n s i s t m o s t l y o f r i f f l e s , 1 a l t h o u g h t h e r e are o c c a s i o n a l s m o o t h - f l o w i n g s e c t i o n s and a few p o o l s . The d e n s i t y o f g u p p i e s appeared s l i g h t l y h i g h e r i n the s m o o t h - f l o w i n g and p o o l s e c t i o n s b u t gu p p i e s were d i s p e r s e d a c r o s s the e n t i r e stream bed, i n c l u d i n g some r i f f l e s (where the v e l o c i t y ranged from 0.17 t o 0.50 m/sec). Guppies were o b s e r v e d t o remai n n e a r the s u b s t r a t e i n these • streams and t o p e r f o r m c o u r t s h i p b e h a v i o u r i n a l l r i v e r s e c t i o n s , i n c l u d i n g r i f f l e s . I n the two l o w l a n d r i v e r s ' , the Guayamare and Caparo, the s i t u a t i o n was e n t i r e l y d i f f e r e n t . These r i v e r s c o n s i s t o f l o n g s m o o t h - f l o w i n g s e c t i o n s . Here g u p p i e s o c c u r r e d i n s c h o o l s n e a r the w a t e r s u r f a c e a t the r i v e r edges. The r i v e r s f l o w e d a t a v e l o c i t y o f 0.1^-0.16 m/sec a t the c e n t r e ; however, the v e l o c i t y a t t h e i r edges was u s u a l l y l e s s . Throughout the l o w l a n d r e g i o n , , g u p p i e s were a l s o found i n d r a i n a g e t r e n c h e s and p o o l s n e a r the r i v e r s , where t h e r e i s alm o s t no stream f l o w . U n l i k e the o t h e r s t r e a m s , l o w l a n d r i v e r s f l u c t u a t e w i d e l y i n depth d u r i n g the wet and d r y seasons and o f t e n o v e r f l o w t h e i r 1'?-banks d u r i n g the r a i n y season, d i s p e r s i n g f i s h . Thus, f o r " >• l o w l a n d p o p u l a t i o n s , the stream v e l o c i t y i n which the g u p p i e s l i v e and p e r f o r m c o u r t s h i p 'is r e l a t i v e l y low ( o f t e n n e a r 0 m/sec and u s u a l l y l e s s t h a n 0.16 m/sec). The mountain s p r i n g , P e t i t e Curucaye", c o n s i s t s o f numerous v e r y s h a l l o w r i f f l e s w h i c h are f r e q u e n t l y b r o k e n by smooth-f l o w i n g s e c t i o n s and p o o l s . Here, stream v e l o c i t y i s f a i r l y s l o w ( l e s s t h a n O.30 m/sec) and g u p p i e s were found d i s p e r s e d o v e r the e n t i r e stream bed. M a i n t a i n i n g S t o c k s E a c h l a b o r a t o r y s t o c k was s t a r t e d w i t h a t l e a s t 50 males and.50 f e m a l e s . A l l s t o c k s were m a i n t a i n e d under s i m i l a r c o n t r o l l e d l a b o r a t o r y c o n d i t i o n s . The f i s h were hous.ed and r e a r e d i n g l a s s t a n k s o f ^3 and 6l l i t r e c a p a c i t y , l o c a t e d i n t h r e e a q u a r i a rooms. E a c h s t o c k was housed i n up t o e i g h t tanks .'which were s p a t i a l l y i s o l a t e d from o t h e r s t o c k s . Young were removed- from the w i l d - c a u g h t f i s h and a l l o w e d t o mature i n s e p a r a t e t a n k s . These i s o l a t e d f i s h were o c c a s i o n a l l y t r a n s f e r r e d between t a n k s o f the same s t o c k to e q u a l i z e d e n s i t i e s and reduce i n b r e e d i n g . A l l t a n k s had beds o f medium o r f i n e g r a v e l and were f i l t e r e d w i t h e x t e r n a l c h a r c o a l * f i l t e r s . The t a n k s were p l a n t e d w i t h V a l l i s n e r i a . C e r a t o p t e r i s . and Lemna. O n e - t h i r d • o f the w a t e r i n each- tank : was changed t w i c e monthly w i t h f r e s h d e c h l o r i n a t e d w a t e r . The t a n k s we r e / " . l i t by 30 o r ^ 0-watt f l u o r e s c e n t t u b e s suspended 15 cm above the w a t e r on a 13L-11D p h o t o p e r i o d . 18 Temperature i n the a q u a r i a rooms was m a i n t a i n e d a t 23-26°C, e l i m i n a t i n g the need f o r i n d i v i d u a l t a n k h e a t e r s . The f i s h were f e d t w i c e d a i l y on a d i e t o f c o m m e r c i a l l y p r e p a r e d d r i e d f o o d , o c c a s i o n a l l y supplemented w i t h f r o z e n b r i n e shrimp and chopped T u b i f e x worms. The Stream Tanks A l l t e s t s were performed i n two s p e c i a l l y c o n s t r u c t e d stream t a n k s ( F i g . 2) d e s i g n e d by L i l e y and m y s e l f . These were c o n s t r u c t e d i n the U.B.C. Department o f Zoology, workshop * from c l e a r p l e x i g l a s and mounted on plywood bases. V a r i o u s stream c u r r e n t s were c r e a t e d by u s i n g a s u b m e r s i b l e pump (Model 4SMD, L i t t l e G i a n t Pump Company) t h a t f o r c e d w a t e r t h r o u g h two 2 .5 cm p l a s t i c t u b e s . These p l a s t i c t u b e s were connected t o two p l e x i g l a s t u b e s , one l o c a t e d a t each end o f the c i r c u l a r stream t a n k c h a n n e l . The p l e x i g l a s tubes each had s i x 6 mm-holes spaced 4 .5 cm a p a r t . Water f o r c e d t h r o u g h these h o l e s c r e a t e d a f a i r l y l - e v e n c u r r e n t a c r o s s the w i d t h o f the stream t a n k c h a n n e l . The stream v e l o c i t y was c o n t r o l l e d by a l t e r i n g a v a r i a b l e a u t o t r a n s f o r m e r ( o u t p u t v o l t a g e range 0-140 V; P o w e r s t a t , Type 3PN, S u p e r i o r E l e c t r i c Company) connected t o the s u b m e r s i b l e pump. The stream v e l o c i t y produced was measured u s i n g a f l o a t i n g v i a l and t i m i n g i t s movement over a 1 meter d i s t a n c e . D u r i n g a l l t e s t s f i s h were r e s t r i c t e d t o the o b s e r v a t i o n a r e a o f the stream t a n k c h a n n e l . T h i s a r e a was 100 X 25 X 15 cm. The f i s h were r e s t r a i n e d by s c r e e n s ( 2 . 5 mm-mesh) l o c a t e d a t each end o f the a r e a . A r e f e r e n c e g r i d o f 10 r e c t a n g l e s ~ (7•5 X 2 0 0 CM 25 CM (D S u b m e r s i b l e pump © P l a s t i c tube ® P l e x i g l a s t u b e s w i t h 6 mm h o l e s © V a r i a b l e a u t o -t r a n s f o r m e r © S c r e e n © O b s e r v a t i o n a r e a w i t h g r i d F i g u r e 2. Schematic diagram o f stream tank. 20 cm) was marked on the f r o n t o f t h i s o b s e r v a t i o n a r e a . A s h e e t o f b l a c k p l e x i g l a s was p l a c e d a t the back o f the o b s e r v a -t i o n a r e a d u r i n g E x p e r i m e n t I , p r o v i d i n g a background a g a i n s t w h i c h the f i s h were e a s i l y o b s e r v e d . D u r i n g E x p e r i m e n t I I a w h i t e p l e x i g l a s s h e e t was used, making the o b s e r v a t i o n a r e a s l i g h t l y b r i g h t e r . The stream t a n k s were l o c a t e d i n a s e p a r a t e l a b o r a t o r y room, k e p t under the same p h o t o p e r i o d and temperature as the a q u a r i a rooms. The stream t a n k s were l i t by e i g h t ^1-0-watt f l u o r e s c e n t t u b e s l o c a t e d 1.9 meters above the w a t e r . E a ch stream t a n k h e l d 500 l i t e r s o f w a t e r , a t l e a s t 10 l i t e r s o f w h i c h was drawn from t a n k s i n w h i c h the s t o c k s had been housed. The t a n k s were f i l t e r e d w i t h a s u b m e r s i b l e c h a r c o a l f i l t e r and a e r a t e d w i t h an a i r s t o n e . R e c o r d i n g o f O b s e r v a t i o n s O b s e r v a t i o n s were made w h i l e s i t t i n g a p p r o x i m a t e l y 1 meter from the f r o n t o f the stream t a n k s . B e h a v i o u r p a t t e r n s were r e c o r d e d on a ^--channel R u s t r a k paper c h a r t event r e c o r d e r a t a c h a r t speed o f 6 cm/min. From these r e c o r d i n g s f r e q u e n c i e s , sequences, o r d u r a t i o n s were c a l c u l a t e d . F i s h d i s t r i b u t i o n was r e c o r d e d by hand u s i n g check s h e e t s c o n t a i n i n g models o f the r e f e r e n c e g r i d . CHAPTER IV EXPERIMENT I : THE SOCIAL BEHAVIOUR OF P. RETICULATA POPULATIONS AT DIFFERENT WATER VELOCITIES I n t r o d u c t i o n I n t h i s e x p e r i m e n t I examine the b e h a v i o u r o f t h r e e s t o c k s o f g u p p i e s , each one b r e d from e i t h e r a headstream, l o w l a n d r i v e r , o r s p r i n g p o p u l a t i o n . The experiment t e s t s the p r e d i c t i o n s t h a t f i s h from the l o w l a n d s t o c k s h o u l d show 1) g r e a t e r c o h e s i o n , 2) l e s s a g g r e s s i v e "behaviour, and 3) g r e a t e r p r e f e r e n c e f o r the s u r f a c e r e g i o n o f stream t a n k s t h a n headstream f i s h . I t a l s o t e s t s the p r e d i c t i o n t h a t l o w l a n d males p e r f o r m fewer s i g m o i d d i s p l a y s b u t more t h r u s t s and g o n o p o d i a l swings t h a n headstream males. The s p r i n g s t o c k was b r e d from a p o p u l a t i o n l i v i n g i n an i n t e r m e d i a t e stream v e l o c i t y and was p r e d i c t e d t o show a l e v e l o f c o u r t s h i p i n t e r m e d i a t e between the l o w l a n d and headstream s t o c k s . The main purpose o f t h i s e x p e r i m e n t was t o examine the e f f e c t o f stream v e l o c i t y on each s t o c k ' s c o u r t s h i p b e h a v i o u r . The t h r e e s t o c k s were t h e r e f o r e t e s t e d i n each o f f o u r stream v e l o c i t i e s . I p r e d i c t e d 1) t h a t c o u r t s h i p b e h a v i o u r s h o u l d decrease f o r a l l s t o c k s as stream v e l o c i t y (.increases and 2) t h a t f i s h from the headstream s t o c k , descendant from f i s h t h a t l i v e d i n f a s t - f l o w i n g w a t e r , s h o u l d be b e t t e r a b l e t o c o n t i n u e p e r f o r m i n g c o u r t s h i p i n f a s t - f l o w i n g w a t e r t h a n f i s h from the l o w l a n d s t o c k . To determine whether d i f f e r e n c e s "between p o p u l a t i o n s are l a r g e l y g e n e t i c , a t l e a s t f i f t h g e n e r a t i o n descendants o f w i l d - c a u g h t f i s h were used. Young were removed from the o r i g i n a l w i l d - c a u g h t f i s h w i t h i n a few days o f b i r t h and a l l o w e d t o mature i n i s o l a t i o n . A l l s t o c k s had- b e e n . m a i n t a i n e d under s i m i l a r ( s t i l l water) c o n d i t i o n s , e l i m i n a t i n g any e n v i r o n m e n t a l e f f e c t o f s t r e a m v e l o c i t y , f o r s e v e r a l g e n e r a t i o n s . M a t e r i a l s and Methods A d u l t g u p p i e s from Caparo ( l o w l a n d ) , P a r i a ( h e a d s t r e a m ) , and P e t i t e Curucaye ( s p r i n g ) s t o c k s were t e s t e d . These s t o c k s , c o n t a i n i n g f i f t h t o e i g h t h g e n e r a t i o n descendants o f w i l d - c a u g h t f i s h , were c u l t u r e d and m a i n t a i n e d as o u t l i n e d i n the G e n e r a l Methods ( C h a p t e r I I I ) . From each s t o c k , f o u r groups o f 10 f i s h , 5 o f each sex, were t e s t e d ( a t o t a l o f 20 males and 20 f e m a l e s p e r s t o c k ) . Each s t o c k ' s f o u r groups were t e s t e d d u r i n g d i f f e r e n t weeks, w i t h each group t e s t e d i n a d i f f e r e n t stream v e l o c i t y on each o f f o u r c o n s e c u t i v e days. The stream v e l o c i t i e s i n w h i c h each group was t e s t e d v a r i e d a c c o r d i n g t o the f o l l o w i n g s c h e d u l e : Dav 1 Dav 2 Day 3 Dav 4 Stream V e l o c i t y (m/sec) Group  1 • ° 7 .03 .10 .20 2 .10 .07 .20 .03 3 • 03 .20 .07 .10 .20 .10 .03 .07 The stream v e l o c i t i e s used l i e w e l l w i t h i n the range o f v e l o c i t i e s f o r streams i n h a b i t e d by g u p p i e s . F a s t e r v e l o c i t i e s were n o t used s i n c e the stream t a n k s d i d n o t c o n t a i n a r e a s o f d e c r e a s e d v e l o c i t y , where g u p p i e s c o u l d r e s t ( e g . b e h i n d r o c k s ) • The 5 males and 5 females f o r each group were drawn from the s t o c k t a n k s f o u r days b e f o r e t e s t i n g and p l a c e d , each sex s e p a r a t e l y , i n two 1 2 - l i t e r h o l d i n g t a n k s . On the morning o f each c o n s e c u t i v e t e s t day t h e s e f i s h were i n t r o d u c e d i n t o the stream t a n k . (The stream v e l o c i t y >in the t a n k was s e t b e f o r e i n t r o d u c i n g n t h e f i s h . ) A t the end o f each o b s e r v a t i o n day the f i s h were r e t u r n e d t o the two h o l d i n g t a n k s . T h i s procedure o f i s o l a t i n g the sexes ensured the s t a r t o f c o u r t s h i p b e h a v i o u r soon a f t e r t h e i r i n t r o d u c t i o n , e l i m i n a t i n g the need f o r a l o n g a c c l i m a t i o n p e r i o d . E a c h o f the group's f i v e males was o b s e r v e d t h r e e t i m e s a day f o r t e n m i n u t e s ; a p p r o x i m a t e l y 1, 3» and 4 h o u r s a f t e r i n t r o d u c t i o n o f the f i s h . I n t o t a l , t h i s p r o c e d u r e produced t h r e e 10-min r e c o r d i n g s f o r 20 males from each o f the t h r e e s t o c k s i n each o f f o u r stream v e l o c i t i e s . The number and d u r a t i o n o f s i g m o i d d i s p l a y s was r e c o r d e d , as w e l l as the number o f g o n o p o d i a l swings, t h r u s t s , c o p u l a t i o n a t t e m p t s , and a g g r e s s i v e a t t a c k s , b o t h i n i t i a t e d and r e c e i v e d . Males were e a s i l y d i s t i n g u i s h e d from one a n o t h e r by t h e i r d i s t i n c t c o l o u r p a t t e r n s , e s p e c i a l l y t h e i r b l a c k m a r k i n g s . D u r i n g each t e s t the d i s t r i b u t i o n o f the t e n f i s h ( b o t h males and females) was a l s o r e c o r d e d . • The p o s i t i o n o f each f i s h was r e c o r d e d u s i n g the g r i d o f 10 r e c t a n g l e s marked-, on,••the f r o n t o f the stream tank. R e c o r d i n g s were made a t 30 sec i n t e r v a l s f o r a 10 minute p e r i o d (20 r e c o r d i n g s ) . T h i s s e r i e s o f r e c o r d i n g s was r e p e a t e d f o u r t i m e s d u r i n g each t e s t day, b e g i n n i n g a p p r o x i m a t e l y 1, 3, 4, and 5 hours a f t e r i n t r o d u c t i o n o f the f i s h . Thus 80 r e c o r d i n g s o f d i s t r i b u t i o n were made f o r each group i n each stream v e l o c t i y . The d i s t r i b u t i o n r e c o r d i n g s were used t o determine group c o h e s i o n and depth. An " i n d e x o f c o h e s i o n " ( d e s i g n e d by Seghers, 1973) was c a l c u l a t e d . F o r each 30 sec o b s e r v a t i o n , the maximum d e n s i t y f o r any o f the 10 g r i d squares was r e c o r d e d . The i n d e x i s the mean maximum d e n s i t y f o r the 80 o b s e r v a t i o n s int-each t e s t . I t has a t h e o r e t i c a l minimum o f l " ( o n e f i s h i n each o f the 10: squares) and a maximum o f 10 ( e n t i r e group i n the a r e a o f one s q u a r e ) . O c c a s i o n a l l y d u r i n g t h i s e x p e r i m e n t a male d i e d o r became " s i c k " . I f so, i t was r e p l a c e d w i t h a n o t h e r f i s h and e l i m i n a t e d from the d a t a a n a l y s i s . F o l l o w i n g the expe r i m e n t each group o f f i s h was a n a e s t h e t i z e d i n MS-222 ( t r i c a i n e m e t h y l s u l p h o n a t e ) , measured w i t h c a l i p e r s , photographed and t h e n housed i n s e p a r a t e p o s t - e x p e r i m e n t b r e e d i n g t a n k s . S t a t i s t i c a l Treatment o f Dat a When comparing the same s t o c k under d i f f e r e n t stream c o n d i t i o n s I used the Friedman two-way a n a l y s i s o f v a r i a n c e ( S i e g e l , 1956)- When comparing d i f f e r e n t s t o c k s under the same stream c o n d i t i o n s the Mann-Whitney U t e s t was used* ( S i e g e l , 1956). C o r r e l a t i o n s between the s i z e o f males and c o u r t s h i p b e h a v i o u r p a t t e r n s (see Appendix) were measured u s i n g the Spearman r a n k c o r r e l a t i o n c o e f f i c i e n t ( S i e g e l , 1956)• R e s u l t s and D i s c u s s i o n Stream Depth L o c a t i o n The depth o f f i s h i s g i v e n i n r e l a t i o n t o stream v e l o c i t y f o r each s t o c k i n F i g u r e 3« A t the s l o w e s t f l o w i n g c o n d i t i o n (0.03 m/sec) the P a r i a (headstream) f i s h were i n the top h a l f o f the tank l e s s t h a n 20% o f the t i m e , whereas the Caparo ( l o w l a n d ) and P e t i t e Gurucaye ( s p r i n g ) f i s h were l o c a t e d i n the t o p h a l f o f the t a n k more t h a n 50% o f the t i m e . Toodetermine the e f f e c t o f stream v e l o c i t y on depth l o c a t i o n , a comparison was made o f the "group depths" f o r each s t o c k a t d i f f e r e n t v e l o c i t i e s ( T a b l e I I ) . No s i g n i f i c a n t d i f f e r e n c e was found between v e l o c i t i e s f o r the P a r i a and P e t i t e Curucaye s t o c k s ( a l t h o u g h f i s h were l o c a t e d l e s s o f t e n i n the top o f the t a n k w i t h i n c r e a s i n g v e l o c i t y , F i g . 3). I n c o n t r a s t , the l o w l a n d Caparo s t o c k showed a s i g n i f i c a n t v a r i a n c e i n i t s group d e p t h s . T h i s v a r i a n c e was c l e a r l y due t o a decrease i n the time s p e n t i n the t o p h a l f o f the s t r e a m t a n k a'ststream v e l o c i t y I n c r e a s e d ( F i g . 3) . The number o f t i m e s f i s h were l o c a t e d i n the t o p h a l f o f the s t r e a m t a n k d e c r e a s e d between the s l o w e s t and f a s t e s t v e l o c i t i e by 28$ f o r the P a r i a s t o c k , by 35$ f o r the P e t i t e C urucaye s t o c k , and by 76$ f o r the Caparo s t o c k ( T a b l e I I ) . Thus, o f the two s t o c k s t h a t showed a p r e f e r e n c e f o r the top o f the s tream t a n k i n s l o w - f l o w i n g w a t e r , the P e t i t e Curucaye F i g u r e 3« "Group_,_depth" i n r e l a t i o n t o stream v e l o c i t y . Means ± 95% c o n f i d e n c e i n t e r v a l s . C = Caparo, P = P a r i a , PC = P e t i t e Curucaye (N = 1 6 ) . (Lowland) (Headstream) ( S p r i n g ) vON T a b l e I I . Comparison o f "group depth" f o r each s t o c k a t d i f f e r e n t stream v e l o c i t i e s . S t o c k Mean number of t i m e s p e r 200 t h a t f i s h were i n the t o p h a l f o f the stream t a n k Stream v e l o c i t y (m/sec) .03 •07 .10 .20 O v e r a l l D i f f e r e n c e ( Friedman 2-way ANOVA) Caparo 109-9 93-9 65.3 26.9 <.01 P e t i t e Curucaye P a r i a 137.4 131.4 113.4 89.I 32.0 28.6 19.8 23.0 N. S. N.S. 28 f i s h ( d e r i v e d from an i n t e r m e d i a t e stream v e l o c i t y p o p u l a t i o n ) were b e t t e r a b l e t o m a i n t a i n t h e i r l o c a t i o n a t the top o f the stream t a n k i n f a s t - f l o w i n g w a t e r , whereas the Caparo f i s h were unable t o do so. Comparing stream l o c a t i o n between the t h r e e s t o c k s ( T a b l e I I I ) , i n the s l o w e s t v e l o c i t y t h e r e was a s i g n i f i c a n t d i f f e r e n c e between Caparo and P a r i a s t o c k s b u t no s i g n i f i c a n t d i f f e r e n c e between Caparo and P e t i t e Curucaye s t o c k s . I n the h i g h e s t v e l o c i t y t h i s s i t u a t i o n was r e v e r s e d , w i t h Caparo and P a r i a s t o c k s n o t s i g n i f i c a n t l y d i f f e r e n t and Caparo and P e t i t e Curucaye s t o c k s now s i g n i f i c a n t l y d i f f e r e n t from each o t h e r . T h i s i s c l e a r l y due t o the change i n the Caparo s t o c k ' s "group depthV ( F i g . 