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Geographic variation in courtship behaviour of the guppy, Poecilia reticulata 1973

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CA- GEOGRAPHIC VARIATION IN COURTSHIP BEHAVIOUR OF THE GUPPY, POECILIA RETICULATA by PETER J . BALLIN A.B., U n i v e r s i t y o f C a l i f o r n i a , Berkeley, 1968 A THESIS SUBMITTED IN REQUIREMENTS MASTER PARTIAL FULFILMENT OF THE FOR THE DEGREE OF OF SCIENCE i n the Department o f Zoology We accept t h i s t h e s i s as conforming t o the re q u i r e d standard THE UNIVERSITY OF BRITISH COLUMBIA December, 1973 In p resent ing t h i s t h e s i s in p a r t i a l f u l f i l m e n t o f the requirements f o r an advanced degree at the U n i v e r s i t y of B r i t i s h Columbia, I agree that the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e fo r reference and study. I f u r t h e r agree tha t permiss ion fo r e x t e n s i v e copying o f t h i s t h e s i s f o r s c h o l a r l y purposes may be granted by the Head of my Department or by h i s r e p r e s e n t a t i v e s . It i s understood that copying or p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l ga in s h a l l not be a l lowed without my w r i t t e n p e r m i s s i o n . Department of OG ^ The U n i v e r s i t y of B r i t i s h Columbia Vancouver 8, Canada Date 3 i i ABSTRACT This t h e s i s attempts to e l u c i d a t e some adaptive m o d i f i c a t i o n s o f behaviour i n response t o environmental i n f l u e n c e s i n g e o g r a p h i c a l l y i s o l a t e d p opulations 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 , I examined c o u r t s h i p behaviour o f d guppies from three T r i n i d a d streams which d i f f e r i n s e v e r a l p h y s i c a l and b i o t i c parameters. Males o f two head- stream p o p u l a t i o n s (the P a r i a and Upper A r i p o R i v e r s ) are l a r g e r and more b r i g h t l y c o l o r e d than dd o f a lowland stream (the Guayamare R i v e r ) . Headstream dd are more conspicuous i n t h e i r c o u r t s h i p than downstream dd i n a one d -one % encounter: they e x h i b i t more d i s p l a y behaviour and move around the % more. I t was concluded that d i f f e r e n c e s i n be- haviour are g e n e t i c . I then i n v e s t i g a t e d e f f e c t s o f d i n t e r a c t i o n s on c o u r t s h i p . P a r i a <̂o* were much more aggressive than Upper A r i p o or Guayamare dd upon encountering other dd of the same race. Increased aggressiveness i n P dd occurred i n the presence o f , suggesting that dd f i g h t over D i s p l a y behaviour was reduced ( e s p e c i a l l y i n P dd , who fought) when two dd were i n t r o d u c e d to one another and a 2 a f t e r an i s o l a t i o n p e r i o d . However, no decrease was noted without an i s o l a t i o n p e r i o d . D i s p l a y be- haviours decreased w i t h the a d d i t i o n o f a t h i r d d i n the P a r i a and Upper A r i p o r a c e s , but not i n the Guayamare. I n c r e a s i n g the number of dd g e n e r a l l y heightened the l e v e l o f ^ - o r i e n t e d a c t i v i t y and reduced the distance between dd and the £. Preferences f o r f i s h o f the same race occurred. When three dd , one of each r a c e , were presented to a v i r g i n 2 s i m u l t a n e o u s l y , P a r i a dd fought only i n the presence o f P a r i a 22 , Upper A r i p o d i s p l a y s were more s u c c e s s f u l i n e l i c i t i n g sexual responses, e s p e c i a l l y from Upper Aripo 22 , and Guayamare dd t h r u s t more at Guayamare . Choice behaviour experiments r e v e a l e d t h a t v i r g i n P a r i a and Guayamare respond s e l e c t i v e l y to dd o f t h e i r own race. In another experiment, Upper A r i p o 22 responded much more r e a d i l y to d i s p l a y s from Upper A r i p o males. Females seem more l i k e l y to complete f u l l sexual responses w i t h dd o f t h e i r own race. I t appears t h a t r e l a t i v e l y l i g h t p r e d a t i o n and good v i s i b i l i t y have r e s u l t e d i n the e v o l u t i o n o f d i s p l a y i n g and f i g h t i n g as the primary mating s t r a t e g i e s i n headstreams. Heavy p r e d a t i o n and poor v i s i b i l i t y have r e s u l t e d i n s e l e c t i o n f o r downstream dd which d i s p l a y l e s s f r e q u e n t l y and r e l y more h e a v i l y on t a c t i l e s i g n a l s to i n s u r e i n s e m i n a t i o n . A simple model i s presented to suggest how b e h a v i o u r a l d i f f e r e n c e s evolved. The r e s u l t s are d i s c u s s e d i n l i g h t o f other s t u d i e s on geographic v a r i a t i o n i n c o l o r and mating behaviour. i v ACKNOWLEDGEMENTS I thank Dr. N. R. L i l e y , my research supervisor, f o r introducing me to guppies, providing support and f a c i l i t i e s , and c r i t i c a l l y reading the manuscript. I am also thankful to my research committee, Dr. I. E. Efford and Dr. J . D. McPhail, f o r comments and discussions. I am especially grateful to Dr. M. Cullen, who as v i s i t i n g professor at U.B.C, gave generously his advice, resourcefulness, and good cheer. I express my appreciation to a number of people who kindly assisted me during t h i s study: To fellow students, especially Dr. D. L. Kramer and Dr. B. H. Seghers, for discussions and comradeship; Mr. W. P. Wishlow, for technical assistance and a perspective on sanity; Mr. C. Parkinson and Mr. A. Koppel for help with equipment; Ms. J . Meredith for c r i t i c a l reading of the manuscript; Mr. S. W. Borden, Ms. D. Lauriente, and Ms. R. Kardynal for the computer work; Ms. L. Duncan for measuring guppy photos; Ms. V. L. Lennox for drawing some figures and putting up with me most of the time; and Ms. P. Waldron for typing. TABLE OF CONTENTS v Page Abstract • i i Acknowledgements • • • • i v L i s t of Tables x L i s t of Figures x i i Chapter 1. Introduction 1 2. The Environment and the Animals 4 A. The environment 4 1. Locations and i s o l a t i o n of the streams.... 4 2. A b i o t i c features 6 3. B i o t i c features 6 B. The f i s h 8 1. Range 8 2. Morphology — . 8 3. Sex r a t i o s 11 4. D i s t r i b u t i o n of f i s h i n the streams....... 13 C. Summary 14 3. Materials and Methods 15 A. Maintenance 15 B. Subjects 16 C. Observational set-ups 17 D. Recording and analyzing instruments 18 4. A Comparison of Male Courtship Strategies 19 v i Page A. General i n t r o d u c t i o n and behaviour p a t t e r n s described • 19 B. A d e s c r i p t i v e a n a l y s i s o f the c o u r t s h i p o f the three populations (Experiment 1) 21 1. I n t r o d u c t i o n 21 2. M a t e r i a l s and Methods 21 3. Re s u l t s 24 a. O r i e n t a t i o n 24 b. Contact movements 29 c. D i s p l a y 29 d. C o r r e l a t i o n s o f behaviours 35 C. Threshold d i s t a n c e s f o r c o u r t s h i p (Experiment 2 ) . . . . 35 1. I n t r o d u c t i o n 35 2. M a t e r i a l s and Methods 36 3. Re s u l t s 36 D. Competition i n c o u r t s h i p I (Experiment 3 ) . . . . 40 1. I n t r o d u c t i o n 40 2. M a t e r i a l s and Methods 40 3. Results 40 E. P i l o t experiments on the r o l e o f male-male aggression during c o u r t s h i p (Experiments 4, 5, and 6 ) . . 42 1. I n t r o d u c t i o n 42 2. Aggression and t e r r i t o r y (Experiment 4 ) . . 44 a. I n t r o d u c t i o n 44 b. M a t e r i a l s and Methods 44 c. R e s u l t s 44 v i i Page Chapter 3. Aggression and females (Experiment 5) . 47 a. Introduction 47 b. Materials and Methods 47 c. Results 47 4. Aggression, females, and density (Experiment 6)... 49 a. Introduction 49 b. Materials and Methods 49 c. Results 49 F. Competition in courtship II (Experiment 7) 50 1. Introduction 50 2. Materials and Methods 50 3. Results 52 G. Competition in courtship III (Experiment 8)...... 59 1. Introduction 59 2. Materials and Methods 59 3. Results 60 a. Effects of the different numbers of males on the courtship performed 60 b. Contributions of different males to the total courtship 61 c. Interactions between the males 63 d. Comparison of the races 67 „ H. Summary of the male's courtship... 70 1. The behaviour of single males 70 2. The behaviour of two or more males '. 70 v i i i Chapter P a g e 5. D i s c u s s i o n o f Male Cou r t s h i p S t r a t e g i e s . 74 6. The Consequences of Geographic I s o l a t i o n 81 A. I n t r o d u c t i o n . . . . . 81 B. Breeding between the races 81 C. I n t e r - p o p u l a t i o n competition i n c o u r t s h i p (Experiment 9) 82 1. I n t r o d u c t i o n " 82 2. M a t e r i a l s and Methods 83 3. Results 83 a. Male behaviours 83 b. Females as r e c i p i e n t s o f male behaviours.... 87 c. Female behaviours 89 d. Male-female i n t e r a c t i o n 92 D. Female s e l e c t i v i t y 94 E. Choice t e s t 1 (Experiment 10). 94 1. I n t r o d u c t i o n 96 2. M a t e r i a l s and Methods 96 3. Re s u l t s 96 F. Choice t e s t 2 (Experiment 11) 99 1. I n t r o d u c t i o n 99 2. M a t e r i a l s and Methods 99 3. Results 101 G. Reactive distances o f females (Experiment 12)....... 101 1. I n t r o d u c t i o n 101 2. M a t e r i a l s and Methods 103 i x Chapter Page 3. Results 103 H. Summary of the female's response 105 7. D i s c u s s i o n o f Geographic V a r i a t i o n 106 A. Geographic v a r i a t i o n i n c o l o r 106 B. Geographic v a r i a t i o n i n mating behaviour 113 L i t e r a t u r e C i t e d 118 Appendix 1. Some S p e c u l a t i o n and Findings about Black Markings o f the Male Guppy. . 131 2. A D e s c r i p t i o n o f Guppy Behaviour Pat t e r n s P e r t a i n i n g t o Courtship 134 X LIST OF TABLES Table Page l a . Temperature, pH, and DH v a r i a t i o n ; T r i n i d a d , 1969. 7 l b . Stream dimensions, f l o w , and v e l o c i t y ; T r i n i d a d , 1969.... 7 l c . Water t u r b i d i t y and c o l o r , s u b s t r a t e composition, and 7 amount of l i g h t i n g ; T r i n i d a d 7 2. Carotenoid pigment i n w i l d f i s h c o l l e c t e d i n 1967 12 3. Sex r a t i o s i n w i l d f i s h 12 4. Standard lengths o f f i s h observed i n Experiment 1........ 23 5a. O r i e n t a t i o n d i s t a n c e s 26 5b. Occurrence o f f i s h w i t h i n one male f i s h - l e n g t h (approx. 2 cm) o f each other 26 6. Angle of male long a x i s to long h o r i z o n t a l a x i s o f female w h i l e o r i e n t a t i n g 27 7. D i s p l a y d i s t a n c e s 32 8. D i f f e r e n c e s i n frequencies o f c o u r t s h i p a c t i v i t i e s o f i n d i v i d u a l males when t e s t e d alone w i t h a female (Experiment 1) or i n the presence o f another male (Experiment 7) 53 9. Male charges i n a competition s i t u a t i o n o f two males and one female. 54 10. Mean percentage of time i n t r i a l i n which a male was w i t h i n one male f i s h - l e n g t h (approx 2 cm) o f a female i n one-male and two-male s i t u a t i o n s 55 11. Occurrence of males w i t h i n a 2 cm r a d i u s o f a female i n the two-male s i t u a t i o n 56 x i Table ' Page 12. Correlation c o e f f i c i e n t s of courtship a c t i v i t i e s i n a two-male, one-female s i t u a t i o n . . . 58 13. Relative amount of display behaviour of f i r s t and second males on days 2 and 3. 66 14. Summary of morphological, behavioural, and environmental differences between the races 73 15. Response indices (# g l i d e s / # displays) f or v i r g i n females with males of d i f f e r e n t races i n competition with one another 95 x i i LIST OF FIGURES Figure Page 1. Northern T r i n i d a d 5 2. Male guppies from the P a r i a , Upper A r i p o , and Guayamare Rivers o f T r i n i d a d . 9 3. S i z e s o f wild-caught male guppies i n T r i n i d a d . . . . 10 4. Three-way choice maze 17 5. R e l a t i v e p o s i t i o n s recorded i n Experiment 1 22 6. Mean angles o f o r i e n t a t i o n by males with respect to the h o r i z o n t a l plane o f the female 28 7. Occurrence of males i n p o s i t i o n s above, below, and i n f r o n t o f a female 30 8. A comparison o f mean number o f bouts o f sigmoid d i s p l a y s and mean percentage o f time i n the t r i a l spent d i s p l a y i n g by males o f three races o f guppies.. 33 9. Schematic r e p r e s e n t a t i o n o f male d i s p l a y s i n va r i o u s p o s i t i o n s r e l a t i v e t o a female.... 34 10. Aquarium set-up f o r Experiment 2, top view 37 11. Mean times u n t i l f i r s t d i s p l a y and mean number o f bouts o f d i s p l a y at the s h o r t e s t d i s t a n c e (0 cm) from the females 39 12. Courtship o f two males i n the presence o f one female, expressed as percentages of t o t a l c o u r t s h i p («*"l + d 2) (a.) and time i n t r i a l (b.) 41 13. Courtship o f two males with one female, expressed i n seconds 43 x i i i F igure Page 14. Number o f charges by males i n each o f three ob s e r v a t i o n periods i n a l l - m a l e a q u a r i a . . . . . . . . . . . . . 46 15. Mean number o f male charges i n : (1) 5-male groups, (2) the same 5-male groups i n t o which 5 females were i n t r o d u c e d , and (3) the same groups as i n (2) from which 3 females were removed 48 16. Number of male charges i n groups o f 5 f i s h o f one sex, and these same groups a f t e r 5 a d d i t i o n a l f i s h o f e i t h e r the same or opposite sex were intro d u c e d 51 17. Comparison o f the c o u r t s h i p performed by d i f f e r e n t numbers o f males with one female 62 18. C o n t r i b u t i o n s o f d i f f e r e n t males t o t o t a l c o u r t s h i p on each day o f the experiment 64 19. Comparison of the c o u r t s h i p performed by males o f the three races on each o f the days o f the t r i a l s . . . 68 20. A simple model showing f a c t o r s i n f l u e n c i n g male conspicuousness 75 21. Experimental set-up f o r Experiment 9.. 84 i 22. Comparison o f the c o u r t s h i p performed by three males, one o f each r a c e , to s i n g l e v i r g i n females o f a l l races 86 23. Comparison o f the c o u r t s h i p performed by three males, one o f each r a c e , to v i r g i n females o f each race 88 x i v Figure Page 24. R e l a t i v e p o s i t i o n s o f f i s h and t h r u s t s r e c e i v e d by v i r g i n females from males o f d i f f e r e n t races i n competition w i t h one another . 90 25. D i s p l a y behaviours r e c e i v e d by v i r g i n females o f d i f f e r e n t races from males o f d i f f e r e n t races i n competition w i t h one another 91 26. Responses o f v i r g i n females t o males o f d i f f e r e n t races 93 27. Experimental set-up f o r Experiment 10 97 28. Experimental set-up f o r Experiment 11 100 29. Preferences f o r males o f d i f f e r e n t races by v i r g i n 1 n o and experienced females 30. Aquarium set-up f o r Experiment 12 104 31. Areas of the male guppy's l a t e r a l s u rface used t o q u a n t i f y b l a c k markings 133 Chapter 1. I n t r o d u c t i o n Numerous s t u d i e s of mating behaviour have been c a r r i e d out at the species l e v e l , but l i t t l e i n q u i r y has been d i r e c t e d toward 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 . Indeed, very l i t t l e e f f o r t has been expended t o c l a r i f y the adaptive nature of animal v a r i a t i o n i n general (see Chapter 7). Since s u r v i v a l depends upon the a b i l i t y o f i n d i v i d u a l s to c o n t r i b u t e to the subsequent genera t i o n , any given p o p u l a t i o n must have evolved or be e v o l v i n g the most e f f i c i e n t means to do so i n i t s p a r t i c u l a r e c o l o g i c a l s i t u a t i o n . There are good reasons f o r b e l i e v i n g t h a t the l o c a l breeding p o p u l a t i o n i s the e v o l u t i o n a r y u n i t of importance (e.g., E h r l i c h and Raven, 1969), and t h e r e f o r e i t would seem p r o p i t i o u s to begin a search f o r b e h a v i o u r a l d i f f e r e n c e s at the p o p u l a t i o n l e v e l . I f we f i n d b e h a v i o u r a l d i f f e r e n c e s between populations o f animals, can we then r e l a t e these d i f f e r e n c e s to d i s s i m i l a r i t i e s i n the environment? I f we can then a s c e r t a i n t h a t the s e l e c t i v e agents i n the environment i n f l u e n c e genotypes a s s o c i a t e d w i t h b e h a v i o u r a l d i f f e r e n c e s , we should gain some understanding o f how behaviour evolves. 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 , i s an i d e a l animal w i t h which t o assess b e h a v i o u r a l d i f f e r e n c e s between n a t u r a l p o p u l a t i o n s . Few animals express such a h i g h degree o f morphological v a r i a b i l i t y and occur i n such a multitude o f d i v e r s e environments. E s p e c i a l l y s t r i k i n g are d i f f e r e n c e s i n c o l o r p a t t e r n s o f dd from d i f f e r e n t areas. These c o l o r p a t t e r n s , not expressed i n the l a r g e r , d r a b l y a t t i r e d ??, seem to be i n v o l v e d i n i n t r a - s p e c i f i c communication and appear t o be important i n mating (Baerends, Brower, and Waterbolk, 1955; Haskins et^ al_. , 1961; L i l e y , 1966). In 2 a d d i t i o n , <£ guppies spend much of t h e i r day i n v o l v e d i n c o u r t s h i p a c t i v i t i e s , and are e a s i l y observed. A complete q u a l i t a t i v e and q u a n t i - t a t i v e d e s c r i p t i o n of guppy mating behaviour by L i l e y (1966) i s a v a i l a b l e as a b a s e l i n e f o r comparison o f n a t u r a l p o p u l a t i o n s . The pop u l a t i o n s chosen f o r t h i s study o r i g i n a t e i n three geographi- c a l l y i s o l a t e d streams i n T r i n i d a d , where the guppy i s n a t i v e , and represent three o f the most d i s s i m i l a r demes w i t h respect to morphology and ecology. Two o f the popu l a t i o n s o r i g i n a t e i n headstreams where the water i s c l e a r , predators r e l a t i v e l y few, and d* guppies l a r g e and b r i g h t l y c o l o r e d . P h y s i c a l f a c t o r s remain f a i r l y constant throughout the year i n these two l o c a t i o n s . However, c o l o r p a t t e r n s o f the <t guppies d i f f e r : those o f the P a r i a R i v e r impress one as being orange-red and those o f the Upper A r i p o R i v e r appear b l u i s h w i t h i r i d e s c e n c e and l a r g e o c e l l a t e d black spots. The t h i r d p o p u l a t i o n comes from a l a r g e r lowland r i v e r where the water i s t u r b i d , predators abundant, and <f guppies s m a l l and r e l a - t i v e l y d u l l i n c o l o r a t i o n . Here, i n the Guayamare R i v e r , p h y s i c a l c o n d i t i o n s such as t u r b i d i t y , water f l o w , and temperature are more v a r i a b l e than i n the headstream l o c a t i o n s . A more ext e n s i v e d e s c r i p t i o n o f the f i s h and the environment i s given i n Chapter 2. Haskins et_ al_. (1961), i n conjunction w i t h an e c o l o g i c a l study o f guppies i n T r i n i d a d , found that l a b - r a i s e d b r i g h t e r (to humans) <*V were more s u c c e s s f u l than " d u l l e r " d"d" i n inseminating ? ? . The study a l s o i n d i c a t e d that the b r i g h t e r guppies were more l i k e l y to s u f f e r p r e d a t i o n . The authors suggested t h a t sexual s e l e c t i o n was p o s s i b l y p r e s s u r i n g f o r more conspicuous d* c o l o r a t i o n , w h i l e p r e d a t i o n was s e l e c t i n g f o r c/ 3 c r y p s i s . In n e i t h e r case was the behaviour of the f i s h taken i n t o con- s i d e r a t i o n . This i s a major omission, as Seghers (1973) has shown w i t h respect to a n t i p r e d a t o r behaviour and I hope to show w i t h respect t o co u r t s h i p behaviour. My f i r s t o b j e c t i v e was to determine, through d e s c r i p t i v e and e x p e r i - mental analyses, whether or not <£ c o u r t s h i p behaviour does indeed d i f f e r from p o p u l a t i o n t o p o p u l a t i o n . My second o b j e c t i v e was to r e l a t e observed d i f f e r e n c e s i n c o u r t s h i p s t r a t e g i e s t o d i f f e r e n c e s i n the n a t u r a l e n v i r o n - ment. T h i r d l y , I examined the success o f d i f f e r e n t c o u r t s h i p s t r a t e g i e s and the responsiveness o f ? ? to va r i o u s oV i n an attempt to e l u c i d a t e the e f f e c t s o f geographic i s o l a t i o n and sexual s e l e c t i o n as mechanisms i n the e v o l u t i o n of behaviour and e t h o l o g i c a l i s o l a t i o n . 