@prefix vivo: . @prefix edm: . @prefix ns0: . @prefix dcterms: . @prefix skos: . vivo:departmentOrSchool "Science, Faculty of"@en, "Zoology, Department of"@en ; edm:dataProvider "DSpace"@en ; ns0:degreeCampus "UBCV"@en ; dcterms:creator "Crow, Richard Thomas"@en ; dcterms:issued "2010-03-23T23:50:46Z"@en, "1981"@en ; vivo:relatedDegree "Master of Science - MSc"@en ; ns0:degreeGrantor "University of British Columbia"@en ; dcterms:description """Populations of guppies living in different streams vary in their "behaviour and morphology. Some populations live in fast-flowing streams while others occupy slow-flowing water. I hypothesized that behavioural differences between the populations may represent adaptations to stream velocity. I tested seven predictions based on this hypothesis in two experiments. In Experiment I, I. examined the behaviour of laboratory reared guppies descendant from three natural populations. These guppies were examined at .03, .07, .10, and .20 m/sec stream velocities. Experiment II used wild-caught guppies from four populations. Their courtship behaviour was examined in still water (.00 m/sec) and at .08 m/sec velocity. As predicted, in Experiment I guppies from slow-flowing water showed l) greater cohesion, 2) less aggressive behaviour, and 3) a greater preference for the surface region of stream tanks than fast water fish. Also as predicted, slow water males performed fewer sigmoid displays "but more thrusts and gonopodial swings than fast water guppies. The persistence of these behavioural differences in laboratory raised descendants of isolated populations demonstrates a genetic contribution to the differences. Therefore the differences are presumably the product of natural selection and represent evolutionary adaptations. Experiment I also showed that stream velocity directly affects the performance of courtship behaviour by males. The frequency of sigmoid displays and gonopodial swings decreased markedly as stream velocity increased. As stream velocity increased, fast water males maintained their frequency and duration of sigmoid displays better than slow water males, thus providing evidence for "behavioural adaptation to stream velocity. The higher ratio of sigmoid displays : thrusts exhibited by fast water fish may also represent an adaptation to stream velocity. Stream velocity had no direct effect on group cohesion and aggression in the guppy. However, it directly affected guppy stream depth preference. Slow water fish could not maintain position at the top of the stream in faster-flowing water, whereas fish bred from an intermediate stream velocity population were able to do so. Fast water fish always preferred the bottom of the stream bed. In Experiment II wild-caught fish from fast and slow-flowing streams were tested together in two stream conditions. Again, as predicted, slow water fish performed fewer sigmoid displays but more thrusts and gonopodial swings than fast water fish. Because of the slow velocity used during the experiment, no effect of a fast stream velocity on courtship behaviour was obtained. During the experiment males generally preferred to court females from their own population. These preferences may represent partial isolating mechanisms. I concluded that differences between guppy populations in courtship behaviour and stream depth preference represent adaptations to different stream velocities. Stream velocity is therefore presumed to have been one of several environmental factors that interacted to shape the guppy's present behaviour."""@en ; edm:aggregatedCHO "https://circle.library.ubc.ca/rest/handle/2429/22415?expand=metadata"@en ; skos:note "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 PC P 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 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 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 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. 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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. 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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 . 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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 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 . "@en ; edm:hasType "Thesis/Dissertation"@en ; edm:isShownAt "10.14288/1.0095144"@en ; dcterms:language "eng"@en ; ns0:degreeDiscipline "Zoology"@en ; edm:provider "Vancouver : University of British Columbia Library"@en ; dcterms:publisher "University of British Columbia"@en ; dcterms:rights "For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use."@en ; ns0:scholarLevel "Graduate"@en ; dcterms:title "Behavioural adaptations to stream velocity in the guppy, Poecilia reticulata"@en ; dcterms:type "Text"@en ; ns0:identifierURI "http://hdl.handle.net/2429/22415"@en .