3). Each s t o c k e x h i b i t e d a s i m i l a r l o c a t i o n i n the stream t a n k t o the l o c a t i o n t h e i r p a r e n t p o p u l a t i o n was o b s e r v e d i n the w i l d (see C h a p t e r I I I ) . The p e r s i s t e n c e o f these d i f f e r e n c e s i n l a b o r a t o r y r a i s e d f i s h s u g g e s t s t h a t t h e r e i s l i k e l y a g e n e t i c b a s i s t o stream depth l o c a t i o n and t h a t these s t o c k s v a r y i n t h i s t r a i t . The f a c t t h a t P e t i t e Curucaye f i s h are b e t t e r a b l e t o m a i n t a i n p o s i t i o n a t the top o f the stream i n f a s t e r - f l o w i n g w a t e r , whereas Caparo f i s h are unable t o do so, may r e p r e s e n t an a d a p t a t i o n by the P e t i t e Curucaye f i s h t o l i v i n g i n f a s t e r - f l o w i n g w a t e r . The P a r i a s t o c k , whose p a r e n t p o p u l a t i o n l i v e d i n the f a s t e s t stream v e l o c i t y , as p r e d i c t e d , e x h i b i t e d a c o n s i s t e n t p r e f e r e n c e f o r the bottom o f the stream tank a t a l l v e l o c i t i e s . I s p e c u l a t e t h a t P a r i a f i s h have been s e l e c t e d t o p r e f e r a p o s i t i o n n e a r the stream bed because m a i n t a i n i n g a p o s i t i o n a t the s u r f a c e i s d i f f i c u l t i n f a s t -water. T a b l e I I I . Comparison o f "group depth" between s t o c k s a t d i f f e r e n t s t r e a m , v e l o c i t i e s . "Group depth" c , , .. Comparison between s t o c k s * Stream v e l o c i t y •> * / / > C > P C ^  PC P ^  PC (m/sec) ' ' P • .03 <.001 N.S. < .002 .07 <.001 N.S. <.002 .10 < . o i <.02 <.002 .20 N.S. <.002 <.002 *Mann-Whitney U t e s t . . C = Caparo, P = Pa r i a ' , PC = P e t i t e Curucaye. 30 Index o f C o h e s i o n Comparing each s t o c k s e p a r a t e l y ( F i g . k), none o f the s t o c k s showed s i g n i f i c a n t v a r i a n c e s i n c o h e s i o n under the f o u r v e l o c i t i e s ( p <c . 0 5 , Friedman t e s t ) . Comparing c o h e s i o n between s t o c k s ( T a b l e I V ) , I found t h a t Caparo had a s i g n i f i c a n t l y h i g h e r i n d e x t h a n P e t i t e Curucaye a t a l l stream v e l o c i t i e s . The Caparo s t o c k i n d i c e s were a l s o s i g n i f i c a n t l y h i g h e r t h a n those o f P a r i a i n the s l o w e s t and f a s t e s t v e l o c i t i e s . The P a r i a and P e t i t e Curucaye i n d i c e s were n o t s i g n i f i c a n t l y d i f f e r e n t i n any o f the stream v e l o c i t i e s . These r e s u l t s s u p p o r t the h y p o t h e s i s t h a t s t o c k s v a r y i n t h e i r tendency t o s c h o o l and t h a t these t e n d e n c i e s are under g e n e t i c c o n t r o l . The p r e d i c t i o n t h a t the l o w l a n d (Caparo) s t o c k would have a g r e a t e r tendency t o s c h o o l t h a n the headstream ( P a r i a ) s t o c k was c o n f i r m e d . The P e t i t e Curucaye s t o c k was s i m i l a r t o the headstream s t o c k i n i t s s c h o o l i n g b e h a v i o u r . I n T r i n i d a d , l o w l a n d f i s h were found i n s c h o o l s w h i l e headstream and s p r i n g p o p u l a t i o n s were d i s p e r s e d over the stream bed (see C h a p t e r I I I ) . A g a i n , each s t o c k e x h i b i t e d b e h a v i o u r s i m i l a r t o the w i l d p o p u l a t i o n from w h i c h i t was descended. The r e s u l t s i n d i c a t e t h a t d i f f e r e n c e s e x i s t i n g between s t o c k s i n t h e i r i n d e x o f c o h e s i o n , o r degree o f s c h o o l i n g , are n o t a f f e c t e d by stream v e l o c i t y , a t l e a s t w i t h i n the range o f v e l o c i t i e s t e s t e d . Perhaps d i f f e r e n c e s i n c o h e s i o n are due t o d i f f e r e n t p r e d a t i o n p r e s s u r e s ( a s suggested by Seghers, 1973) o r t o o t h e r f a c t o r s , such as stream t u r b i d i t y , o r t o a c o m b i n a t i o n o f f a c t o r s . F i g u r e 4. Index o f C o h e s i o n i n r e l a t i o n t o stream v e l o c i t y . Means i 95% c o n f i d e n c e i n t e r v a l s . C = Caparo ( L o w l a n d ) , P = P a r i a (Headstream), PC = P e t i t e Curucaye ( S p r i n g ) , ( N = 16). T a b l e IV. Comparison o f "Index o f C o h e s i o n " betwe s t o c k s a t d i f f e r e n t stream v e l o c i t i e s . Stream Index o f C o h e s i o n v e l o c i t y Comparison between s t o c k s * (m/sec) O P C > PC P <J!PC .03 < . 0 l <.03 N.S. .07 N..S. < . 0 l N.S. (~.06) .10 N.S. < .01 N.S. (^.08) .20 <.01 < . 0 1 N.S. *Mann-Whitney U t e s t ( P r e d i c t i o n s based on Seghers, 1973)-C = Caparo, P = P a r i a , PC = P e t i t e Curucaye. Male A g g r e s s i o n F o r each s t o c k male a g g r e s s i o n i n r e l a t i o n t o stream v e l o c i t y i s g i v e n i n F i g u r e .5. The number o f male a t t a c k s d i d n o t d i f f e r s i g n i f i c a n t l y between stream v e l o c i t i e s f o r any o f the s t o c k s (p <.05, Friedman t e s t ) , a l t h o u g h i t d i d d e c r ease somewhat f o r the P a r i a s t o c k . A l t h o u g h a g g r e s s i o n v a r i e d w i d e l y among i n d i v i d u a l P a r i a males ( F i g . 5)1 t h e y were s i g n i f i c a n t l y more a g g r e s s i v e t h a n Caparo and P e t i t e Curucaye males a t most stream v e l o c i t i e s ( T a b l e V ) . B a l l i n (1973) found P a r i a males t o be more a g g r e s s i v e t h a n a n o t h e r l o w l a n d p o p u l a t i o n o f males (Guayamare). The r e s u l t s o f t h i s e x p e r i m e n t c o n f i r m my p r e d i c t i o n t h a t P a r i a (headstream) males s h o u l d be more a g g r e s s i v e t h a n l o w l a n d males (Caparo) and a l s o i n d i c a t e t h a t the s p r i n g p o p u l a t i o n ( P e t i t e Curucaye, w h i c h had n o t p r e v i o u s l y been s t u d i e d ) i s r e l a t i v e l y non-a g g r e s s i v e . Once a g a i n , t h e s e b e h a v i o u r a l d i f f e r e n c e s between p o p u l a t i o n s l i k e l y have a g e n e t i c b a s i s . Stream v e l o c i t y does n o t appear t o a f f e e t . a g g r e s s i o n among males d i r e c t l y , a l t h o u g h t h e r e may be a s l i g h t decrease i n a g g r e s s i o n w i t h i n c r e a s i n g v e l o c i t y . 20 J 15-MEAN NUMBER OF ATTACKS PER MALE 10-PER 30 MIN 5 .03 .07 ' ' .10 STREAM VELOCITY (M/SEC) F i g u r e 5« Male a g g r e s s i o n i n r e l a t i o n t o stream v e l o c i t y . Means i 95% c o n f i d e n c e I n t e r v a l s . . C = Caparo (Lowland; N = 19), P = P a r i a (Headstream; N = 19), PC = P e t i t e Curucaye ( S p r i n g ; N = 17). 35 T a b l e V. Comparison o f Male A g g r e s s i o n a t d i f f e r e n t s tream v e l o c i t i e s . Stream Male A t t a c k s v e l o c i t y Comparison between s t o c k s * (m/sec) C < P C =^PC P ^  PC .03 < . 0 0 l N . S . <.002 .07 < .o25 N . S . .10 <.05 N . S . ^ . 0 2 .20 <.01 N . S . N . S . *Mann-Whitney U t e s t , 1 - t a i l e d f o r C < P, ' 2 - t a i l e d f o r C =5* PC.,. P=5* PC. C = Caparo', P = P a r i a , PC = P e t i t e Curucaye. 36 C o u r t s h i p B e h a v i o u r P a t t e r n s  T h r u s t s and Si g m o i d D i s p l a y s The r e l a t i o n s h i p 7 , b e t w e e n the mean number o f t h r u s t s p erformed by males and stream v e l o c i t y i s shown i n F i g u r e 6. Comparing each s t o c k s e p a r a t e l y , t h e r e was no s i g n i f i c a n t v a r i a n c e i n the number o f t h r u s t s performed a t the f o u r v e l o c i t i e s ( T a b l e V I ) . As p r e d i c t e d , Caparo males c o n s i s t e n t l y e x h i b i t e d more t h r u s t s a t a l l v e l o c i t i e s t h a n P e t i t e Curucaye males. P e t i t e Curucaye males i n t u r n c o n s i s t e n t l y performed more t h r u s t s t h a n P a r i a males. These d i f f e r e n c e s were s i g n i f i c a n t between Caparo and P a r i a males a t the two f a s t e s t v e l o c i t i e s ( T a b l e V I I ) . F o r each s t o c k t h e r e was a s i g n i f i c a n t v a r i a n c e i n the number o f s i g m o i d d i s p l a y s performed a t the d i f f e r e n t stream v e l o c i t i e s . T h i s v a r i a n c e was due t o a decrease i n the number o f s i g m o i d d i s p l a y s performed by males as stream v e l o c i t y i n c r e a s e d ( F i g . 7) . A l s o as p r e d i c t e d , P a r i a males performed more s i g m o i d d i s p l a y s a t a l l stream v e l o c i t i e s t h a n P e t i t e Curucaye males, and P e t i t e Curucaye males i n t u r n always d i s p l a y e d more f r e q u e n t l y t h a n Caparo males. The d i f f e r e n c e s between P a r i a and P e t i t e Curucaye and between P a r i a and Caparo were s i g n i f i c a n t a t the two s l o w e s t v e l o c i t i e s ( T a b l e V I I ) . Each p o p u l a t i o n ' s r a t i o o f s i g m o i d d i s p l a y s : t h r u s t s a t the f o u r stream v e l o c i t i e s i s g i v e n i n F i g u r e 8. A l l t h r e e s t o c k s showed a s i g n i f i c a n t v a r i a n c e i n t h e i r r a t i o s between the f o u r v s t r e a m v e l o c i t i e s . The v a r i a n c e was due t o a .03 .0? .10 .20 STREAM VELOCITY (M/SEG) F i g u r e 6 . Number o f t h r u s t s i n r e l a t i o n t o stream v e l o c i t y . Means ± 9 5 % c o n f i d e n c e i n t e r v a l s . C = Caparo (Lowland; N = 19), P = P a r i a (Headstream; N = 19) PC = P e t i t e Curucaye ( S p r i n g ; N = 17). \j0 38 T a b l e V I . Comparison o f number o f T h r u s t s , S i g m o i d D i s p l a y s , and the r a t i o o f S i g m o i d D i s p l a y s : T h r u s t s f o r each s t o c k a t d i f f e r e n t stream v e l o c i t i e s . S t o c k Stream v e l o c i t y (m/sec) • 03 •0? .10 .20 Mean number o f T h r u s t s p e r male p e r 30 mins O v e r a l l D i f f e r e n c e ( Friedman 2-way ANOVA) P Caparo 25-9 34.0 28 . 2 24 . 5 N.S. P e t i t e Curucaye 23-5 30 .1 24.1 22.5 N.S. P a r i a 23.5 25.9 19.4 18 . 1 N. S. Mean number o f Si g m o i d • D i s p l a y s p e r male p e r 30 mins Caparo 33-9 29.3 22.4 11.1 <.001 P e t i t e Curucaye 34 .5 36 .6 33 .5 20.6 <.01 P a r i a 49-4 48 . 1 34.1 24 . 2 <.001 R a t i o o f S i g m o i d D i s p l a y s : T h r u s t s Caparo 1.31 0.86 0.79 0.46 ^ . 0 1 P e t i t e Curucaye 1.4-7 1.22 1-39 0.92 • <".0l P a r i a 2.10 1.85 1.76 1.34 <.oi T a b l e V I I . Comparison of number o f T h r u s t s , S i g m o i d D i s p l a y s and the r a t i o o f S i g m o id D i s p l a y s : T h r u s t s between s t o c k s a t d i f f e r e n t v e l o c i t i e s . Stream Number o f T h r u s t s Number of Si g m o i d D i s p l a y s R a t i o o f D i s p l a y s : T h r u s t s v e l o c i t y Comparison between s t o c k s * Comparison between s t o c k s * Comparison between s t o c k s * (m/sec) C > P C > P C P <: PC C < P C < P C P > P C C <: P C < PC P > PC .03 N.S. N.S. N.S. <.05 N.S. <.05 <.01 N.S. <-025 .07 N.S. N.S. N.S. < t 0 l N.S. N.S. <.01 N.S. =.025 C ^ . 0 5 ) .10 <.025 N.S. <.05 N.S. N.S. N.S. N.S. N.S. N.S. .20 <.05 N.S. N.S. N.S. N.S. N.S. <.025 N.S. N.S. (^.05) *Mann-Whitney U t e s t . C = Caparo, P = P a r i a , PC = P e t i t e Curucaye, 50 ko MEAN NUMBER OF SIGMOID DISPLAYS PER MALE PER 30 MIN 30 20 10 03 .07 .10 STREAM VELOCITY (M/SEC) .20 P PC 50 .30 20 l i o F i g u r e 7- Number o f s i g m o i d d i s p l a y s i n r e l a t i o n t o stream v e l o c i t y . Means ± 95% c o n f i d e n c e i n t e r v a l s . Cr=.-Oaparo (Lowland; N = 19) , P = P a r i a (Headstream; N = 19) , PC = P e t i t e Curucaye ( S p r i n g ; N = 17). o 2.00. •2.00 RATIO OF SIGMOID DISPLAYS : THRUSTS 1.50, 1.00 PC PC PC '1.50 •1.00 0.50 •0.50 03 .07 .10 STREAM VELOCITY (M/SEC) .20 F i g u r e 8. R a t i o o f s i g m o i d d i s p l a y s : t h r u s t s i n r e l a t i o n t o stream v e l o c i t y . C = Caparo (Lowland; N = 19), P = P a r i a (Headstream; N = 19), PC = P e t i t e Curucaye ( S p r i n g ; N = 17). k2 decrease i n the r a t i o as stream v e l o c i t y i n c r e a s e d ( F i g . 8 ) . T h i s means t h a t , as p r e d i c t e d , the f r e q u e n c y o f s i g m o i d d i s p l a y s d e c r e a s e d more t h a n the f r e q u e n c y o f t h r u s t s as stream v e l o c i t y i n c r e a s e d . A t a l l v e l o c i t i e s P a r i a had the h i g h e s t r a t i o o f s i g m o i d d i s p l a y s : t h r u s t s and P e t i t e Curucaye i n t u r n had a h i g h e r r a t i o t h a n Caparo. These d i f f e r e n c e s i n c o u r t s h i p were s i g n i f i c a n t "between the P a r i a and Caparo s t o c k s a t t h r e e o f the v e l o c i t i e s and between P a r i a and P e t i t e Curucaye a t two o f the v e l o c i t i e s ( T a b l e V I I ) . D i f f e r e n c e s i n the f r e q u e n c i e s o f t h r u s t s and s i g m o i d d i s p l a y s between the Caparo and P a r i a s t o c k s are c o n s i s t e n t w i t h r e s u l t s f o r s i m i l a r s t o c k s t e s t e d i n s t i l l w a t e r ( B a l l i n , 1 9 7 3 f Snyder, 1 9 7 8 ) • As p r e d i c t e d , the headstream p o p u l a t i o n used more d i s p l a y s w h i l e l o w l a n d f i s h used more t h r u s t s . The P e t i t e Curucaye s t o c k , b r e d from an i n t e r m e d i a t e s t r e a m v e l o c i t y p o p u l a t i o n , used an i n t e r m e d i a t e c o u r t s h i p s t r a t e g y . These d i f f e r e n c e s between s t o c k s a g a i n presumably r e f l e c t g e n e t i c d i f f e r e n c e s . The p r e d i c t i o n t h a t each p o p u l a t i o n d i f f e r s i n i t s a b i l i t y t o p e r f o r m c o u r t s h i p i n i n c r e a s i n g stream v e l o c i t y was su p p o r t e d . S p e c i f i c a l l y , i n f a s t e r - f l o w i n g w a t e r headstream f i s h were b e t t e r a b l e t o m a i n t a i n t h e i r f r e q u e n c y o f d i s p l a y s t h a n l o w l a n d f i s h . I n s l o w - f l o w i n g w a t e r the Caparo s t o c k d i s p l a y e d more t h a n i t t h r u s t e d , however, i t was u n a b l e t o m a i n t a i n t h i s r a t i o i n f a s t e r v e l o c i t i e s . I n f a c t , i n the f a s t e s t v e l o c i t y i t d i s p l a y e d l e s s t h a n h a l f as f r e q u e n t l y as i t t h r u s t e d ( F i g . 8 , T a b l e V I ) . The P a r i a s t o c k performed more t h a n t w i c e as many s i g m o i d d i s p l a y s as t h r u s t i n slow-f l o w i n g w a t e r , and a t the f a s t e r v e l o c i t i e s i t was always a b l e t o m a i n t a i n a h i g h e r f r e q u e n c y o f d i s p l a y s t h a n t h r u s t s . The r a t i o o f s i g m o i d d i s p l a y s : t h r u s t s d e c r e a s e d between the s l o w e s t and f a s t e s t v e l o c i t i e s by 65% f o r t h e Caparo s t o c k and by o n l y 36% f o r the P a r i a s t o c k . Thus P a r i a (headstream) f i s h appear b e t t e r adapted t o d i s p l a y i n g i n f a s t e r - f l o w i n g w ater t h a n Caparo ( l o w l a n d ) f i s h . (The P e t i t e Curucaye s t o c k had an i n t e r m e d i a t e r a t i o and were a b l e t o m a i n t a i n t h i s r a t i o t o about the same degree as the P a r i a s t o c k - the r a t i o d e c r e a s e d fry 37% between the f a s t e s t and s l o w e s t stream v e l o c i t i e s . ) The r a t i o o f s i g m o i d d i s p l a y s : t h r u s t s f o r Caparo i n s l o w - f l o w i n g w a t e r ( l . 3 l ) was s i m i l a r t o the r a t i o f o r P a r i a a t the f a s t e s t v e l o c i t y (1 . 