4 Chapter 2. The Environment and the Animals A. The environment 1. Locations and i s o l a t i o n o f the streams The three streams from which the f i s h o r i g i n a t e — the P a r i a , Upper A r i p o , and Guayamare R i v e r s - - a r e shown on the accompanying map of n o r t h - west T r i n i d a d ( F i g . 1). The P a r i a and the Upper A r i p o begin i n the Northern Mountain range at a l t i t u d e s o f approximately 1000 m and course through r e l a t i v e l y u n t r a c t a b l e j u n g l e . The Guayamare i s a lowland stream which flows through open country c u l t i v a t e d mostly w i t h sugar cane. A ten-meter w a t e r f a l l at the mouth o f the P a r i a and a f i v e - m e t e r w a t e r f a l l between the Upper and Lower A r i p o e f f e c t i v e l y separate these streams from any upstream movements o f guppies. Thus, we can c o n s i d e r the guppy populations o f these two streams t o be i n absolute geographic i s o l a t i o n . Guppies can be washed down stream, but the chance o f any o f the three p o p u l a t i o n s under study mixing are s l i m . To reach the Caroni system,gene flow from the P a r i a would have t o extend through many k i l o - meters of ocean, where guppies are r a r e l y , i f ever, found. Gene flow from the Upper A r i p o would i n v o l v e d about 20 k i l o m e t e r s o f the Lower Ar i p o and the C a r o n i , a canal to the Guayamare, and then s e v e r a l k i l o m e t e r s downstream.* In a d d i t i o n , data from Haskins et a l . (1961) i n d i c a t e t h a t guppies tend to adhere to l o c a l i z e d groups, suggesting that a d i s p l a c e d f i s h might cease i t s wanderings upon encountering more guppies. Furthermore, Eaton *The exi s t e n c e of t h i s canal was report e d t o L i l e y and Seghers but never observed by them. 5 F i g . 1. Northern T r i n i d a d . Arrows i n d i c a t e sources o f populations s t u d i e d . A f t e r Seghers (1973).  6 (1970) and Ehrlich and Raven (1969) suggest that reproduction by some migrants may not significantly affect the unique spectrum of genotypes in a population. Therefore, I believe that we may safely refer to the three populations as being geographically isolated. 2. Abiotic features Some measurements of chemical and physical parameters of the three streams may be found in Tables l a , b, and c. Note that the lowland river, the Guayamare, may be distinguished from the other two streams by i t s higher temperature, lack of shading, greater depth, larger volume of flow, and, perhaps most important to courtship, i t s turbidity. 3. Biotic features Vegetation i s absent except during flood waters in the Guayamare, when plants along i t s banks are submerged. The guppies seem to feed principally on invertebrate d r i f t . Most important for this study i s what feeds upon guppies. The ubiquitous cyprinodontid Rivulus h a r t i i has circumvented the waterfall barriers to the isolated headstreams, joining an otherwise impoverished fish fauna. This f i s h is moderately abundant in the Upper Aripo and relatively scarce in the Paria. As Seghers (1973) has demon- strated, Rivulus is an important predator mostly upon immature and young d" guppies. Potential aerial predators in the form of kingfishers (Chloroceryle spp.) have been sighted along the Paria, The predator situation in the Guayamare is quite different. Here, among an abundance of large fishes, the characid Hoplias malabaricus and the c i c h l i d 7 Table l a . Temperature, PH, and DH v a r i a t i o n , T r i n i d a d , 1969. Stream Dates N Temp, mean and range pH mean and range DH(ppm) mean and range Guayamare 16/3-30/6 9 29. r 27-31 7.0 6 . 8 - 7 . 1 108.6 70-130 Upper A r i p o 29/3-3/7 3 24.6 2 4 . 5 - 2 4 . 8 7.5 7 . 4 - 7 . 6 183.3 150-210 P a r i a 18/4-29/6 4 25.4 25 -26 .5 7.0 7 . 0 - 7 . 1 96.7 90-100 Table l b . Stream dimensions, f l o w , and v e l o c i t y ; T r i n i d a d , 1969. Stream Date Width mean Depth mean Volume o f flow V e l o c i t y § range(m) g range(m) (m 3/sec) (m/sec) Guayamare 30/6 2.00 1.50 1,080 .400 no data s i m i l a r to P a r i a Upper A r i p o P a r i a 18/4 §29/6 3.50 3-4 .17 . 1 4 - . 2 0 .0779 .0729- .0828 .168 163- .172 Table l c . Water t u r b i d i t y and c o l o r , s u b s t r a t e composition, and amount of l i g h t i n g ; T r i n i d a d . Stream T u r b i d i t y Guayamare Upper A r i p o P a r i a t u r b i d - - always, but v a r i a b l e c l e a r c l e a r C o l o r brown white l i g h t l y s t a i n e d Substrate L i g h t i n g (Cover) mud and s i l t r o cky, s i l t i n pools rocky no cover to o c c a s i o n a l sugar canes along shore 75% cover * o f low bush- es --medium to dense shade w i t h only a few spots exposed 50% cover o f low bushes -medium shade % o f cover i n d i c a t e s how much sky i s obscured by v e g e t a t i o n , a f t e r Seghers, 1973 8 C r e n i c i c h l a a l t a are the most s i g n i f i c a n t guppy predators (Seghers, 1973). A more d e t a i l e d treatment of guppy environments may be found i n Seghers (1973). Haskins et_ al_. (1961) give a general account of guppy ecology. B. The f i s h 1. Range The o r i g i n a l d i s t r i b u t i o n o f P o e c i l i a r e t i c u l a t a i s f r e s h water o f the i s l a n d of T r i n i d a d and the n o r t h e a s t e r n corner o f South America, o f which T r i n i d a d i s f a u n i s t i c a l l y a p a r t . Because of i t s remarkable adapta- b i l i t y , the guppy has been int r o d u c e d i n t o t r o p i c a l waters a l l over the world to a i d i n mosquito c o n t r o l . 2. Morphology ? guppies from the three p o p u l a t i o n s are v i r t u a l l y i n d i s t i n g u i s h a b l e , although a f t e r p r a c t i c e , I can d i s c e r n P a r i a from the other two types by t h e i r deeper bodies and darker shading. In marked c o n t r a s t , the c o l o r - f u l , s m a l l e r cfd* d i f f e r g r e a t l y and are easy to a s s i g n t o t h e i r home streams. In the c l e a r headwaters of the P a r i a and Upper A r i p o , the oV are r e l a t i v e l y l a r g e and conspicuously c o l o r e d . Compare them w i t h the s m a l l e r and much l e s s conspicuous Guayamare <*V ( F i g s . 2 and 3). L i l e y (unpubl.) has shown a g e n e t i c b a s i s f o r these s i z e d i f f e r e n c e s . Note the presence o f l a r g e areas o f orange-red i n the P a r i a f i s h . Seghers has compared the percentage of the body surface covered by ca r o t e n o i d pigments i n s e v e r a l races and has q u a n t i t a t i v e l y confirmed t h i s impression (Table 2; L i l e y and Seghers, unpubl). Furthermore, the q u a l i t y o f the c a r otenoids seems 9 F i g . 2 . Male guppies from the P a r i a , Upper A r i p o , and Guayamare Ri v e r s of T r i n i d a d . (Ektachrome: N.R. L i l e y ) . 9a 10 F i g . 3. S i z e s of wild-caught <t guppies i n T r i n i d a d . The v e r t i c a l l i n e i s the mean, the shaded b ar +_ 2 S.E., the empty bar +_ 1 S . D . , the h o r i z o n t a l l i n e the range, and the number i n d i c a t e s the sample s i z e . From Seghers, 1973. UPPER A R 1 P O ' ^«8i I 48 PAR 1A G U A Y A M A R E 1 0 0 58 i 1 •1 » * i 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Cf T O T A L L E N G T H (mm) o P3 11 d i f f e r e n t from those o f the other races. Turning t o other c o l o r s , Upper A r i p o f i s h appear b l u i s h , c o n t a i n i n g guanidine pigment, and e x h i b i t i r i d e s c e n c e and la r g e b l a c k s p o t s , o f t e n c i r c l e d w i t h i r i d e s c e n t white. The Guayamare f i s h express a great v a r i e t y o f c o l o r s , but they are subdued. Furthermore, they l a c k the markings on the body and t a i l which make the headwater f i s h conspicuous to the human and, presumedly, to the p i s c i n e eye. An a n a l y s i s o f the amount o f bl a c k markings and t h e i r p o s s i b l e s i g n i f i c a n c e was undertaken and i s re p o r t e d i n Appendix I. Two c o r r e l a t i o n s should be considered: (1) the more conspicuous dd occur i n c l e a r water and the l e s s conspicuous*/ occurs i n t u r b i d water; (2) the l a r g e r dd occur w i t h a s m a l l predator (Rivulus i n the Upper Ar i p o and P a r i a ) and the s m a l l e r d occurs w i t h l a r g e predators ( C r e n i c i - c h l a and Hoplias i n the Guayamare). Regarding the ca u s a l b a s i s o f the second c o r r e l a t i o n , Seghers (1973) has observed t h a t l a r g e guppies g i v e R i v u l u s h a n d l i n g d i f f i c u l t i e s and dd are eaten more r e a d i l y than ; whereas small guppies appear to be more e f f e c t i v e i n evading l a r g e preda- t o r s and ? ? are at no advantage. 3. Sex r a t i o s Seghers (1973) has found that unbalanced guppy sex r a t i o s c o i n c i d e w i t h the abundance of R i v u l u s . Thus we f i n d t h a t outnumber dd by 2 to 1 i n the Upper A r i p o , w h i l e the other two streams have more n e a r l y balanced sex r a t i o s (Table 3). Laboratory reared f i s h from a l l popula- t i o n s e x h i b i t a 1:1 sex r a t i o . Seghers presents c o n v i n c i n g evidence t h a t 12 Table 2. Carotenoid pigment i n w i l d f i s h c o l l e c t e d i n 1967. Expressed as the percentage of surface area covered on the l e f t s i d e o f the body. From Seghers, 1973. Stream N Avg SD Range P a r i a 33 28.9 11.3 10.4-50. .7 Upper A r i p o 40 12.4 " 7.7 1.4-33. ,8 Guayamare 50 9.4 4.1 1.4-20. .8 Table 3. Sex r a t i o s i n w i l d f i s h . From Seghers, 1973. Stream dV Immatures N dV? P a r i a 292 256 212 760 1.14 Upper A r i p o 252 528 565 1345 .48 Guayamare 110 120 85 315 .92 13 Rivulus i s indeed the cause o f t h i s imbalance. Male guppies were l e s s adept at a v o i d i n g capture than and were at a disadvantage i n s i z e - s e l e c t i v e .predatibn,., , 4. D i s t r i b u t i o n o f f i s h i n the streams Observations by Seghers i n d i c a t e t h a t guppies tend t o i n h a b i t pools and back-eddies where water v e l o c i t i e s are n i l or very c l o s e t o i t . F i e l d and l a b o r a t o r y observations by Seghers show t h a t Guayamare f i s h swim near the water su r f a c e and c l o s e to shore, w h i l e the headstream f i s h swim near the s u b s t r a t e and show no preference o f p o s i t i o n i n r e l a - t i o n t o shore. P o s i t i o n s taken by guppies i n the Guayamare seem t o c o r r e - spond t o where the predators are not. The degree o f s c h o o l i n g behaviour shown by the guppies corresponds to the degree o f p r e d a t i o n upon them. Thus, we f i n d s c h o o l i n g behaviour wellydeveloped i n f i s h from the Guayamare, p o o r l y developed i n the Upper A r i p o , and absent i n the P a r i a (Seghers, 1973). These d i f f e r e n c e s i n p o s i t i o n a l preferences and s c h o o l i n g behaviour p e r s i s t i n l a b o r a t o r y - r e a r e d s t o c k s . Seghers and I t h e r e f o r e , b e l i e v e t h a t these d i f f e r e n c e s 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 which r e s u l t from s e l e c t i o n due to p r e d a t i o n . 14 C. Summary 1. Three g e o g r a p h i c a l l y i s o l a t e d p o p u l a t i o n s o f guppies o r i g i n a t e from three e c o l o g i c a l l y d i f f e r e n t streams i n T r i n i d a d . 2. The populations w i t h l a r g e r , more conspicuous <£d frequent c l e a r headstreams of the P a r i a and Upper A r i p o Rivers,which c o n t a i n o n l y a small guppy predator. The s m a l l e r , l e s s conspicuous d occurs i n a t u r b i d lowland stream, the Guayamare, i n which s e v e r a l l a r g e predators occur. 3. The predator R i v u l u s i s probably r e s p o n s i b l e f o r an unbalanced sex r a t i o ( Id" :2 ??) i n the Upper A r i p o R i v e r . Sex r a t i o s are n e a r l y balanced i n the other two streams. 4. D i f f e r e n c e s i n p o s i t i o n s i n streams seem t o have r e s u l t e d from s e l e c t i o n by p r e d a t o r s . 5. The degree of s c h o o l i n g expressed by guppies corresponds to the degree o f p r e d a t i o n upon them. 6. D i f f e r e n c e i n c o l o r a t i o n , s i z e , and behaviour p e r s i s t i n l a b o r a t o r y p o p u l a t i o n s . This i m p l i e s t h a t the d i f f e r e n c e s have a g e n e t i c b a s i s . 15 Chapter 3. M a t e r i a l s and Methods A. Maintenance F i s h from the P a r i a , Upper A r i p o , and Guayamare R i v e r s (the f i s h p o p u l a t i o n s w i l l h e r e a f t e r be r e f e r r e d t o as P, UA, and G, r e s p e c t i v e l y ) were housed i n p h y s i c a l and v i s u a l i s o l a t i o n from one another i n 43 l i t e r (51.5 cm x 27 cm x 31 cm deep) and 61 l i t e r (62 cm x 32 cm x 31 cm deep) a q u a r i a . S i m i l a r c o n d i t i o n s p r e v a i l e d i n a l l the stock a q u a r i a , as f o l l o w s : Photoperiod: 12L : 12D L i g h t i n g : cool white 40 or 30-watt f l u o r e s c e n t bulbs suspended 15 cm above the water Subs t r a t e : medium g r a v e l V e g e t a t i o n : a l l p o s s i b l e combinations o f 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. Water: one h a l f to o n e - t h i r d o f each aquarium was changed r e g u l a r l y w i t h Vancouver c i t y water and l o c a l w e l l water pH: approx 6.0 F i l t r a t i o n : o u t s i d e f i l t e r s o f cha r c o a l and f i b e r g l a s s wool. Some aquaria used sub-gravel f i l t e r s , but these were r e p l a c e d due t o a tendency f o r the water t o become a c i d . Food: twice d a i l y on Tetra-Min, t r o u t chow, frozen b r i n e shrimp, and chopped Tubifex worms Temperature: during the f i r s t p a r t o f t h i s study, f i s h were housed i n four separate rooms. Temperature was c o n t r o l l e d by heater-thermo- s t a t s a t about 25 C i n three o f the rooms: the f o u r t h room was supposed- l y under t h e r m o s t a t i c c o n t r o l , but i n f a c t v a r i e d from 24 to 31 C. F i s h were moved to new f a c i l i t i e s i n October, 1970, where the c o n t r o l l e d temperature room kept the water at 25 + .5 C. Density: an attempt was made to keep aquaria at approximately equal d e n s i t i e s by n o n - s e l e c t i v e l y removing immature f i s h to l a r g e troughs. G f i s h seemed to m u l t i p l y more q u i c k l y than e i t h e r o f the other r a c e s . 16 In a d d i t i o n , a quaria w i t h the most p l a n t s u s u a l l y contained the most young. An "average" 43 1 aquarium h e l d about 50 f i s h , o f which s l i g h t l y more than h a l f were immature. B. Subjects F i s h were c o l l e c t e d i n T r i n i d a d i n 1967 ( L i l e y and Seghers) and 1969 (Seghers). See Seghers (1973) f o r c o l l e c t i n g techniques. W i l d - caught t o s i x t h generation l a b o r a t o r y - b r e d animals were observed i n experiments. A l l f i s h observed, except v i r g i n were from the stock aqu a r i a . Care was e x e r c i s e d to s e l e c t f i s h from as many aqu a r i a as p o s s i b l e t o minimize p o s s i b l e i n b r e e d i n g and d r i f t e f f e c t s . With the exception of the seven-month p e r i o d preceding Experiment 1, f i s h o f the same race were o c c a s i o n a l l y interchanged between aqu a r i a . V i r g i n ? ? were obtained by a l l o w i n g about a dozen pregnant to drop young i n a w e l l - p l a n t e d 43 1 aquarium. The mothers were removed when s u f f i c i e n t numbers o f young appeared, u s u a l l y i n a month's time. Males were removed when t h e i r sex became apparent. Before a l l b e h a v i o u r a l r e c o r d i n g s , f i s h were given some time t o become accustomed to the t e s t s i t u a t i o n . F i s h which d i d not remain calm were l e f t u n t i l they became so, or e l s e f i n a l l y r e j e c t e d . "Calm" i s defined as swimming about i n a r e l a x e d f a s h i o n , not remaining motionless w i t h r a p i d l y b e a t i n g p e c t o r a l f i n s , and not swimming e n e r g e t i c a l l y at the sides o f the aquarium. White-cloud Mountain f i s h , Tanichthys albonubes L i n , were u t i l i z e d as " d i t h e r f i s h " (Barlow, 1968a) t o calm guppies i n s e v e r a l experiments. Only mature f i s h were used i n experiments. F i s h were never fed p r i o r to o b s e r v a t i o n sessions on a given day. 17 At the c o n c l u s i o n of experiments 1, 3, 7, and 8 f i s h were anesthe- t i z e d i n MS 222 and were e i t h e r photographed f o r l a t e r measurement or measured w i t h c a l i p e r s . Males not photographed were sketched i n s t e n c i l e d o u t l i n e s to maintain a record o f markings. A l l f i s h were returned t o stock aquaria. c. O b s e r v a t i o n a l set-ups F i s h were observed i n three types o f co n t a i n e r . None contained v e g e t a t i o n . Food, water c o n d i t i o n s , temperature, and photoperiod were the same as i n the stock aquaria. Observation c o n t a i n e r s always i n c l u d e d some water i n which f i s h had l i v e d . 1. Nine a q u a r i a , h e r e a f t e r r e f e r r e d to as the obs e r v a t i o n a q u a r i a , were employed i n s e v e r a l experiments. Each had a volume o f 23 1 and dimensions of 41 cm x 21.5 cm x 26 cm deep. 2. Another aquarium, h e r e a f t e r r e f e r r e d to as the long aquarium, was used f o r s e v e r a l t e s t s . The volume was 22-1 and the dimensions were 61.5 cm x 17 cm x 21 cm deep. 3. A three-way choice maze was co n s t r u c t e d by Mr. C o l i n Parkinson of the Department o f Zoology workshop. S p e c i f i c a t i o n s : T o p I- F i g . 4. Three-way Choice Maze 18 The maze was l i g h t e d by fo u r 40-watt f l u o r e s c e n t bulbs 206 cm above the water and one 100-watt incandescent bulb 82 cm above the water 4. I observed f i s h i n the obs e r v a t i o n aquaria and the long aquarium by s i t t i n g q u i e t l y between 40 and 70 cm i n f r o n t o f them. F i s h i n the maze were observed from a di s t a n c e o f approximately 130 cm above and t o one si d e of the apparatus. D. Recording and a n a l y z i n g instruments The major equipment employed i s l i s t e d here and r e f e r r e d to i n the experimental s e c t i o n s . I photographed f i s h f o r measurement w i t h a Pentax Spotmatic 35 mm camera and Kodak High Speed Ek t a - chrome Type B f i l m . An Olympus 35 mm camera, e s p e c i a l l y o u t f i t t e d f o r b u l k - l o a d i n g and timed half-frame exposures photo- graphed f i s h on Kodak T r i - X Pan f i l m i n experiments 1 and 7. A Vanguard Motion Analyzer was used t o analyze f i l m obtained i n experiments 1 and 7. Measurements were punched d i r e c t l y onto p e r f o r a t o r tape which was de- coded i n an IBM 1130 computer. I b u i l t a keyboard which t r a n s f e r r e d my observations t o a computerized data a c q u i s i t i o n t e r m i n a l (here- a f t e r r e f e r r e d to as CDAT), b u i l t by Mr. Stephen Borden o f the Bio-Science Data Centre. As I observed f i s h , I pressed buttons corresponding to t h e i r be- haviour p a t t e r n s and p o s i t i o n s . The machine r e - ceived t h i s i n f o r m a t i o n and punched i t on p e r f o r a t o r tape, which was l a t e r decoded by the IBM 1130. Fre- quencies, d u r a t i o n s , i n t e r v a l s , and sequences o f a c t i v i t i e s were then a v a i l a b l e f o r p r i n t - o u t s and s t a t i s t i c a l analyses. A four-channel Rustrak event recorder A P h i l l i p s c a s s e t t e tape recorder 19 Chapter 4. A Comparison of Male Courtship S t r a t e g i e s A. General I n t r o d u c t i o n and Behaviour Pat t e r n s Described My i n i t i a l goal was to determine whether o r not p o p u l a t i o n d i f f e r - ences i n d" p a t t e r n s and c o l o r a t i o n have any s i g n i f i c a n c e i n c o u r t s h i p . I t soon became apparent t h a t d i f f e r e n c e s i n behaviour were more important features to observe. Color p a t t e r n s have probably evolved t o enhance the s i g n a l value of behaviour p a t t e r n s r a t h e r than the converse. When one gazes i n t o an aquarium o f guppies, one cannot help but be impressed by the seemingly i n c e s s a n t a t t e n t i o n given t o by <t<t. For convenience, we may d i v i d e the d"'s c o u r t s h i p a c t i v i t i e s i n t o three cate- g o r i e s : o r i e n t a t i o n , contact movements, and d i s p l a y ( L i l e y , 1966). O r i e n t a t i o n i s simply m a i n t a i n i n g v i s u a l and s p a t i a l bearings on the ? , u s u a l l y f a c i n g her. Contact movements: a d" may t h r u s t h i s gonopodium at the g e n i t a l pore o f a ?, but t h i s r a r e l y inseminates her. From time t o time a d" d i s p l a y s to a ? . When t h i s sigmoid d i s p l a y (Baerends et^ al_. 1955) i s performed to a r e c e p t i v e ?, i t may e l i c i t a sexu a l response r e - s u l t i n g i n c o p u l a t i o n , the normal mode o f sperm t r a n s f e r . However, s i n c e a ? only becomes r e c e p t i v e at approximately three-week i n t e r v a l s ( L i l e y , 1966: 43), most o f the d"'s d i s p l a y s j u s t l e a d to more d" c o u r t s h i p . The d i s p l a y , which l a s t s about two seconds, i s h i g h l y r i t u a l i z e d and i s empha- s i z e d by changing c o l o u r and marking p a t t e r n s , spreading median f i n s , q u i v e r i n g , and r o c k i n g to and f r o . I t s e f f e c t i v e n e s s as a s i g n a l i s pre- sumedly thereby enhanced. Of a l l the d" • s c o u r t s h i p a c t i v i t i e s , the 20 d i s p l a y most o f t e n leads to c o p u l a t i o n . A number o f s t u d i e s of guppy r e p r o d u c t i v e behaviour have been reported i n the l i t e r a t u r e (see L i l e y , 1966: 26-28). Sexual communication appears to be l a r g e l y v i s u a l , although Amouriq (1964, 1965a, b, and 1967) and G a n d o l f i (1969) r e p o r t the presence of o l f a c t o r y cues. L i l e y (1969) f i n d s d i f f i c u l t y i n a t t a c h i n g importance to a chemical sex a t t r a c t a n t i n guppies. For a d e t a i l e d d e s c r i p t i o n and a n a l y s i s o f guppy c o u r t s h i p r e f e r to L i l e y (1966),and Appendix 2). The accompanying l i s t o f o* behaviour p a t t e r n s recorded i n my e x p e r i - ments f o l l o w s L i l e y (1966) except where noted. O r i e n t a t i n g : i n c l u d e s F o l l o w i n g , Watching, C i r c l i n g , R e t r e a t i n g , and Weak sigmoids Gonopodial swing: ( O c c a s i o n a l l y performed when the <f was not c o u r t i n g ) . Sigmoid d i s p l a y : o n l y the f u l l y developed d i s p l a y was recorded The a d j e c t i v e s f r o n t a l and general were dropped i n fa v o r o f l o c a t i n g the d i s p l a y s by denoting them as " i n f r o n t " i f they were performed w i t h i n a twenty-degree angle extending h o r i z o n t a l l y forward from a p o i n t between the ? *s eyes, or "not i n f r o n t " . The o b j e c t i o n t o " f r o n t a l " i s t h a t the term i s used t o denote a type o f d i s p l a y i n many f i s h e s and not i t s l o c a t i o n . Leap Thrust C o p u l a t i o n attempt and C o p u l a t i o n Jerk Snout contact w i t h g e n i t a l pore o f £: t h i s behaviour d i d not occur i n the f i s h L i l e y s t u d i e d , even though he looked f o r i t . I t d i d occur i n f r e q u e n t l y i n the populations observed here. Chase: a d* i n i t i a t e s a f l e e i n g response by the ? , u s u a l l y by contact w i t h her g e n i t a l r e g i o n , and pursues her. Non-courtship behaviour a s s o c i a t e d w i t h c o u r t s h i p o c c u r r i n g between dV: S p a r r i n g T a i l - b e a t i n g Charge: aggression which i n c l u d e s b i t e s at another f i s h , attempted b i t e s , and chasing c u l m i n a t i n g i n attempted b i t e s . Few, i f any, b i t e s a c t u a l l y made conta c t . B. A d e s c r i p t i v e a n a l y s i s o f the c o u r t s h i p o f the three p o p u l a t i o n s (Experiment 1) 1. I n t r o d u c t i o n The purpose o f t h i s set o f observations was to determine whether there are d i f f e r e n c e s i n c o u r t s h i p between dV of the P a r i a , Upper A r i p o , and Guayamare R i v e r s , and t o d e s c r i b e the nature o f these d i f f e r e n c e s . 2. M a t e r i a l s and Methods A ? and a <f from one race which had been r e s i d i n g i n separate aquaria were i n t r o d u c e d , at about 0900 hours, i n t o one s i d e o f an obser- v a t i o n aquarium which had been d i v i d e d i n h a l f (20 cm x 21.5 x 25 cm deep). At about 1700 hours a brown, opaque p l e x i g l a s p a r t i t i o n was placed between the two f i s h , then removed at about 0900 hours the f o l l o w - i n g morning. Observations commenced i f both f i s h were calm. I f the f i s h were not calm, they were l e f t together u n t i l 1700 hours, when they were separated u n t i l the next morning. T h i s procedure was continued u n t i l the f i s h met the beha v i o u r a l c r i t e r i a , which was u s u a l l y i n two or three days. A few f i s h never calmed s u f f i c i e n t l y and were not used. Of 18 independent t r i a l s attempted f o r each r a c e , 13 P, 16 UA, and 17 G were completed. The standard lengths o f the f i s h observed are found i n Table 4. Each observation p e r i o d l a s t e d 15 minutes and a l l t r i a l s were r e - corded between 0900 and 1300 hours ( l i g h t s on at 0800 h r s . ) . A l l o f the c o u r t s h i p behaviour l i s t e d i n Chapter 4.A., along w i t h i n f o r m a t i o n on the r e l a t i v e p o s i t i o n of the d t o the $ was recorded with CDAT. R e l a t i v e p o s i t i o n s recorded were as f o l l o w s : A d moved, above or below a ? from the l e v e l p o s i t i o n . JA&OVE F i g . 5 R e l a t i v e p o s i t i o n s recorded i n Experiment 1. Occurrence o f a d" w i t h i n a 2 cm r a d i u s around the ? was a l s o noted. Two cm represents approximately one o* f i s h length and was thus e a s i l y estimated. Every 15 seconds f o r the d u r a t i o n o f a t r i a l , the Olympus camera photographed the observation chamber and an overhead m i r r o r , which allowed a view from the top. Measurements o f o r i e n t a t i o n and d i s p l a y d i s t a n c e s and angles were made on the motion anal y z e r . U n f o r t u n a t e l y the camera f a i l e d r e p e a t e d l y so that o n l y about one-half the t r i a l s were photographed. The r a t i o n a l e f o r measuring s p a t i a l r e l a t i o n s h i p s and amount o f d movement to v a r i o u s p o s i t i o n s r e l a t i v e t o the ? i s as f o l l o w s . Males 23 Table 4. Standard lengths o f f i s h observed i n Experiment 1. Race dV mean(mm) P 16.40 UA 16.40 G 15.75 Range mean(mm) 14.50-17.75 15.25-19.25 13.75-19.75 Range 24.90 23.00-27.00 25.30 22.50-29.00 26.18 22.50-30.25 24 who changed p o s i t i o n more o f t e n would presumedly catch the eye o f a predator and a ? more r e a d i l y than who changed p o s i t i o n l e s s . Greater distances from the ¥ might p l a c e over deeper water where predators might l i e i n w a i t . Since the environments of the p o p u l a t i o n s d i f f e r i n both number of predators and v i s i b i l i t y , I thought t h a t the dV might e x h i b i t adaptive d i f f e r e n c e s i n t h e i r u t i l i z a t i o n o f space. 3. Results Data was f i r s t analyzed p a r a m e t r i c a l l y (one-way a n a l y s i s of v a r i a n c e ) , but B a r t l e t t ' s t e s t i n d i c a t e d t h a t the v a r i a n c e s o f most o f the beha- v i o u r a l measures were probably not homogeneous. The non-parametric K r u s k a l - W a l l i s one-way a n a l y s i s of v a r i a n c e was t h e r e f o r e employed t o compare the p o p u l a t i o n s . On the photographic d a t a , a parametric one-way a n a l y s i s o f v a r i a n c e was j u s t i f i e d and used. Comparisons o f p a i r s o f races was done by K r u s k a l - W a l l i s simultaneous p r o b a b i l i t i e s i n the one case, and Scheffe's t e s t f o r m u l t i p l e comparisons w i t h unequal sample s i z e i n the o t h e r case. a. O r i e n t a t i o n 1) Time spent o r i e n t a t i n g The three races d i f f e r e d i n percentage o f time i n the t r i a l spent o r i e n t a t i n g and the l e n g t h o f each bout of o r i e n t a t i o n . Fewer d i s p l a y s by G dV (see p a r t c) r e s u l t e d i n more and longer o r i e n t a t i o n p e r i o d s . G d V o r i e n t e d to the 93% of the t o t a l t r i a l time, w h i l e P rfd" d i d so 82% and UA oV , 85% of the time (p = . 0 4 2 ) . The mean bout lengths o f o r i e n t a t i o n were: G, 51.1 seconds; P, 30.8 seconds, UA, 36.2 seconds — A l l p r o b a b i l i t y values a r i s e from the K r u s k a l - W a l l i s one-way a n a l y s i s of v a r i a n c e unless otherwise s t a t e d . 25 (p = .003). Time and number of times not a t t e n d i n g t o the ? d i d not d i f f e r between the r aces. 2) Distance o f d from ? d u ring o r i e n t a t i o n Photographic a n a l y s i s r evealed t h a t the mean d i s t a n c e o f the o* from the ? d u r ing o r i e n t a t i o n was s i g n i f i c a n t l y l e s s i n the UA than i n the P and G races (p<.001, parametric one-way a n a l y s i s o f v a r i a n c e ; Table 5a). However, a d i f f e r e n t impression was gained from l e s s p r e c i s e data c o l - l e c t e d on the data a c q u i s i t i o n system (though the source o f t h i s d i f f e r - ence i s not c l e a r ) . Here the presence of a <t w i t h i n one d f i s h - l e n g t h t o a ? was scored. The r e s u l t s (Table 5b) show P oV came w i t h i n a f i s h - l e n g t h of a ? s i g n i f i c a n t l y l e s s o f t e n than UA o r G dd (p = .04) and spent l e s s time there (p = .001). Once G dd moved w i t h i n t h e i r l e n g t h o f a ?, they remained there longer than P o r UA ^ ( p = .0002). 3) O r i e n t a t i o n angles o f d w i t h respect to $ The angles at which dd o r i e n t e d to %% were measured from the f i l m . An uncanny c o n s i s t e n c y of d long a x i s d i r e c t i o n i n r e l a t i o n to the long ax i s i n the h o r i z o n t a l plane o f the ? was recorded: 90° on e i t h e r s i d e o f her i n a l l races (Table 6 ) . Angles above and below the h o r i z o n t a l plane o f the % showed great v a r i a t i o n ( F i g . 6 ) , P dd averaged s l i g h t l y g r e a t e r angles below the than d i d UA dd who s l i g h t l y exceeded G dd. 4) Changes i n d p o s i t i o n w i t h respect to % As s t a t e d e a r l i e r , oVspent most o f t h e i r time o r i e n t a t i n g , o f t e n changing p o s i t i o n r e l a t i v e to the ? . When movement o f the dd to p o s i - t i o n s above and below the plane of the are examined, r a c i a l d i f f e r e n c e s 26 Table 5a. O r i e n t a t i o n d i s t a n c e s . Race P UA G Number o f f i s h 7 9 5 Number o f measurements 65 71 50 Mean di s t a n c e (cm) 4.5 3.4 4.9 S.D. (cm) 2.6 1.9 2.3 Range (cm) 1.5-13.4 1.0-14.6 1.4-11.1 One-way a n a l y s i s o f v a r i a n c e , p<.001. Table 5b. Occurrence of f i s h w i t h i n one <f f i s h - l e n g t h (approx. 2 cm) of each other . Race P UA G K r u s k a l - W a l l i s one- n 13 16 17 way a n a l y s i s of v a r i a n c e Mean number o f bouts 20.6 36.6 34.1 p = .04 Mean percentage o f time 5.28 12.71 19.34 p = .001 Mean bout length (sec) 2.12 2.77 5.61 p = .0002 Table 6. Angle o f d" long a x i s to long h o r i z o n t a l a x i s o f ? wh i l e o r i e n t a t i n g . Race No. o f No. o f Mean angle S.D. f i s h Measures ( r i g h t or l e f t ) P 7 65 91.0 10.1 UA 9 71 89.5 2.9 C 5 50 90.1 1.6 One-way a n a l y s i s o f v a r i a n c e , p-**. 1. 28 F i g . 6. Mean angles o f o r i e n t a t i o n by </c/ w i t h respect t o the h o r i z o n t a l plane of the ? . Angles were the same on both the l e f t and r i g h t s i d e s o f the The wedges c l o s e s t to the ? represent standard d e v i a t i o n s around the mean. One-way analys o f variance i n d i c a t e d that p >.l th a t the d i f f e r e n c e s arose by chance. 28a [ / \ / \ / ' j \ / / 1 v / A \ / \ 29 become apparent: ( F i g . 7a). G <i<£ moved to p o s i t i o n s below the ? l e s s o f t e n (p = .04) and remained there f o r the s m a l l e s t percentage o f time (p = .1). P d V tended t o spend a g r e a t e r percentage o f time both above and below the ? than other d V ( F i g . 7b). Besides moving above the l e s s o f t e n and f o r l e s s time (p = .01), UA d V ' mean bout length i n that p o s i t i o n was a l s o s h o r t e r (p = .03). Mean bout length below the ? d i d not d i f f e r between the races ( F i g . 7 c ) . The times above and below do not t o t a l 100% because d"d* were o f t e n l e v e l w i t h the ?; i . e . , some p a r t o f the d "% body l a y w i t h i n two h o r i z o n t a l planes extending from the ? 's most d o r s a l and most v e n t r a l body p a r t s ( F i g . 5). The p r o b a b i l i t i e s o f d i f f e r e n c e s between the races i n being i n a p o s i t i o n w i t h i n a 20° h o r i z o n t a l angle d i r e c t l y i n f r o n t of the ? i s s l i g h t ( F i g . 7a, b, c ) . O v e r a l l there was an i n d i c a t i o n t h a t P and UA <̂ d" moved around the more than G d V w h i l e o r i e n t a t i n g (mean p o s i t i o n changes i n t r i a l : P, 69.5; UA, 68.6; G, 63.1). b. Contact movements The frequency o f t h r u s t s d i d not d i f f e r s i g n i f i c a n t l y between races i n t h i s experimental s i t u a t i o n (P = 1.3, UA = .6, G = 1.0; p> .5). Very few c o p u l a t i o n attempts occurred because a l l but e i g h t (3 P, 1 UA, 4 G) were un r e c e p t i v e . There was a suggestion t h a t snout contact w i t h the ?.'s g e n i t a l pore, though i n f r e q u e n t , occurred more o f t e n i n UA d V than others (P = 1.7, UA = 3.1, G = 2.2; p < . 3 ) . c. D i s p l a y The d i s t a n c e from the % at which the c/d" performed sigmoid d i s p l a y s was approximately f i v e cm and d i d not d i f f e r between the races (Table 7). 30 F i g . 7. Occurrence o f d<£ i n p o s i t i o n s above, below, and i n f r o n t o f a ? . N = 13 f o r P, 16 f o r UA, and 17 f o r G. P r o b a b i l i t y values are d e r i v e d from the K r u s k a l - W a l l i s one-way a n a l y s i s o f v a r i a n c e . a. Mean number of times oV moved i n t o d i f f e r e n t p o s i t i o n s , b. Mean percentage o f time c/V spent i n d i f f e r e n t p o s i t i o n s , c. Mean length o f time o V spent i n d i f f e r e n t p o s i t i o n s . N = 11 f o r P, 13 f o r UA, and 11 f o r G i n the p o s i t i o n below the ? . 30a . 0 2 u > o < CO Ui x: o 03 hi e» S3 » 5 5 5 5 Ui o •J Ui 3 5 3 0 2 5 2 0 1 5 1 0 5 0 5 1 0 U A P = . 0 4 P > .4 0 5 10 IN FRONT 30b w X In O w a < H SS Ui o 0 5 ( 4 OH SS •< w as w > o O •J Ui 14 1 2 10 r5 6 4 2 0 2 4 P = . 0 1 U A P > .8 P = .1 i i i > 0 2 4 IN FRONT b . MEAN LENGTH OF TINE (SEC) BELOW ABOVE O ro to cn TJ v 'ro C > TJ II o O » o 2 H 3 1 G d'd" d i s p l a y e d l e s s f r e q u e n t l y and f o r l e s s time when a l l races are compared (p = .02 and .04 r e s p e c t i v e l y , F i g . 8). D i f f e r e n c e i n p o s i t i o n r e l a t i v e t o d u r i n g d i s p l a y occurred not j u s t because of v a r i a t i o n i n t o t a l d i s p l a y a c t i v i t i e s between the races. For i n s t a n c e , P <JV d i s p l a y e d above the ? longer and more o f t e n (p = .0002 and .001, r e s p e c t i v e l y ) than UA and G d'd", and UA dV d i s p l a y e d w i t h i n a f i s h - l e n g t h (approximately 2 cm) o f the ? more o f t e n and f o r longer times (p = .0009 and .0008, r e s p e c t i v e l y ) than P and G dV. Other d i f f e r e n c e s between races i n l o - c a t i o n of d i s p l a y more c l o s e l y f o l l o w e d the o v e r a l l d i f f e r e n c e s i n bouts and percentage time o f d i s p l a y mentioned above and i n F i g . 8 ( F i g . 9a,b), The average number o f changes i n d i s p l a y p o s i t i o n (above, below, l e v e l ; i n s i d e or outside one f i s h - l e n g t h ) during a t r i a l was 7.7 f o r G tfd", 28.2 f o r P dV and 27.9 f o r UA d'd1, but the number o f p o s i t i o n changes per d i s p l a y d i d not d i f f e r (P, 2; UA, 1.8; G, 1.8). I c o n s i d e r the num- ber o f p o s i t i o n changes i n a time p e r i o d the most e c o l o g i c a l l y r e l e v a n t measure because the amount o f motion complements r a c i a l d i f f e r e n c e s i n the very obvious d i s p l a y behaviour and thereby enhances r a c i a l d i f f e r e n c e s i n conspicuousness. I f we examine d i s p l a y times i n v a r i o u s p o s i t i o n s as a p r o p o r t i o n o f t o t a l d i s p l a y times f o r each race s e p a r a t e l y , we f i n d G d'd" i n f r o n t o f the ? more o f t e n (32%) than P and UA d'd" (20% and 14%, r e s p e c t i v e l y ) . P d'd" remained above most and UA d'd" remained w i t h i n a f i s h - l e n g t h most ( F i g . 9 c ) . While r e l a t i v e p o s i t i o n s o f two f i s h n e c e s s a r i l y depends upon both of t h e i r movements, I b e l i e v e that the d i f f e r e n c e s found here are due to d i f f e r e n c e s i n the d'd* r a t h e r than a r e f l e c t i o n o f ? response p a t t e r n s . Table 7. D i s p l a y Distances Race n d i s t a n c e Range (cm) (cm) P 8 4.5 1-13 UA 14 5.3 2-15 G 6 5.2 3-8 One d i s p l a y (the f i r s t c l e a r l y measurable on the f i l m ) was measured f o r each f i s h . 33 F i g . 8. A comparison o f mean number o f bouts o f sigmoid d i s p l a y s and mean percentage of time i n the t r i a l spent d i s p l a y i n g by dV of three races o f guppies. K r u s k a l - W a l l i s one-way a n a l y s i s o f var i a n c e . °/o T I M E O F T R I A L CN oo CN CM CM <N 00 o II O i i CN 00 CN S i no8 34 F i g . 9. Schematic r e p r e s e n t a t i o n o f <? d i s p l a y s i n v a r i o u s p o s i t i o n s r e l a t i v e to a ? . The f i s h represents a ? , the dotted c i r c l e r e - presents a 2 cm c y l i n d e r w i t h i t s a x i s h o r i z o n t a l and c o i n c i d e n t w i t h the f i s h ' s long a x i s . Each group of histograms represents the occur- rence of P, UA, and G oV ( i n t h a t order) d i s p l a y i n g i n v a r i o u s p o s i t i o n s r e l a t i v e to the $ : above, below, l e v e l , i n f r o n t , and i n s i d e o r out- s i d e approximately 2 cm o f the ? . Level d i s p l a y s occurred on both si d e s o f the ?. P r o b a b i l i t y values from the K r u s k a l - W a l l i s one-way a n a l y s i s o f variance are i n s e r t e d where a d i f f e r e n c e between races e x i s t s . a. Number o f times <f<? were found d i s p l a y i n g i n v a r i o u s p o s i t i o n s r e l a t i v e t o a ?. b. Percentage of time i n t r i a l oV were found d i s p l a y i n g i n v a r i o u s p o s i t i o n s r e l a t i v e to a $, c. Percentage of time <f<? were found d i s p l a y i n g i n v a r i o u s p o s i t i o n s r e l a t i v e to a ? , expressed as percentages o f t o t a l d i s p l a y time f o r each race ( i . e . , each race d i s p l a y e d 100%). 34a P = .001 54 a. 3 4 b 34c C . 35 F i s h d i d not d i f f e r i n mean number of gonopodial swings (P = 4.6 per t r i a l , UA = 4.2, G = 5.0; p > . 