3 ^ ) and t o P e t i t e Curucaye*s r a t i o a t the second f a s t e s t v e l o c i t y (1 .39)• A l t h o u g h t h i s c o u l d be c o i n c i d e n t a l i t i s i n t e r e s t i n g t h a t i n the w i l d t h e s e p o p u l a t i o n s p e r f o r m c o u r t s h i p a t these r e l a t i v e v e l o c i t i e s and th u s may be a c h i e v i n g r o u g h l y s i m i l a r r a t i o s . Perhaps males p e r f o r m an o p t i m a l r a t i o o f s i g m o i d d i s p l a y s : t h r u s t s f o r s u c c e s s f u l m a t i n g . I f an o p t i m a l r a t i o o f s i g m o i d d i s p l a y s : t h r u s t s does e x i s t , t h e n the p r e v i o u s l y o b s e r v e d d i f f e r e n c e s between p o p u l a t i o n s i n t h e i r r a t i o o f s i g m o i d d i s p l a y s : t h r u s t s c o u l d r e p r e s e n t a d a p t a t i o n s t o d i f f e r e n t stream v e l o c i t i e s . S i n c e s i g m o i d d i s p l a y s decrease more t h a n t h r u s t s w i t h i n c r e a s i n g s t r e a m v e l o c i t y , males t h a t l i v e i n f a s t - f l o w i n g w a t e r may have e v o l v e d a tendency to p e r f o r m a h i g h e r r a t i o o f s i g m o i d d i s p l a y s : t h r u s t s (as observed i n slow water) i n o r d e r t o s t i l l be p e r f o r m i n g a t the o p t i m a l r a t i o when i n f a s t - f l o w i n g w a t e r . As n o t e d , when headstream f i s h were obse r v e d i n f a s t - f l o w i n g w a t e r t h e i r r a t i o was c l o s e t o t h a t o f l o w l a n d f i s h when observ e d i n s l o w - f l o w i n g w a t e r . Thus, apparent d i f f e r e n c e s ' i n male c o u r t s h i p o b s e r v e d between p o p u l a t i o n s i n s t i l l w a t e r may n o t a c t u a l l y e x i s t i n the w i l d . T h i s p o i n t i s i m p o r t a n t when c o n s i d e r i n g the a d a p t i v e s i g n i f i c a n c e o f v a r i a t i o n i n guppy c o u r t s h i p b e h a v i o u r . P r e v i o u s l y observed c o u r t s h i p d i f f e r e n c e s may r e p r e s e n t a d a p t i v e r e s p o n s e s t o i n c r e a s i n g s tream v e l o c i t y r a t h e r t h a n a d a p t a t i o n s l o n l y t o t u r b i d i t y and p r e d a t i o n as suggested by B a l l i n (1973)' The mean number and d u r a t i o n o f s i g m o i d d i s p l a y s , mean number o f s i g m o i d d i s p l a y s l o n g e r t h a n 1.5 s e e s , and p e r c e n t a g e o f s i g m o i d d i s p l a y s l o n g e r t h a n 1.5- sees are g i v e n i n Ta b l e V I I I f o r each s t o c k a t the f o u r stream v e l o c i t i e s . I n g e n e r a l the d u r a t i o n o f d i s p l a y s and per c e n t a g e o f d i s p l a y s l o n g e r t h a n 1-5 sees d e c r e a s e d as stream v e l o c i t y i n c r e a s e d . A t a l l stream v e l o c i t i e s P e t i t e Curucaye males have, the l o n g e s t s i g m o i d d i s p l a y s and the g r e a t e s t p e r c e n t a g e o f d i s p l a y s l o n g e r t h a n 1.5 sees. A t s l o w e r v e l o c i t i e s Caparo males have s l i g h t l y l o n g e r d i s p l a y s and more d i s p l a y s l o n g e r t h a n 1.5 sees t h a n P a r i a males. However, as p r e d i c t e d , a t the f a s t e r t s t r e a m v e l o c i t i e s the o p p o s i t e i s the cas e , w i t h P a r i a males h a v i n g s l i g h t l y l o n g e r d i s p l a y s t h a n Caparo males and more s i g m o i d d i s p l a y s l o n g e r t h a n 1.5 sees. As e x p e c t e d , i n c r e a s i n g stream v e l o c i t y does decrease the d u r a t i o n o f s i g m o i d d i s p l a y s f o r f i s h from a l l t h r e e s t o c k s . However, t h e r e was n o t always a d i r e c t r e l a t i o n s h i p T a b l e V I I I . Mean number and d u r a t i o n o f S i g m o i d D i s p l a y s a t f o u r stream v e l o c i t i e s . Stream Mean number o f v e l o c i t y S igmoid D i s p l a y s /male /30 mins C PC P .03 33.9 34.5 49.4 .07 29.3 36.6 48 . 1 .10 22.4 33-5 34.1 . 20 11.1 20.6 24.2 Mean d u r a t i o n o f Sigmoid D i s p l a y s (sees) Mean number o f S i g m o i d D i s p l a y s > 1 . 5 sees P e r c e n t a g e o f Sig m o i d D i s p l a y s >4.5 sees C PC P C PC P C PC P 1.4 1185 1.2 13.1 18.8 18.2 38.4 54.5 36.7 1.3 1 .5 1.1 10 . 5 16.8 14 . 9 35.7 45.8 31.0 1.0 1.3 1.0 4.2 14.0 8.7 18.8 41.8 25.6 0.9 1.5 1.0 1.8 8.9 5-9 16.5 43.4 24 . 6 4 6 between a s t o c k ' s a b i l i t y t o p e r f o r m l o n g e r s i g m o i d d i s p l a y s and i t s n a t u r a l stream v e l o c i t y . F i s h d e r i v e d from p o p u l a t i o n s l i v i n g i n f a s t e r - f l o w i n g w a t e r ( P a r i a and P e t i t e Curucaye) d i d , as p r e d i c t e d , p e r f o r m l o n g e r d i s p l a y s i n the f a s t e r v e l o c i t i e s t h a n the l o w l a n d (Caparo) f i s h . However, the males from the i n t e r m e d i a t e stream v e l o c i t y ( P e t i t e C u r u c a y e ) , performed d i s p l a y s o f the l o n g e s t mean d u r a t i o n a t a l l stream v e l o c i t i e s , w h i c h was n o t p r e d i c t e d . G o n o p o d i a l Swings The mean number o f g o n o p o d i a l swings performed by each s t o c k i n r e l a t i o n t o stream v e l o c i t y i s shown i n F i g u r e 9» A l l s t o c k s e x h i b i t e d a s i g n i f i c a n t v a r i a n c e i n the number o f g o n o p o d i a l swings performed a t d i f f e r e n t v e l o c i t i e s ( T a b l e I X ) . T h i s v a r i a n c e was due t o a decrease i n g o n o p o d i a l swings as stream v e l o c i t y i n c r e a s e d ( F i g . 9). C l e a r l y the performance of g o n o p o d i a l swings i s a f f e c t e d by stream v e l o c i t y . Under a l l stream v e l o c i t y c o n d i t i o n s b o t h the Caparo and P e t i t e Curucaye s t o c k s performed s i g n i f i c a n t l y more g o n o p o d i a l swings t h a n the P a r i a s t o c k ( T a b l e X ) . The Caparo and P e t i t e Curucaye s t o c k s were n o t s i g n i f i c a n t l y d i f f e r e n t a t any o f 'the v e l o c i t i e s . The d i f f e r e n c e between the Caparo and P a r i a s t o c k s c o n f i r m s my p r e d i c t i o n t h a t l o w l a n d males s h o u l d p e r f o r m more g o n o p o d i a l swings t h a n headstream males. T h i s p r e d i c t i o n was based on the d i f f e r e n c e s found between s i m i l a r headstream and l o w l a n d p o p u l a t i o n s by B a l l i n (1973)-vand Snyder (1978). The p r e v i o u s l y u n s t u d i e d P e t i t e Curucaye s t o c k ' s performance o f 03 .07 .10 .20 STREAM VELOCITY (M/SEC) F i g u r e 9. Number o f g o n o p o d i a l swings i n r e l a t i o n t o stream v e l o c i t y . Means ± 95% c o n f i d e n c e i n t e r v a l s . ' C = Caparo (Lowland; N = 19), P = P a r i a (Headstream; N = 19), PC = P e t i t e Curucaye ( S p r i n g ; N = 17). 48 T a b l e IX. Comparison o f number o f G o n o p o d i a l Swings performed art d i f f e r e n t stream v e l o c i t i e s f o r each s t o c k . StcSitock Caparo P e t i t e Curucaye P a r i a Mean number o f G o n o p o d i a l Swings Stream v e l o c i t y (m/sec) 03 .07 .10 32.8 26.5 31.9 32.6 18.7 18.8 25-5 32.1 13.8 .20 18.3 21.0 11.5 O v e r a l l D i f f e r e n c e (Friedman 2-way ANOVA) <.001 <.01 <.001 49 T a b l e X. Comparison o f number o f G o n o p o d i a l Swings between s t o c k s a t d i f f e r e n t s t r e a m v e l o c i t i e s . Stream Number o f G o n o p o d i a l Swings v e l o c i t y Comparison between s t o c k s * (m/sec) C > P O PC P < P C P .03 < . 0 0 i N.S. <.001 .07 <C«025 N.S. <-.00l .10 < . 0 0 1 N.S. < .001 .20 < . 0 0 1 N.S. <-025 *Mann-Whitney U t e s t . C = Caparo, P = P a r i a , PC = P e t i t e Curucaye. the h i g h e s t f r e q u e n c y o f g o n o p o d i a l swings a t a l l stream v e l o c i t i e s was n o t p r e d i c t e d . The s i g n i f i c a n c e o f t h i s f i n d i n g , ' however, i s d i f f i c u l t t o i n t e r p r e t , e s p e c i a l l y s i n c e g o n o p o d i a l swings i n f a c t o c c u r d u r i n g "both c o u r t s h i p and n o n - c o u r t s h i p and t h e i r f u n c t i o n remains unknown. ( I n the Appendix, w h i c h d e a l s w i t h the e f f e c t o f stream v e l o c i t y on c o r r e l a t i o n s between c o u r t s h i p b e h a v i o u r p a t t e r n s , I c o n s i d e r i n m o r e - d e t a i l the f u n c t i o n o f g o n o p o d i a l swings.) A t p r e s e n t the signifi'.caneei'ofnthe d i f f e r e n c e s found between s t o c k s i n the performance o f g o n o p o d i a l swings remains unknown. C o p u l a t i o n A t t e m p t s The mean number o f c o p u l a t i o n a t t e m p t s performed by males o f each s t o c k a t the f o u r s t r e a m v e l o c i t i e s and the p e r c e n t a g e s o f s i g m o i d d i s p l a y s t h a t were f o l l o w e d by c o p u l a t i o n a t t e m p t s are l i s t e d i n Table X I . No a c t u a l c o p u l a t i o n s were obse r v e d d u r i n g the e x p e r i m e n t . Because c o p u l a t i o n a t t e m p t s o c c u r r e d so i n f r e q u e n t l y ( l e s s t h a n one p e r male p e r 30 m i n s ) , I d i d n o t a n a l y z e them s t a t i s t i c a l l y . The number of c o p u l a t i o n a t t e m p t s d e c r e a s e d w i t h i n c r e a s i n g stream v e l o c i t y , e x c e p t f o r the P a r i a s t o c k . S i n c e c o p u l a t i o n a t t e m p t s are always preceded by s i g m o i d d i s p l a y s , t h i s decrease may r e f l e c t the d e c r e a s i n g number o f s i g m o i d d i s p l a y s performed by males as stream v e l o c i t y i n c r e a s e d ( F i g . 7) . L i l e y (1966) n o t e d t h a t c o p u l a t i o n a t t e m p t s are dependent on f e m a l e s m a i n t a i n i n g t h e i r p o s i t i o n d u r i n g and i m m e d i a t e l y f o l l o w i n g a s i g m o i d d i s p l a y . C o p u l a t i o n a t t e m p t s are 51 T a b l e X I . Mean number o f C o p u l a t i o n A t t e m p t s and pe r c e n t a g e o f S i g m o i d D i s p l a y s f o l l o w e d by C o p u l a t i o n A t t e m p t s . Mean number o f P e r c e n t a g e o f S i g m o i d Stream C o p u l a t i o n A t t e m p t s D i s p l a y s : r f o l l o w e d "by v e l o c i t y /male / 3 0 mins C o p u l a t i o n A t t e m p t s (m/sec) C PC P c PC P . 0 3 1 .1 0 . 7 0 . 3 3 . 3 2 . 0 0 . 6 .07:; ' 0 . 8 0 . 5 0 . 7 2 . 7 1 .3 1 . 4 . 1 0 0 . 4 0 . 5 0 . 3 1 .6 1 .5 -0 .8 . 2 0 0 . 2 0 . 1 0 . 5 1 .9 0 . 6 2 . 2 C = Caparo, PC = P e t i t e Curucaye, P = P a r i a . u n s u c c e s s f u l because f e m a l e s are seldom r e c e p t i v e , and when u n r e c e p t i v e t h e y r a r e l y m a i n t a i n t h e i r p o s i t i o n n e a r a d i s p l a y i n g male. Thus a l a c k o f female r e c e p t i v i t y r e d u c e s t h e number o f c o p u l a t i o n a t t e m p t s performed by males because f e m a l e s move away from d i s p l a y i n g males. However, when males p e r f o r m more c o p u l a t i o n a t t e m p t s t h i s does n o t mean t h a t f e males were n e c e s s a r i l y more r e c e p t i v e . T h i s i s because many c o p u l a t i o n a t t e m p t s a r S l p e r f o r m e d t o u n r e c e p t i v e f e m a l e s who have ( i n a d v e r t e n t l y ? ) t e m p o r a r i l y m a i n t a i n e d t h e i r p o s i t i o n d u r i n g a male's d i s p l a y . Thus c o p u l a t i o n a t t e m p t s r e f l e c t female p o s i t i o n i m m e d i a t e l y f o l l o w i n g a d i s p l a y and n o t r e c e p t i v i t y . (When females are r e c e p t i v e , t hey c o n t i n u e 1 m a i n t a i n i n g t h e i r p o s t i t i o n f o l l o w i n g s i g m o i d d i s p l a y s , r e s u l t i n g i n s u c c e s s f u l c o p u l a t i o n s . Thus c o p u l a t i o n s r e f l e c t female r e c e p t i v i t y . ) Z-~ .. The f l u c t u a t i o n i n the percentage o f s i g m o i d d i s p l a y s t h a t were f o l l o w e d by c o p u l a t i o n a t t e m p t s a t d i f f e r e n t stream v e l o c i t i e s ( T a b l e XI) l i k e l y s i m p l y r e f l e c t s v a r i a t i o n s i n female p o s i t i o n d u r i n g s i g m o i d d i s p l a y s . Summary o f R e s u l t s Guppies b r e d from p o p u l a t i o n s l i v i n g i n s l o w - f l o w i n g (Caparo) and f a s t - f l o w i n g ( P a r i a ) streams d i f f e r e d i n the f o l l o w i n g ways: 1) Caparo g u p p i e s were l o c a t e d i n the top h a l f o f the s t r e a m t a n k s i g n i f i c a n t l y more o f t e n t h a n P a r i a g u p p i e s ( e x c e p t a t the f a s t e s t stream v e l o c i t y , when t h e y were unable t o m a i n t a i n t h e i r p o s i t i o n ) . 2) Caparo g u p p i e s were s i g n i f i c a n t l y more c o h e s i v e t h a n 5 3 P a r i a g u p p i e s a t b o t h the s l o w e s t and f a s t e s t v e l o c i t i e s . 3 ) Caparo males were s i g n i f i c a n t l y l e s s a g g r e s s i v e t h a n P a r i a males a t a l l stream v e l o c i t i e s . 4) Caparo males performed s i g n i f i c a n t l y fewer s i g m o i d d i s p l a y s and more t h r u s t s and g o n o p o d i a l swings t h a n P a r i a males i n s l o w - f l o w i n g w a t e r . . 5 ) F o r b o t h guppy p o p u l a t i o n s the f r e q u e n c y o f s i g m o i d d i s p l a y s , t h r u s t s , and g o n o p o d i a l swings d e c r e a s e d as stream v e l o c i t y i n c r e a s e d . The f r e q u e n c y o f s i g m o i d d i s p l a y s d i s p l a y s d e c r e a s e d more t h a n the f r e q u e n c y o f t h r u s t s as stream v e l o c i t y i n c r e a s e d . 6) Caparo males were l e s s a b l e to m a i n t a i n t h e i r c o u r t s h i p b e h a v i o u r and stream p o s i t i o n a t h i g h v e l o c i t i e s t h a n P a r i a males. Caparo males showed a g r e a t e r decrease i n the r a t i o o f s i g m o i d d i s p l a y s : t h r u s t s t h a n P a r i a males as stream v e l o c i t y i n c r e a s e d . 7) I n f a s t e r - f l o w i n g w a t e r the s i g m o i d d i s p l a y s performed by Caparo males were o f s h o r t e r d u r a t i o n t h a n those o f P a r i a males. Thus, a l l seven o r i g i n a l p r e d i c t i o n s r e g a r d i n g these p o p u l a t i o n s were i n l a r g e p a r t c o n f i r m e d . I n a d d i t i o n , as p r e d i c t e d , most o f the c o u r t s h i p b e h a v i o u r p a t t e r n s o f the i n t e r m e d i a t e stream v e l o c i t y p o p u l a t i o n ( P e t i t e Curucaye) were i n t e r m e d i a t e between the headstream and l o w l a n d p o p u l a t i o n s . THe. p e r s i s t e n c e of. t h e s e d i f f e r e n c e s i n b e h a v i o u r .in l a b o r a t o r y r a i s e d descendants demonstrates t h a t t h e r e i s a g e n e t i c c o n t r i b u t i o n t o the d i f f e r e n c e s . TKe d i f f e r e n c e s t h e r e f o r e presumably r e p r e s e n t the p r o d u c t o f n a t u r a l s e l e c t i o n . Stream v e l o c i t y was found t o have a d i r e c t e f f e c t on guppy depth l o c a t i o n . However, no d i r e c t e f f e c t o f stream v e l o c i t y on c o h e s i o n and male a g g r e s s i o n was found. The..performance o f c o u r t s h i p b e h a v i o u r was c l e a r l y a f f e c t e d by stream v e l o c i t y , w i t h b o t h s i g m o i d d i s p l a y s and g o n o p o d i a l swings b e i n g markedly d e c r e a s e d by i n c r e a s i n g v e l o c i t y . S u pport was g a i n e d f o r the h y p o t h e s i s t h a t p o p u l a t i o n d i f f e r e n c e s , e s p e c i a l l y i n male c o u r t s h i p b e h a v i o u r , r e p r e s e n t a d a p t i v e r e s p o n s e s t o stream v e l o c i t y . CHAPTER V 5 5 EXPERIMENT I I : MALE P. RETICULATA COURTSHIP BEHAVIOUR AND MATE PREFERENCE IN STILL AND FLOWING WATER CONDITIONS I n t r o d u c t i o n I n t h i s e x periment I s t u d y the c o u r t s h i p b e h a v i o u r o f w i l d - c a u g h t g u p p i e s from two p a i r s o f headstream and l o w l a n d p o p u l a t i o n s . The f o u r p o p u l a t i o n s were t e s t e d i n s t i l l w a t e r and i n one f l o w i n g w a t e r c o n d i t i o n . U n l i k e E x p e r i m e n t I , the f i s h were m a i n t a i n e d i n the stream c o n d i t i o n f o r a f u l l week. However, I a g a i n t e s t e d the p r e d i c t i o n s t h a t 1) l o w l a n d males p e r f o r m fewer s i g m o i d d i s p l a y s b u t more t h r u s t s and g o n o p o d i a l swings t h a n headstream males, 2) c o u r t s h i p b e h a v i o u r s h o u l d decrease f o r a l l s t o c k s i n the f l o w i n g w a t e r , and 3) f i s h from the headstream p o p u l a t i o n s s h o u l d be b e t t e r a b l e t o m a i n t a i n c o u r t s h i p i n f l o w i n g w a t e r t h a n l o w l a n d f i s h . S t r i k i n g b e h a v i o u r a l d i f f e r e n c e s between these w i l d -caught p o p u l a t i o n s might be e x p e c t e d , due to t h e i r p r i o r e x p e r i e n c e i n d i f f e r e n t stream v e l o c i t i e s and the l a c k o f any l a b o r a t o r y s e l e c t i o n o c c u r r i n g i n s t i l l w a t e r t a n k s . Two p a i r s o f p o p u l a t i o n s were s t u d i e d s i n c e p a r a l l e l d i f f e r e n c e s between them, r e f l e c t i n g d i f f e r e n c e s found between s t o c k s i n E x p e r i m e n t I , would p r o v i d e a d d i t i o n a l s u p p o r t f o r g e n e r a l i t y o f the r e s u l t s . To examine c o u r t s h i p b e h a v i o u r i n more d e t a i l I d e t e r m i n e d the number o f " c o u r t s h i p b o u t s " performed by each p o p u l a t i o n o f males. (A c o u r t s h i p bout was d e f i n e d as a s e r i e s o f c o n s e c u t i v e s i g m o i d d i s p l a y s and/or t h r u s t s performed by a male t o the same female.) S i n c e , i n E x p e r i m e n t I , b o t h s i g m o i d d i s p l a y s and t h r u s t s were found t o decrease w i t h i n c r e a s i n g stream v e l o c i t y , I p r e d i c t t h a t headstream males s h o u l d p e r f o r m more c o u r t s h i p b o u t s ( o b s e r v e d i n s l o w - f l o w i n g water) i n o r d e r t o m a i n t a i n t h e i r l e v e l o f c o u r t s h i p i n f a s t - f l o w i n g w a t e r . The number o f b e h a v i o u r p a t t e r n s performed d u r i n g c o u r t s h i p • b o u t s was a l s o examined. T h i s was done t o determine wfiether a l l p o p u l a t i o n s p e r f o r m , on average, the same number o f b e h a v i o u r p a t t e r n s t o i n d i v i d u a l f e m ales once t h e y b e g i n c o u r t i n g them. A n o t h e r o b j e c t i v e o f t h i s e x p e r i m e n t was t o determine male mate p r e f e r e n c e f o r f e m a l e s from d i f f e r e n t p o p u l a t i o n s . I examined mate p r e f e r e n c e t o t e s t the p r e d i c t i o n t h a t males s h o u l d c o u r t f e m a l e s from t h e i r own p o p u l a t i o n more t h a n f e m a l e s from a n o t h e r p o p u l a t i o n . T h i s p r e d i c t i o n was based on B a l l i n ' s (1973)Mstudy,which found a degree o f s e l e c t i v i t y by d i f f e r e n t p o p u l a t i o n s o f males f o r f emales o f t h e i r own p o p u l a t i o n . B a l l i n ' s r e s u l t s , however, were i n c o n c l u s i v e . D u r i n g t h i s e x periment male and female mate p r e f e r e n c e s were a c t u a l l y t e s t e d s i m u l t a n e o u s l y . T d e t e r m i n e d male mate p r e f e r e n c e d i r e c t l y by o b s e r v i n g c o u r t s h i p b e h a v i o u r and r e c o r d i n g w h i c h f e m a l e s males c o u r t e d . Female c h o i c e and male m a t i n g s u c c e s s were d e t e r m i n e d a t the same time b u t i n d i r e c t l y . T h i s was done by L i l e y and L u y t e n , u s i n g an a u t o r a d i o g r a p h i c t e c h n i q u e , measuring':;labelled and u n l a b e l l e d sperm c o l l e c t e d from the f e m a l e s ' o v i d u c t s a t the end o f the e x p e r i m e n t . The a u t o r a d i o g r a p h i c t e c h n i q u e was used t o determine whether