8 ) , or leaps (P = .8, UA = .8, G = .5, p > 8 ) . d. C o r r e l a t i o n s o f behaviours C o r r e l a t i o n c o e f f i c i e n t s were obtained between a l l recorded aspects o f c o u r t s h i p , between ? l e n g t h and a l l aspects o f <S c o u r t s h i p and s p a t i a l r e l a t i o n s , and between <f length and a l l aspects o f h i s c o u r t - s h i p and s p a t i a l r e l a t i o n s . The o n l y s i g n i f i c a n t r e l a t i o n obtained was a s t r o n g p o s i t i v e c o r r e l a t i o n between numbers of d i s p l a y s and leaps i n G (R = .82, p<.0001). I know from personal observations that leaps are always preceded by d i s p l a y s - - P and UA d'd* d i d not leap enough t o y i e l d s i g n i f i c a n t c o r r e l a t i o n c o e f f i c i e n t s . Apparently the s i z e o f e i t h e r the d" or $ f i s h had no b e a r i n g on d* c o u r t s h i p a c t i v i t y i n t h i s s i t u a - t i o n . C. Threshold d i s t a n c e s f o r c o u r t s h i p (Experiment 2) 1. I n t r o d u c t i o n This experiment was undertaken before the photographic a n a l y s i s o f Experiment 1 was completed. Because of the g r e a t e r t u r b i d i t y and h i g h e r degree of p r e d a t i o n i n the Guayamare R i v e r I hypothesized t h a t P and UA d'd" would d i s p l a y at g r e a t e r d i s t a n c e s from the $ than G d'd* . The experiment t h e r e f o r e was designed t o compare the c o u r t s h i p of the d'd1 of the three races when prevented from approaching nearer than c e r t a i n d i s - tances to . Furthermore,having shown the discrepancy i n d i s p l a y f r e - quencies between the races i n the previous experiment, I hypothesized that 3 6 P and UA dd would a l s o d i s p l a y more f r e q u e n t l y and w i t h s h o r t e r l a t e n c i e s than G dd . 2. M a t e r i a l s and Methods Three o f the same s i z e (24.2 +_ .1 mm), one o f each r a c e , were pl a c e d i n the long aquarium as shown i n F i g . 10. These ? ? were chosen f o r calmness. E i g h t dd of each race were i n d i v i d u a l l y i s o l a t e d the same day. The f o l l o w i n g day, s i x dd. of each race were t e s t e d three times each w i t h three d i f f e r e n t minimum di s t a n c e s from the ? ? --0, 5, and 10 cm—determined by i n s e r t i o n o f c l e a r p l e x i g l a s p a r t i t i o n s ( F i g . 10). Males were observed i n an order (P, G, UA) so that they had app r o x i - mately equal i s o l a t i o n periods between t r i a l s . The order i n which a d^ was t e s t e d at the minimum d i s t a n c e s was determined by chance. D i t h e r f i s h swam i n an aquarium behind the long aquarium ( F i g . 10). I recorded the f o l l o w i n g : time u n t i l f i r s t d i s p l a y , number o f d i s - p l a y s , d i s p l a y d i s t a n c e s (+1 cm, di s t a n c e s marked on aquarium) and whether o r not the d ever attended to the % during the t e s t , A t t e n t i v e - ness was def i n e d as d o r i e n t a t i o n and approach to the ? ? , 3. R e s u l t s When dd were p l a c e d i n the long aquarium they g e n e r a l l y began atte n d i n g to the immediately i f they were going to attend at a l l . One UA d d i d not behave calmly enough on h i s f i r s t t r i a l and was replaced, Contrary to e x p e c t a t i o n , no f i s h , w i t h the exception o f one P o* , d i s p l a y e d w i t h the 5 and 10 cm p a r t i t i o n s i n p l a c e . This was not because the f i s h d i s p l a y e d only w h i l e very c l o s e to the , because v i r t u a l l y 37 F i g . 10. Aquarium set-up f o r Experiment 2, top view. Three • enclosed i n a 5 cm wide s e c t i o n bounded by opaque p l e x i g l a s on one s i d e and c l e a r p l e x i g l a s on the s i d e o f the <f . The could swim f r e e l y throughout most of the aquarium (approaching to w i t h i n 2 mm of the *"?) hut could be l i m i t e d i n h i s most proximal approach to the ?? by a c l e a r p l e x i g l a s p a r t i t i o n placed at e i t h e r 5 or 10 cm from the ? ? * s p a r t i t i o n ( p o s i t i o n s shown by dotted l i n e s ) . i DITHER FISH ^ V ' \ \ / *** r T \ P P n r f . 1 I ! ' ! 1 1 1 1 1 1 * fcw • — - -VJ • 1 1 1 •* %% TEST <£ 38 a l l the f i s h d i s p l a y e d between 4 and 7 cm from them as i n Experiment 1 (Table 7 ). The apparent reason f o r t h i s behaviour i s th a t the d" must f i r s t come very c l o s e to the ? before i n i t i a t i n g the d i s p l a y . Almost a l l d i s p l a y s were preceded by the <? and ? being separated only by the thic k n e s s of the p l e x i g l a s p a r t i t i o n (3 mm), w i t h the <t backing o f f t o perform. F i g . 11 shows times u n t i l f i r s t d i s p l a y s and frequencies o f d i s - p l a y s . The K r u s k a l - W a l l i s one-way a n a l y s i s o f v a r i a n c e r e f l e c t s the d i f f e r e n c e s between a l l three races i n time u n t i l the f i r s t d i s p l a y (p<.009). P and UA d'd" d i s p l a y e d most f r e q u e n t l y ( f o r both P-G and UA-G comparisons, p = .004, Mann-Whitney U t e s t , o n e - t a i l e d ) and w i t h a s h o r t e r l a t e n c y to the f i r s t d i s p l a y (P-G, p = .067; UA-G, p - .047; Mann-Whitney U t e s t , o n e - t a i l e d ) . UA d'd1 took longer t o d i s p l a y than P dV (p = .064, Mann-Whitney U t e s t , t w o - t a i l e d ) . At the two gr e a t e r d i s t a n c e s G d'd" p a i d l e s s a t t e n t i o n t o the than d i d other d'd*. In 1/12 cases w i t h UA, 3/12 w i t h P, and 7/12 w i t h G, the d* d i d not attend to the at a l l during the fi v e - m i n u t e t r i a l s w i t h the p a r t i t i o n s 5 or 10 cm from the ? ? . Expected frequencies were 2 too low i n too many c e l l s to compare the races w i t h the X t e s t , but a comparison o f each p a i r o f races w i t h the F i s h e r exact p r o b a b i l i t y t e s t y i e l d e d a t w o - t a i l e d p r o b a b i l i t y value o f .05 f o r the discrepancy between UA and G d'd" t o occur by chance. My impression was that most o f the G d'd" not at t e n d i n g d i d not n o t i c e the . 39 Fig. 11. Mean times until f i r s t display and mean number of bouts of display at the shortest distance (0 cm) from the ?? . Proba- bility values are from the Kruskal-Wallis one-way analysis of variance. The dots are the data points. See text for further statistical comparisons. T I M E U N T I L F I R S T D I S P L A Y (sec) M M IS> M CO N> 0\ © O 0 O O O O O O 1 • • I I I I I \ I I I I 4 TJ • • C > o ' C D A O K > In) * • U > O N s i noa 40 D. Competition i n c o u r t s h i p I (Experiment 3) 1. I n t r o d u c t i o n Because o f the s o c i a l nature o f guppies, a d probably would have l i t t l e o p p o r t u n i t y to court ? ? i n the absence of other dd.. The f o l l o w - i n g questions may be posed: Does the manner and amount o f c o u r t s h i p change i n the presence o f another d o f the same race? Is there compe- t i t i o n ? Are the d i f f e r e n c e s between the races r e t a i n e d i n a c o m p e t i t i v e s i t u a t i o n ? This experiment was designed t o begin to answer these questions. 2. M a t e r i a l s and Methods One ? and two dd o f one race were pla c e d i n an o b s e r v a t i o n aquarium between 1400 and 1800 hours. Observations took p l a c e the f o l l o w i n g morn- i n g , u s u a l l y between 1000 and 1300 hours. Each t r i a l l a s t e d t e n minutes. A Rustrak event r e c o r d e r was employed to chart the d u r a t i o n o f time each ^ was c o u r t i n g . Although 18 independent t r i a l s were attempted f o r each r a c e , f i s h which d i d not behave calmly enough reduced the number o f t r i a l s analyzed to 15 P, 13 UA, and 15 G. 3. Results Although one o f the p a i r of dd courted an average o f n e a r l y two- t h i r d s o f the time both dd courted, there i s no reason to b e l i e v e t h a t the r e s u l t s r e f l e c t any d i f f e r e n c e s i n c o u r t s h i p time between dd w i t h i n any of the races (one-way a n a l y s i s o f v a r i a n c e ; F i g . 12a). However, 41 F i g . 12. Courtship of two dV i n the presence o f one $ , expressed as percentages o f t o t a l c o u r t s h i p ( d l + d"2) (a.) and time i n the t r i a l ( b . ) . The h o r i z o n t a l l i n e s represent the mean values f o r 15 P, 13 UA, and 15 G d'd". The r e c t a n g l are the 5% confidence l i m i t s and the v e r t i c a l l i n e s are the ranges. 100 90 80 J 70 60 50 UA COURTSHIP OF o* WHO COURTED MORE a. UA r 100 8 0 COURTSHIP OF WHO COURTED MORE (TOP) COURTSHIP OF o" WHO COURTED LESS (BOTTOM) 42 r a c i a l d i f f e r e n c e s appeared i n the time spent i n c o u r t s h i p by the d" who courted more P d V courted most (p = .05; F i g . 12b). T o t a l c o u r t s h i p time (d# 1 p l u s <f#2 )tended to be higher f o r P d V (p = .08). The time spent i n simultaneous c o u r t s h i p d i d not d i f f e r between races ( F i g . 13). There were no grounds f o r expecting these r e s u l t s on the b a s i s of f i n d i n g s i n Experiment 1. C o r r e l a t i o n c o e f f i c i e n t s were obtained f o r length o f a l l f i s h w i t h amount o f c o u r t s h i p . Male c o u r t s h i p time was c o r r e l a t e d w i t h n e i t h e r d* nor ? l e n g t h . These f i n d i n g s do not n e c e s s a r i l y c o n t r a d i c t those o f Baerends et^ al_. (1955), who found t h a t d'd" courted l a r g e r ? ? i f given a choice. My r e s u l t s show t h a t the length o f ? i n the s i z e range o f f e r e d (20-28 mm S . L . ) d i d not e f f e c t the amount o f c o u r t s h i p when the d'd" had no choice. This f i n d i n g allows me t o assume t h a t ? ? o f d i f f e r - ent s i z e s i n the one- ? experiments do not have d i f f e r e n t s t i m u l a t o r y p r o p e r t i e s . The r e s u l t s and impressions from these observations suggest t h a t some mechanisms are i n o p e r a t i o n which determine which d'd* get the most opp o r t u n i t y t o mate. E. P i l o t experiments on the r o l e ofd*—d* aggression d u r i n g c o u r t s h i p (Experiments 4, 5, and 6) 1. I n t r o d u c t i o n Observations i n Experiment 3 and d a i l y checks of the stock aquaria at the onset of t h i s study suggested that P a r i a f i s h engaged i n c o n s i d e r - able aggressive a c t i v i t y , something which was n o t i c e a b l y absent i n the 43 F i g . 13. Courtship o f twooV w i t h one ? , expressed i n seconds. The h o r i z o n t a l l i n e s represent mean values f o r 15 p a i r s o f P, 13 p a i r s of UA, and 15 p a i r s o f G oV . The r e c t a n g l e s are the 5% confidence l i m i t s and the v e r t i c a l l i n e s are the ranges. One-way a n a l y s i s o f v a r i a n c e y i e l d e d the p r o b a b i l i t y v a l u e s . P =.08 10 9 8 7 6 5 4 3 2 1 0 u P < .0 5 UN TOTAL COURTSHIP SIMULTANEOUS COURTSHIP NO COURTSHIP 44 other races. For a c o n t r o l l e d check on d i f f e r e n c e s i n aggression and f o r some clues as to i t s f u n c t i o n a l s i g n i f i c a n c e and r e l a t i o n to c o u r t s h i p , the f o l l o w i n g experiments were performed. 2. Aggression and t e r r i t o r y (Experiment 4) a. I n t r o d u c t i o n This experiment was performed t o i n v e s t i g a t e the d i f f e r e n c e s i n aggression between P a r i a and the other two r a c e s , and the p o s s i b l e defence o f t e r r i t o r i e s or formation o f dominance h i e r a r c h i e s . ( F i e l d data suggest the p o s s i b i l i t y of t e r r i t o r i e s i n the P a r i a stream-Seghers, pers. comm.) b. M a t e r i a l s and Methods Each of three o b s e r v a t i o n a q u a r i a were arranged w i t h three rocks i n a l i n e p a r a l l e l to the f r o n t o f the aquarium, approximately midway between f r o n t and back, and e q u i d i s t a n t from one another and the s i d e s . The rocks were provided as r e f e r e n c e p o i n t s should a f i s h wish to e s t a b l i s h a t e r r i t o r y . S i x dV from each o f the three races were p l a c e d s e p a r a t e l y i n each o f three o b s e r v a t i o n a q u a r i a . F i s h were i n d i v i d u a l l y r e c o g n i z a b l e . A f t e r s i x days f i s h were observed f o r ten-minute p e r i o d s . Observations were repeated a f t e r seven and nine days. I sat q u i e t l y i n f r o n t o f the aquarium and t a l l i e d charges and noted s p a r r i n g and t a i l - b e a t i n g . c. R e s u l t s F i g . 14 shows scores f o r each o f the three days the f i s h were observed. C l e a r l y , P d'd" were more aggressive than UA and G d'd". The t o t a l scores 45 were not a r e s u l t o f the a c t i v i t y o f a l l the f i s h , however. In most cases one or two f i s h d i d a l l the charging. I found no evidence o f a dominance h i e r a r c h y . The only t e r r i t o r y formed was by a P a r i a f i s h - - t h a t i s , he always was found i n the same pla c e and always returned to i t a f t e r chasing another f i s h . This f i s h had a p e c u l i a r wobble, but was not o b v i o u s l y i l l . L a t e r observations have shown t h i s a s s o c i a t i o n - - w o b b l e , s i t e t e n a c i t y , and aggression--to occur o c c a s i o n a l l y i n both Pdd and ? ? . These f i s h d i d not d i e and u s u a l l y resumed normal swimming when re p l a c e d i n t o stock aquaria. I have a l s o observed t h i s wobble as an o c c a s i o n a l impermanent c o n d i t i o n i n stock a q u a r i a . I have no e x p l a n a t i o n o f t h i s behaviour and I d i d not pursue the problem because i t d i d not seem to have bea r i n g on c o u r t s h i p . Observations were terminated due to an i n c r e a s i n g confusion between aggressive and sexual behaviour. I n i t i a l l y , s p a r r i n g and chasing were c l e a r l y aggressive. S p a r r i n g dd assumed p o s i t i o n s p a r a l l e l or a n t i - p a r a l l e l t o one another and chases were u s u a l l y terminated by a b i t e attempt and no f u r t h e r p u r s u i t by the aggressor. L a t e r , chases p e r s i s t e d and a t t e n t i o n was d i r e c t e d at the g e n i t a l r e g i o n of the other d . In a d d i t i o n , sigmoid d i s p l a y s were a l s o performed. I t i s p o s s i b l e t h a t the sigmoid d i s p l a y has some appeasement f u n c t i o n , as the d u s u a l l y per- forms i t to the much l a r g e r ? , who o c c a s i o n a l l y charges (see a l s o Appendix 1 r e g a r d i n g the p o s s i b l e f u n c t i o n s of bl a c k c o l o r a t i o n i n dd ). When ?? were introduced t o these dd a f t e r day 9, a few dd p e r s i s t e d i n c o u r t i n g other dd and attempting c o p u l a t i o n w i t h them. 46 F i g . 14. Number of charges by oV i n each o f three o b s e r v a t i o n periods i n all-c»" aquaria.  47 I i n t e r p r e t t h i s as abnormal behaviour r e s u l t i n g from the de p r i v a t i o n of a proper sex object i n an animal with an extremely low response threshold f o r sexual a c t i v i t y . 3. Aggression and females (Experiment 5) a. Introduction The previous experiment and observations by L i l e y ( dd r a i s e d i n i s o l a t i o n from S? tend to become homosexual; pers. comm.) suggested that are a necessary part of the environment f o r the development o f normal d responses. This experiment was designed to t e s t the e f f e c t s of ? presence on d aggression, and the p o s s i b i l i t y that d aggression serves as a mechanism of competition f o r , as seen i n two species of the genus Gambusia (Warburton, Hubbs, and Hagen, 1957; M c A l i s t e r , 1958). b. Materials and Methods The observation aquaria were employed minus the rocks. Two aquaria were used f o r each race, and f i v e dd from stock aquaria were placed i n each. The next day they were scored f o r ten-minute periods f o r aggres- sion as i n the previous experiment. At the conclusion o f observations, f i v e ?$ were added t o each aquarium, and scoring commenced on day 2. At the end of t h i s s e r i e s of t e s t s , three o f the were removed to stimu- la t e a more h i g h l y competitive s i t u a t i o n f o r the dd , i f indeed they were competing f or the ?? . c. Results F i g . 15 shows that the addition of increased the t o t a l amount o f aggression i n a l l races, with the most aggression by f a r occurring i n 48 F i g . 15. Mean number o f <f charges i n : (1) 5-<f groups, (2) the same 5-d" groups i n t o which 5 ? ? were i n t r o d u c e d , and (3) the same groups as i n (2) from which 3 ? ? were removed. S o l i d l i n e i n d i c a t e s P groups, dashed l i n e , UA, and dotted l i n e , G. N = 2 groups f o r each ra c e . Cf C H A R G E S / T O M I N CO 49 P a r i a . In a d d i t i o n , one P ? defended a t e r r i t o r y and charged other ? ? twelve times and a d once on day 2, and charged dd f o u r times on day 3. The r e d u c t i o n i n aggression on day 3 i m p l i e s one or more o f the f o l l o w i n g : (1) fewer ? ? meant the dd were l e s s s t i m u l a t e d to f i g h t , (2) the dd had e s t a b l i s h e d more s t a b l e r e l a t i o n s h i p s , (3) the decrease i n aggression was dependent upon the a d d i t i o n of f i s h r e g a r d l e s s o f sex. 4. Aggression, females, and d e n s i t y (Experiment 6) a. I n t r o d u c t i o n The previous experiment posed the problem of whether the i n c r e a s e d d aggression was a f u n c t i o n of the presence of ? ? or j u s t a h i g h e r den- s i t y o f f i s h . The present experiment was designed to get an i n d i c a t i o n o f the e f f e c t o f sex and d e n s i t y on aggression. b. M a t e r i a l s and Methods The manner o f s c o r i n g and the length o f s c o r i n g p e r i o d s were as i n the previous experiment. Three o b s e r v a t i o n aquaria were used f o r each race. The day before the f i r s t t e s t two of these a q u a r i a r e c e i v e d f i v e dd each and one aquarium r e c e i v e d f i v e ? ? . At the c o n c l u s i o n o f the f i r s t s c o r i n g s e s s i o n , f i v e a d d i t i o n a l dd were added to one o f the d a q u a r i a , f i v e ? ? were added t o the other d aquarium, and f i v e ? ? were added to the ? aquarium. The a l l - d 1 and the a l l - ? t r i a l s were run as c o n t r o l s f o r d e n s i t y and ? r o l e s i n aggression. c. Results The only aggressive acts on day 1 were i n a l l - d " P a q u a r i a . The o n l y noteworthy i n c r e a s e i n aggression on day 2 occurred where ?? were added 50 to P dd ( F i g . 16). These r e s u l t s suggest t h a t f i s h may s t i m u l a t e aggression among P dd , and that i n c r e a s e d d e n s i t y alone may not be the primary cause o f aggressive i n t e r a c t i o n s . F. Competition i n c o u r t s h i p I I (Experiment 7) 1. I n t r o d u c t i o n To f u r t h e r i n v e s t i g a t e mechanisms o f competition I undertook a d e t a i l e d a n a l y s i s o f how a d e s t a b l i s h e d h i m s e l f as the dominant s u i t o r , i f he indeed d i d so. This a n a l y s i s was much strengthened by u s i n g the dd of Experiment 1, who had some previous c o u r t s h i p recorded. An analy- s i s o f changes i n c o u r t s h i p behaviour was thereby p o s s i b l e . 2. M a t e r i a l s and Methods F i s h were i s o l a t e d i n each o b s e r v a t i o n aquarium a f t e r o b s e r v a t i o n i n Experiment 1, at about 1700 hours. Between 1250 and 1600 hours the f o l l o w i n g a f t e r n o o n , the center p a r t i t i o n was removed and both dd and one o f the ? ? were allowed i n the center s e c t i o n . Recording commenced immediately. Each t r i a l l a s t e d ten minutes. Nine independent t r i a l s were attempted f o r each r a c e , and 9 P, 8 UA, and 8 G were completed. The f o l l o w i n g d behaviours were recorded on the CDAT: d i s p l a y , l e a p , t h r u s t , charge, charge by the ? , chase, and amount o f time each d spent w i t h i n 2 cm of the % . S p a r r i n g and any unusual aspects o f a t r i a l were noted. The Olympus camera shot a frame every 15 seconds, but due t o i t s i n c e s s a n t m a l f u n c t i o n i n g , o n l y 5 P, 4 UA, and 3 G t r i a l s y i e l d e d photographs s u i t a b l e f o r a n a l y s i s . 51 F i g . 16. Number of <t charges i n groups o f 5 f i s h o f one sex, and these same groups a f t e r 5 a d d i t i o n a l f i s h o f e i t h e r the same or opposite sex were int r o d u c e d . Only groups where charges occurred are shown. S o l i d l i n e s i n d i c a t e P groups; dashed l i n e , UA. 51a D A Y 1 D A Y 2 5 2 3 . R e s u l t s . Changes i n c o u r t s h i p from the ld*-l? Experiment 1 were q u i t e evident w i t h i n each race i n t h i s 2 dd - 1 ? s i t u a t i o n (Table 8 ) . Frequency o f d i s p l a y s and leaps o f s i n g l e dd were reduced i n a l l r a c e s . P dd de- creased t h e i r frequency o f t h r u s t s g r e a t l y whereas UA and G dd i n c r e a s e d t h e i r s s l i g h t l y . I f we compare races we f i n d the degree o f changes much gr e a t e r i n PdV than i n UA and G dd ( d i s p l a y s : p < . 0 2 ; l e a p s ; p < , 0 0 1 ; t h r u s t s : p< . 0 2 ) . Furthermore, V dd seemed to r e l y on a d i f f e r e n t s t r a - tegy than the other d'd". They fought (Table 9 ) . There was a tendency f o r p a i r s o f UAdd t o d i s p l a y more than p a i r s of P and G dd (means: UA = 1 0 , P = 4 , G = 2 ; p < . l ) 3 . UA d'd" ai s o tended to d i s p l a y w i t h i n 2 cm more o f t e n than P or G d'd1 (JJA 5/8 t r i a l s , 1 3 times t o t a l ; P 2 / 9 , 4 ; G 2 / 8 , 3 ; p = . 1 1 ) . No d i f f e r e n c e between the races i n mean number o f chases, l e a p s , o r t h r u s t s were recorded. A l l dd decreased t h e i r d i s t a n c e from the ? when another d was p r e s e n t . The percentage o f time i n a t r i a l i n which the d was w i t h i n a d f i s h - length o f a ? d i d not d i f f e r between the races i n the competitive s i t u a - t i o n , although i t d i d d i f f e r when the d was alone w i t h a $ (Table 1 0 ) . Note t h a t P dd increased t h e i r time very c l o s e to a ? more than f i v e f o l d , UA dd by j u s t under three f o l d , and G dd by j u s t over two f o l d from the 1-d" t o the 2-d* experiment. The data i n Table 1 1 arose from sampling the p o s i t i o n s o f the dd every 1 5 seconds i n the t r i a l . One or But see F i g . 1 3 i n Experiment 3 . There, t o t a l c o u r t s h i p was measured. Because o f the d e p r i v a t i o n p e r i o d p r i o r t o observation here, almost a l l of the f i s h were c o u r t i n g f o r the d u r a t i o n of the t r i a l . 53 Table 8. D i f f e r e n c e s i n frequencies o f c o u r t s h i p a c t i v i t i e s o f i n d i v i d u a l dd when t e s t e d alone w i t h a ? (Experiment 1) or i n the.presence of another d (Experiment 7 ). Di f f e r e n c e expressed as mean % change i n number o f bouts performed f o r the same dd from Experiment 1 to Experiment 7. UA Disp l a y s Leaps Thrusts 73.3 reduct. 71.4 reduct. 66.3 reduct. 27.4 r e d u c t . 19.0 reduct. 9.3 i n c r e a s e 54.6 reduct p < .02 22.3 reduct. p < .001 9.5 i n c r e a s e p < .02 K r u s k a l - W a l l i s one-way a n a l y s i s o f v a r i a n c e , 2 d f , c o r r e c t e d f o r t i e s , Numbers f o r ra n k i n g were a r r i v e d at by the f o l l o w i n g formula: % change = # bouts i n competition/(.667) (# bouts alone) where .667 i s a c o r r e c t i o n f a c t o r f o r the d i f f e r e n c e i n the length o f the t r i a l s . When both the numerator and the denominator were 0, the t r i a l was discard e d . When the numerator was 0, the number a r r i v e d a t was 0. When the denominator was 0, the number a r r i v e d at was i n f i n i t y . 54 Table 9. Male charges i n a competition s i t u a t i o n of two oV and one ?. P UA G Mean number of charges 28 4 4 p< .02 Median number of charges 26 0 0 Number of t r i a l s i n which changes occurred 7/9 2/8 2/8 Kruskal-Wallis one-way analysis of variance, 2 df. Table 10. Mean percentage o f time i n t r i a l i n which a was w i t h i n one d* f i s h - l e n g t h (approx 2 cm) o f a ..? i n one-d" (Experiment 1) and two- d* (Experiment 7) s i t u a t i o n s . P UA G lrf-1? 5 12 19 p = .001 2dV_i? 26 36 44 p < .3 K r u s k a l - W a l l i s one-way a n a l y s i s o f v a r i a n c e , 2 df. N = 13 and 18 f o r P, 16 and 16 f o r UA, and 17 and 16 f o r G. Table 11. Occurrence of dd w i t h i n a 2 cm r a d i u s o f a ? i n the two-o" s i t u a t i o n . Numbers- represent the per- centage of photographs i n which no dd , one d t or two dd appeared w i t h i n the 2 cm r a d i u s . P UA G N ( p a i r s o f dd ) 5 6 3 % no dd 57 57 54 % Id 30 32 38 % 2dd 13 11 8 Each e n t r y i s the average o f at l e a s t 35 frames and u s u a l l y 40 frames measured f o r each p a i r o f dd . 57 both o f the were w i t h i n 2 cm of a ? i n almost h a l f o f the observa- t i o n s i n a l l races (P, 43%, UA 43%; G, 46%). C o r r e l a t i o n c o e f f i c i e n t s were obtained between a l l measures taken. There was no i n d i c a t i o n that the l a r g e r d'd* were i n the c l o s e r p o s i t i o n r e l a t i v e to a ? i n any of the races. S i z e was n e g a t i v e l y c o r r e l a t e d w i t h both number of d i s p l a y s and number o f t h r u s t s i n the G race only (p <.008 and p <.05, r e s p e c t i v e l y ) . No other c o r r e l a t i o n s between s i z e and behaviour appeared. I t f o l l o w s t h a t l a r g e r o r s m a l l e r s i z e confers no advantage t o one d* over another i n the frequency o f performance o f some c o u r t s h i p a c t i v i t i e s , w i t h the above exception i n the G race. C e r t a i n behaviour p a t t e r n s were c o r r e l a t e d w i t h one another, as w e l l as w i t h c l o s e p r o x i m i t y to a ? . Many more s i g n i f i c a n t p o s i t i v e c o r r e l a - t i o n s i n d i s p l a y and contact behaviour were found i n P d'd" (Table 12). This i n d i c a t e s t h a t when a P d" performs one d i s p l a y o r contact behaviour more f r e q u e n t l y , he a l s o does more o f e v e r y t h i n g e l s e . Since these c o r r e - l a t i o n s d i d not appear i n the one d*-one % experiment, t h i s may be a response to competition. P who were charged more tended to d i s p l a y l e s s , and charged l e s s when c l o s e to a J . On the other hand, more aggressive P d'd1 were n e i t h e r l a r g e r nor d i d they d i s p l a y more than l e s s aggressive d'd1 . The h i g h p o s i t i v e c o r r e l a t i o n between charges and d i s p l a y s and charges and leaps i n UA d'd" r e s u l t s from the e f f e c t i v e n e s s o f o n l y two d'd1, one o f whom only charged once. D i s p l a y s , l e a p s , and t h r u s t s performed by one <S d i d not appear to i n f l u e n c e the performance o f those behaviours i n the other d*. 58 Table 12. C o r r e l a t i o n c o e f f i c i e n t s o f c o u r t s h i p a c t i v i t i e s i s a two-d", one-? s i t u a t i o n . A c t i v i t i e s c o r r e l a t e d Number o f d i s p l a y s and percentage of time o f t r i a l d" i s w i t h i n 2 cm o f ? Race R P r o b a b i l i t y o f R being 0 p .16 > .1 UA .02 > .1 G -.14 > .1 Number o f leaps and number o f d i s p l a y s Number o f t h r u s t s and number of d i s p l a y s P .71 .0008 UA .90 < .0001 G .37 > .1 P' .65 .003 UA -.23 > .1 G .61 .01 Number of charges and number of d i s p l a y s P -.35 > .1 UA .80 .0001 G -.13 > .1 Number o f times charged and P -.41 .09 number of d i s p l a y s UA .05 > .1 G .08 > .1 Number of times w i t h i n 2 cm o f P .40 > .1 ? and number o f leaps UA .05 > .1 G -.34 > .1 Number o f times w i t h i n 2 cm P .63 .005 of ? and number of t h r u s t s UA .33 > .1 G .22 > .1 Number of times w i t h i n 2 cm of $ P -.44 .07 and number o f charges UA .11 > .1 G .21 > .1 Number of leaps and number o f P .55 .02 t h r u s t s UA -.22 > .1 G .21 > .1 Number of leaps and number o f P -.03 > .1 charges UA .74 .0009 G -.13 > .1 Number o f t h r u s t s and number P -.21 > .1 of charges UA -.18 > .1 G -.20 > .1 59 Previous experience w i t h a p a r t i c u l a r t e s t $ had no e f f e c t on the d 's performance i n competition. In a d d i t i o n , the frequency o f co u r t s h i p behaviours when a was alone w i t h a ? i n Experiment 1 had no b e a r i n g on h i s performance i n t h i s experiment. Thus, a very a c t i v e c o u r t e r i n the s i n g l e d s i t u a t i o n d i d not n e c e s s a r i l y outperform a l e s s a c t i v e c o u r t e r when they were p l a c e d i n co m p e t i t i o n . C. Competition i n c o u r t s h i p I I I (Experiment 8) 1. I n t r o d u c t i o n The r e s u l t s o f Experiments 3-7 suggest f u r t h e r i n v e s t i g a t i o n of the r o l e s o f agg r e s s i o n , t e r r i t o r y , and "possession" o f a S i n r e l a t i o n to c o u r t s h i p . Braddock (1949) found t h a t p r i o r residence gave p l a t y f i s h , Xiphophorus maculatus, a g r e a t e r p o t e n t i a l f o r dominance. Heuts (1968) gathered s i m i l a r evidence f o r % Xiphophorus h y b r i d s . In Experiment 8 the experimental design allowed examination o f the e f f e c t s o f d i f f e r e n t num- bers o f oVupon the c o u r t s h i p performed to one ? , the c o n t r i b u t i o n to co u r t s h i p by each o f three oV w i t h d i f f e r e n t residency p e r i o d s w i t h the ? , and the i n t e r a c t i o n s between the oV . 2. M a t e r i a l s and Methods Females were s e l e c t e d f o r tameness and one ? was plac e d i n each observation tank at about 1000 hours. In the afternoon ad" was added. Observation took p l a c e the f o l l o w i n g morning, f o r 10 minutes between 0945 and 1335 hours. Another d" of the same race was added t h a t afternoon between 1600 and 1845 hours, and the three f i s h were observed the next morning. This procedure was repeated once more so th a t a t o t a l o f three 60 dd were observed w i t h a ? over a three-day p e r i o d . A c o n t r o l s e r i e s was run wherein:'.; s i n g l e dd were observed f o r three days i n the same way as i n the experimental t r i a l s . A Rustrak event r e c o r d e r was employed to r e g i s t e r d i s p l a y s and chasing, and charges and leaps were w r i t t e n down. No dV were used more than once. Of 15 t r i a l s attempted f o r each r a c e , 15 P, 15 UA, and 13 G were completed. 3. R e s u l t s a. E f f e c t s of the d i f f e r e n t numbers o f d'd* on the c o u r t s h i p performed. I hypothesized t h a t i f no competition took p l a c e between the d'd" , the t o t a l number o f d i s p l a y s , chases, and leaps would on a l l days be a m u l t i p l e of day 1 o f the t r i a l - - w h e n only one d* was present. Note t h a t there i s no d e p r i v a t i o n p e r i o d as i n Experiment 7. The assumption t h a t s i n g l e d'd1 courted much the same on each o f three consecutive days was t e s t e d . Guppies whose parents came from both the Diego M a r t i n and P e t i t e Curacaye streams i n T r i n i d a d were used due to a shortage o f other f i s h , but my impression i s that these f i n d i n g s can be g e n e r a l i z e d . S i x t e e n r e p l i c a t e s f a i l e d to disprove my assumption (Wilcoxon t e s t between each 4 , p a i r o f days ). In f a c t , d i s p l a y frequency rose on the t h i r d day o f the t r i a l s (means: day 1, 1.63; day 2, 1.81; day 3, 2.88). To t e s t the h y p o t h e s i s , t h a t no c o m p e t i t i o n took p l a c e between dd expected frequencies and durations were de r i v e d i n the f o l l o w i n g way. The average frequency or d u r a t i o n o f an a c t i v i t y by a l l dd on day 1, i n H e r e a f t e r , p r o b a b i l i t y values f o l l o w e d by "Wilcoxon" w i l l r e f e r to the Wilcoxon matched-pairs signed-ranks t e s t , t w o - t a i l e d . each race, was added t o the frequency or d u r a t i o n of t h a t a c t i v i t y o f each i n d i v i d u a l o f the race to give expected numbers f o r day 2. S i m i - l a r l y , twice the average frequency or d u r a t i o n was added to i n d i v i d u a l r e s u l t s o f day 1 to y i e l d expected numbers f o r day 3. Thus, i f the presence o f other dd d i d not a f f e c t another d * s performance, the ex- pected and observed f i g u r e s f o r each day would be equal. T r i a l s i n which a given behaviour never occurred were excluded from a n a l y s i s o f t h a t be-, haviour. The r e s u l t s are summarized i n F i g . 17. A l l the p r o b a b i l i t y values f o l l o w i n g are from the Wilcoxon t e s t . Frequency and t o t a l d u r a t i o n o f d i s p l a y s were s i g n i f i c a n t l y below expected on the t h i r d day i n P and UA dd (p< .01), and d i s p l a y d u r a t i o n was a l s o low on the second day i n UA dd (p< .01). Thus, i n c r e a s i n g numbers o f dd i n h i b i t e d these behaviours. GoV showed no evidence o f change i n d i s p l a y s ( F i g . 17a), which means th a t each d d i s p l a y e d as i f no other dd were present. Both P and UA dd leaped l e s s than expected on the t h i r d day (P: p<.05; UA: p<.02). G dd, i n c o n t r a s t , leaped more on the t h i r d day ( F i g . 17b). Frequency and t o t a l time o f chasing i n c r e a s e d more than expected on each consecutive day i n a l l races (day 2: p<.01, w i t h the exception o f UA frequency, p<.05; day 3: p <.01; F i g . 17c). Not s u r p r i s i n g l y , i n c r e a s i n g numbers of dd enhanced chasing, which appears to be a d"'s attempt to remove a ¥ from the presence o f other dd . b. C o n t r i b u t i o n s o f d i f f e r e n t males to the t o t a l c o u r t s h i p I f we sum the amount o f a given behaviour on one day o f the t r i a l and d i v i d e that t o t a l by the number of p a r t i c i p a n t s we a r r i v e at an 62 F i g . 17. Comparison o f the c o u r t s h i p performed by d i f f e r e n t numbers of dd w i t h one ? . One d was present on day 1, two on day 2, and three on day 3. The darkened c i r c l e s and s o l i d l i n e s represent ob- served data and the open c i r c l e s and dashed l i n e s are expected v a l u e s . The number o f samples f o r each data p o i n t - a r e shown under the race d e s i g n a t i o n s . ** s i g n i f i e s p<.01 and * s i g n i f i e s p< .05. P r o b a b i l i t y values are d e r i v e d from the Wilcoxon matched-pairs signed-ranks t e s t , two t a i l e d . a. Comparison o f mean frequency and d u r a t i o n o f d i s p l a y s . b. Comparison o f mean frequency o f leaps. c. Comparison o f mean frequency and d u r a t i o n o f chases. DISPLAYS MEAN DURATION (SEC) MEAN FREQUENCY O Wi © u% o ~1 I I 1 1 G > LEAPS MEAN FREQUENCY o qz9 CHASES MEAN DURATION (SEC) MEAN FREQUENCY ?Z9 63 expected l e v e l o f performance f o r a d i f a l l dd were c o n t r i b u t i n g e q u a l l y . I f p r i o r residence confers any dominance to the f i r s t d we would expect him to exceed the other d or dd and the average amount o f a c t i v i t y toward the ? . F i g . 18 compares the performances o f d i s p l a y s and leaps f o r a l l the dd on each o f the three days o f the t r i a l . In no case i s there a s t a t i s t i c a l l y s i g n i f i c a n t i n d i c a t i o n t h a t the f i r s t d had an advantage over the o t h e r s , o r t h a t any o f the dd d i f f e r e d from one another on days 2 and 3. The low frequency o f leaps precludes the seemingly l a r g e d i f f e r e n c e s e x h i b i t e d i n F i g . 18 from r e a c h i n g s t a t i s t i c a l s i g n i f i c a n c e . The decreased l e v e l of d i s p l a y behaviours observed w i t h i n c r e a s e d <J d e n s i t y i n the P and UA races was t h e r e f o r e not d i c t a t e d by a t e r r i t o r i a l or " p o s s e s s i v e " d , but by some other i n t e r a c t i o n s o f the f i s h . c. I n t e r a c t i o n s between the males The mechanisms o f i n t e r a c t i o n s between dd were not always c l e a r . I could see no e f f e c t s o f s u b t l e body contacts d u r i n g chasing and changes i n body and f i n posture to the ? on ̂  behaviour. F i g h t i n g was the only a c t i v i t y which o b v i o u s l y changed©* - d behaviour. Here, t h e i r a t t e n t i o n s were t o t a l l y d i r e c t e d toward one another r a t h e r than toward the ? . Aggressive behaviour need only be considered in P dd . Only f o u r charges occurred i n 750 fish-minutes (number o f f i s h m u l t i p l i e d by obser- v a t i o n times where at l e a s t two dd were present) i n UA and only two charges occurred i n 650 fish-minutes i n G; whereas 247 charges occurred i n 700 fish-minutes i n P ( i n 11/14 t r i a l s ) . The amount o f P aggression i n t h i s experiment when two dd were present (47.86 charges/100 f i s h - 64 F i g . 18. C o n t r i b u t i o n s o f d i f f e r e n t dV t o t o t a l c o u r t s h i p on each day o f the experiment. For each day, d" 1 i s on the l e f t , e t c . Dashed l i n e s represent the average values f o r a l l the d'd* and the expected value f o r each d" . No s t a t i s t i c a l l y s i g n i f i c a n t d i f f e r e n c e s appeared. See t e x t f o r d i s c u s s i o n . LEAPS MEAN FREQUENCY DISPLAYS MEAN DURATION MEAN FREQUENCY (SEC) >• K 11 tl 1 a > K 5 > 65 minutes) was markedly lower than i n Experiment 7 (140.00 charges/100 f i s h minutes; p = .0344, Mann-Whitney U t e s t c o r r e c t e d f o r t i e s ) . Apparently f a m i l i a r i t y w i t h the other d and the ? reduced the l e v e l of aggression. Friedman two-way a n a l y s i s of v a r i a n c e shows no d i f f e r - ences i n the frequency of charges between P dd . In the nine t r i a l s where charging occurred on day 2, f i r s t dd out-charged secondoV by n e a r l y three t o one (92-32), but t h i s d i f f e r e n c e i s s t a t i s t i c a l l y i n s i g - n i f i c a n t (Wilcoxon) because one d charged 49 times. On day 3 f i r s t and second dd charged e q u a l l y (27 and 24 t i m e s ) , w h i l e t h i r d dd charged more (72 t i m e s ) . Again, d i f f e r e n c e s were not s t a t i s t i c a l l y r e l i a b l e . No c o n s i s t e n c y appeared i n who charged whom between f i r s t and second dd on the two days they were observed together. In a d d i t i o n , charges d i d not bear any r e l a t i o n t o d i s p l a y i n g i n any o f the races. However, one d Q f the f i r s t two introduced performed more d i s p l a y behaviour than the o t her on both the second and t h i r d days of the e x p e r i - ment. The l i k e l i h o o d t h a t t h i s r e s u l t s bv chance are s l i m . (Table 13). The r e s u l t s o f experiments 1 and 7"* suggest that i n t e r a c t i o n s are essen- t i a l i n determining which d d i s p l a y s most. This experiment suggests that the r e s u l t s o f these i n t e r a c t i o n s are s t a b l e f o r at l e a s t a two-day p e r i o d . Remember that f i s h were not separated from one another i n t h i s experiment. The e f f e c t s o f s i z e on d-d i n t e r a c t i o n s appear to be n e g l i g i b l e . Length (P, X = 17.2 mm; UA, X = 18.8 mm; G, X = 18.2 mm) was s i g n i f i c a n t l y c o r r e l a t e d w i t h d i s p l a y i n g i n s e v e r a l i n s t a n c e s , mainly i n P and UA, but ^No r e l a t i o n e x i s t e d between the amount of d i s p l a y i n g o f s i n g l e dd i n non-competitive and competitive s i t u a t i o n s . 6 6 Table 1 3 . R e l a t i v e amount o f d i s p l a y behaviour o f f i r s t and second <f<f on days 2 and 3. P r o b a b i l i t y values are d e r i v e d from the binomi a l t e s t . Race T o t a l No. No. o f t r i a l s i n which o f T r i a l s same d* d i s p l a y e d most both days No. o f t r i a l s i n which same d" d i d not d i s p l a y most both days P UA G 1 3 1 4 1 2 1 1 1 0 9 2 4 3 p = . 0 1 1 p = .090 p = . 0 7 3 Race No. o f T r i a l s i n which leaps occurred P 1 1 UA 5 G 6 No. o f t r i a l s i n which d" who d i s p l a y e d most both days a l s o leaped most 9 5 5 No. o f t r i a l s i n which d" who d i s p l a y e d most both days d i d not leap most 2 0 1 p = .033 p = .031 p = .109 67 d i d not c o r r e l a t e w i t h the d who d i s p l a y e d most on the t h i r d year. Leaps and charges bore no r e l a t i o n to length. d. Comparison o f the races K r u s k a l - W a l l i s one-way a n a l y s i s o f var i a n c e was employed t o compare the behaviour of dd o f the three races over the three days. F i g . 