one s t o c k o f males had g r e a t e r p o t e n t i a l r e p r o d u c t i v e s u c c e s s ( i e . i n s e m i n a t e d more females) and whether t h i s r e p r o d u c t i v e s u c c e s s was a f f e c t e d by stream v e l o c i t y c o n d i t i o n . U n f o r t u n a t e l y , the r e s u l t s from t h i s t e c h n i q u e have n o t y e t been a n a l y z e d . ( D e t a i l s o f the t e c h n i q u e used and the r e s u l t s w i l l be r e p o r t e d elsewhere by L i l e y and Luyten.) M a t e r i a l s and Methods The p r o c e d u r e used i n t h i s e x periment was d e s i g n e d i n c o n j u n c t i o n w i t h L i l e y and L u y t e n . W i l d - c a u g h t a d u l t g u p p i e s from f o u r T r i n i d a d p o p u l a t i o n s were t e s t e d - Guayamare ( l o w l a n d ) , Upper A r i p o ( h e a d s t r e a m ) , Caparo ( l o w l a n d ) , and P a r i a (headstream). F o l l o w i n g t h e i r t r a n s p o r t t o Vancouver t h e s e p o p u l a t i o n s were m a i n t a i n e d under s i m i l a r c o n d i t i o n s (see G e n e r a l Methods, C h a p t e r I I I ) . Guayamare and Upper A r i p o f i s h were t e s t e d t o g e t h e r i n groups c o n t a i n i n g 20 f i s h , 5 o f each s e x from b o t h p o p u l a t i o n s . I n each group, males from one o f the two p o p u l a t i o n s had a r a d i o a c t i v e l a b e l i n c o r p o r a t e d i n t h e i r sperm. Each group o f males was t e s t e d i n b o t h s t i l l and f l o w i n g w a t e r c o n d i t i o n s b u t w i t h a d i f f e r e n t group o f f e m a l e s i n each c o n d i t i o n . The groups were as f o l l o w s : Females i n Females i n Groups o f M a l e s S t i l l w a t e r 0.08 m/sec (A) (B) ; 5 UA* 5 UA 5 UA 1 5GG 5 G 5 G 5 UA 5 UA 5 UA 5 G* 5 G 5 G 58 Groups o f Males Females i n S t i l l Water 3 5 UA* 5 G 5 UA 5 G 5 UA 5 G 5 UA 5 G* 5 UA 5GG 5 UA 5 G *Males i n j e c t e d w i t h r a d i o a c t i v e l a b e l . UA = Upper A r i p o , G = Guayamarer, Male s from Groups 1 and 2 were t e s t e d f i r s t i n s t i l l w a t e r ( w i t h Group 1A and 2A females) and t h e n i n a stream v e l o c i t y o f 0.08 m/sec ( w i t h Group IB and 2B f e m a l e s ) . I n c o n t r a s t , males from Groups 3 and 4 were t e s t e d f i r s t i n f l o w i n g w a t e r and t h e n i n s t i l l w a t e r . F o l l o w i n g each t e s t the f e m a l e s were k i l l e d and sampled f o r sperm. The same 20 males from each p o p u l a t i o n were t e s t e d i n b o t h s t i l l and f l o w i n g w a t e r , whereas, 40 f e m a l e s from each p o p u l a t i o n were t e s t e d b u t h a l f i n s t i l l w a t e r o n l y and h a l f i n f l o w i n g w a t e r o n l y . The 0.08 m/sec v e l o c i t y was chosen, assuming i t t o r e p r e s e n t a f a i r l y f a s t v e l o c i t y c o n s i d e r i n g t h a t f i s h were to be m a i n t a i n e d i n i t f o r a f u l l week. (The second s l o w e s t v e l o c i t y i n E x p e r i m e n t I (0 .07 m/sec) had o n l y a s l i g h t e f f e c t on c o u r t s h i p b e h a v i o u r , however, f i s h were m a i n t a i n e d i n i t f o r l e s s t h a n a d u r i n g the experiment.) Males f o r each group were drawn from p o p u l a t i o n t a n k s 25 days b e f o r e t e s t i n g and p l a c e d i n i s o l a t e d h o l d i n g t a n k s w i t h d o m e s t i c s t i m u l u s f e m a l e s . These males were i n j e c t e d w i t h t h y m i d i n e - ( m e t h y l - C) 25, 20, and 10 days b e f o r e t e s t i n g . C o n t r o l males were i n j e c t e d w i t h s a l i n e . The s t i m u l u s f e males were removed from the h o l d i n g t a n k s f i v e days b e f o r e t e s t i n g , 59 e n s u r i n g the s t a r t o f c o u r t s h i p b e h a v i o u r by the males soon a f t e r i n t r o d u c t i o n t o the st r e a m t a n k s . A t the end o f the f i r s t t e s t the males were r e t u r n e d t o i s o l a t e d h o l d i n g t a n k s . L a t e r t hey were i n t r o d u c e d t o a second stream tank under the a l t e r n a t e s t r e a m c o n d i t i o n , w i t h the second group o f f e m a l e s . A f t e r t h i s second t e s t the males were k i l l e d . Females f o r each group were drawn from the p o p u l a t i o n t a n k s a p p r o x i m a t e l y 25 days b e f o r e t e s t i n g and p l a c e d d i r e c t l y i n the stream t a n k s . F i v e t o c e i g h t days b e f o r e t e s t i n g , the females were marked w i t h a s m a l l . d o t on the top o r bottom o f t h e i r t a i l s t o d i s t i n g u i s h them by p o p u l a t i o n . The d o t was made by i n t r a m u s c u l a r i n j e c t i o n w i t h i n d e l i b l e Trypan b l u e i n k . The fe m a l e s were t h e n r e t u r n e d t o the stream t a n k which was s e t a t the v e l o c i t y t o be used d u r i n g the t e s t . The t e s t began when the f e m a l e s r e c o v e r e d from the ma r k i n g p r o c e d u r e ( 5 t o 8 d a y s ) . A t the end o f each t e s t f e m ales were k i l l e d and o v i d u c t samples f o r sperm were t a k e n . Each t e s t l a s t e d one week, d u r i n g which time the group o f 20 f i s h (eg. Group IA) was housed i n the stream tank. The v e l o c i t y was k e p t c o n s t a n t , a t e i t h e r 0 . 0 8 m/sec o r w i t h no c u r r e n t , f o r the e n t i r e seven days. Theysecond t e s t f o r each group o f males ( e g . Group IB, a t the second v e l o c i t y ) o c c u r r e d 5 t o 8 days a f t e r t he end o f the f i r s t t e s t . On days 1 , 3 i 5» and 7 o f each t e s t , two 1 0-min r e c o r d i n g s were made f o r each o f - t h e group's 10 males. On each o f these days one r e c o r d i n g was made i n the morning and one i n the a f t e r n o o n . Thus a t o t a l o f e i g h t 10-min r e c o r d i n g s was made f o r each male. M a l e s were d i s t i n g u i s h e d from one a n o t h e r by t h e i r i n d i v i d u a l c o l o u r p a t t e r n s . . E ach r e c o r d i n g c o n t a i n e d the number o f s i g m o i d d i s p l a y s , g o n o p o d i a l swings, s i d e -s w i t c h e s , leaps,- and ...copulation a t t e m p t s performed, by the male. ( S i d e - s w i t c h e s have n o t p r e v i o u s l y been d e s c r i b e d . They o c c u r d u r i n g s i g m o i d d i s p l a y s when the male, w h i l e d i s p l a y i n g , s w i t c h e s the s i d e o f h i s body w h i c h f a c e s the f e m a l e . T h i s i s b r o u g h t about by a r a p i d t u r n i n the h o r i z o n t a l p l a n e , head t o t a i l , f o l l o w i n g w h i c h the s i g m o i d d i s p l a y c o n t i n u e s . ) F o r each b e h a v i o u r p a t t e r n performed by a male the p o p u l a t i o n t o w h i c h the female he c o u r t e d b e l o n g e d was a l s o r e c o r d e d . Mate p r e f e r e n c e o f males and the number and l e n g t h o f c o u r t s h i p b o u t s c o u l d t h e r e f o r e be de t e r m i n e d . T h i s e x p e r i m e n t a l p r o c e d u r e was r e p e a t e d u s i n g Caparo and P a r i a f i s h , however, the males were n o t i n j e c t e d w i t h r a d i o a c t i v e l a b e l . Thus, i n t o t a l , the procedure produced e i g h t 10-min r e c o r d i n g s f o r 20 males from each o f the f o u r p o p u l a t i o n s i n each o f two stream v e l o c i t y c o n d i t i o n s . O c c a s i o n a l l y d u r i n g the expe r i m e n t a f i s h d i e d o r became " s i c k " . I f so, i t was r e p l a c e d w i t h a n o t h e r f i s h and e l i m i n a t e d from the d a t a a n a l y s i s . F o l l o w i n g the experiment each,group o f males was a n a e s t h e t i z e d , measured w i t h c a l i p e r s , p h o t o -graphed and had a sperm smear t a k e n . S t a t i s t i c a l Treatment o f the Dat a When comparing the same s t o c k under the two stream c o n d i t i o n s and when d e t e r m i n i n g male mate p r e f e r e n c e f o r f e m a l e s , I used the W i l c o x o n m a t c h e d - p a i r s s i g n e d - r a n k s t e s t ( S i e g e l , 1956). When comparing d i f f e r e n t s t o c k s under the same s t r e a m . c o n d i t i o n s , the Mann-Whitney U - t e s t was used ( S i e g e l , 1956). C o r r e l a t i o n s between the s i z e o f males and v a r i o u s c o u r t s h i p b e h a v i o u r p a t t e r n s (see Appendix) were measured u s i n g the Spearman r a n k c o r r e l a t i o n c o e f f i c i e n t ( S i e g e l , 1956). R e s u l t s and D i s c u s s i o n T h r u s t s and Si g m o i d D i s p l a y s The mean numbers o f t h r u s t s performed by males i n the two stream c o n d i t i o n s are g i v e n i n F i g u r e 10. A l l f o u r s t o c k s p erformed more t h r u s t s i n the 0.08 m/sec v e l o c i t y compared t o s t i l l w a t e r . The i n c r e a s e s , however, were n o t s i g n i f i c a n t (p < .05 , W i l c o x o n t e s t ) . Comparing each p a i r o f l o w l a n d and headstream s t o c k s (Caparo w i t h P a r i a ; Guayamare w i t h Upper A r i p o ) , l o w l a n d f i s h u s u a l l y performed more t h r u s t s t h a n headstream f i s h and i n s t i l l w a t e r the d i f f e r e n c e between Guayamare and Upper A r i p o males was s i g n i f i c a n t ( F i g . 10) . The mean numbers o f s i g m o i d d i s p l a y s performed by each s t o c k i n the two stream c o n d i t i o n s are g i v e n i n F i g u r e 11. The s t o c k s performed e i t h e r a p p r o x i m a t e l y the same o r a dec r e a s e d number o f s i g m o i d d i s p l a y s i n f l o w i n g w a t e r . The decrease was s i g n i f i c a n t o n l y f o r the P a r i a s t o c k (p<c . 0 5 , W i l c o x o n t e s t ) . As p r e d i c t e d , under b o t h stream c o n d i t i o n s l o w l a n d males performed s i g n i f i c a n t l y f ewer s i g m o i d d i s p l a y s t h a n headstream males ( F i g . 11) . 20 4 N.S. MEAN NUMBER OF THRUSTS. PER MALE PER 40 MINS 15J 1 0 1 5 J N.S. p < .025 G UA N.S. . 00 ~ToE Stream v e l o c i t y (m/sec) G UA F i g u r e 10. Number o f t h r u s t s i n r e l a t i o n t o stream v e l o c i t y . Means i t 9 5 % c o n f i d e n c e i n t e r v a l s . P r o b a b i l i t y v a l u e s are from the Mann-Whitney U - t e s t , 1 - t a i l e d f o r C > P, G > UA. C = Caparo (N(.OO) = 19; N(.08) = 17)., P = P a r i a (N(.OO) = 20; N(.08) = 19), G = Guayamare (N(.OO) = 17; N(.08) = 1 7 ) , UA = Upper A r i p o (N(.OO) = 19; N(.08) = 17). 120 A MEAN NUMBER OF SIGMOID DISPLAYS ? PER MALE PER 40 MINS 90 J 60 4 ?3<H p < . 001 p < . 0 0 1 p < . 001 P < . o i I 90 UA UA 120 6o r 30 .00 . 0 8 Stream v e l o c i t y (m/sec) F i g u r e 11 . Number o f s i g m o i d d i s p l a y s i n r e l a t i o n t o stream v e l o c i t y . Means ±95% c o n f i d e n c e i n t e r v a l s . P r o b a b i l i t y v a l u e s are from the Mann-Whitney U - t e s t , 1 - t a i l e d f o r P ;> C, UA > G. C = Caparo, P = P a r i a , G = Guayamare, UA = Upper A r i p o . ON A l l f o u r s t o c k s had a l o w e r r a t i o o f s i g m o i d d i s p l a y s : t h r u s t s i n f l o w i n g w a t e r t h a n i n s t i l l w a t e r ( F i g . 1 2 ) ..This d i f f e r e n c e i n r a t i o was s i g n i f i c a n t f o r the P a r i a and Upper A r i p o s t o c k s (p<>05, W i l c o x o n t e s t ) . Comparisons between each p a i r o f s t o c k s showed t h a t , as p r e d i c t e d , the headstream s t o c k s had s i g n i f i c a n t l y h i g h e r r a t i o s o f s i g m o i d d i s p l a y s : t h r u s t s t h a n the l o w l a n d s t o c k s i n b o t h stream c o n d i t i o n s ( F i g . 12). These d i f f e r e n c e s are a l s o c o n s i s t e n t w i t h those f o u n d i n E x p e r i m e n t I . I n summary, d i f f e r e n c e s between these w i l d - c a u g h t p o p u l a t i o n s i n the f r e q u e n c i e s o f b o t h t h r u s t s and s i g m o i d d i s p l a y s and the r a t i o o f s i g m o i d d i s p l a y s : t h r u s t s are c o n s i s t e n t w i t h d i f f e r e n c e s found between Caparo and P a r i a s t o c k s i n E x p e r i m e n t I . I n b o t h e x p e r i m e n t s l o w l a n d f i s h p e rformed fewer s i g m o i d d i s p l a y s and more t h r u s t s t h a n the headstream f i s h . However, the marked e f f e c t s o f i n c r e a s i n g stream v e l o c i t y f o u n d i n E x p e r i m e n t I were n o t found between the two stream c o n d i t i o n s h e r e . There was no s u p p o r t f o r the p r e d i c t i o n t h a t headstream f i s h are b e t t e r a b l e t o m a i n t a i n d i s p l a y s i n f a s t e r - f l o w i n g w a t e r t h a n l o w l a n d f i s h . Comparing the r a t i o o f s i g m o i d d i s p l a y s : t h r u s t s f o r each s t o c k i n s t i l l w a t e r and a t 0.08 m/sec, the r a t i o d e c r e a s e d between the two' c o n d i t i o n s by 30% f o r Caparo, 29% f o r P a r i a , 3% f o r Guayamare, and 30% f o r Upper A r i p o ( F i g . 12). Thus the l o w l a n d p o p u l a t i o n s ' r a t i o s d e c r e a s e d by the same amount o r l e s s t h a n the headstream r a t i o s . I t s h o u l d be n o t e d , however, t h a t headstream males s t i l l used d i s p l a y s s i g n i f i c a n t l y more f r e q u e n t l y t h a n l o w l a n d 16, 1 4 J P <.ooi •16 .14 RA1I0 OF SIGMOID DISPLAYS : THRUSTS 12 10 8 6 4 P<«01 p <.001 p< . 0 5 "12: "10 •'8 6 L4 G UA G PJA .00 .08 Stream v e l o c i t y (m/sec) F i g u r e 12. R a t i o o f s i g m o i d d i s p l a y s : t h r u s t s i n r e l a t i o n t o stream v e l o c i t y . ' P r o b a b i l i t y v a l u e s are from the Mann-Whitney U t e s t , 1 - . t a i l e d f o r C < P, G < U A . C = Caparo, P = P a r i a , G = Guayamare, UA = Upper A r i p o . 66 males and the headstream r a t i o s o f s i g m o i d d i s p l a y s : t h r u s t s were s i g n i f i c a n t l y h i g h e r i n b o t h stream c o n d i t i o n s . The p r e d i c t i o n t h a t headstream- f i s h are b e t t e r a b l e t o m a i n t a i n c o u r t s h i p i n f a s t - f l o w i n g w a t e r t h a n l o w l a n d f i s h was n o t supported^ l i k e l y because o f the r e l a t i v e l y slow stream v e l o c i t y used d u r i n g the ex p e r i m e n t . U n l i k e E x p e r i m e n t I , the e f f e c t o f a f a s t v e l o c i t y was n o t a c t u a l l y t e s t e d . D i f f e r e n c e s i n the f r e q u e n c i e s o f t h r u s t s and s i g m o i d d i s p l a y s i n E x p e r i m e n t I between 0.03 m/sec and 0.07 m/sec (the.two s l o w e s t v e l o c i t i e s ; F i g s . 6 and 7) are a c t u a l l y c o n s i s t e n t w i t h the r e s u l t s o b t a i n e d i n t h i s e x p e r i m e n t between s t i l l w a t e r (0.00 m/sec) and 0.08 m/sec. I n b o t h e x p e r i m e n t s t h r u s t s i n c r e a s e d s l i g h t l y and s i g m o i d d i s p l a y s u s u a l l y d i d n o t change s i g n i f i c a n t l y . Only a t the h i g h e r v e l o c i t i e s i n E x p e r i m e n t I were the e f f e c t s o f i n c r e a s i n g stream v e l o c i t y e v i d e n t . The r e s u l t s o f the two e x p e r i m e n t s , however, cannot be compared d i r e c t l y because t h e y t e s t e d f i s h f o r d i f f e r e n t p e r i o d s o f t i m e . I n a d d i t i o n , E x p e r i m e n t I I examined f i s h i n s t i l l w a t e r (0.00 m/sec) wh i c h r e p r e s e n t s a c o n d i t i o n v e r y d i f f e r e n t from t h a t o f f l o w i n g w a t e r , even of a slow v e l o c i t y , s i n c e f i s h .doynot o r i e n t a t e upstream and malespmay show h i g h e r t h a n normal r a t e s o f c o u r t s h i p , I n s t i l l w a t e r males may o r i e n t a t e t o females a^dvn court' I them from any d i r e c t i o n . As p r e v i o u s l y , n o t e d , I chose the 0.08 m/sec v e l o c i t y f o r t h i s e x p e r i m e n t b e l i e v i n g i t t o be a r e a s o n a b l y f a s t v e l o c i t y s i n c e f i s h were t o be m a i n t a i n e d i n i t f o r a f u l l week. I had assumed t h a t a s l o w e r v e l o c i t y t h a n the f a s t e r v e l o c i t i e s o f E x p e r i m e n t I s h o u l d he used, s i n c e i n E x p e r i m e n t I f i s h were m a i n t a i n e d i n the v e l o c i t y f o r o n l y one day. The r e s u l t s o b t a i n e d here c o n t r a d i c t t h i s a s s u m p t i o n , s i n c e the e f f e c t s o f a f a s t stream v e l o c i t y were n o t o b t a i n e d . T h i s was a l s o perhaps due t o the use o f w i l d - c a u g h t g u p p i e s d u r i n g t h i s e x p e r i m e n t . These g u p p i e s had p r e v i o u s l ' e x p e r i e n c e i n streams and would t h e r e f o r e l i k e l y be l i t t l e a f f e c t e d by a slow v e l o c i t y . G o n o p o d i a l Swings The mean numbers o f g o n o p o d i a l swings performed by each s t o c k i n the two stream c o n d i t i o n s are g i v e n i n F i g u r e 13. A l l f o u r s t o c k s performed s l i g h t l y fewer g o n o p o d i a l swings i n the f l o w i n g w a t e r c o n d i t i o n , t h i s d i f f e r e n c e was s i g n i f i c a n t o n l y f o r the Caparo s t o c k (p<.01, W i l c o x o n t e s t ) . Comparing s t o c k s , l o w l a n d males g e n e r a l l y performed more g o n o p o d i a l swings t h a n headstream males and the d i f f e r e n c e s were s i g n i f i c a n t between Guayamare and Upper A r i p o males i n b o t h stream c o n d i t i o n s ( F i g . 1 3 ) . These d i f f e r e n c e s are c o n s i s t e n t w i t h the d i f f e r e n c e s between Caparo and P a r i a s t o c k s i n E x p e r i m e n t I . ( C o r r e l a t i o n s between male s i z e and s i g m o i d d i s p l a y s , t h r u s t s and g o n o p o d i a l swings are p r e s e n t e d f o r t h i s e x p e r i m e n t i n the Appendix.) 4-0 MEAN NUMBER OF GONOPODIAL SWINGS PER MALE PER 40 MINS 30 A 20 10 p <.001 N.S. G fcJA p <.025 N.S. KJA h4o .30 20 10 . 00 .08 Stream v e l o c i t y (m/sec) F i g u r e 13. Number o f g o n o p o d i a l swings i n r e l a t i o n t o stream v e l o c i t y . Means ± 95% c o n f i f e n c e i n t e r v a l s . P r o b a b i l i t y v a l u e s are from the Mann-Whitney U - t e s t , 1 - t a i l e d f o r C > P, G^>UA. C = Caparo, P = P a r i a , G = Guayamare, UA = Upper A r i p o . 