19 summarizes the comparison o f d i s p l a y s , l e a p s , and chases. On day 1, G dd d i s p l a y e d l e s s than the other dd } but not s i g n i f i c a n t l y l e s s as i n Ex- periment 1 ( t h i s was probably owing t o the s h o r t e r o b s e r v a t i o n t i m e ) . UA dd performed more leaps than the other dd ( p < . 0 5 ) , a d i f f e r e n c e not detected i n the c o n d i t i o n s o f Experiment 1. A l l dd spent about the same amounts o f time chasing ( p > . 2 ) , but UA dd chased more o f t e n than the others (p< .01). The t o t a l time d i s p l a y i n g doubled i n P and G dd on the second day, but increased onlv s l i g h t l y over day 1 i n UA dd . P spent the most time d i s p l a y i n g (p< .05). The number o f d i s p l a y s d i d i n c r e a s e i n UA dd , but P dd doubled and G d'd* more than doubled t h e i r d i s p l a y f r e q u e n c i e s . P dd d i s p l a y e d more f r e q u e n t l y and G dd d i s p l a y e d l e s s f r e q u e n t l y (p = .05). The mean d i s p l a y bout length o f f i r s t dd i n P and G remained at about two seconds on each o f the three days, but dropped from 2.8 seconds on day 1 to 1.9 and 1.8 seconds on days 2 and 3, r e s p e c t i v e l y , i n UA (p< .05, Friedman two-way a n a l y s i s o f v a r i a n c e ) . A l l races i n c r e a s e d t h e i r f r e - quency o f leaps on day 2, P most and UA l e a s t , but G dd leaped l e s s (p< .05). These r e s u l t s c o n t r a s t w i t h those o f Experiment 7, where i n a two- d s i t u a t i o n frequencies o f d i s p l a y s and leaps were reduced when 68 F i g . 19. Comparison o f the c o u r t s h i p performed bv dd o f the three races on each o f the days o f the t r i a l s . Each group o f t h r e e histograms represents P, UA, and G dd , i n t h a t order. K r u s k a l - W a l l i s one-way a n a l y s i s o f v a r i a n c e p r o b a b i l i t i e s appear above the histograms. Sample s i z e s are shown on the f i r s t group o f histograms f o r a given behaviour. DAY 1 DAY 2 DAY MEAN DISPLAY FREQUENCY 20 IS 10 5 0 «.05 >.2 . i t l r u t s MEAN DISPLAY DURATION (SEC) 40 r 30 20 10 >.2 14 <.05 >.8 MEAN LEAP FREQUENCY 1 . 0 <.05 ^ 4 L5j tL <.0S MEAN CHASE FREQUENCY 10 s 6 4 2 0 <.2 <.2 <.01 141512 MEAN CHASE DURATION (SEC) 25 20 IS 10 s 0 <,2 >.2 _ r - f ~ r - l . . 14 IS 12 n 6 9 compared t o the one-d" s i t u a t i o n o f Experiment 1. Furthermore, i t was the P dd who reduced these behaviours the most. The d i f f e r e n c e s are that i n the present experiment no p e r i o d o f i s o l a t i o n was imposed upon the dd , one d was w i t h the % longer than the o t h e r , and the dd had the opportunity to l e a r n about one another and the ¥ . G dd tended to do more chasing (p <. 2). No d i f f e r e n c e i n chasing were found i n E x p e r i - ment 7. By the t h i r d day d i f f e r e n c e s i n d i s p l a y i n g disappeared (p> .8). P dd d i d not d i s p l a y more than on the second day, UA dd d i s p l a y e d o n l y s l i g h t l y more, and G dd d i s p l a y e d more, i n p r o p o r t i o n w i t h the i n c r e a s e from day 1 to day 2. Leaps d i f f e r e d , but P dd leaped l e s s than the other races (p< .05). The p a t t e r n o f change of l e a p i n g d i f f e r e d q u i t e s t r i k i n g l y . Two P dd together leaped much more f r e q u e n t l y than one, but three P dd leaped w i t h the same frequency as one. The amount of l e a p i n g o f UA dd on the t h i r d day was mid-way between the scores o f days 1 and 2. G dd simply doubled t h e i r average number o f leaps on consecutive days. UA dd spent l e s s time chasing on d a y 3 (p<.05) and tended to chase l e s s o f t e n (p< .2). The a d d i t i o n of the t h i r d P d induced a very sharp upward surge i n chasing when compared to the previous days, and G dd chased more i n d i r e c t p r o p o r t i o n to t h e i r i n c r e a s e i n numbers over day 2. As noted i n p a r t c above, the presence of aggressive a c t i o n s i n P and the absence o f i t i n UA and G are o f an almost a l l or n o t h i n g nature. D i f f e r e n c e s i n behaviour of i n d i v i d u a l dd between the races are mentioned i n p a r t s a, b, and c of t h i s experiment and g e n e r a l l y f o l l o w the d i f f e r e n c e s discussed above. 70 H. Summary o f the male's c o u r t s h i p I. The behaviour o f s i n g l e males P and U A dd , through behaviour and c o l o r p a t t e r n s , are probably more obvious than G dd i n c o u r t s h i p . P and U A <JV d i s p l a y e d more than G dd , but di s t a n c e from the ? during d i s p l a y was the same and c l o s e p r o x i m i t y to the ? was mandatory to i n i t i a t e d i s p l a y i n a l l races. P dd o r i e n t a t e d at g r e a t e r d i s t a n c e s and at g r e a t e r angles r e l a t i v e to the ?' and moved above her and d i s p l a y e d there more f r e q u e n t l y . G dd p o s i t i o n e d themselves a t more acute angles above and below the ? , and, w h i l e d i s p l a y i n g , changed p o s i t i o n s r e l a t i v e to the ? l e a s t o f t e n . U A d<f came c l o s e r t o a ? w h i l e d i s p l a y i n g , chased her more o f t e n , and leaped more than the other races when there was a longer i n t r o d u c t o r y p e r i o d w i t h a ? . P dd had a longer and G dd , a s h o r t e r , l a t e n c y to d i s p l a y . G dd p a i d the l e a s t a t t e n t i o n t o ? ? at short enforced d i s t a n c e s from them. Gonopodial swings and t h r u s t s were s i m i l a r f o r a l l r a c e s . 2. The behaviour o f two or more males N e i t h e r previous experience w i t h a ?, previous performance i n a oned* -one? s i t u a t i o n , p r i o r r e s i d e n c e , nor s i z e c o r r e l a t e d w i t h a d 's performance i n the presence o f other dd . However, a co n s i s t e n c y e x i s t e d i n one d ' s c o u r t s h i p behaviour i n r e l a t i o n to another d . P dd were much more aggressive than U A and G dd upon encountering other dd. Increased aggressiveness occurred i n the presence o f ? ? , suggesting t h a t dd f i g h t over ?? . Pdd who were charged tended to d i s p l a y l e s s when f i r s t encountering one another, but t h i s r e l a t i o n s h i p 71 d i d not h o l d a f t e r some time together, and the l e v e l of aggression dropped. P a i r s o f P dd courted and d i s p l a y e d more than p a i r s o f UA and G dd a f t e r an afternoon and n i g h t w i t h a ? . When only the top c o u r t e r s of each p a i r were considered, P dd courted more. Two dd i n t r o d u c e d to one another and a $ a f t e r an i s o l a t i o n 'period d i s p l a y e d and leaped l e s s than they d i d i n d i v i d u a l l y w i t h a ? . However, i f two dd had time t o - i n t e r a c t p r i o r t o o b s e r v a t i o n , no decrease was noted. The a d d i t i o n o f a t h i r d d w i t h time f o r l e a r n i n g l e d to l e s s d i s p l a y i n g and l e a p i n g than expected i n P and UA dd but not i n G dd. My impression i s t h a t dd u s u a l l y attempt to maximize the amount o f a t t e n t i o n they r e c e i v e from the ? before d i s p l a y i n g , and the presence of another d o r dd made t h i s d i f f i c u l t . Upon being i n t r o d u c e d to one another, a l l dd moved c l o s e r t o the ¥ t o the extent t h a t i n t e r r a c i a l d i f f e r e n c e s disappeared. One or both dd were w i t h i n a f i s h - l e n g t h o f the ? f o r almost h a l f the time o f the t r i a l i n the two- d s i t u a t i o n , and one, two, or three dd o f d i f f e r e n t races remained c l o s e even longer. P dd decreased t h e i r frequency o f t h r u s t s g r e a t l y i n the presence o f a second CJ* , whereas UA and G dd i n c r e a s e d t h e i r s s l i g h t l y over the s i n g l e d s i t u a t i o n . Smaller G dd d i s p l a y e d and t h r u s t more than l a r g e r ones. UA dd tended to d i s p l a y more and more c l o s e l y to the ? . More dd meant more chasing i n a l l r a c e s . There were no i n t e r r a c i a l d i f f e r e n c e s i n d i s p l a y frequency when three dd were present (see Experiment 9, whether o f the same race or n o t ) . In three-d" s i t u a t i o n s Pdd leaped l e s s than o t h e r r a c e s , and G dd t h r u s t more. G dd behaved almost as i f no other dd were present, 72 Table 14 summarizes m o r p h o l o g i c a l , b e h a v i o u r a l , and environmental d i f f e r e n c e s between the races by ranking each race from 1 to 3 ( 1 > 2 > 3 ) f o r each parameter considered. 73 Table 14. Summary o f morp h o l o g i c a l , b e h a v i o u r a l , and environmental d i f f e r e n c e s between the races. Rank 1>2>3. An a s t e r i s k a f t e r a race denotes a s t a t i s t i c a l l y v a l i d d i f f e r e n c e be- tween that race and the others. More than one a s t e r i s k means that the races marked d i f f e r s i g n i f i c a n t l y . Rank 1 2 3 Parameter S i z e UA* P* G* . - Brightness P and UA G Sex r a t i o P* G* UA* Water c l a r i t y P and UA G Predators G UA G Schooling G* UA P % time c l o s e p r o x i m i t y t o $ G* UA* P* Angle o f o r i e n t a t i o n P UA G P o s i t i o n changes d u r i n g c o u r t s h i p P UA G Bouts o f sigmoid d i s p l a y UA P G* Latency to d i s p l a y P* UA* G* At t e n t i v e n e s s t o $ at a di s t a n c e UA* P G* Charges between dd P* UA and G Reduction i n d i s p l a y and contact behaviours i n the presence o f a second d ( a f t e r i s o l a t i o n ) P* G UA Leaps w i t h 3 dd present G UA P* Thrusts w i t h 3 dd present G* P UA 74 Chapter 5. D i s c u s s i o n of Male Courtship S t r a t e g i e s I t i s tempting to assume that behaviour p a t t e r n s have evolved i n the same manner as other f e a t u r e s o f animal p o p u l a t i o n s , by the s e l e c t i o n o f i n - h e r i t a b l e d i f f e r e n c e s . I t i s impossible to be c e r t a i n , however s t r o n g the i m p l i c a t i o n about the e v o l u t i o n o f behaviour, unless one can demonstrate the e x i s t e n c e o f " g e n e t i c " v a r i a t i o n s i n behaviour upon which se- . ' l e c t i o n could a c t . Bastock (1956) The f i e l d and experimental evidence gathered by Seghers (1973) pr o v i d e s s t r o n g arguments i n f a v o r o f the adaptive nature o f a n t i p r e d a t o r s t r a t e g y , and i t seems l i k e l y t h a t the same for c e s have e f f e c t e d the evo- l u t i o n o f c o u r t s h i p behaviour. F i r s t c o nsider the behaviour o f s i n g l e dd i n r e f e r e n c e t o the simple model presented i n F i g . 20. I t i s s a f e t o say t h a t the </'s c o u r t s h i p behaviour i s goal d i r e c t e d to c o p u l a t i o n w i t h a $• To achieve t h i s goal maximum conspicuousness, w i t h behaviours such as d i s p l a y s , i s probably o p t i m a l . I f , however, the environment i n c l u d e s the eyes o f p i s c i v o r e s as w e l l as those o f guppy , there must e x i s t an e v o l u t i o n a r y t r a d e - o f f i n conspicuousness. Quite s i m p l y , the g r e a t e r the predator component o f the model i s , the l e s s conspicuous can the behaviour o f the d guppy be. Conversely, reduced p r e d a t i o n pressure allows f o r maximization o f ^ - a t t r a c t i n g a c t i v i t i e s . The guppies s t u d i e d f i t the model w e l l . G dd are not as quick to d i s p l a y and are l e s s conspicuous i n d i s p l a y behaviour, u t i l i z a t i o n o f space, s i z e , and c o l o r than are P and UA dd . Seghers' f i n d i n g s suggest 75 F i g . 2 0 . A simple model showing f a c t o r s i n f l u e n c i n g conspicuousness.  76 t h a t c o l o r i s not important i n prey s e l e c t i o n by guppy pr e d a t o r s . The r e l a t i v e l y d u l l c o l o r a t i o n o f G dd probably i s a s s o c i a t e d w i t h the t u r b i d waters which they i n h a b i t (see Chpt. 7). These guppies a l s o show a g e n e t i c preference f o r the shallow waters near shore. I f the dd f i x e d t h e i r a t t e n t i o n on at r e l a t i v e l y l a r g e d i s t a n c e s , not only might they l o s e s i g h t o f them, but they might f i n d themselves over deeper waters where predators l u r k . On the other hand, i n the streams where pr e d a t i o n pressure i s r e l a t i v e l y low, the dd e x h i b i t e l a b o r a t e d i s p l a y behaviour, d i s p l a y r e a d i l y , u t i l i z e more space (which may a l s o be a f u n c t i o n o f the c l e a r w a t e r ) , and are l a r g e r and b r i g h t e r . The d i s p l a y i t s e l f and the d i s t a n c e from the ? at which i t i s performed seem conservative components i n the d 's behaviour r e p e r t o i r e , apparently not as e a s i l y a f f e c t e d by s e l e c t i v e pressures as most other c o u r t s h i p a c t i v i t i e s . Observations o f d i s p l a y behaviour and d i s t a n c e i n t u r b i d water would be i n s t r u c t i v e . The model f i t s w e l l w i t h the ideas o f G i e s e l (1972), who suggests t h a t the p o t e n t i a l r a t e of e v o l u t i o n i n species where dd s u f f e r h i g h e r m o r t a l i t y than ? ? may be g r e a t e r than expected from e x i s t i n g theory. He proposes that such species should have g r e a t e r niche breadth, be b e t t e r able to t r a c k short-term environmental changes g e n e t i c a l l y , and be more e f f i c i e n t c o l o n i z e r s . I t may be wise t o emphasize that a l l three races o f d'd" perform a l l the same behaviours, and t h a t the major d i f f e r e n c e s between them are q u a n t i t a t i v e . S i m i l a r l y , Seghers f i n d s a n t i p r e d a t o r adaptations to d i f f e r q u a n t i t a t i v e l y . P f i s h h a r d l y respond t o predators w h i l e G f i s h are 77 h i g h l y responsive to them. UA guppies f a l l between these two extremes, as they d i d w i t h many o f the behavioural measures I employed. Moving c l o s e r to the ? i n the presence o f other dd seems to be a way i n which ad gains the ¥ 's a t t e n t i o n and minimizes the a t t e n t i o n she can get from other dd . I t i s probably s i g n i f i c a n t that G dd t h r u s t more than the competitors i n the presence o f others. Thrusts may occa- s i o n a l l y r e s u l t i n insemination and thus allow a d to tr a n s m i t h i s gene's without endangering h i s s u r v i v a l as much as by d i s p l a y i n g . In a d d i t i o n , the low v i s i b i l i t y i n the Guayamare might allow more o f these t h r u s t s t o r e s u l t i n success than would the c l e a r waters o f the other two streams. Insemination through t h r u s t s probably does not i n v o l v e cooperation by the ¥ and a d i n t u r b i d water would probably have a b e t t e r chance o f approaching a ¥ unnoticed. A l s o , s m a l l e r G dd t h r u s t and d i s p l a y e d more than l a r g e r ones. Seghers (1973) has evidence t h a t s m a l l e r dd are b e t t e r at a v o i d i n g large p r e d a t o r s . Perhaps s m a l l e r G dd can " a f f o r d " t o be more obvious. The f l u r r y o f a c t i v i t y when s e v e r a l dd encounter a ¥ i s q u i t e con- spicuous, even through the t o t a l space occupied by a l l the f i s h at one moment may be l e s s than that occupied when a s i n g l e d and ¥ are i n t e r a c t - i n g . Perhaps the group o f f i s h g i ve a s c h o o l i n g e f f e c t , i . e . , make i t d i f f i c u l t f o r a predator to s i n g l e out an i n d i v i d u a l f o r a t t a c k . I t may a l s o be t h a t there are more eyes w i t h which to spot a p r e d a t o r , but the ¥ seems to have the dd 's undivided a t t e n t i o n . Observations i n the f i e l d could c o n t r i b u t e much i n f o r m a t i o n to c l a r i f y t h i s problem. Other d i f f e r e n c e s emerge i n s i t u a t i o n s where more than one d i s present. For in s t a n c e consider the aggressive behaviour o f P dd . Many 78 P dd even have a s l i g h t s p i k e , o u t l i n e d i n b l a c k , on the v e n t r a l edge o f the caudal f i n , and e x h i b i t a "backing" motion re m i n i s c e n t of sword- t a i l s , where the s p i k e f u n c t i o n s i n aggression between dd (Hemens, 1966). F i g h t i n g i s a s t r a t e g y which has evolved here t o f u r t h e r a d 's chance of s u c c e s s f u l i n s e m i n a t i o n . I t i s a l s o a behaviour which makes a f i s h very conspicuous, so we can understand why i t i s not o f t e n seen among G dd . But why do P dd f i g h t so much more than UA dd ? I b e l i e v e t h a t we can t u r n to R i v u l u s f o r the answer. Seghers found t h a t . R i v u l u s d e n s i t y i n the P a r i a was very low, w i t h few l a r g e i n d i v i d u a l s . This i s probably the reason f o r sex r a t i o d i f f e r e n c e s : P,1.14, and UA, .48. The P a r i a had the h i g h e s t r a t i o o f dd t o ?$ o f 19 streams which Seghers checked, and a very dense guppy p o p u l a t i o n . Could the low preda- t o r pressure and increased competition between dd have opened the gates f o r aggression? Has aggression emerged as a p o p u l a t i o n c o n t r o l device i n the absence of p r e d a t i o n ( c f . Breder and Coates, 1932)? The l a t t e r hypo- t h e s i s can be t e s t e d . S o c i a l s t a t u s may g r e a t l y i n f l u e n c e i n s e m i n a t i o n success w i t h i n a p o p u l a t i o n . Using d i f f e r e n t genetic types, but c o n t r o l l i n g f o r the d i f - f e r e n c e s , G a n d o l f i (1971) f i n d s t h a t the dominant d o f a p a i r leaves f a r more o f f s p r i n g than the subordinate. Though there are no success s t a t i s - t i c s , dominant dd who e x h i b i t e d t h e i r ranks by chasing other dd away from ?? i n both Gambusia h e t e r o c h i r (Warburton et^ a l _ . , 1957) and G. h u r t a d o i ( M c A l i s t e r , 1958) were more i n t e n s e l y c o l o r e d . Perhaps competition i s a clue to the c o l o r polymorphism i n guppy popu l a t i o n s (see Chapt 7 and Appendix 1). As w i t h the guppies, s i z e was not c o r r e l a t e d w i t h aggressive- ness i n the l a t t e r two s t u d i e s . In M o l l i e n e s i a ( = P o e c i l i a ) l a t i p i n n a 79 l a r g e r dd dominated s m a l l e r ones. Males were more aggressive when c o u r t i n g , but l e v e l s o f aggression dropped when s e v e r a l dd were t h r u s t i n g or attempting c o p u l a t i o n ( P a r z e f a l l , 1969). There seems to be a s i m i l a r r e l a t i o n s h i p between c o u r t s h i p and aggression i n m o l l i e s and guppies ( a l s o see Baerends ejt a l _ . , 1955) . The absence o f obvious s t a b l e dominance h i e r a r c h i e s i n guppies may be r e l a t e d to a comparatively low l e v e l of aggression ( C o l l i n s et_ a l _ . , 1967). Contrary to my r e s u l t s and those o f Henderson (unpubl.), F a r r (1972) f i n d s an i n c r e a s e i n d i s p l a y behaviour from the one d-one ? s i t u a t i o n t o two dd -one ? to two dd -two ¥$ . In higher d e n s i t i e s up t o 15 p a i r s , d i s p l a y s per i n d i v i d u a l remained constant. Henderson found a decrease i n r e p r o d u c t i v e a c t i v i t y at h i g h e r d e n s i t i e s . I b e l i e v e these d i f f e r e n c e s emphasize the need to examine and compare pop u l a t i o n s o r i g i n a t i n g from d i f f e r e n t e c o l o g i c a l circumstances. R e s u l t s o f the competition experiments suggest t h a t G dd change t h e i r behaviour r e l a t i v e l y l i t t l e i n the presence o f o t h e r dd . Perhaps much o f the e v o l u t i o n of the b r i g h t e r c o l o r s i n P and UA dd can be ex- p l a i n e d by i n t e r - c ompetition (see Chapts. 