69 S i d e - s w i t c h e s , Leaps," C o p u l a t i o n A t t e m p t s , and C o p u l a t i o n s Table X I I g i v e s the mean numbers o f s i g m o i d d i s p l a y Y' s i d e - s w i t c h e s , l e a p s , and c o p u l a t i o n a t t e m p t s performed by males o f each s t o c k i n the two stream c o n d i t i o n s . I t a l s o g i v e s the p e r c e n t a g e s o f s i g m o i d d i s p l a y s d u r i n g w h i c h s i d e -switch.es were performed and the p e r c e n t a g e s o f s i g m o i d d i s p l a y s f o l l o w e d by l e a p s and c o p u l a t i o n a t t e m p t s . These b e h a v i o u r p a t t e r n s o c c u r r e d i n f r e q u e n t l y and were t h e r e f o r e n o t a n a l y z e d s t a t i s t i c a l l y . A decrease was g e n e r a l l y seen i n the f r e q u e n c i e s o f l e a p s and c o p u l a t i o n a t t e m p t s p e r formed i n f l o w i n g w a t e r r e l a t i v e t o t h e i r f r e q u e n c y i n s t i l l w a t e r . Only s i x c o p u l a t i o n s were obser v e d d u r i n g the e x p e r i m e n t . W h i l e i n s t i l l w a t e r t h r e e Upper A r i p o f e m a l e s were r e c e p t i v e : two t o Upper A r i p o males and one t o a Guayamare male, one P a r i a female was r e c e p t i v e t o a Caparo male, and one Guayamare female was r e c e p t i v e t o an Upper A r i p o male. I n the 0.08 m/sec v e l o c i t y one c o p u l a t i o n was o b s e r v e d and i t was between a P a r i a male and f e m a l e . T h i s s m a l l number of c o p u l a t i o n s a t l e a s t i n d i c a t e s t h a t f e m a l e s w i l l mate w i t h males from b o t h l o w l a n d and headstream p o p u l a t i o n s r e g a r d l e s s o f t h e i r own p o p u l a t i o n o f o r i g i n . D i r e c t o b s e r v a t i o n s o f c o p u l a t i o n s however were too i n f r e q u e n t t o draw f u r t h e r c o n c l u s i o n s r e g a r d i n g s e x u a l s e l e c t i o n by f e m a l e s . 70 T a b l e X I I . Mean number and percentage o f S i g m o i d D i s p l a y s w i t h o r f o l l o w e d by S i d e - s w i t c h e s , Leaps, and C o p u l a t i o n A t t e m p t s f o r males from f o u r s t o c k s i n two stream c o n d i t i o n s . Caparo P a r i a Guayamare Upper A r i p o Caparo P a r i a Guayamare Upper A r i p o Mean number o f Si g m o i d D i s p l a y S i d e - s w i t c h e s / male / 40 mins Stream v e l o c i t y (m/ sec) P e r c e n t a g e o f S i g m o i d D i s p l a y s w i t h S i d e - s w i t c h e s Stream v e l o c i t y (m/sec) .00 .08 .00 .08 1.4 2.0 1.8 0.8 0.3 1.3 2.0 1.2 4.0 2.1 3.4 1.1 0.9 1.7 3.8 1.6 fie;an number o f Leaps / male / 40 mins Stream v e l o c i t y (m/sec) P e r c e n t a g e o f D i s p l a y s F o l l o w e d by Leaps Stream v e l o c i t y (m/sec) .00 .08 .00 .08 0.9 0 . 6 2 .6 2.0 1.0 0 . 4 1.1 0.5 2.2 1.-5 4.2 2.8 3.1 2.2 4.0 2.9 Mean number o f C o p u l a t i o n A t t e m p t s / male / 40 mins P e r c e n t a g e o f S i g m o i d D i s p l a y s f o l l o w e d by C o p u l a t i o n A t t e m p t s Stream v e l o c i t y (m/sec) .00 .08 Stream v e l o c i t y (m/sec) .00 .08 Caparo P a r i a Guayamare Upper A r i p o 0.1 0.3 0.4 0.3 o.o 0.2 0.2 o.'3 0.3 0.3 0.8 0.3 o.o 0.2 0.4 0.4 7 1 C o u r t s h i p Bouts and the Number of B e h a v i o u r P a t t e r n s p e r  C o u r t s h i p Bout T a b l e X I I I g i v e s the mean number o f c o u r t s h i p b o u t s performed by males o f each p o p u l a t i o n i n the two stream c o n d i t i o n s . As p r e d i c t e d , males from the headstream s t o c k s performed more c o u r t s h i p b o u t s t h a n l o w l a n d males. The d i f f e r e n c e s were s i g n i f i c a n t between P a r i a and Caparo i n b o t h stream c o n d i t i o n s . Headstream males may have e v o l v e d a tendency t o p e r f o r m more c o u r t s h i p b o u t s i n o r d e r t o m a i n t a i n an o p t i m a l number o f c o u r t s h i p b o u t s i n f a s t - f l o w i n g w a t e r . Comparing each p o p u l a t i o n w i t h i t s e l f i n the two stream c o n d i t i o n s , no s i g n i f i c a n t d i f f e r e n c e s were found i n the number o f c o u r t s h i p b o u t s performed ( T a b l e X I I I ; W i l c o x o n t e s t ) . T h e r e f o r e , i n c o n t r a s t t o e x p e c t a t i o n , an i n c r e a s e i n stream v e l o c i t y d i d n o t decrease the number o f c o u r t s h i p b o u t s performed. E i t h e r my h y p o t h e s i s was wrong o r the stream v e l o c i t y used was n o t f a s t enough t o d e t e c t the e f f e c t o f stream v e l o c i t y on the f r e q u e n c y o f c o u r t s h i p b o u t s . The p r o p o r t i o n o f c o u r t s h i p b o u t s w i t h one, two, and t h r e e o r more s i g m o i d d i s p l a y s and t h r u s t s i s shown i n F i g u r e 14. Headstream males d i d n o t d i f f e r from l o w l a n d males i n the number o f b e h a v i o u r p a t t e r n s performed t o f e m a l e s d u r i n g i n d i v i d u a l c o u r t s h i p b o u t s . I n f a c t , b o t h c l a s s e s o f f i s h p e r f o r med r e m a r k a b l y s i m i l a r p r o p o r t i o n s o f b o u t s comprised o f one, two, and t h r e e o r more c o u r t s h i p b e h a v i o u r p a t t e r n s . T h i s r e s u l t " l e a d s me t o s p e c u l a t e t h a t , once a male b e g i n s c o u r t i n g a f e m a l e , t h e r e i s an o p t i m a l number o f s i g m o i d d i s p l a y s and t h r u s t s f o r w h i c h i t i s advantageous f o r the 72 T a b l e X I I I . Mean number o f c o u r t s h i p b o u t s p e r male f o r each s t o c k i n two stream c o n d i t i o n s . Caparo P a r i a Stream v e l o c i t y (m/sec) . 00 3 2 . 9 7 8 . 0 Mean number o f c o u r t s h i p b o u t s * p e r male p e r 40 mins D i f f e r e n c e * * between s t o c k s P < . Q 2 £ Stream v e l o c i t y (m/sec) . 0 8 3 2 . 5 6 4 . 7 D i f f e r e n c e * * between s t o c k s P <OQ2'5 Guayamare 4 6 . 7 Upper A r i p o 5 4 . 9 N.S. 4 9 . 1 5 2 . 5 N.S. *A c o u r t s h i p bout i s d e f i n e d as a s e r i e s o f c o n s e c u t i v e s i g m o i d d i s p l a y s and/or t h r u s t s p erformed by a male t o the same fe m a l e . **Mann-Whitney U - t e s t , 1 - t a i l e d f o r P > C, U A > G. PROPORTION OF COURTSHIP BOUTS IN PERCENT 80 -70 -60 50 40' 30 G G UA 20' 10 i 1 2 3+ 1 2 3+ 123+ 1 2 3+ 1 2 3+ 1 2 3+ 1 2 3+ 1 2 3+ .00 .08 Stream v e l o c i t y (m/sec) NUMBER OF BEHAVIOUR PATTERNS PER BOUT F i g u r e 14. P r o p o r t i o n o f c o u r t s h i p b o u t s w i t h one, two, and t h r e e o r more b e h a v i o u r p a t t e r n s p e r c o u r t s h i p b o u t . C = Caparo, P = P a r i a , G = Guayamare, UA = Upper A r i p o . male t o p e r f o r m . Perhaps males do n o t i n c r e a s e t h e i r chance o f m a t i n g s u c c e s s by p e r f o r m i n g more "faehaviour p a t t e r n s t o the same female d u r i n g a c o u r t s h i p bout. I t may be o f g r e a t e r advantage t o l e a v e the female a f t e r one o r two d i s p l a y s o r t h r u s t s and seek out a n o t h e r f e m a l e . F o r each s t o c k the p r o p o r t i o n s o f c o u r t s h i p b o u t s w i t h one, two, and t h r e e o r more b e h a v i o u r p a t t e r n s were ve.ryy s i m i l a r under b o t h c o n d i t i o n s ( F i g . 14). Stream v e l o c i t y d i d n o t a f f e c t the number o f b e h a v i o u r p a t t e r n s performed d u r i n g c o u r t s h i p b o u t s . Mate P r e f e r e n c e o f M a l e s M a l e s from b o t h headstream p o p u l a t i o n s e x h i b i t e d a p r e f e r e n c e f o r f e m a l e s o f t h e i r own s t o c k , c o n s i s t e n t l y p e r f o r m i n g more s i g m o i d d i s p l a y s and t h r u s t s t o headstream f e m a l e s i n b o t h stream c o n d i t i o n s ( T a b l e X I V ) . M a l e s from the two l o w l a n d s t o c k s , however, v a r i e d i n t h e i r mate p r e f e r e n c e . Caparo males e x h i b i t e d a s i g n i f i c a n t p r e f e r e n c e f o r fe m a l e s o f t h e i r own s t o c k when obser v e d i n f l o w i n g w a t e r , whereas Guayamare m a l e s . c o u r t e d headstream females more t h a n f e m a l e s from t h e i r own s t o c k . Mate p r e f e r e n c e s were g e n e r a l l y s i m i l a r i n b o t h s t i l l and f l o w i n g w a t e r c o n d i t i o n s . I t has o f t e n been assumed t h a t male g u p p i e s are v e r y promiscuous, c o u r t i n g a l l f e m a l e s r e g a r d l e s s o f s t o c k , and t h a t s e x u a l s e l e c t i o n i s e x e r c i s e d o n l y by females ( H a s k i n s e t a l . , 1 9 6 l s F a r r , 1 9 7 6 , 1 9 7 7 ; and E n d l e r , I 98O). I n t h i s e x periment t h r e e o f the f o u r p o p u l a t i o n s e x h i b i t e d a p r e f e r e n c e f o r fe m a l e s o f t h e i r own p o p u l a t i o n , as p r e d i c t e d . They d i d n o t 75 T a b l e XIV. P e r c e n t a g e o f s i g m o i d d i s p l a y s and t h r u s t s p erformed by males t o f e m a l e s o f t h e i r own o r a n o t h e r s t o c k . Males P e r c e n t a g e o f t o t a l P e r c e n t a g e o f t o t a l Females s i g m o i d d i s p l a y s t h r u s t s C o u r t e d -, Stream v e l o c i t y Stream v e l o c i t y (m/sec) (m/sec) .00 .08 .00 .08 Caparo Caparo P a r i a 48 . 8 51.2 65.0** 35-0 49.7 50.3 68.9** 31.1 P a r i a C aparo P a r i a 37.8 62.2** 48 . 1 51.9 30.1 69.9** 40.7 59.3* Guayamare Guayamare U. A r i p o 41 . 0 59.0 42 . 1 57-9 49.0 51.0 39.0 61.0 U. A r i p o Guayamare U. A r i p o 41 . 6 58.4 43.0 57-0 46 . 0 54.0 34.3 65.7* p <.0:25 W i l c o x o n t e s t , o n e - t a i l e d f o r a p r e f e r e n c e P <• 005 f o r fe m a l e s from the same p o p u l a t i o n as males (based on raw d a t a and n o t the p e r c e n t a g e s shown). s i m p l y c o u r t f e m a l e s randomly. The r e a s o n s f o r the mate p r e f e r e n c e s e x h i b i t e d by the p o p u l a t i o n s o f males are n o t e n t i r e l y c l e a r . Male p r e f e r e n c e f o r f e m a l e s may, a t l e a s t i n p a r t , be i n f l u e n c e d by female r e s p o n s e s t o male c o u r t s h i p . I f t h i s i s the c a s e , t h e n male mate p r e f e r e n c e s may a c t u a l l y r e f l e c t female s e l e c t i o n o f males. Whether t h i s i s the case o r n o t , the r e s u l t s i n d i c a t e some i n t e r - p o p u l a t i o n d i s c r i m i n a t i o n and t h i s may r e s t r i c t i n t e r - p o p u l a t i o n b r e e d i n g . The p r e f e r e n c e s may t h e r e f o r e r e p r e s e n t p a r t i a l i s o l a t i n g mechanisms between p o p u l a t i o n s . The f a c t t h a t males e x e r c i s e a c h o i c e i n t h e i r c o u r t s h i p does n o t n e c e s s a r i l y a l t e r the r o l e t h a t females p l a y i n s e x u a l s e l e c t i o n , e s p e c i a l l y s i n c e female c o o p e r a t i o n i s c r i t i c a l f o r s u c c e s s f u l c o p u l a t i o n ( L i l e y , I966). D u r i n g the e x p e r i m e n t , even when males e x h i b i t e d a p r e f e r e n c e f o r one s t o c k o f f e m a l e s they s t i l l d i r e c t e d a t l e a s t 30% o f t h e i r c o u r t s h i p towards f e m a l e s o f the a l t e r n a t e s t o c k . T h e r e f o r e s e x u a l s e l e c t i o n c o u l d s t i l l be e x e r c i s e d by f e m a l e s . The r e s u l t s o f t h i s e x periment do,lihowever, i n d i c a t e t h a t s e x u a l s e l e c t i o n i n P. r e t i c u l a t a i s n o t n e c e s s a r i l y e n t i r e l y c o n t r o l l e d by female c h o i c e and i n t e r - m a l e c o m p e t i t i o n . F u t u r e s t u d i e s on i n t e r - p o p u l a t i o n s e x u a l s e l e c t i o n i n the guppy s h o u l d examine b o t h male and female mate p r e f e r e n c e s . 77 Summary o f R e s u l t s P o p u l a t i o n d i f f e r e n c e s i n the f r e q u e n c i e s o f c o u r t s h i p "behaviour p a t t e r n s between w i l d - c a u g h t headstream and l o w l a n d f i s h were c o n s i s t e n t w i t h d i f f e r e n c e s found between the Caparo ( l o w l a n d ) and P a r i a (headstream) s t o c k s t e s t e d i n E x p e r i m e n t I . Lowland males were a g a i n found t o use fewer s i g m o i d d i s p l a y s and more t h r u s t s and g o n o p o d i a l swings t h a n headstream males. S i n c e b o t h p a i r s o f p o p u l a t i o n s showed r e s u l t s c o n s i s t e n t w i t h those o b t a i n e d p r e v i o u s l y i t seems r e a s o n a b l e t o suggest t h a t the d i f f e r e n c e s o b s e r v e d are r e p r e s e n t a t i v e o f headstream and l o w l a n d p o p u l a t i o n s i n g e n e r a l . The e f f e c t o f stream v e l o c i t y on male c o u r t s h i p b e h a v i o u r c l e a r l y demonstrated i n E x p e r i m e n t I was much l e s s pronounced i n t h i s e x p e r i m e n t . A l t h o u g h the f r e q u e n c i e s o f s i g m o i d d i s p l a y s and g o n o p o d i a l swings g e n e r a l l y d e c r e a s e d s l i g h t l y i n f l o w i n g w a t e r compared t o s t i l l w a t e r , i n most cases the d e c r e a s e s were n o t s i g n i f i c a n t . Lowland males d i d n o t show t h e p r e d i c t e d g r e a t e r decrease i n t h e i r c o u r t s h i p b e h a v i o u r t h a n headstream males. T h i s i s b e l i e v e d t o be due t o the slow s t r e a m v e l o c i t y used d u r i n g t h i s e x periment and the f a c t t h a t w i l d - c a u g h t g u p p i e s were t e s t e d . As p r e d i c t e d , headstream males performed more c o u r t s h i p b o u t s t h a n l o w l a n d males and t h i s may r e p r e s e n t an a d a p t a t i o n t o stream v e l o c i t y . A l l p o p u l a t i o n s performed r o u g h l y the same number o f b e h a v i o u r p a t t e r n s d u r i n g c o u r t s h i p b o u t s , s u g g e s t i n g t h a t males may p e r f o r m an o p t i m a l number o f s i g m o i d d i s p l a y s and t h r u s t s t o i n d i v i d u a l f e m a l e s b e f o r e l e a v i n g the female and c o u r t i n g a n o t h e r one. Three o f the f o u r p o p u l a t i o n s e x h i b i t e d a mate p r e f e r e n c e f o r f e m a l e s o f t h e i r own p o p u l a t i o n . These mate p r e f e r e n c e s may r e p r e s e n t p a r t i a l i s o l a t i n g mechanisms between p o p u l a t i o n s . 7 9 CHAPTER V I GENERAL DISCUSSION The E v o l u t i o n o f B e h a v i o u r and Morphology i n P. r e t i c u l a t a I n t h i s d i s c u s s i o n I f i r s t b r i e f l y r e v i e w the r e s u l t s o f my e x p e r i m e n t s and note t h a t t h e y p r o v i d e e v i d e n c e o f b e h a v i o u r a l a d a p t a t i o n t o stream v e l o c i t y . Then I r e v i e w the s t u d i e s done on n a t u r a l p o p u l a t i o n s o f the guppy, combining my f i n d i n g s w i t h those o f o t h e r s , t o d e v e l o p an o v e r v i e w o f the f a c t o r s w h i c h have l i k e l y a c t e d as s e l e c t i o n p r e s s u r e s t o mold the guppy's p r e s e n t morphology and b e h a v i o u r . F i n a l l y , I c o n s i d e r my r e s u l t s on male mate p r e f e r e n c e s and the p o s s i b l e f o r m a t i o n o f b e h a v i o u r a l i s o l a t i n g mechanisms. S t u d i e s o f the e c o l o g i c a l f a c t o r s t h a t are i m p o r t a n t i n the e v o l u t i o n and maintenance o f b e h a v i o u r :in a p o p u l a t i o n are becoming i n c r e a s i n g l y common (see Brown, 1 9 7 5 ; K r e b s and D a v i e s , 1 9 7 8 ; and K e e n l e y s i d e , 1 9 7 9 ) . Many o f the s t u d i e s , however, do n o t go beyond n o t i n g c o r r e l a t i o n s between b e h a v i o u r a l d i f f e r e n c e s and e n v i r o n m e n t a l f a c t o r s . I n t h i s t h e s i s , however, I went beyond n o t i n g such c o r r e l a t i o n s . My l a b o r a t o r y e x p e r i m e n t s on n a t u r a l p o p u l a t i o n s o f g u p p i e s t e s t e d seven p r e d i c t i o n s based on the h y p o t h e s i s t h a t guppy s o c i a l b e h a v i o u r , and s p e c i f i c a l l y guppy c o u r t s h i p b e h a v i o u r , i s adapted t o stream v e l o c i t y * c o n d i t i o n s . I n E x p e r i m e n t I , l o w l a n d and headstream guppy p o p u l a t i o n s showed a l l o f the p r e d i c t e d b e h a v i o u r a l d i f f e r e n c e s . F i s h b r e d from a l o w l a n d p o p u l a t i o n showed g r e a t e r c o h e s i o n , 80 l e s s a g g r e s s i v e b e h a v i o u r , and a g r e a t e r p r e f e r e n c e f o r the s u r f a c e r e g i o n o f stream t a n k s t h a n headstream f i s h . Lowland males performed fewer s i g m o i d d i s p l a y s b u t more t h r u s t s and g o n o p o d i a l swings t h a n headstream males. S i m i l a r p o p u l a t i o n d i f f e r e n c e s i n male c o u r t s h i p b e h a v i o u r were a g a i n found i n E x p e r i m e n t I I . Thus, th e s e b e h a v i o u r a l d i f f e r e n c e s are v e r y l i k e l y r e p r e s e n t a t i v e o f l o w l a n d and headstream p o p u l a t i o n s i n g e n e r a l . The p e r s i s t e n c e o f the b e h a v i o u r a l d i f f e r e n c e s i n l a b o r a t o r y r a i s e d descendants o f i s o l a t e d p o p u l a t i o n s p r o v e s a g e n e t i c c o n t r i b u t i o n t o the d i f f e r e n c e s (Ehrman and P a r s o n s , I976). Such g e n e t i c d i f f e r e n c e s are presumably the p r o d u c t o f n a t u r a l s e l e c t i o n and r e p r e s e n t e v o l u t i o n a r y a d a p t a t i o n s . The d i r e c t e f f e c t o f stream v e l o c i t y on male c o u r t s h i p b e h a v i o u r was c l e a r l y demonstrated i n E x p e r i m e n t I . F o r a l l s t o c k s o f g u p p i e s the f r e q u e n c y o f s i g m o i d d i s p l a y s and g o n o p o d i a l swings d e c r e a s e d m a r k e d l y as stream v e l o c i t y i n c r e a s e d . The b e s t e v i d e n c e o f b e h a v i o u r a l a d a p t a t i o n t o str e a m v e l o c i t y was o b t a i n e d when headstream males were found t o be b e t t e r a b l e t o m a i n t a i n t h e i r r a t i o o f s i g m o i d d i s p l a y s : t h r u s t s t h a n l o w l a n d males as stream v e l o c i t y i n c r e a s e d . I n a d d i t i o n , as p r e d i c t e d , i n f a s