6 § 7) . In a d d i t i o n , r e s u l t s in:/6hapterx4e:: : and Experiment 9 i n the next chapter suggest t h a t dd o f each race might have a dominant mating s t r a t e g y . G dd t h r u s t , P dd f i g h t , and UA dd have p a r t i c u l a r l y e f f e c t i v e d i s p l a y s . V a r i a b i l i t y w i t h i n populations must be mentioned along w i t h v a r i a t i o n between pop u l a t i o n s (see a l s o Barlow, 1961). For most behaviours, measurements from i n d i v i d u a l s from a l l the races overlap almost completely. To quote Lindsey (1962): "Perhaps, w i t h i n a s p e c i e s , each p o p u l a t i o n can c a r r y i n i t s pool o f b u i l t - i n v a r i a b i l i t y the p o t e n t i a l to a l t e r r a p i d l y 8 0 so as t o resemble any other p o p u l a t i o n , given only the a p p r o p r i a t e s e l e c t i v e pressures a c t i n g on a l l e l e s a l ready present". The i d e a l way i n which to a s c e r t a i n t h i s would be t o take a T r i n i d a d stream devoid o f f i s h e s , screen o f f s e c t i o n s , and introduce various guppy po p u l a t i o n s and v a r i o u s predator p o p u l a t i o n s i n the appropriate combinations, w i t h c o n t r o l s . There are such streams a v a i l a b l e . Behavioural and morpholo- g i c a l sampling could take p l a c e p e r i o d i c a l l y . I f T r i n i d a d could not be used, predator complements could be added to l a r g e a q u a r i a ( s e e Seghers, 1973:176) and observations could be made on which guppies were most r e a d i l y preyed upon. 81 Chapter 6. The Consequences of Geographic I s o l a t i o n A. I n t r o d u c t i o n L i k e most researchers working w i t h g e o g r a p h i c a l l y i s o l a t e d popula- t i o n s , I was i n t e r e s t e d i n the p o s s i b i l i t y o f occurrence o f r e p r o d u c t i v e i s o l a t i o n between r a c e s . Reproductive i s o l a t i o n i s f i r s t , presumedly, a by-product o f the accumulation of genetic changes between d i v e r g i n g races. When e f f e c t i v e r e p r o d u c t i v e i s o l a t i o n occurs, races become species (Dobzhansky, 1970: Chpt. 11). Many b o r d e r l i n e cases between " r a c e s " and species have been examined by Mayr (1963). Examples are the d e s c r i p t i v e and experimental s t u d i e s of r e p r o d u c t i v e i s o l a t i o n between " i n c i p i e n t s p e c i e s " or "semispecies" o f f r u i t f l i e s , undertaken by Dobzhansky and h i s students (see Chapter 7 ) . In Chapter 6 I sought to determine to what extent divergence i n c o u r t s h i p behaviour of the guppy has evolved by i n v o l v i n g f i s h o f a l l three races i n experiments together. B. Breeding between the races A l l p o s s i b l e crosses between the races (4 wild-caught o V p l a c e d w i t h 4 v i r g i n ) produced v i a b l e , f e r t i l e o f f s p r i n g . The range of v a r i a t i o n w i t h i n each race would have made many r e p l i c a t i o n s necessary to e s t a b l i s h h e r i t a b i l i t y c o e f f i c i e n t s o f behaviours f o r the " h y b r i d " o f f s p r i n g . Lack o f space ( f o r 6 " h y b r i d " groups p l u s 3 non-hybrid c o n t r o l groups) precluded such a b e h a v i o u r a l a n a l y s i s . Examination o f o* c o l o r p a t t e r n s suggested t h a t most o f the o f f s p r i n g were s i r e d by one <J" . G e n e r a l l y , the d"d* of the more b r i g h t l y c o l o r e d races l e f t more c o l o r f u l d" o f f s p r i n g . In a d d i t i o n to the predominance o f Y - l i n k e d c o l o r p a t t e r n s (see Winge, 1922a, b, 1927) , the P oV seemed to c o n t r i b u t e a l o t o f c o l o r to t h e i r CJ" young 82 (e.g., LV x P ? F l oV were as b r i g h t as P d*d* ). Atz (1962) found t h a t r e c i p r o c a l crosses of s e v e r a l Xiphophorus species d i d not always produce s i m i l a r l y pigmented o f f s p r i n g (see a l s o Kallman, 1970b). I attempted to determine comparative r e p r o d u c t i v e success o f by comparing c o l o r p a t t e r n s of p o t e n t i a l f a t h e r s and d" o f f s p r i n g . S i x dV o f each race were pla c e d w i t h s i x v i r g i n of a s i n g l e race f o r two weeks. The ¥$ were then removed to i n d i v i d u a l quarters i n 4 - l i t e r j a r s , where they dropped young. U n f o r t u n a t e l y , space was i n s u f f i c i e n t and not enough young were r a i s e d to permit conclusions to be drawn. However, the method o f f o l l o w i n g d* parentage by c o l o r phenotype seems reasonably accurate. I n d i v i d u a l d e l i v e r e d young from more than one <f , but r e - s u l t s suggested that one o* was r e s p o n s i b l e f o r most of the o f f s p r i n g o f one ?, (see Hildemann and Wagner, 1954). Further experiments i n t h i s area could be important i n e l u c i d a t i n g some f a c t o r s o f p o p u l a t i o n s t r u c t u r e as w e l l as i n t e r r a c i a l competition. C. I n t e r - p o p u l a t i o n competition i n c o u r t s h i p (Experiment 9) 1. I n t r o d u c t i o n The major question asked i n t h i s experiment was: does one race o f d V w i t h i t s p a r t i c u l a r combination o f morphology and behaviour stand a g r e a t e r chance of r e p r o d u c t i v e success than another race when competing f o r the same ¥ ? The r e s u l t s are presented i n two p a r t s : one concerning the e f f e c t s o f i n t e r r a c i a l c o m p etition on the d*d* *s behaviour, and the other concerning the responses of the ¥? to the dV 's behaviour. 83 2. M a t e r i a l s and Methods For each t r i a l one d" of each r a c e , a f t e r an i s o l a t i o n p e r i o d o f about two days, was intr o d u c e d i n t o the long aquarium, arranged as i l l u s t r a t e d i n F i g . 21. A f t e r the d'd* had about ten minutes o f e x p l o r a - t i o n time, a v i r g i n ¥ was intro d u c e d to them. Seven ¥¥ o f each race were observed f o r a t o t a l o f 21 independent t r i a l s . A t r i a l l a s t e d 30 minutes or u n t i l c o p u l a t i o n took p l a c e . The CDAT was employed to r e c o r d frequency and d u r a t i o n o f behaviours and the i d e n t i t y o f the a c t o r i n the case o f the dcf and response behaviour and the i d e n t i t y of i t s e l i c i t o r i n the ¥ . Male behaviours recorded were d i s p l a y , l e a p , t h r u s t , copula- t i o n and which f i s h was c l o s e s t t o the ¥ . In a d d i t i o n ; a ggression, j e r k s , and other noteworthy events were spoken i n t o a tape r e c o r d e r . 3. R e s u l t s a. Male behaviours Very i n t e n s e ¥-oriented a c t i v i t y commenced when the h i g h l y responsive ) v i r g i n ¥ was presented w i t h p r e v i o u s l y i s o l a t e d d'd" . Only one copula- t i o n occurred (Gd1 and UA ¥ ) , however, d e s p i t e the ¥¥ 's r e c e p t i v i t y . The reason was obvious: as soon as one d" d i s p l a y e d to a ¥ and e l i c i t e d a response, another d" c l o s e r to her attempted c o p u l a t i o n - - t h e d i s p l a y i n g d" then rushed toward the ¥ and d i s r u p t e d the attempt o f the other <J* , w i t h no c o p u l a t i o n ensuing. This sequence o f events was repeated many times i n each t r i a l . I t appeared t h a t the dV showed no r a c i a l d i s c r i m i n a t i o n toward one another--they behaved as they would have t o members o f the same race. The comparison of r a c e s , lumping a l l the ¥¥ , c l o s e l y resembles that o f the 84 17 era DITHER FISH J t / i s \ , — e= CLEAR PLEXIGLAS 20 cm. F i g . 2 1 . Experimental set-up f o r experiment 9. Three oV , one of each race, were pla c e d i n the empty compartment along w i t h a v i r g i n ? . Di t h e r f i s h were v i s i b l e to the experimental f i s h on a l l s i d e s but the observer's. 85 three-d" s i t u a t i o n o f Experiment 8: the frequency and d u r a t i o n o f d i s - p l a y s d i d not d i f f e r and P dd tended to leap l e s s than other dd ( F i g . 22a, b, and e) . Bouts o f d i s p l a y tended to be longer i n UA dd, however ( F i g . 22c). The r e l a t i v e l y low frequency o f d i s p l a y s (7-15 i n 30 minutes f o r a l l dd as opposed t o 4-16 i n 15 minutes f o r a l l s i n g l e oV i n Ex- periment 1) probably arose from the v i g o r o f the dd 's p u r s u i t s , which kept the moving r a t h e r q u i c k l y and thereby made i t d i f f i c u l t f o r the dd t o p o s i t i o n themselves f o r d i s p l a y . The r e l a t i v e l y low d i s p l a y f r e - quency of UA dd may be r e l a t e d to t h e i r performance o f j e r k s i n s i x t r i a l s (G,2; P,0). Although j e r k s are commonly a s s o c i a t e d w i t h s u c c e s s f u l c o p u l a t i o n , no UA dV copulated s u c c e s s f u l l y . The j e r k may be a "consum- matory" s o r t o f a c t i v i t y and have a d i m i n i s h i n g e f f e c t on f u r t h e r c o u r t - s h i p . G dd t h r u s t more o f t e n than other dd (p <.01, Friedman two-way a n a l y s i s of variance;** F i g . 22d) . Males o f any one race were not c o n s i s - t e n t l y c l o s e r t o the ? ? • The r e l a t i v e infrequency o f aggression on the p a r t of P d"d" was i n i - t i a l l y p u z z l i n g . Charges occurred i n o n l y f o u r of the 21 t r i a l s . C l o s e r examination of the data r e v e a l e d that a l l f o u r of these t r i a l s i n v o l v e d P ¥? . Furthermore, P dd engaged i n another aggressive behaviour i n four t r i a l s , two of these w i t h P %% (no overlap w i t h t r i a l s i n which charges occurred). These f i s h pushed t h e i r t a i l s i n another d 's f a c e , an a c t i o n which sometimes precedes t a i l - b e a t i n g or an attempted b i t e , and u s u a l l y r e s u l t s i n the other f i s h moving away. Thus, we f i n d th'at some P r o b a b i l i t y values throughout t h i s experiment arose from the Friedman two-way a n a l y s i s of v a r i a n c e , 2df. 86 F i g . 22. Comparison of the courtship performed by three dd one of each race, to sin g l e v i r g i n %% o f a l l races. Each group of histograms represents the behaviour o f dd from the P, UA, and G races, i n that order. P r o b a b i l i t y values derived from the Friedman two-way analysis of variance appear above the histograms. Sample si z e s appear on the histograms. MEAN DISPLAY FREQUENCY MEAN DISPLAY DURATION (% TIME OF TRIAL) MEAN DISPLAY BOUT LENGTH (SEC) MEAN THRUST FREQUENCY NUMBER OF TRIALS IN NHICH LEAPS OCCURRED 87 form of r e c o g n i z a b l e P d aggression took p l a c e i n s i x o f the seven P ¥ t r i a l s and two o f the fourteen t r i a l s w i t h other ¥¥ . The only- other aggression was from a UA d i n the presence o f a UA ¥ . The p o s s i b i l i t y o f some s e l e c t i v i t y t a k i n g p l a c e between dd and ¥¥ prompted the examination o f the dd's behaviour to ¥¥ o f each race s e p a r a t e l y . V dd d i s p l a y e d to t h e i r own ¥¥ more than the other dd i n f i v e o f seven t r i a l s (p <. 1). Males tended t o e x h i b i t h i g h e r f r e q u e n c i e s , d u r a t i o n s , and average bout lengths o f d i s p l a y than o t h e r dd to ¥¥ of t h e i r own r a c e , w i t h the exception o f G dd ( F i g . 23a, b, and c ) . G dd t h r u s t more than other dd t o t h e i r own ¥¥ (p = ,02; F i g . 23d). Few leaps o c c u r r e d , but P dd leaped o n l y w i t h P ¥¥ . p dd tended to spend the most time as the c l o s e s t d t o P ¥¥ ( F i g . 23a). My impression i s t h a t (1) there was an a f f i n i t y between P f i s h , and (2) i f UA and G dd d i d not show a preference f o r t h e i r own ¥¥ , they showed an avoidance of P ¥¥ ( F i g . 23e). No comparative score o f success (insemination) c o u l d be obtained i n t h i s experiment because the i n t e n s e competition between the dd prevented c o p u l a t i o n . However, i t seems reasonable t o suggest t h a t the d* e x h i b i t - i n g the g r e a t e s t amount of c o u r t s h i p behaviour and remaining c l o s e s t to a¥ has the h i g h e s t p r o b a b i l i t y o f success. b. Females as r e c i p i e n t s o f d behaviours I t seems l i k e l y t h a t dd r e c e i v e some cues from ¥¥ which increase:', t h e i r p r o p e n s i t y to court them. C e r t a i n l y dd are much more responsive to v i r g i n ¥¥ than n o n - v i r g i n ¥¥ , even i f no apparent o v e r t sexual response on the ¥¥'s p a r t i s i n v o l v e d . Compare the f o l l o w i n g r e s u l t s , where 88 F i g . 23. Comparison o f the c o u r t s h i p performed by three dd , one of each r a c e , to v i r g i n %% o f each race. Each group of histograms represents the behaviour of dd from the P, UA, and G r a c e s , i n t h a t order. P r o b a b i l i t y values d e r i v e d from the Friedman two-way a n a l y s i s o f v a r i a n c e appear above the histograms. N = 7 f o r each race. TO P 88a TO UA TO G a, MEAN DISPLAY FREQUENCY 25 20 15 10 5 0 <.l >.2 n >.2 b. MEAN DISPLAY DURATION (Z TIME OF TRIAL) 3.5 3 .0 2 . 5 2 . 0 1 .5 1 .0 . 5 0 <.08 <.1.9 m d >.2 MEAN DISPLAY BOUT LENGTH (SEC) <.05 ' . 1 9 <.19 d. MEAN THRUST FREQUENCY 15 10 <.2 - . 0 2 <.2 MEAN TIME CLOSEST TO * (Z TIME OF TRIAL) 60 50 40 30 20 10 <.2 >o2 >.2 89 a p p l i c a b l e , w i t h the d competition i n F i g . 23. P ? ? were c l o s e s t to P dd f o r a g r e a t e r percentage o f time and greater average lengths o f time than UA and G (p = .06 and .05, r e s p e c t i v e l y ; F i g . 24a and b ) . Although the other were c l o s e s t to t h e i r own dV s l i g h t l y more of the time, d i f f e r e n c e s were i n s i g n i f i c a n t . Both P and G were approached most c l o s e l y more o f t e n by P and G dd than were UA (p = .07 and .06, r e s p e c t i v e l y ; F i g . 24c). Females r e c e i v e d more t h r u s t s from dd o f t h e i r own race (p<.02, 2 X ). However, these r e s u l t s a r i s e l a r g e l y because G ? ? were t h r u s t at more by t h e i r own dd than others (p = .02). UA ?? tended to r e c e i v e fewer t h r u s t s from P<*V than d i d the other (p .= .09; F i g . 24d) . G dd t h r u s t more to a l l and G ? ? were t h r u s t at more by a l l dd (p<.01, Friedman, and <.05, K r u s k a l - W a l l i s , r e s p e c t i v e l y ; F i g . 24e). Bouts o f d i s p l a y s were r e c e i v e d more from members o f the same race 2 than from others (p< .01, X ) , but c l o s e a s s o c i a t i o n s between d and ? P guppies and d and ? G guppies seemed to account f o r t h i s . P ? ? r e c e i v e d longer d i s p l a y s from P dd than other (p<.02), UA ? ? r e - ceived s h o r t e r d i s p l a y s from G dd than d i d UA ? ? (p<.02; F i g . 25a). P ? ? a l s o got a gre a t e r percentage of d i s p l a y time from (p = .03), i n c o n t r a s t to UA ?? who tended to get l e s s d i s p l a y time from P dd than other dd (p = .19; F i g . 25b). D i s p l a y frequencies f o l l o w e d the same p a t t e r n ( F i g . 25c). P r e c e i v e d leaps only from P dd (p = .12) and UA ¥$ r e c e i v e d fewer leaps from P dd (p = .13; F i g . 25d). c. Female behaviours Female guppies e x h i b i t a r a t h e r stereotyped sexual response, as 90 F i g . 24. R e l a t i v e p o s i t i o n s of f i s h and t h r u s t s r e c e i v e d by v i r g i n ¥$ from dd o f d i f f e r e n t races i n competition w i t h one another. Each set o f histograms represent a c t i v i t i e s o f P, UA, and G dd , i n t hat order. K r u s k a l - W a l l i s one-way a n a l y s i s o f v a r i a n c e . The f i r s t s e t o f histograms i n e. represent dd , and Friedman two-way a n a l y s i s o f variance i s used. 90a P dV UA oV G dV a . b. X TIME OF TRIAL WHEN d* AND $ ARE CLOSEST MEAN LENGTH OF TIME d* AND ? REMAIN CLOSEST (SEC) MEAN NUMBER OF TIMES ? WAS APPROACHED MOST CLOSELY BY d" MEAN NUMBER OF THRUSTS RECEIVED MEAN NUMBER OF THRUSTS 60 50 40 30 20 10 1 5 1 2 9 6 3 O 1 2 5 1 0 0 7 5 5 0 2 5 0 1 5 1 2 9 6 3 0 1 0 . e> 6 A . 2 . 0 P = .06 P > . 2 P > , 2 P = .05 P > . 2 P > . 2 P- .07 P > . 2 P=.06 P = .09 P> .2 P = .02 TO ALL FROM ALL dV P<.01 P<.05 9 1 Fig. 25. Display behaviours received by v i r g i n ?? of d i f f e r e n t races from oV of di f f e r e n t races i n competition with one another. Each set of histograms represent P, UA, and G ?? , i n that order. Kruskal-Wallis one-way analysis of variance. 91a FROM P dV FROM UA 4<S FROM G dV b. d. MEAN DURATION OF DISPLAY (SEC) MEAN % TIME OF TRIAL DISPLAYING MEAN DISPLAY FREQUENCY NUMBER OF TRIALS IN WHICH LEAPS OCCURRED 25 20 15 10 .5 0 5 4 3 2 1 0 25 20 15 10 5 0 5 4 3 2 1 O P<02 P< 02 P = 03 P = .19 >=12 P=.19 P = .12 P=13 P< .02 P>.2 P>.2 P>.2 92 described by L i l e y (1966). See Appendix 2. The occurrence of the re- sponse depends upon a combination of the physiological readiness of the and the motivating capacities of the d , and appears to be i d e n t i c a l i n a l l three races. The glide i s the f i r s t response of a receptive $ to a displaying d". Females tended to glide to t h e i r own d'd" i n more t r i a l s than to others . 2 (p< .1, X ). Upon closer analysis, P ?¥ .tended to glide more to P d'd" (p = .17 ) and less to UA and G d'd" (p = .10 and .09, respectively) than UA and G (Fig. 26a). P?$ tended toward longer bouts of g l i d i n g to P d'd* (p = .12) and G had longer bouts of g l i d i n g to G d'd" (p<.05) than did the other (Fig. 26b). There were tendencies for P?? to glide f o r a greater t o t a l time to P d'd* (p = .09), UA $¥ to glide more to UA dV (p = .14), and G to glide less to P dd (p = .07) than did the other (Fig. 26c). The subsequent ? responses, arching and wheeling, were infrequent. Nevertheless, the number of t r i a l s i n which arches occurred was highest 2 with f i s h of the same race (p<.05, X ). P ?? performed arches and wheels more for P dd than did the other ¥? (p = .06 and .03, respectively; Fig. 26d and e). d. Male-female interaction The d who e l i c i t e d the f i r s t ¥ response i n a t r i a l was of the same 2 race as the ? (p<.01, X ). An index of response was formulated by 7 Unless otherwise mentioned, p r o b a b i l i t y values are derived from the Kruskal-Wallis one-way analysis of variance. 93 F i g . 26. Responses o f v i r g i n to oV of d i f f e r e n t races. Each set of histograms represent a c t i v i t i e s o f P, UA, and G , i n t h a t order. K r u s k a l - W a l l i s one-way a n a l y s i s o f v a r i a n c e . 93a b. d. NUMBER OF TRIALS IN WHICH GLIDES OCCURRED MEAN BOUT LENGTHS OF GLIDES (SEC) MEAN % TIME OF TRIAL GLIDING NUMBER OF TRIALS IN WHICH ARCHES OCCURRED NUMBER OF TRIALS IN WHICH WHEELS OCCURRED 10 8 6 4 2 O 2.5 2.0 1.5 1,0 .5 O .5 ,4 .3 .2 -1 O 5 4 . 3 2 1 O 5 4 3 2 1 O TO P P = 17 P = .12 P = .09 TO UA P =.10 TO G P = .09 P>.2 P< .05 P = .14 P = .07 _LZt Ll P= .06 P >.2 P > . 2 P = .03 P>.2 P=.12 94 d i v i d i n g the number o f g l i d e s by the number o f d d i s p l a y s . I t seems c l e a r that UA dd have very a t t r a c t i v e d i s p l a y s . They were able t o e l i c i t more responses from a l l c o m b i n e d than the other dd (p < .01) s but t h i s was coupled w i t h the g r e a t e r r e s p o n s i v i t y o f UA %% t o a l l dd (p <.05; Table 15a). UA dd e l i c i t e d more responses from UA and G than d i d other dd , and P dd e l i c i t e d fewer (p = .194 and <.005, r e s p e c t i v e l y : Friedman two-way a n a l y s i s . G dd evoked fewer responses from P than d i d P and UA dd (p< .039, Friedman two-way a n a l y s i s ) . UA and G dd evoked more responses from UA ? ? than other (p< .01 and <.02, r e s p e c t i v e l y ) . UA dd and were much more s u c c e s s f u l i n r e - sponding to one another than dd and o f other races (p <.001; Table 15b). D. Female s e l e c t i v i t y The purpose of the f o l l o w i n g experiments i s to examine the s e l e c t i v i - t y o f the t o dd o f d i f f e r e n t races suggested i n the p r e v i o u s e x p e r i - ment. Two major problems appear i n attempting to assess the responses o f the $ : (1) experienced r a r e l y respond to dd , and (2) v i r g i n respond so r e a d i l y to dd t h a t anything but d -ness i s probably not n o t i c e d . Despite these d i f f i c u l t i e s , I thought t h a t might d i s c r i m i n a t e between i f given a c h o i c e , even i f t h e i r s e l e c t i o n s were not s e x u a l l y motivated (e.g. s c h o o l i n g ) . E. Choice Test 1 (Experiment 10) _ I once a c c i d e n t a l l y bent a ? w h i l e t r a n s f e r r i n g her to an aquarium o f v i r g i n s . Almost immediately another 2 began a sexual response to t h i s apparently d i s p l a y i n g f i s h . Females do not seem t o respond t o models, hswever ( L i l e y , p e r s . comm.). 