t e r - f l o w i n g w a t e r th.e.0.sigmoid d i s p l a y s o f headstream males were o f l o n g e r d u r a t i o n t h a n those o f l o w l a n d males. Thus, headstream males appear b e t t e r adapted t o d i s p l a y i n g i n f a s t - f l o w i n g water. The h i g h e r r a t i o o f s i g m o i d d i s p l a y s : t h r u s t s e x h i b i t e d by headstream males may i t s e l f r e p r e s e n t an a d a p t a t i o n t o stream v e l o c i t y . S i n c e s i g m o i d d i s p l a y s decrease more t h a n t h r u s t s w i t h i n c r e a s i n g stream v e l o c i t y , males l i v i n g i n f a s t - f l o w i n g w a t e r may have e v o l v e d the tendency t o p e r f o r m a h i g h e r r a t i o o f s i g m o i d d i s p l a y s : t h r u s t s (when obse r v e d i n s l ow water) i n o r d e r t o s t i l l be p e r f o r m i n g a t an o p t i m a l r a t i o when i n f a s t - f l o w i n g w a t e r . A l t h o u g h d i f f e r e n c e s i n the f r e q u e n c y o f p e r f o r m i n g c o u r t s h i p b e h a v i o u r p a t t e r n s between p o p u l a t i o n s were the same i n b o t h e x p e r i m e n t s , the d i r e c t e f f e c t o f stream v e l o c i t y on male c o u r t s h i p b e h a v i o u r was l e s s pronounced i n E x p e r i m e n t I I . T h i s was l i k e l y due t o the sl o w st r e a m v e l o c i t y u sed d u r i n g t h i s e x p e r i m e n t . Stream v e l o c i t y was found t o d i r e c t l y a f f e c t guppy depth l o c a t i o n i n E x p e r i m e n t I . I n c r e a s i n g v e l o c i t y produced a decrease i n the time spent a t the top o f the stream t a n k by l o w l a n d f i s h . F i s h from the i n t e r m e d i a t e v e l o c i t y s p r i n g p o p u l a t i o n , however, were b e t t e r a b l e t o m a i n t a i n t h e i r p o s i t i o n a t the top o f the stream t a n k t h a n l o w l a n d f i s h . T h i s r e s u l t l i k e l y i n d i c a t e s a n o t h e r a d a p t a t i o n t o stream v e l o c i t y . I n a d d i t i o n , headstream f i s h showed a p r e f e r e n c e f o r the bottom o f the stream i n a l l v e l o c i t i e s and I suggest t h e y e v o l v e d t h i s p r e f e r e n c e i n o r d e r t o h o l d t h e i r p o s i t i o n i n f a s t - f l o w i n g w a t e r and make use o f the d e c e l e r a t i o n o o f w a t e r c l o s e t o the s u b s t r a t e . D i f f e r e n c e s between p o p u l a t i o n s o f g u p p i e s i n b o t h male c o u r t s h i p and depth l o c a t i o n appear t o r e f l e c t a d a p t a t i o n s to d i f f e r e n t stream v e l o c i t i e s . T h i s , however, does n o t mean t h a t o t h e r e n v i r o n m e n t a l f a c t o r s d i d n o t a l s o p l a y a r o l e i n s h a p i n g t h e s e b e h a v i o u r s . I n f a c t , i t i s o f t e n wrong t o s e a r c h 82 f o r a s i n g l e b i o l o g i c a l f u n c t i o n o r a d a p t a t i o n o f a p i e c e o f b e h a v i o u r o r morphology. I agree w i t h L i l e y and Seghers (1975) t h a t a f u l l assessment o f the e v o l u t i o n a r y s i g n i f i c a n c e o f n a t u r a l v a r i a t i o n i n the guppy r e q u i r e s c o n s i d e r a t i o n o f many f e a t u r e s o f the environment. B o t h p h y s i c a l and b i o t i c s e l e c t i o n p r e s s u r e s h a v e e l i k e l y a f f e c t e d the morphology and b e h a v i o u r o f gu p p i e s . The s t u d i e s d e a l i n g w i t h g u p p i e s i n Trinidad.- 1. ( H a s k i n s e t a l . , 196I; Seghers, 1 9 7 3 , 1974a, 1974b; B a l l i n , 1 9 7 3 ; L i l e y and Seghers, 1975; F a r r , 1975; E n d l e r , 1978, 1980; and t h i s study) suggest t o me t h a t the f o l l o w i n g s e l e c t i o n p r e s s u r e s may have i n t e r a c t e d t o produce the observ e d d i f f e r e n c e s between guppy p o p u l a t i o n s ; . P h y s i c a l S e l e c t i v e Agents Morphology and B e h a v i o u r B i o t i c S e l e c t i v e Agents Temperature Stream V e l o c i t y Stream T u r b i d i t y Stream Background P a t t e r n C o l o u r a t i o n S i z e C o u r t s h i p B e h a v i o u Avoidance _ B e h a v i o u r S c h o o l i n g B e h a v i o u r y A g g r e s s i v e / B e h a v i o u r ' Depth P r e f e r e n c e ' S e x u a l S e l e c t i o n ( S o l i d l i n e s i n d i c a t e demonstrated e v i d e n c e f o r s e l e c t i v e i n f l u e n c e s . B r o k e n l i n e s i n d i c a t e p o s s i b l e s e l e c t i v e i n f l u e n c e s . ) F o r each c h a r a c t e r o f morphology and b e h a v i o u r l i s t e d I w i l l b r i e f l y r e v i e w the e v i d e n c e f o r s p e c i f i c f a c t o r s a c t i n g as s e l e c t i o n p r e s s u r e s . 83 Male C o l o u r a t i o n . The extreme polymorphism o f male c o l o u r p a t t e r n i n P. r e t i c u l a t a has l o n g been n o t e d and the g e n e t i c s o f c o l o u r i n h e r i t a n c e has been s t u d i e d i n c o n s i d e r a b l e d e t a i l (Winge, 1922, 1927; F i s h e r , 1930; Winge and D i t l e v s e n , 1947; H a s k i n s and Druzba, 1938; G o o d r i c h , J o s ephson, T r i n k h a u s , and S l a t e , 1944; H a s k i n s and H a s k i n s , 1951» 1954; H a s k i n s , Young, H e w i t t , and H a s k i n s , 1970; and Yamamoto, 1975)* N a t u r a l p o p u l a t i o n s o f the guppy were f i r s t s t u d i e d by H a s k i n s e t a l . (I96I) t o g a i n an u n d e r s t a n d i n g f o r the c o l o u r polymorphism e x h i b i t e d i n the w i l d . They suggested t h a t c o l o u r p a t t e r n s i n a g i v e n n a t u r a l p o p u l a t i o n may r e p r e s e n t a b a l a n c e between s e x u a l s e l e c t i o n , making the p a t t e r n s b r i g h t e r and more v i s i b l e , and p r e d a t i o n , making the p a t t e r n l e s s c o n s p i c u o u s . E n d l e r (1978) found t h a t the c o l o u r p a t t e r n s o f p o p u l a t i o n s o f g u p p i e s i n the w i l d show a marked change w i t h p r e d a t i o n i n t e n s i t y . Male c o l o u r p a t t e r n s were l e s s c o n s p i c u o u s a t h i g h , compared t o low, p r e d a t i o n i n t e n s i t i e s . I n a n o t h e r s t u d y , E n d l e r (1980) p r o v i d e d a d i r e c t t e s t o f the h y p o t h e s i s t h a t male c o l o u r p a t t e r n i s s u b j e c t t o n a t u r a l s e l e c t i o n . I n l o n g term l a b o r a t o r y and f i e l d e x p e r i m e n t s he demonstrated t h a t p r e d a t i o n i n t e n s i t y and stream background c o l o u r p a t t e r n s have p r e d i c t e d e f f e c t s on the c o l o u r p a t t e r n s o f male g u p p i e s . Guppies became l e s s c o n s p i c u o u s a t h i g h e r compared t o l o w e r p r e d a t i o n i n t e n s i t y . I n a d d i t i o n , s e x u a l s e l e c t i o n by fem a l e s appeared t o produce males as d i f f e r e n t f r o m t t h e i r s t r e a m background as p o s s i b l e . I n l a b o r a t o r y c h o i c e e x p e r i m e n t s u s i n g n a t u r a l guppy p o p u l a t i o n s , B a l l i n (1973) found t h a t b r i g h t c o l o u r a t i o n o f males d i d n o t i n f l u e n c e female c h o i c e o f mates. U s i n g l a b o r a t o r y s t r a i n s o f g u p p i e s , F a r r ( 1 9 8 0 a ) f o u n d t h a t f e males p r e f e r c o n s p i c u o u s males o n l y i f a l l males e x h i b i t e q u a l c o u r t s h i p d i s p l a y r a t e s . He s u g g e s t s t h a t male c o l o u r a t i o n does n o t i n f l u e n c e female c h o i c e o f males b u t r a t h e r t h a t f e m a l e s p r e f e r males w i t h h i g h e r d i s p l a y r a t e s . ( D u r i n g h i s e x p e r i m e n t s male r e p r o d u c t i v e s u c c e s s was measured d i r e c t l y by d e t e r m i n i n g the parentage o f o f f s p r i n g . ) F a r r ( 1 9 7 7 » 1980a ) a l s o found t h a t w i t h i n a group o f competing males, f e m a l e s s e l e c t e d males w i t h l e s s f r e q u e n t o r r a r e c o l o u r p a t t e r n s . I t t h u s appears t h a t f e m a l e s are more r e c e p t i v e t o males whose c o l o u r a t i o n i s d i f f e r e n t from e i t h e r l ) t h e i r stream background ( E n d l e r , I98O) o r 2) o t h e r males w i t h i n a group ( F a r r , 1 9 7 7 i 1 9 8 0 a )• Both p r e d a t i o n and s e x u a l s e l e c t i o n have been demonstrated t o a c t as s e l e c t i o n p r e s s u r e s p r o d u c i n g -v a r i a b i l i t y i n male c o l o u r a t i o n . Male S i z e . E x p e r i m e n t s i n w h i c h g u p p i e s from two d i f f e r e n t n a t u r a l p o p u l a t i o n s were r a i s e d a t d i f f e r e n t t e m p e r a t u r e s have i n d i c a t e d t h a t i n t e r - p o p u l a t i o n d i f f e r e n c e s i n the s i z e o f a d u l t g u p p i e s , p a r t i c u l a r l y males, are p a r t l y d e t e r m i n e d by g e n e t i c d i f f e r e n c e s and are p a r t l y a p h e n o t y p i c response t o e n v i r o n m e n t a l temperature c o n d i t i o n s ( L i l e y and Seghers, 1 9 7 5 ) * E v i d e n c e t h a t p r e d a t i o n i s s i z e - s e l e c t i v e has a l s o been p r o v i d e d by e x p e r i m e n t s i n which g u p p i e s were exposed t o a v a r i e t y o f n a t u r a l p r e d a t o r s ( S e g h e r s , 1 9 7 3 ; L i l e y and Seghers, 1 9 7 5 )• Thus s i z e s e l e c t i v e p r e d a t i o n may a l s o be a f a c t o r i n v o l v e d i n the e v o l u t i o n o f i n t e r - p o p u l a t i o n d i f f e r e n c e s i n male s i z e . 85 L i l e y and Seghers (1975) s u g g e s t t h a t body s i z e may be adapted t o stream v e l o c i t y and perhaps a l s o r e p r e s e n t some form o f m a t i n g advantage. Large body s i z e might a l l o w f i s h t o b e t t e r manoeuvre i n f a s t - f l o w i n g streams, and thus g a i n them an advantage i n i n t r a - s p e c i f i c b e h a v i o u r and escape from p r e d a t i o n . (Hubbs (l94l) has n o t e d t h a t f i s h l i v i n g i n f a s t e r s tream v e l o c i t i e s are g e n e r a l l y l a r g e r t h a n those i n s l o w e r -f l o w i n g water.) S e x u a l s e l e c t i o n s h o u l d fa.vor l a r g e r g u p p i e s i f f e m a les choose l a r g e r (and presumably f i t t e r ) males. N e i t h e r o f thes e p o s s i b i l i t i e s have as y e t been t e s t e d e x p e r i m e n t a l l y . Only c o r r e l a t i o n s between guppy s i z e and stream v e l o c i t y have been n o t e d . The e f f e c t o f s e x u a l s e l e c t i o n and stream v e l o c i t y on f i s h s i z e c o u l d be t e s t e d by m a i n t a i n i n g g u p p i e s under d i f f e r e n t stream v e l o c i t i e s f o r s e v e r a l g e n e r a t i o n s . Such e x p e r i m e n t s c o u l d determine whether l a r g e r males are more s u c c e s s f u l than-', s m a l l males i n m a t i n g w i t h f e m a l e s a t d i f f e r e n t v e l o c i t i e s . A v oidance Behaviour.-.. Models o f a e r i a l p r e d a t o r s have been f o u n d " t o e l i c i t d i f f e r e n t r e s p o n s e s fromttwo p o p u l a t i o n s o f g u p p i e s and t h e i r l a b o r a t o r y - r e a r e d progeny ( S e g h e r s , 1973, 1974a) •. Headstream males moved i n t o deeper w a t e r and remained q u i e s c e n t w h i l e l l o w l a n d males d i d so to a much l e s s e r degree. Seghers s u g g e s t s t h a t t h i s g e n e t i c v a r i a t i o n i n b e h a v i o u r r e f l e c t s d i f f e r e n c e s i n s e l e c t i o n p r e s s u r e s e x e r t e d by a q u a t i c v e r s u s a e r i a l p r e d a t o r s . C o h e s i o n . Group c o h e s i o n o r s c h o o l i n g may have e v o l v e d as an a n t i - p r e d a t o r s t r a t e g y (Shaw, 1970)• I n l a b o r a t o r y e x p e r i m e n t s , Seghers ( 1 9 7 3 * 1 9 7 4 b ) demonstrated t h a t p o p u l a t i o n s o f g u p p i e s h a v i n g a g r e a t e r tendency t o H s c h o o l were r e l a t i v e l y l e s s v u l n e r a b l e t o p r e d a t i o n . He s u g g ested t h a t g e n e t i c d i f f e r e n c e s between p o p u l a t i o n s i n s c h o o l i n g b e h a v i o u r , a l o n g w i t h r e a c t i o n d i s t a n c e t o p r e d a t o r s , a l a r m t h r e s h o l d , and m i c r o h a b i t a t s e l e c t i o n , are components o f a coadapted complex o f a n t i p r e d a t o r a d a p t a t i o n s . I n a f i e l d s t u d y , F a r r ( 1 9 7 5 ) found t h a t p o p u l a t i o n s o f g u p p i e s l i v i n g i n streams c o n t a i n i n g R i v u l u s h a r t i i (and n o t l a r g e r p r e d a t o r s ) were d i s p e r s e d s p a r s e l y a c r o s s the e n t i r e stream bed (and d i s p l a y e d low r a t e s o f s e x u a l a c t i v i t y ) . P o p u l a t i o n s l i v i n g i n streams w i t h l a r g e p r e d a t o r s , however, l i v e d i n dense a g g r e g a t e s a l o n g the edges o f the streams and males e x h i b i t e d h i g h e r r a t e s o f s i g m o i d d i s p l a y s and t h r u s t s . He s p e c u l a t e d t h a t the o b s e r v e d d i f f e r e n c e s i n s c h o o l i n g and c o u r t s h i p b e h a v i o u r were e n t i r e l y due t o the presence o r absence o f R i v u l u s . He d i d n o t , however, t e s t t h i s h y p o t h e s i s . I n a d d i t i o n t o p r e d a t i o n , stream t u r b i d i t y may have a c t e d as a s e l e c t i v e agent i n p r o d u c i n g p o p u l a t i o n d i f f e r e n c e s incschooling b e h a v i o u r . As n o t e d e a r l i e r , i n t u r b i d w a t e r one might e x p e c t f i s h t o Keep c l o s e t o g e t h e r f o r the purpose o f communication. Because o f the r e l a t i o n s h i p between stream v e l o c i t y and t u r b i d i t y ( s l o w - f l o w i n g l o w l a n d r i v e r s are t u r b i d w h i l e f a s t - f l o w i n g headstreams are c l e a r ) , i f t u r b i d i t y a f f e c t s s c h o o l i n g , stream v e l o c i t y would i n d i r e c t l y a f f e c t s c h o o l i n g b e h a v i o u r . I examined group c o h e s i o n i n s e v e r a l stream v e l o c i t i e s and found no d i r e c t e f f e c t o f stream v e l o c i t y on s c h o o l i n g b e h a v i o u r , a t l e a s t w i t h i n the v e l o c i t i e s t e s t e d . 87 A g g r e s s i v e B e h a v i o u r . A g g r e s s i o n i n the guppy may s i m p l y he coadapted w i t h s c h o o l i n g b e h a v i o u r s i n c e i t i s l o g i c a l t h a t f i s h l l i v i n g i n s c h o o l s s h o u l d b e l l e s s a g g r e s s i v e t h a n i f d i s t r i b u t e d o v e r the stream bed. A f t e r f i n d i n g t h a t Guayamare l o w l a n d r i v e r g u p p i e s are l e s s a g g r e s s i v e t h a n P a r i a headstream guppies', B a l l i n (1973) s u g g e s t e d t h a t a g g r e s s i o n i n headstream p o p u l a t i o n s may be due t o the absence o f p r e d a t i o n and presence o f i n t e r - m a l e c o m p e t i t i o n f o r f e m a l e s . G o r l i c k (1976) s u g g e s t e d t h a t a g g r e s s i o n may be an i m p o r t a n t f a c t o r i n d e t e r m i n i n g male dominance among d o m e s t i c g u p p i e s ? . However, F a r r ( 1 9 8 0 a ) , u s i n g l a b o r a t o r y s t r a i n s o f g u p p i e s , found t h a t more a g g r e s s i v e males d i d n o t i n c r e a s e t h e i r r e p r o d u c t i v e s u c c e s s , i n f a c t t h e y d e c r e a s e d i t . A t p r e s e n t , t h e r e i s no c l e a r r e a s o n as t o why headstream males are a g g r e s s i v e . My e x p e r i m e n t s found no d i r e c t e f f e c t o f stream v e l o c i t y on a g g r e s s i o n i n males. P e r h a p s c o m p e t i t i o n f o r r e s o u r c e s , such as f o o d , has produced i n t e r - m a l e a g g r e s s i o n i n headstream males. T h e r e i i s , however, no ev i d e n c e f o r t h i s p o s s i b i l i t y a t p r e s e n t . Depth P r e f e r e n c e . The presumed g e n e t i c d i f f e r e n c e s i n depth p r e f e r e n c e o f d i f f e r e n t guppy p o p u l a t i o n s may r e p r e s e n t a d a p t a t i o n s t o stream v e l o c i t y . I o u t l i n e d e a r l i e r the e v i d e n c e from my experiment f o r t h i s p o s s i b i l i t y . Stream t u r b i d i t y may a l s o have s e l e c t e d f o r d i f f e r e n c e s i n depth p r e f e r e n c e . F i s h i n t u r b i d l o w l a n d w a t e r s may have e v o l v e d a p r e f e r e n c e f o r the s u r f a c e r e g i o n o f streams s i n c e t h e y would l i k e l y be a s s i s t e d in, c.;schooling and f i n d each o t h e r more e a s i l y i n the w e l l - l i t s u r f a c e r e g i o n o f r i v e r s . The e f f e c t 88 o f s t r e a m t u r b i d i t y on depth p r e f e r e n c e (as w e l l as - on , o t h e r b e h a v i o u r ) i s p r e s e n t l y b e i n g s t u d i e d ( L u y t e n , p e r s o n a l c o m m u n i c a t i o n ) . . . Courtshit),,Behaviour. The r e p r o d u c t i v e b i o l o g y and c o u r t s h i p b e h a v i o u r o f P. r e t i c u l a t a has.been s t u d i e d i n d e t a i l (eg. B r e d e r and C o a t e s , 1935; C l a r k and Aronson,' 1951; Rosen and Gordon, 1953; Hildeman and Wagner, 1954; Kadow, 1954; Baerends, Brouwer, and W a t e r b o l k , 1955; Rosen and Tucke r , 196l; B r e d e r and Rosen, I966; L i l e y , 1966; and L i l e y and Wishlow, 1974). Fa.rr:"..(..'1980bX s t u d i e d the r o l e o f .sigmoid d i s p l a y s and t h r u s t s i n a l a b o r a t o r y s t r a i n o f g u p p i e s . He found t h a t males e x h i b i t e d the same mean t o t a l number o f d i s p l a y s r e g a r d l e s s o f t h e i r p r i o r s e x u a l e x p e r i e n c e o r the r e c e p t i v i t y o f females t h e y c o u r t e d . However, he found t h a t males t h r u s t more f r e q u e n t l y when w i t h u n r e c e p t i v e f e males t h a n w i t h re.ee p t i v e -;.ones. F a r r t h e r e f o r e s u g g e s t e d t h a t males u t i l i z e t h r u s t s , which o n l y r a r e l y r e s u l t i n s u c c e s s f u l i n s e m i n a t i o n s ( C l a r k and Aronson, 1951; Baerends e t a l . , 1955; and L i l e y , 1966), i n o r d e r t o "rape" u n r e c e p t i v e f e m a l e s . U n f o r t u n a t e l y , h i s s t u d y does n o t d e a l w i t h n a t u r a l p o p u l a t i o n s o f g u p p i e s t h a t v a r y g e n e t i c a l l y i n t h e i r f r e q u e n c y and r a t i o o f p e r f o r m i n g s i g m o i d d i s p l a y s s t h r u s t s . W o rking w i t h n a t u r a l p o p u l a t i o n s o f g u p p i e s , Ballin.( 1 9 7 3 ) s p e c u l a t e d t h a t the l o w l a n d male g u p p i e s d i s p l a y l e s s f r e q u e n t l y t h a n headstream males because o f i n c r e a s e d p r e d a t i o n i n l o w l a n d r i v e r s , assuming males t h a t d i s p l a y more f r e q u e n t l y i n c r e a s e t h e i r r i s k o f b e i n g e a t e n by p r e d a t o r s . He a l s o s u g g ested t h a t , due t o poor v i s i b i l i t y , males i n t u r b i d w a t e r would "b e n e f i t l e s s from d i s p l a y i n g and more from a t t e m p t i n g c o p u l a t i o n s by p e r f o r m i n g t h r u s t s . However, B a l l i n d i d n o t t e s t t h e s e s p e c u l a t i o n s . F a r r ( 1 9 7 5 ) p r e v i o u s l y n o t e d c o r r e l a t i o n s between guppy c o u r t s h i p b e h a v i o u r and the presence of p r e d a t o r s . He suggested t h a t d i f f e r e n c e s i n c o u r t s h i p b e h a v i o u r r e f l e c t a b a l a n c e between a d a p t a t i o n t o p r e d a t i o n and s e x u a l s e l e c t i o n . b y f e m a l e s . R e c e n t l y , F a r r ( 1 9 8 0 a ) showed t h a t among l a b o r a t o r y s t r a i n s o f guppies', males w h i c h d i s p l a y e d a t h i g h e r r a t e s were p r e f e r r e d by females and demonstrated g r e a t e r r e p r o d u c t i v e s u c c e s s t h a n males who d i s p l a y e d l e s s f r e q u e n t l y . Thus he demonstrated t h a t s e x u a l s e l e c t i o n by fe m a l e s f a v o u r s a h i g h r a t e o f d i s p l a y i n g i n males. The e f f e c t o f p r e d a t i o n on d i s p l a y r a t e , however, remains t o be t e s t e d . My f i r s t e x p e r i m e n t demonstrated t h a t d i f f e r e n c e s i n c o u r t s h i p b e h a v i o u r between n a t u r a l p o p u l a t i o n s have a g e n e t i c component. I t showed t h a t c o u r t s h i p d i f f e r e n c e s between p o p u l a t i o n s may r e p r e s e n t a d a p t a t i o n s t o d i f f e r e n t stream v e l o c i t i e s . The h i g h e r a t e s o f p e r f o r m i n g s i g m o i d d i s p l a y s e x h i b i t e d ' , by headstream males and t h e i r h i g h r a t i o o f s i g m o i d d i s p l a y s : t h r u s t s may r e p r e s e n t a d a p t a t i o n s t o f a s t e r - f l o w i n g w a t e r , a l l o w i n g them t o m a i n t a i n an o p t i m a l r a t i o o f s i g m o i d d i s p l a y s : t h r u s t s . Headstream males were a l s o found t o be b e t t e r a b l e t o m a i n t a i n t h e i r c o u r t s h i p i n f a s t e r - f l o w i n g w a t e r t h a n l o w l a n d males. Thus d i f f e r e n c e s i n c o u r t s h i p b e h a v i o u r between p o p u l a t i o n s may n o t s i m p l y r e p r e s e n t a d a t a t i o n t o the b i o t i c s e l e c t i o n p r e s s u r e s o f p r e d a t i o n and s e x u a l s e l e c t i o n . 90 My f i n d i n g , t h a t d i f f e r e n t p o p u l a t i o n s o f a s p e c i e s v a r y g e n e t i c a l l y i n t h e i r r a t e s o f p e r f o r m i n g b e h a v i o u r p a t t e r n s i s n o t new. W i t h i n s p e c i e s g e n e t i c v a r i a t i o n i n c o u r t s h i p b e h a v i o u r has p r e v i o u s l y been found t o be m a i n l y q u a n t i t a t i v e and l i k e l y polygene t i c (see r e v i e w s by B a s t o c k , 1967'; and B r o a d h u r s t , F u l k e r , ' and W i l c o c k , 197^ ) • How genes a c t t o produce d i f f e r e n t l e v e l s o f c o u r t s h i p i n d i f f e r e n t p o p u l a t i o n s remains u n s o l v e d . However, B a s t o c k (1967) s u g g e s t s t h a t such d i f f e r e n c e s are due t o d i f f e r e n t t h r e s h o l d l e v e l s i n the mechanisms c o n t r o l l i n g b e h a v i o u r . The above r e v i e w shows t h a t numerous f a c t o r s have p l a y e d a r o l e i n s h a p i n g each c h a r a c t e r o f the guppy*s p r e s e n t morphology and b e h a v i o u r . My r e s u l t s , i n p a r t i c u l a r , have shown t h a t i t i s i n c o r r e c t t o c o n c e n t r a t e on o n l y b i o t i c s e l e c t i o n p r e s s u r e s when e x a m i n i n g p o p u l a t i o n d i f f e r e n c e s i n c o u r t s h i p b e h a v i o u r . I n t e r p o p u l a t i o n v a r i a b i l i t y o r i g i n a l l y a t t r i b u t e d t o p r e d a t i o n may i n f a c t a l s o be due t o a c o m b i n a t i o n of p h y s i c a l f e a t u r e s such as stream v e l o c i t y and t u r b i d i t y . To u n d e r s t a n d the n a t u r e o f m i c r o - e v o l u t i o n a r y changes more f u l l y we need e v e n t u a l l y t o a s s e s s the r e l a t i v e c o n t r i b u t i o n s o f d i f f e r e n t s e l e c t i v e p r e s s u r e s i n s h a p i n g b e h a v i o u r and morphology. T h i s s h o u l d be p o s s i b l e by c o n t i n u i n g t o st u d y n a t u r a l p o p u l a t i o n s o f the guppy. By p e r f o r m i n g l o n g term e x p e r i m e n t s , and s y s t e m a t i c a l l y v a r y i n g stream v e l o c i t y , t u r b i d i t y , and p r e d a t o r c o n d i t i o n s i t may be p o s s i b l e t o e v a l u a t e t h e s e s e l e c t i v e a g e n t s ' r e l a t i v e e f f e c t s . i n s h a p i n g guppy morphology and b e h a v i o u r . I n a d d i t i o n , u s i n g c o m p e t i t i o n e x p e r i m e n t s s i m i l a r t o t h o s e i n E x p e r i m e n t II.";' males from d i f f e r e n t p o p u l a t i o n s w i t h d i f f e r e n t c h a r a c t e r i s t i c s c o u l d be t e s t e d t o determine whether s p e c i f i c c h a r a c t e r i s t i c s g a i n any m a t i n g advantages f o r i n d i v i d u a l s . Thus, the guppy s h o u l d prove v e r y u s e f u l i n s t u d y i n g s e x u a l s e l e c t i o n n o t o n l y u s i n g l a b o r a t o r y s t r a i n s (as F a r r (1980a) has done)-, b u t a l s o u s i n g n a t u r a l p o p u l a t i o n s . The r e l a t i v e r o l e o f male s i z e , c o l o u r a t i o n , a g g r e s s i v e n e s s , and r a t e o f c o u r t s h i p d i s p l a y s h o u l d be a s s e s s e d , n o t o n l y under one c o n d i t i o n b u t under s e v e r a l d i f f e r e n t c o n d i t i o n s . I t I s by e x a m i n i n g n a t u r a l p o p u l a t i o n s under d i f f e r e n t c o n d i t i o n s t h a t the a d a p t i v e s i g n i f i c a n c e o f v a r i o u s c h a r a c t e r i s t i c s becomes more c l e a r . E v e n t u a l l y a d e t a i l e d u n d e r s t a n d i n g s h o u l d be g a i n e d o f the i n t e r a c t i o n o f s e l e c t i o n f a c t o r s i n s h a p i n g morphology and b e h a v i o u r and o f the a d a p t i v e s i g n i f i c a n c e o f s p e c i f i c p o p u l a t i o n c h a r a c t e r i s t i c s . So f a r , my s t u d y , a l o n g w i t h o t h e r s , have i n d i c a t e d t h a t s p e c i f i c c h a r a c t e r i s t i c s . o f guppy morphology and b e h a v i o u r are adapted t o s p e c i f i c e n v i r o n m e n t a l f a c t o r s . I t remains now t o t e s t t h e i r r e l a t i v e importance under d i f f e r e n t c o n d i t i o n s . A d a p t a t i o n o f d i f f e r e n t p o p u l a t i o n s t o s p e c i f i c o e nvironments may e v e n t u a l l y r e s u l t i n t h e f o r m a t i o n o f d i f f e r e n t s p e c i e s . T h i s o c c u r s when i n d i v i d u a l s from d i f f e r e n t p o p u l a t i o n s ne? l o n g e . r s i n t e r b r e e d (Mayr, 1970) • A l t h o u g h the p o p u l a t i o n s o f g u p p i e s I s t u d i e d r e m a i n capable o f i n t e r b r e e d i n g , i t i s i n t e r e s t i n g t o note t h a t some i n t e r - p o p u l a t i o n d i s c r i m i n a t i o n was demonstrated d u r i n g my second e x p e r i m e n t . The p r e f e r e n c e s o f males f o r f e m a l e s from 92 t h e i r own p o p u l a t i o n may r e p r e s e n t a p a r t i a l h a r r i e r t o gene f l o w between p o p u l a t i o n s . S e x u a l s e l e c t i o n e x c e r c i s e d by males (and/or females) may be m a i n t a i n i n g d i f f e r e n c e s between p o p u l a t i o n s . H a s k i n s and H a s k i n s (1950) found a c o u r t s h i p p r e f e r e n c e by l a b o r a t o r y s t r a i n s o f males f o r f e m a l e s from t h e i r own s t r a i n and by w i l d - c a u g h t males f o r w i l d - c a u g h t f e m a l e s . M y r e s u l t S j u s i n g ; " d i f f e r e ' r i t ? I w i l d y c a u g h t p o p u l a t i o n s , s u p p o r t t h e i r f i n d i n g o f i n t e r - p o p u l a t i o n d i s c r i m i n a t i o n . One p o s s i b l e e x p l a n a t i o n f o r the p r e f e r e n t i a l c o u r t s h i p e x h i b i t e d by males d u r i n g my expe r i m e n t i s t h a t f e m a l e s may r e l e a s e d i f f e r e n t and i d e n t i f i a b l e pheromones. Female g u p p i e s have been shown t o r e l e a s e a s e x u a l pheromone, e s p e c i a l l y d u r i n g the time o f t h e i r r e c e p t i v i t y (Crow, 1976; Crow and L i l e y , 1979)• The re s p o n s e s o f males t o s e x u a l pheromones produced by headstream and l o w l a n d f e m a l e s have been s t u d i e d by Snyder (1978)- She found t h a t males from each s t o c k d i s p l a y e d t o c o n t r o l f e males more when water which had p r e v i o u s l y h e l d f e m a l e s from t h e i r own s t o c k was added t o t h e i r t a n k - t h a n when wa t e r from a n o t h e r s t o c k was added. Thus, some f o r m r o f o l f a c t o r y d i s c r i m i n a t i o n may d i f f e r e n t i a t e p o p u l a t i o n s o f f e m a l e s , and t h i s may a c c o u n t ' f o r the o b s e r v e d mate p r e f e r e n c e s o f males. C o n t i n u e d s t u d y o f the guppy may p r o v i d e f u r t h e r i n s i g h t i n t o how i s o l a t i n g mechanisms d e v e l o p . D i f f e r e n c e s i n c o u r t s h i p b e h a v i o u r between the guppy and t h r e e c l o s e l y r e l a t e d s p e c i e s have been shown t o f u n c t i o n as e t h o l o g i c a l i s o l a t i n g mechanisms ( H a s k i n s and H a s k i n s , 1949 ; L i l e y , 1966). I n t h i study, d i f f e r e n c e s i n c o u r t s h i p "behaviour were found between p o p u l a t i o n s o f g u p p i e s and a degree o f i n t e r - p o p u l a t i o n d i s c r i m i n a t i o n e x i s t e d "between the p o p u l a t i o n s . I t i s a d a p t a t i o n t o d i f f e r e n t e n v i r o n m e n t s , perhaps s i m i l a r t o those found i n t h i s s t u d y , t h a t may e v e n t u a l l y "bring about b e h a v i o u r a l i s o l a t i o n between p o p u l a t i o n s . I n c l o s i n g , I would l i k e t o s t r e s s t h a t p r e d i c t i o n s about the r o l e s o f d i f f e r e n t s e l e c t i v e f a c t o r s and t h e i r e f f e c t s on guppy b e h a v i o u r s h o u l d e v e n t u a l l y be t e s t e d i n f i e l d e x p e r i m e n t s . My s t u d y has made apparent the importanc o f e x a m i n i n g f i s h i n d i f f e r e n t stream v e l o c i t y c o n d i t i o n s . When p o p u l a t i o n s are adapted t o d i f f e r e n t stream v e l o c i t i e s , u n l e s s t h e y are examined i n f l o w i n g w a t e r , the a d a p t i v e s i g n i f i c a n c e o f t h e i r b e h a v i o u r may be m i s i n t e r p r e t e d ^ . My s t u d y showed t h a t d i f f e r e n c e s between guppy p o p u l a t i o n s i n c o u r t s h i p b e h a v i o u r and stream depth p r e f e r e n c e l i k e l y r e p r e s e n t a d a p t a t i o n s t o stream v e l o c i t y . U n t i l t h i s s t u d y , t h e s e p o p u l a t i o n d i f f e r e n c e s had been c o n s i d e r e d o n l y as a d a p t a t i o n s t o b i o t i c s e l e c t i o n p r e s s u r e s , such as p r e d a t i o n . LITERATURE CITED 94 B a e r e n d s , G.P., R. Brouwer, and H.T. W a t e r b o l k . 1955* E t h o l o g i c a l s t u d i e s on L e b i s t e s r e t i c u l a t u s ( P e t e r s ) . B e h a v i o u r 8 : 24-9-334. B a l l i n , P . J . 1 9 7 3 « Geographic v a r i a t i o n i n c o u r t s h i p b e h a v i o u r o f the guppy, P o e c i l i a r e t i c u l a t a . M.Sc. T h e s i s . U n i v e r s i t y o f B r i t i s h C olumbia. B a s t o c k , M. 1967' C o u r t s h i p : a z o o l o g i c a l s t u d y . Heinemann, London. Boeseman, M. i960. The f r e s h - w a t e r Wishes o f the i s l a n d o f T r i n i d a d . S t u d . Fauna Curacao 10: 72-153. Boeseman, M. - 1 9 6 4 . The f r e s h - w a t e r f i s h e s o f the i s l a n d o f T r i n i d a d : addenda, e r r a t a , e t c o r r i g e n d a . S t u d . Fauna Curacao 20: 52-57. B r e d e r , CM., J r . and CW. Coa t e s . 1 9 3 5 « Sex r e c o g n i t i o n i n the guppy, L e b i s t e s r e t i c u l a t u s P e t e r s . Z o o l o g i c a 19s 187 - 2 0 7 . B r e d e r , C M . and D.E. Rosen. 1966. Modes o f r e p r o d u c t i o n i n f i s h e s . N a t u r a l H i s t o r y P r e s s , Garden C i t y . B r o a d h u r s t , P.L., D.W. F u l k e r , and J . W i l c o c k . 1974. B e h a v i o r a l g e n e t i c s . Ann. Rev. P s y c h o l . 25: 3 8 9 - 4 l 5 « Brown, J . L . 1 9 7 5 • The e v o l u t i o n o f b e h a v i o r . W.W. N o r t o n and Company, New Yo r k . C l a r k , E. and L.R. Aronson. 1 9 5 1 • S e x u a l b e h a v i o r i n the guppy, L e b i s t e s r e t i c u l a t u s ( P e t e r s ) • Z o o l o g i c a 36": 49-66. Crow, R.T. 1976. A s e x u a l pheromone i n the guppy, P o e c i l i a r e t i c u l a t a ( P e t e r s ) . B.Sc. T h e s i s , U n i v e r s i t y o f B r i t i s h C o lumbia. Crow, R.T.. .and N.R. L i l e y . 1 9 7 9 « A s e x u a l pheromone i n the g u p p y . / P o e c i l i a r e t i c u l a t a ( P e t e r s ) - Can. J . Z o o l . 57: 1 8 4 - 1 8 8 . Ehrman, L. and P.A. P a r s o n s . 1 9 7 6 " . The g e n e t i c s o f b e h a v i o r . S i n a u e r A s s o c i a t e s , S u n d e r l a n d , Mass. E n d l e r , J.A. 1 9 7 8 . A p r e d a t o r ' s v i e w o f a n i m a l c o l o r p a t t e r n s . E v o l . B i o l . 11: 3 1 9 - 3 6 4 . E n d l e r , J.A. 1980. N a t u r a l s e l e c t i o n on c o l o r p a t t e r n s i n P o e c i l i a r e t i c u l a t a . E v o l u t i o n 34: 76-91. F a r r , J.A. 1975' The r o l e o f p r e d a t i o n i n the e v o l u t i o n o f s o c i a l b e h a v i o r r o f n a t u r a l p o p u l a t i o n s o f the guppy, P o e c i l i a r e t i c u l a t a ( P i s c e s : P o e c i l i i d a e ) . E v o l u t i o n 29: 151-158. F a r r , J.A. 1976. S o c i a l f a c i l i t a t i o n o f male s e x u a l b e h a v i o r i n t r a s e x u a l c o m p e t i t i o n , and s e x u a l - s e l e c t i o n i n the guppy, P o e c i l i a r e t i c u l a t a ( P i s c e s : P o e c i l i i d a e ) . E v o l u t i o n 30: 707-747. F a r r , J.A. 1977• Male r a r i t y o r n o v e l t y , female c h o i c e b e h a v i o r , and s e x u a l s e l e c t i o n i n the guppy, P o e c i l i a  r e t i c u l a t a P e t e r s ( P i s c e s : P o e c i l i i d a e ) . E v o l u t i o n 31' 1 6 2 -168 . F a r r , J.A. 1980a. S o c i a l b e h a v i o r p a t t e r n s as d e t e r m i n a n t s o f r e p r o d u c t i v e s u c c e s s i n the guppy, P o e c i l i a r e t i c u l a t a P e t e r s ( P i s c e s : P o e c i l i i d a e ) - an e x p e r i m e n t a l s t u d y o f the e f f e c t s o f i n t e r m a l e c o m p e t i t i o n , female c h o i c e , and s e x u a l s e l e c t i o n . B e h a v i o u r 74: 38-91• F a r r , J.A. 1980b. The e f f e c t s o f s e x u a l e x p e r i e n c e and fem a l r e c e p t i v i t y on c o u r t s h i p - rape d e c i s i o n s i n male gu p p i e s P o e c i l i a r e t i c u l a t a ( P i s c e s : P o e c i l i i d a e ) . Anim. Behav. 28: 1195-1201. F i s h e r , R.A. 1930. The e v o l u t i o n o f dominance i n c e r t a i n p o l y m o r p h i c s p e c i e s . Amer. Nat. 6 4 : 385-406. G o o d r i c h , H.B., N.O. Jo s e p h s o n , J.P. T r i n k h a u s , and J.M. S l a t e 1944. The c e l l u l a r e x p r e s s i o n and g e n e t i c s o f two new genes i n L e b i s t e s r e t i c u l a t u s . G e n e t i c s 29: 584-592. G d r l i c k , D.L. 1976. Dominance h i e r a r c h i e s and f a c t o r s i n f l u e n c i n g dominance i n the guppy, P o e c i l i a r e t i c u l a t a ( P e t e r s ) . Anim. Behav. 2 4 : 3 3 6 - 3 46 . H a s k i n s , C.P. and J.P. Druzba. 1938. Note on anomalous i n h e r i t a n c e o f s e x - l i n k e d c o l o u r f a c t o r s i n the guppy. Amer. Nat. 72: 571-57^. H a s k i n s , C.P. and E.F. H a s k i n s . 1949. The r o l e o f s e x u a l s e l e c t i o n as a n . i s o l a t i n g mechanism i n t h r e e s p e c i e s o f p o e c i l i i d f i s h e s . E v o l u t i o n 3:. 16O-I69. H a s k i n s , C^P. and E.F. H a s k i n s . 1950. F a c t o r s g o v e r n i n g s e x u a l s e l e c t i o n as an i s o l a t i n g mechanism i n the p o e c i l i i d f i s h L e b i s t e s r e t i c u l a t u s . P r o c . Nat. Acad. S c i e n c e s 36: 4 6 4 - 4 7 6 . H a s k i n s , C.P. and E.F. H a s k i n s . 1951- The i n h e r i t a n c e o f c e r t a i n c o l o r p a t t e r n s i n w i l d p o p u l a t i o n s o f L e b i s t e s r e t i c u l a t u s i n T r i n i d a d . E v o l u t i o n 5: 216-225. 9 6 H a s k i n s , C P . and E.F. H a s k i n s . 1 9 5 4 . Note on a "permanent" e x p e r i m e n t a l a l t e r a t i o n o f g e n e t i c c o n s t i t u t i o n i n a n a t u r a l p o p u l a t i o n . P r o c . Nat. Acad. S c i . 4 0 : 6 2 7 - 6 3 5 ' H a s k i n s , C P . , E.F. H a s k i n s , J.J.A. M c L a u g h l i n , and R.E. H e w i t t . 1 9 6 1 . . Polymorphism and p o p u l a t i o n s t r u c t u r e i n L e b i s t e s  r e t i c u l a t u s . an . e c o l o g i c a l s t u d y . I n : V e r t e b r a t e s p e c i a t i o n . ( e d . W.F. B l a i r ) , pp. 3 2 0 - 3 9 5 . U n i v e r s i t y o f Texas P r e s s , A u s t i n . H a s k i n s , C P . , P. Young, R.E. H e w i t t , and E.F. H a s k i n s . 1 9 7 0 . S t a b i l i s e d h e t e r o z y g o s i s o f supergenes m e d i a t i n g c e r t a i n Y - l i n k e d c o l o u r p a t t e r n s i n p o p u l a t i o n s o f L e b i s t e s  r e t i c u l a t u s . H e r e d i t y 2 5 : 5 7 5 - 5 8 9 . Hildemann, W.H. and E.D. Wagner. 1 9 5 4 . I n t r a s p e c i f i c sperm c o m p e t i t i o n i n L e b i s t e s . Amer. Nat. 8 8 : 8 7 - 9 1 . H i n d e , R.A. 1 9 7 5 • The concept o f f u n c t i o n . I n : F u n c t i o n and e v o l u t i o n i n b e h a v i o u r . ( e d s . G. Baerends, C. Beer, and A. Manning), pp. 3 - 1 5 - C l a r e n d o n P r e s s , O x f o r d . Hubbs, C.L. 1 9 4 1 . R e l a t i o n o f h y d r o l o g i c a l c o n d i t i o n s t o s p e c i a t i o n i n f i s h e s . I n : A symposium on h y d r o b i o l o g y . pp. 1 8 2 - 1 9 5 . U n i v e r s i t y o f W i s c o n s i n P r e s s , Madison. Kadow', P. 1 9 5 4 . An a n a l y s i s o f s e x u a l b e h a v i o r 1and r e p r o d u c t i v e p h y s i o l o g y i n the guppy, L e b i s t e s r e t i c u l a t u s ( P e t e r s ) . Ph.D. T h e s i s , New Y o r k U n i v e r s i t y . x K e e n l e y s i d e , M.H.A. 1 9 7 9 * D i v e r s i t y and a d a p t a t i o n i n f i s h b e h a v i o u r . S p r i n g e r - V e r l a g , B e r l i n . K r e b s , J.R. and N.B. D a v i e s . 1 9 7 8 . B e h a v i o u r a l e c o l o g y : an e v o l u t i o n a r y approach. B l a c k w e l l S c i e n t i f i c P u b l i c a t i o n s , O x f o r d . L i l e y , N.R. 1 9 6 6 . E t h o l o g i c a l i s o l a t i n g mechanisms i n f o u r s y m p a t r i c s p e c i e s o f p o e c i l i i d f i s h e s . B e h a v i o u r , S u p p l . 1 3 , 1 - 1 9 7 . L i l e y , N.R. and B.H. Seghers. 1 9 7 5 . F a c t o r s a f f e c t i n g the morphology and b e h a v i o u r o f g u p p i e s i n T r i n i d a d . I n : F u n c t i o n and e v o l u t i o n i n b e h a v i o u r . ( eds. G. Baerends, C. Beer, and A. Manning), pp. 9 2-118. C l a r e n d o n P r e s s , O x f o r d . L i l e y , N.R. and W. Wishlow. 1 9 7 4 . The i n t e r a c t i o n o f e n d o c r i n e and e x p e r i m e n t a l f a c t o r s i n the r e g u l a t i o n o f s e x u a l b e h a v i o u r i n the female guppy, P o e c i l i a r e t i c u l a t a . B e h a v i o u r 48: 1 8 5 - 2 1 4 . Mayr, E. 1 9 7 0 . P o p u l a t i o n s , - s p e c i e s , and e v o l u t i o n . H a r v a r d U n i v e r s i t y P r e s s , Cambridge. 9 7 Rosen, D.E. and.JR.M. B a i l e y . 1 9 6 3 . The P o e c i l i i d f i s h e s ( C y p r i n o d o n t i f o r m e s ) , t h e i r s t r u c t u r e , zoogeography, and s y s t e m a t i c s . B u l l . Amer. Mus. Nat. H i s t . 126: 5-176. Rosen, D.E. and M. Gordon. 1 9 5 3 ' F u n c t i o n a l anatomy and e v o l u t i o n o f -male g e n i t a l i a i n P o e c i l i i d f i s h e s . Z o o l o g i c a 3 8 : 1 - 4 7 . Rosen, D.E. and A. Tucker. I 9 6 I . E v o l u t i o n o f secondary s e x u a l c h a r a c t e r s and s e x u a l b e h a v i o r p a t t e r n s i n a f a m i l y o f v i v i p a r o u s f i s h e s ( C y p r i n o d o n t i f o r m e s : P o e c i l i i d a e ) . C o p e i a I 9 6 I : . 2 0 1 - 2 1 2 . Seghers, B.H. 1 9 7 3• An a n a l y s i s o f g e o g r a p h i c v a r i a t i o n i n the a n t i p r e d a t o . r a d a p t a t i o n s o f the guppy, P o e c i l i a  r e t i c u l a t a . Ph.D. T h e s i s , U n i v e r s i t y o f B r i t i s h Columbia. Seghers, B.H. 1 9 7 4 a . G e o g r a p h i c v a r i a t i o n i n the r e s p o n s e s o f guppies- ; ( P o e c i l i a r e t i c u l a t a ) t o a e r i a l p r e d a t o r s . O e c o l o g i a 1 4 : 9 3 - 9 8 . Seghers, B.H. 1 9 7 4 b . S c h o o l i n g b e h a v i o r i n the guppy ( P o e c i l i a r e t i c u l a t a ) : an e v o l u t i o n a r y response t o p r e d a t i o n . E v o l u t i o n 2 8 : 4 8 6 - 4 8 9 . Shaw, E-. 1 9 7 0 . S c h o o l i n g i n f i s h e s : c r i t i q u e and r e v i e w . I n : Development and e v o l u t i o n o f b e h a v i o u r . (eds. L.R. Aronson, E. Tobach, D.S. Lehrman, and J.S. R o s e n b l a t t } pp. 4 5 2 - 4 8 0 . Freeman, San F r a n c i s c o . S i e g e l , S. 1 9 5 6 . N o n p a r a m e t r i c s t a t i s t i c s f o r the b e h a v i o u r a l s c i e n c e s . M c G r a w - H i l l , New Y o r k . Snyder, B.E. 1 9 7 8 . A comparison o f r e s p o n s e s t o the s e x u a l pheromones produced by two a l l o p a t r i c r a c e s o f guppy, ( P o e c i l i a r e t i c u l a t a . P e t e r s ) . B.Sc. T h e s i s , U n i v e r s i t y o f B r i t i s h Columbia. Winge, 0. 1 9 2 2 . A p e c u l i a r mode o f i n h e r i t a n c e and i t s c y t o l o g i c a l e x p l a n a t i o n . J . Genet. 1 2 : 1 3 7 - 1 4 4 . Winge, j ^ . 1 9 2 7 . The l o c a t i o n of: e i g h t e e n genes i n L e b i s t e s  r e t i c u l a t u s . . J . Genet. 1 8 : 1 - 4 2 . Winge, 0, and E. D i t l e v s e n . 1947' C o l o u r i n h e r i t a n c e and sex d e t e r m i n a t i o n i n L e b i s t e s . H e r e d i t y 1: 6 5 - 8 3 . Yamamoto, T. 1 9 7 5 ' T h e medaka., Orvz-ias l a t i p e s , and the guppy, L e b i s t e s r e t i c u l a r i s . I n : Handbook of g e n e t i c s . V o l . 4. V e r t e b r a t e s o f g e n e t i c i n t e r e s t . (ed. R.C. K i n g ) , pp. 1 3 3 - 1 4 9 . Plenum P r e s s , New Y ork. 98 APPENDIX C o r r e l a t i o n s between Male S i z e and C o u r t s h i p B e h a v i o u r P a t t e r n s  E x p e r i m e n t I The mean t o t a l l e n g t h f o r each p o p u l a t i o n o f males t e s t e d i n E x p e r i m e n t I i s g i v e n i n F i g u r e 15• P e t i t e Curucaye males were s l i g h t l y l a r g e r on average t h a n P a r i a males and s i g n i f i c a n t l y Cp<.05) l a r g e r t h a n Caparo males (Mann-Whitney U - t e s t , one t a i l e d f o r C < P , C <PC, and P-CPC). These d i f f e r e n c e s are c o n s i s t e n t w i t h those found between w i l d -caught g u p p i e s c o l l e c t e d from s i m i l a r streams (see Seghers, 1973)• Se.ghers (1973) and L i l e y and Seghers (1975) showed t h a t d i f f e r e n c e s i n the s i z e o f a d u l t male g u p p i e s are p a r t l y g e n e t i c and p a r t l y a p h e n o t y p i c response t o e n v i r o n m e n t a l t e m p e r a t u r e . They suggest t h a t s i z e - s e l e c t i v e p r e d a t i o n may be i n v o l v e d i n the e v o l u t i o n o f i n t e r - p o p u l a t i o n d i f f e r e n c e s i n the s i z e o f mature f i s h . The d a t a on male s i z e p r e s e n t e d here s u p p o r t the f i n d i n g t h a t s i z e d i f f e r e n c e s are p a r t l y g e n e t i c , s i n c e the d i f f e r e n c e s were o b t a i n e d between l a b o r a t o r y s t o c k s r a i s e d under the same c o n d i t i o n s . To examine whether t h e r e i s a r e l a t i o n s h i p between male s i z e and the performance o f v a r i o u s c o u r t s h i p b e h a v i o u r p a t t e r n s I l o o k e d f o r c o r r e l a t i o n s between male s i z e and the f r e q u e n c y o f g o n o p o d i a l swings, t h r u s t s , and s i g m o i d d i s p l a y s . T h i s was done t o determine whether, f o r example, l a r g e r 99 PC 24 MALE TOTAL LENGTH (MM) 23 A 22 21 A 20-1 19 A 18-F i g u r e 15« T o t a l l e n g t h o f males t e s t e d i n E x p e r i m e n t I . H o r i z o n t a l l i n e s are means, "bars are 95% c o n f i d e n c e i n t e r v a l s , and v e r t i c a l l i n e s are r anges. C = Caparo (N = 19), P = P a r i a (N = 19), PC = P e t i t e Curucaye (N = 17). 100 males w i t h i n a p o p u l a t i o n p e r f o r m more g o n o p o d i a l s w ings, t h r u s t s , and s i g m o i d d i s p l a y s . I n a d d i t i o n , by comparing the c o r r e l a t i o n s between these v a r i a b l e s a t the f o u r stream v e l o c i t i e s , I hoped t o d e t e c t any e f f e c t o f stream v e l o c i t y on the c o r r e l a t i o n s . There were o n l y two s i g n i f i c a n t c o r r e l a t i o n s between .male s i z e and the f r e q u e n c y o f v a r i o u s b e h a v i o u r p a t t e r n s ( T a b l e XV). Two s i g n i f i c a n t c o r r e l a t i o n s i n t h i r t y - s i x c o mparisons would be e x p e c t e d by chance alone and I t h e r e f o r e a t t a c h no meaning t o them. ' I n a d d i t i o n , no e f f e c t o f stream v e l o c i t y on the c o r r e l a t i o n s was d e t e c t e d . B a l l i n (1973) a l s o found no s i g n i f i c a n t c o r r e l a t i o n s between male s i z e and c o u r t s h i p b e h a v i o u r p a t t e r n s . The s i z e o f i n d i v i d u a l males w i t h i n a p o p u l a t i o n does n o t appear t o have a b e a r i n g on t h e i r c o u r t s h i p a c t i v i t y . A l t h o u g h the P a r i a and Caparo s t o c k s d i d n o t v a r y s i g n i f i c a n t l y i n male s i z e , t h e y d i f f e r e d s i g n i f i c a n t l y i n t h e i r c o u r t s h i p b e h a v i o u r (see C h a p t e r I V ) . Thus, males o f a p p r o x i m a t e l y the same s i z e b u t from d i f f e r e n t p o p u l a t i o n s can v a r y g r e a t l y i n t h e i r c o u r t s h i p a c t i v i t y . The s i s e o f i n d i v i d u a l .rar.leB E x p e r i m e n t I I I n E x p e r i m e n t I I , w i l d - c a u g h t Upper A r i p o males were s i g n i f i c a n t l y (p <.01) l a r g e r t h a n P a r i a males, which i n t u r n were s i g n i f i c a n t l y (p< . 0 0 l ) l a r g e r t h a n b o t h Caparo and Guayamare males ( F i g . 16). The l o w l a n d s t o c k s d i d n o t d i f f e r T a b l e XV. Spearman rank c o r r e l a t i o n c o e f f i c i e n t s between male s i z e and c o u r t s h i p b e h a v i o u r p a t t e r n s and between v a r i o u s c o u r t s h i p b e h a v i o u r p a t t e r n s . S t r e am v e l o c i t y (m/sec) .03 .07 .10 . 20 G.S. S.D. Th G.S. S.D. Th G.S. S.D. Th G.S. S.D. Th Caparo S i z e .228 .221 .156 . 203 .167' - .081 ; .247 . 202 -.018 1 -.017 .063 .111 Th .050 .310 • 395* .054 .113 -.302 1 .206 .322 S.D. . 281 • 399* .518* .758$ P e t i t e Curucaye S i z e ; -.223 -.296 .154 •' -.449 -.346 .362 -.125 . 226 .654*. -.264 -.310 • 139 Th •• -.083 .332 .017 -.324 .059 .276 .278 .429* S.D. .332 .312 .474* .886$ P a r i a S i z e . -.093 -.010 .224 .180 .064 .027 .061 .071 •578J .043 • 039 .079 Th ' .345 .418* • 5 2 9 5 .056 .518* .352 • .720$ •534$ S.D. . 182 .316 .804$ .624$ S i z e = Male S i z e , Th = T h r u s t s , S.D. = S i g m o i d D i s p l a y s , G.S. = G o n o p o d i a l Swings *p < . 0 5 Spearman r a n k c o r r e l a t i o n c o e f f i c i e n t s , # ' O n e - t a i l e d t e s t f o r p o s i t i v e c o r r e l a t i o n s . 102 30 28 MALE TOTAL LENGTH ($M) 26 24 UA 22 J 20 J 18 F i g u r e 16. T o t a l l e n g t h o f males t e s t e d f o r each s t o c k . H o r i z o n t a l l i n e s are means, oars are 95% c o n f i d e n c e i n t e r v a l s , and v e r t i c a l l i n e s are ranges. C = Caparo (N = 19), P = P a r i a (N = 20), G = Guayamare (N = 17), UA = Upper A r i p o (N = 19). s i g n i f i c a n t l y . (Mann-Whitney U - t e s t , o n e - t a i l e d f o r U A > P > G .yC t w o - t a i l e d f o r G 5 * C.) . These d i f f e r e n c e s i n male s i z e a re c o n s i s t e n t w i t h d i f f e r e n c e s p r e v i o u s l y found i n w i l d - c a u g h t f i s h ( S e g h e r s , 1973)• There were no c o n s i s t e n t l y s i g n i f i c a n t c o r r e l a t i o n s between male s i z e and the f r e q u e n c y o f g o n o p o d i a l swings, t h r u s t s , o r s i g m o i d d i s p l a y s ( T a b l e X V I ) . (There was a s i g n i f i c a n t c o r r e l a t i o n between male s i z e and the f r e q u e n c y o f t h r u s t s p e r f o rmed by P a r i a males i n b o t h stream c o n d i t i o n s , however, t h i s was n o t f o u n d i n the o t h e r p o p u l a t i o n s . ) A l a c k o f s i g n i f i c a n t c o r r e l a t i o n s between male s i z e and male c o u r t s h i p b e h a v i o u r p a t t e r n s i s c o n s i s t e n t w i t h the r e s u l t s o b t a i n e d i n E x p e r i m e n t I . The s i z e o f i n d i v i d u a l males does n o t appear t o have a b e a r i n g on t h e i r c o u r t s h i p ] > a c t i v i t y . C o r r e l a t i o n s between C o u r t s h i p B e h a v i o u r P a t t e r n s E x p e r i m e n t I To examine whether t h e r e i s a r e l a t i o n s h i p between v a r i o u s c o u r t s h i p b e h a v i o u r p a t t e r n s performed by males I l o o k e d f o r c o r r e l a t i o n s between the f r e q u e n c i e s o f g o n o p o d i a l swings, t h r u s t s , and s i g m o i d d i s p l a y s p e r f ormed by i n d i v i d u a l males. T a b l e XV l i s t s the c o r r e l a t i o n c o e f f i c i e n t s f o r each s t o c k a t the f o u r stream v e l o c i t i e s i n w h i c h they were t e s t e d . There were s i g n i f i c a n t c o r r e l a t i o n s between the f r e q u e n c i e s o f g o n o p o d i a l swings and s i g m o i d d i s p l a y s f o r a l l t h r e e s t o c k s i n the two f a s t e s t stream v e l o c i t i e s . There was a l s o a c o n s i s t e n t l y s i g n i f i c a n t c o r r e l a t i o n between g o n o p o d i a l swings 104 T a b l e XVI. Spearman r a n k c o r r e l a t i o n c o e f f i c i e n t s between male s i z e and c o u r t s h i p b e h a v i o u r p a t t e r n s and between v a r i o u s c o u r t s h i p b e h a v i o u r p a t t e r n s . E x p e r i m e n t I I . Caparo Male S i z e T h r u s t s S i g m o i d D i s p l a y s P a r i a Male S i z e T h r u s t s S i g m o i d D i s p l a y s Guayamare Male S i z e T h r u s t s S i g m o i d D i s p l a y s Upper A r i p o Male S i z e T h r u s t s S i g m o i d D i s p l a y s Stream v e l o c i t y (m/sec) .00 .08 Gonopod S i g m o i d T h r u s t s Gonopod S i g m o i d T h r u s t s Swings D i s p l a y Swings D i s p l a y .004 -.025 .508* .050 -.461 .006 .•459* -.002 -.069 .319 .006 .180 .525* ••554 • 398* -.335 -.314 .315 .340 .277 .255 •.442 ••396 •.223 .064 .513* .748* .096 .152 •596t .257 -.034 .626*. .1188 ••398 • 093 .219 .318 .433* .396* • .010 .365 .021 .026 .188 103 . 106 .000 Spearman r a n k c o r r e l a t i o n c o e f f i c i e n t s , O n e - t a i l e d t e s t f o r p o s i t i v e c o r r e l a t i o n s . *P < . 0 5 , £p < .01 105 and t h r u s t s performed by P a r i a males. I t appears t h a t the r e l a t i o n s h i p between g o n o p o d i a l swings and s i g m o i d d i s p l a y s i s a f f e c t e d by stream v e l o c i t y . A l t h o u g h the c o r r e l a t i o n s were n o t s i g n i f i c a n t i n the s l o w e r stream v e l o c i t i e s ( t h e y were n e a r l y s i g n i f i c a n t a t 0.07 m/sec), they g e n e r a l l y became h i g h e r as stream v e l o c i t y i n c r e a s e d and were s i g n i f i c a n t i n the f a s t e r v e l o c i t i e s . I b e l i e v e t h a t these changes i n the c o r r e l a t i o n s between g o n o p o d i a l swings and s i g m o i d d i s p l a y s i n d i f f e r e n t stream v e l o c i t i e s h e l p t o c l a r i f y the unknown f u n c t i o n o f g o n o p o d i a l swings. I s p e c u l a t e t h a t g o n o p o d i a l s w i n g i n g has a d u a l f u n c t i o n and t h a t each o f these f u n c t i o n s i s seen t o a g r e a t e r e x t e n t depending on the f i s h ' s environment. I n f a s t e r - f l o w i n g w a t e r , males t h a t d i s p l a y f r e q u e n t l y a l s o g o n o p o d i a l swing f r e q u e n t l y and those t h a t d i s p l a y i n f r e q u e n t l y r a r e l y g o n o p o d i a l swing. These r e s u l t s s u p p o r t the v i e w t h a t g o n o p o d i a l s w i n g i n g i s r e l a t e d t o s e x u a l m o t i v a t i o n , as s u g g e s t e d by C l a r k and Aronson (1951) and L i l e y (1966). Thus, g o n o p o d i a l s w i n g i n g may f u n c t i o n as an " i n t e n t i o n movement" o r p r e p a r a t o r y movement o c c u r r i n g b e f o r e d i s p l a y i n g . ( F o r the P a r i a males i t may a l s o be s i m i l a r l y r e l a t e d t o t h r u s t i n g . ) I t i s i n s t i l l w a t e r t h a t a second f u n c t i o n becomes more app a r e n t - t h a t o f b e i n g a type o f " d i s p l a c e m e n t a c t i v i t y " . I found t h a t g o n o p o d i a l s w i n g i n g was performed d u r i n g non- c o u r t s h i p a t a h i g h e r f r e q u e n c y when f i s h were i n s l o w - f l o w i n g w a t e r . T h i s " o u t - o f - c o n t e x t " b e h a v i o u r may r e p r e s e n t a d i s p l a c e m e n t a c t i v i t y , p e r f ormed by males when they are s l o w l y swimming about a t a n k . M a l e s perhaps have l e s s time o r energy 106 t o p e r f o r m such d i s p l a c e m e n t a c t i v i t i e s i n f a s t - f l o w i n g w a t e r and the r e l a t i o n s h i p between g o n o p o d i a l swings and s e x u a l m o t i v a t i o n would become more e v i d e n t i n f a s t - f l o w i n g w a t e r . A d m i t t e d l y t h e s e s u g g e s t i o n s a re s p e c u l a t i v e , however, t h e y c o u l d e x p l a i n the i n t e r e s t i n g a f f e c t o f stream v e l o c i t y on the c o r r e l a t i o n s between g o n o p o d i a l swings and s i g m o i d d i s p l a y s . They a l s o c o u l d e x p l a i n why B a l l i n (1973) d i d n o t f i n d a c o r r e l a t i o n between g o n o p o d i a l swings- and s i g m o i d d i s p l a y s when he obs e r v e d f i s h o n l y i n s t i l l w a t e r . I n any cas e , stream v e l o c i t y does appear t o a f f e c t c o r r e l a t i o n s between the two b e h a v i o u r p a t t e r n . E x p e r i m e n t I I I n E x p e r i m e n t I I , males from t h r e e o f the f o u r s t o c k s showed a s i g n i f i c a n t c o r r e l a t i o n between s i g m o i d d i s p l a y s and g o n o p o d i a l swings i n f l o w i n g w a t e r , as d i d Caparo males i n s t i l l w a t e r ( T a b l e X V I ) . These r e s u l t s t h e r e f o r s u p p o r t those o f E x p e r i m e n t I . Stream v e l o c i t y a f f e c t s the c o r r e l a t i o n s between th e s e two b e h a v i o u r p a t t e r n s and perhaps t h i s may be due t o g o n o p o d i a l swings e x h i b i t i n g , to- a greater.^ and l e s s e r degree, two d i f f e r e n t f u n c t i o n s i n each stream c o n d i t i o n . 

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