95 Table 15. Response indices (# glides/ # displays) for virgin SS with dd of different races in competition with one another. PSS UASS G SS All dd .134 .437 .112 a. P dd Vkdd G dd All SS .126 .306 .222 PSS UA SS G SS p dd b. UA dd G dd ^185"**- .138"""- .079 • ̂  .130 - ̂  . 652"* - , .459" .052 .280 .089"" P< .039 P = .194 P <" .005 p< .05 p< .01 p < .2 p < .01 p < .02 p < .00? 96 1. I n t r o d u c t i o n I gave v i r g i n and experienced deprived o f r e c e n t experience w i t h d'd* a choice o f swimming to one o f three dd of d i f f e r e n t races. The experimental hypothesis was that of one race would make c o n s i s - t e n t choices o f dd o f one r a c e , not n e c e s s a r i l y t h e i r own ( r e c a l l Haskins et a l . , 1961; s e l e c t b r i g h t e r d'd" ). 2. M a t e r i a l s and Methods F i r s t , one j o f each race was introduced i n t o the three-way choice maze, then one ? was p l a c e d behind c l e a r p l e x i g l a s p a r t i t i o n s , as i l - l u s t r a t e d i n F i g . 27 (see a l s o F i g . 4). A f t e r f i v e minutes, I r a i s e d the p a r t i t i o n s by a p u l l e y system, and the ? was f r e e to proceed to a d . The £ completed her t r i a l when she touched a p a r t i t i o n w i t h a d behind i t . I recorded her choice of d and the length o f time she took to reach him. A $ had f i v e minutes to complete her t r i a l before I terminated i t . S i x White Cloud Mountain minnows served as d i t h e r s i n each o f the three s i d e compartments o f the maze. A l l t r i a l s were independent. P o s i t i o n e f f e c t s were c o n t r o l l e d by r o t a t i n g d'd" t o d i f f e r e n t arms of the maze f o r each t r i a l , so t h a t ? ? saw dd o f a given race i n each o f the three arms approximately e q u a l l y . Twenty-four G and 23 P v i r g i n s were t e s t e d (no UA were a v a i l a b l e at the time). Twelve experienced o f each race, i s o l a t e d from d'd" (but not from one another) f o r 28-36 days, were t e s t e d . 3. R e s u l t s General observations of d i f f e r e n c e s i n behaviour between v i r g i n s and experienced i n the maze must f i r s t be noted. When a v i r g i n was 97 F i g . 27. Experimental set-up f o r Experiment 10. The c l e a r p a r t i - t i o n s surrounding the ? were removed by a p u l l e y system. A l l l i n e s but the outer ones represent c l e a r p l e x i g l a s . 98 plac e d i n the maze, she g e n e r a l l y swam around u n t i l she apparently n o t i c e d a d then swam immediately to him. In c o n t r a s t , the e x p e r i - enced seemed to take no more n o t i c e o f the dd than o f the d i t h e r f i s h . F i v e o f the experienced %% never reached a d , and those t h a t d i d took an average o f 82.9 seconds, compared t o 43.6 seconds f o r the v i r g i n s (p = .00006, Mann-Whitney U t e s t , t w o - t a i l e d ) . Females e x h i b i t e d no preferences o f . dd . N e i t h e r d i d they show a b i a s i n t h e i r s e l e c t i o n o f arms o f the maze. The behaviour o f the dd i n t h i s experiment and the next was q u i t e c o n s i s t e n t : almost a l l o f them swam at the c l e a r p a r t i t i o n , o r i e n t a t i n g t o the Experienced ?$ of a l l races demonstrated no d i f f e r e n c e s i n the length o f time taken to reach any race o f d-.'. P v i r g i n s a l s o d i d not d i f f e r , but G v i r g i n s tended to take l e s s time to reach G dd ( p < . l , 9 K r u s k a l - W a l l i s )„ When the data f o r experienced were lumped, a trend appeared i n the d i r e c t i o n o f l e s s time taken to reach the G dd (p< .1). P (both v i r g i n s and n o n - v i r g i n s ) took longer t o reach & d- than other ?$ ( v i r g i n s : p< .011, Mann-Whitney U t e s t ; n o n - v i r g i n s : p<.05, K r u s k a l - W a l l i s ) . I a t t r i b u t e t h i s d i f f e r e n c e to the tendency o f P ? ? to f r e e z e near the s u b s t r a t e i n u n f a m i l i a r surroundings (see Seghers, 1973); whereas UA and G f i s h tend to swim about r a p i d l y . " K r u s k a l - W a l l i s " h e r e a f t e r r e f e r s to the K r u s k a l - W a l l i s one-way a n a l y s i s o f v a r i a n c e . 99 F. Choice t e s t 2 (Experiment 11) 1. I n t r o d u c t i o n This choice t e s t was designed to measure r e l a t i v e length of time spent near dV of the three races. I t seemed th a t the h i g h l y e x p l o r a t o r y could then make choices based on comparison. The experimental hy- pothesis f o r the experienced *¥ was that a race o f $ would spend d i f - f e r e n t amounts o f time c l o s e to d*d* o f d i f f e r e n t races. For the v i r g i n s , two p o s s i b i l i t i e s were advanced: (1) would p r e f e r dV of t h e i r own r a c e , and (2) would p r e f e r the races which appear b r i g h t e r t o the human eye (P and UA) over the d u l l e r one (G). 2. M a t e r i a l s and Methods The maze was arranged as i l l u s t r a t e d i n F i g . 28. D i t h e r f i s h were employed. Males were introduced and t h e i r p o s i t i o n s changed between t r i a l s as i n the previous experiment. One * was in t r o d u c e d i n t o the center of the maze and a stopwatch began when she began moving. Each t r i a l , thus begun, l a s t e d ten minutes. The time the $ spent near each d" began when she made contact w i t h the p a r t i t i o n behind which he swam, and ended when she swam out of h i s area (see F i g . 28). In t h i s way, t o t a l time spent w i t h each d" and number o f approaches to each d" were recorded. The same experienced were used as i n the previous experiment, now i s o l a t e d from dV f o r 37-41 days, w i t h the exception o f t h a t e x p e r i - ment. Some of the v i r g i n s t e s t e d p r e v i o u s l y p a r t i c i p a t e d i n t h i s e x p e r i - ment, w i t h the a d d i t i o n o f new UA v i r g i n s . Twelve v i r g i n s and 12 non- v i r g i n s o f each race were used. 100 Fig. 28. Experimental set-up for Experiment 11. The dashed lines delimit a a* ?s "area". A l l lines but the outer ones represent clear plexiglas. 101 3. Results Most f i s h swam up to each d before choosing one a second time. As i n Experiment 10, the v i r g i n s were markedly more responsive to the dd . They made more approaches to the dd and spent more time i n t h e i r areas than the n o n - v i r g i n s (p = .008 and .034, r e s p e c t i v e l y ; Mann- Whitney U t e s t ) . Females showed no p o s i t i o n a l b i a s e s . No v i r g i n showed d i f f e r e n c e s i n a c t i v i t y , measured by number o f approaches, but the experienced d i d (p< .05, K r u s k a l - W a l l i s ) , w i t h P $$ being l e a s t a c t i v e (P-UA: p = .142; P-G: p = .007; Mann-Whitney U t e s t ) . F i g . 29 r e v e a l s t h a t experienced showed no preferences f o r dd of any r a c e , w i t h one exception. P a i r s comparison was p e r m i s s i b l e f o r P ? ? (p<.01, Friedman two-way a n a l y s i s o f v a r i a n c e ) , where they spent longer average times w i t h UA dd than t h e i r own (p <.02, Wilcoxon). V i r g i n $? , on the other hand, e x h i b i t e d d i s t i n c t preferences (p< .01, 2 X , 1 df) as i n d i c a t e d by the number o f t r i a l s i n which approached most and spent most time w i t h d V o f t h e i r own race. While P and G s e l e c t e d t h e i r own d'd* i n p a i r s comparisons, UA d i d not. No showed preferences when the p a i r s comparison d i d not i n c l u d e a d o f t h e i r race. No evidence was found t o support the hypothesis t h a t p r e f e r the dd b r i g h t e r t o humans. G. Reactive instances of (Experiment 12) 1. I n t r o d u c t i o n This experiment was designed w i t h the f o l l o w i n g i n mind: (1) a more conspicuously c o l o r e d d should be more n o t i c e a b l e t o a ? at a 102 F i g . 29. Preferences f o r d*d* of d i f f e r e n t races by v i r g i n and experienced . Each set o f three histograms represents responses of o f one race to P, UA, and G oV , i n t h a t order. The boxes below the f i g u r e s show the p r o b a b i l i t i e s o f v i r g i n choosing d*d* o f races o t h e r than t h e i r own by chance (Wilcoxon matched-pairs signed-ranks t e s t , o n e - t a i l e d ) . Under each column the comparison i s made between d"d* of that race and the ?*s own race. N = 12 f o r each group of . 102a >< u as 14 E> or W OS h i X o < o 04 ft. ft. < SB < 10 8 6 4 2 0 i UA VIRGIN 8 * P UA G EXPERIENCED «? PdV UArfrf Grfrf COp SS < .01 N.S. 3 UA OS M > G N.S . .005 < .02 N.S. 12 10 8 6 it 2 0 u w w OS < u SS w 300. 250. 200 150 100 50 0 PA UA VIRGIN P UA EXPERIENCED 8? ,300 • 250 . 200 . 150 100 . 50 _ 0 103 d i s t a n c e , (2) i n a s s o c i a t i o n w i t h the t u r b i d water o f t h e i r n a t u r a l h a b i t a t , G S S might take longer t o n o t i c e dd at r e l a t i v e l y great distances (see experiment 2 ) , and (3) SS might p e r c e i v e t h e i r own race o f d at a grea t e r d i s t a n c e . 2. M a t e r i a l s and Methods To ensure that 22 were re s p o n s i v e , v i r g i n s were used (25 P, 22 G, but only 4 UA were a v a i l a b l e at the time).. D i t h e r f i s h were employed. A cf was introduced behind a c l e a r p a r t i t i o n i n the long tank, f o l l o w e d by a ? , as i l l u s t r a t e d i n F i g . 30. A f t e r the S calmed, the opaque p a r t i t i o n b l o c k i n g her view o f the d was removed. One stopwatch r e - corded the time from removal o f the p a r t i t i o n u n t i l the 2 began swimming i n a s t r a i g h t l i n e towards the df and another stopwatch recorded the length o f time taken by a S t o reach the d's p a r t i t i o n once she began swimming toward him. A d i f f e r e n t d was used f o r each t r i a l and dd o f the three races were presented i n a r e g u l a r sequence. Each 2 p a r t i c i p a - t e d i n three t r i a l s , one w i t h each race o f d . Observer b i a s was avoided by p l a c i n g S S i n d i v i d u a l l y i n j a r s i n c o n s p i c u o u s l y l a b e l e d and having someone mix the j a r s up. Thus, I d i d not know the race o f the S I was t e s t i n g . Males were c o n s i s t e n t i n swimming at the p a r t i t i o n between them and the ? , u s u a l l y o r i e n t a t i n g t o her. 3. Results I t was g e n e r a l l y c l e a r when a 2 n o t i c e d a d . She would cease swimming about or s i t t i n g on the bottom and swim r a p i d l y s t r a i g h t toward him. No d i f f e r e n c e s appeared i n the di s t a n c e s at which the S S reacted 104 * i CLEAR PLEXIGLAS F i g . 30. Aquarium set-up f o r Experiment 12. The d was confined behind a c l e a r p l e x i g l a s p a r t i t i o n on the l e f t , and the % was r e - leased from behind an opaque p a r t i t i o n on the r i g h t . D i t h e r f i s h swim behind the experimental aquarium. 105 to the dd , e i t h e r between ? ? o f d i f f e r e n t r a c e s , o r between dd o f d i f f e r e n t races w i t h o f one race (average = 34.6 cm f o r 79 runs on P , 8 on UA, and 64 on G, each ¥ being used a maximum o f three t i m e s ) . Females o f one race d i d not vary e i t h e r i n the time taken to s t a r t toward the d or i n the time taken to swim to dd o f the d i f f e r e n t p o p u l a t i o n s . I t i s evident from the l a s t three experiments that v i r g i n o f the P and G races d i s c r i m i n a t e i n f a v o r o f t h e i r own race o f dd , but o n l y when given o p p o r t u n i t y f o r c l o s e o b s e r v a t i o n and comparison. H. Summary of the female's response V i r g i n ? ? o f the P and G races d i s c r i m i n a t e d i n f a v o r o f dd o f t h e i r own races i f they were given o p p o r t u n i t y f o r c l o s e o b s e r v a t i o n and comparison o f a l l three races o f dd . I f given o p p o r t u n i t y t o i n t e r a c t w i t h a l l three races o f dd at once, ? ? tended t o respond more t o dd o f t h e i r own race. This was accompanied by the tendency o f dd to d i r e c t more d i s p l a y and contact behaviour toward t h e i r own . F i r s t responses by were d i r e c t e d to t h e i r own dd when dd o f each race were present. Response i n d i c e s i n d i c a t e d t h a t UA responded much more r e a d i l y to UA d d i s p l a y s than d i d o f other races to t h e i r dd's d i s p l a y s . Thus, whether by i n i t i a l i nnate r e c o g n i t i o n (P and G *'*> ) , or by inc r e a s e d responsiveness to d i s p l a y s (UA ), of each race seemed more l i k e l y to complete f u l l sexual responses w i t h dd o f t h e i r own race. 1 0 6 Chapter 7. D i s c u s s i o n o f Geographic V a r i a t i o n Geographic v a r i a t i o n has g e n e r a l l y been regarded as the manifesta- t i o n o f adaptation at the p o p u l a t i o n l e v e l . Geographic b a r r i e r s maintain d i f f e r e n c e s between pop u l a t i o n s i n d i f f e r e n t e c o l o g i c a l s i t u a t i o n s ' : whereas lack o f p h y s i c a l b a r r i e r s a l l o w l e s s d i s t i n c t and more gradual d i f f e r e n c e s between p o p u l a t i o n s ( c l i n i a l v a r i a t i o n ) . Numerous accounts of geographic v a r i a t i o n i n c o l o r and c o n s i d e r a b l y fewer o f v a r i a t i o n i n mating behaviour have appeared i n the l i t e r a t u r e . However, few s t u d i e s suggest the s e l e c t i v e agents i n v o l v e d , or the adaptive s i g n i f i c a n c e o f these v a r i a t i o n s . I can do l i t t l e more than add to the l i s t o f observa- t i o n s and s p e c u l a t i o n s on c o l o r v a r i a t i o n . However, i n f o r m a t i o n about v a r i a t i o n i n mating behaviour i n the guppy, as discussed i n Chapter 5, adds t o the knowledge about the e v o l u t i o n o f races and s p e c i e s . A. Geographic v a r i a t i o n i n c o l o r Subspecies o f f i e l d mice from environmentally s i m i l a r i s l a n d s d i f f e r i n coat c o l o r , at l e a s t p a r t l y due t o a founder e f f e c t (Berry, 1970). The presence of few ground predators may have hastened the development o f these d i f f e r e n c e s (Delany, 1970). With the guppies we have d i s s i m i l a r en- vironments, but a p a r a l l e l can be drawn between the oceanic i s l a n d s o f t e r r e s t r i a l animals and the land-bounded " i s l a n d s " o f the guppies. I suspect that lowland r i v e r guppies were a n c e s t r a l t o the upstream popula- t i o n s . A e r i a l predators and tornadoes could have been d i s p e r s a l agents. Seghers and I both have the impression t h a t the Guayamare race harbors c o n s i d e r a b l y more v a r i a t i o n than the P a r i a r a c e , and not i n c o l o r alone. In our support, Bromley (unpubl.) has demonstrated a polymorphism f o r 1 0 7 malate dehydrogenase i n G f i s h w h i l e UA and P are monomorphic ( c f . Northcote, et_ , 1970; c o l o r and m e r i s t i c d i f f e r e n c e s o f rainbow t r o u t d i d not match l a c t a t e dehydrogenase d i f f e r e n c e s i n s i m i l a r en- vironments above and below f a l l s ) . Despite the l a r g e c o l o r and c o l o r - p a t t e r n d i f f e r e n c e s between the guppy r a c e s , o c c a s i o n a l males from the Guayamare R i v e r look very much l i k e Upper A r i p o or P a r i a males. Even r a r e r are UA males which resemble G males, and P males seem never to appear l i k e members o f the UA and G races. Remember that I was working w i t h three of the m o r p h o l o g i c a l l y most d i s s i m i l a r races. A l l the races i n T r i n i d a d are polymorphic, no two are the same, and the extent o f polymorphism seems t o vary. Kallman and Atz (1966) f i n d t h a t species or subspecies o f Xiphophorus w i t h ex- t e n s i v e geographic ranges are more polymorphic than those w i t h r e s t r i c t e d ranges, but remark: "There i s as yet no answer t o the q u e s t i o n why c e r - t a i n p a t t e r n s are widespread w h i l e others occur only i n s i n g l e species or are absent from c e r t a i n populations o f o t h e r s " (p. 128). Hershkovitz (1968: he regards d i f f e r e n c e s i n c o l o r or c o l o r - p a t t e r n i n marmoset races non-adaptive) t h e o r i z e s that when c e r t a i n mammals be- come r e l a t i v e l y f r e e o f p r e d a t i o n , c o l o r loses i t s concealment f u n c t i o n s and becomes e i t h e r more a t t r a c t i v e or n e u t r a l , which I i n t e r p r e t as s e l e c t i o n f o r i n t r a s p e c i f i c communication or no s e l e c t i o n at a l l . Contrast t h i s w i t h the drab plumage of i s l a n d b i r d s which s u f f e r l e s s p r e d a t i o n than r e l a t e d s p e c i e s , o f t e n c o l o r f u l , on the mainland (Grant, 1965). S u p e r f i c i a l l y i t appears t h a t w i t h marmosets and mice we have a s i t u a t i o n s i m i l a r t o the guppies--relax p r e d a t i o n and the c o l o r s emerge. However, there i s no good evidence to suggest t h a t guppy c o l o r has a d i r e c t l i n k 108 w i t h v u l n e r a b i l i t y t o p r e d a t i o n (Seghers, 1973; Chpt. 4, suggests care- f u l re-examination o f Haskins et a l . , 1961). Furthermore, the r e l a t i v e importance o f v i s u a l communication to d i f f e r e n t species must be considered. While v i s i o n appears t o be o f primary importance to guppies, I expect t h a t o l f a c t i o n , a u d i t i o n , and t a c t i o n are more important t o mice. I f c o l o r s were very important to i n t r a s p e c i f i c communication they would e x i s t i n the presence o f p r e d a t i o n a l s o ( c f . Selander, 1965). Many species o f animals e x h i b i t c o l o r o r p a t t e r n v a r i a t i o n between a l l o p a t r i c p o p u l a t i o n s w i t h no apparent c o r r e l a t i o n w i t h the s e v e r i t y o f e c o l o g i c a l b a r r i e r s o r d i s t a n c e between them (e.g., b u t t e r f l i e s ; Dowdeswell and Ford, 1953; f r o g s ; Volpe, 1961; cyprinodont f i s h e s : Gordon, 1947; Gordon and Gordon, 1957; Rosen and Kallman, 1969; S c h e e l , 1970; b i r d s : Moreau, 1957; Moreau and Southern, 1958; Selander, 1964; S i b l e y and Short, 1964; H a l l e_t a l _ . , 1966; V u i l l e u m i e r , 1971). How much c o l o r v a r i a - t i o n i s due t o random ge n e t i c d r i f t ? How much i s due to adaptive d i f f e r - ences i n sexual-aggressive communication i n d i f f e r e n t geographic areas? How s p e c i f i c are responses between animals i n the same p o p u l a t i o n compared with animals from d i f f e r e n t p o p u l a t i o n s ? Other cases o f c o l o r v a r i a t i o n e x i s t where the i n v e s t i g a t o r s were able to get some c o r r e l a t i o n w i t h environment or even an i n d i c a t i o n o f s e l e c t i v e v a l u e : porpoises--predatory behaviour and more s t r i k i n g counter- shading i n c l e a r e r waters ( P e r r i n , 1969; pers. comm.); b i r d s - - v e g e t a t i o n and s u b s t r a t e c o l o r (Davis, 1951; Buchanan, 1964; Chaniot, 1970; Barlow and W i l l i a m s , 1971; Johnson and Brush, 1972); q u a n t i t a t i v e aspects o f t e r r i t o r i a l d i s p l a y and p o s s i b l y p r e d a t i o n ( C o l l i a s and C o l l i a s , 1971); 109 absence o f r e l a t e d or s i m i l a r species ( S i b l e y , 1961; Mayr, 1963: 318-319; c f . Cody, 1969); l i z a r d s - - m a t e d i s c r i m i n a t i o n (McKinney, 1971; but con- t r a s t some b i r d s : Selander, 1964; Short, 1965); frogs--amount o f l i g h t on the f o r e s t f l o o r (Savage and Emerson, 1970): f i s h e s - - a l a r v a l escape r e - sponse and a pre d a t o r (McPhail, 1969); p o t e n t i a l p r edators ( F r y e r , 1959; 237-281; McKenzie and Keenleyside, 1970); b u t t e r f l i e s - - a c t i v i t y p e r i o d s (Hovanitz, 1953); spid e r s - - h e a t a b s o r p t i o n and/or camouflage (Muniz, i n • L e v i n s , 1968); s n a i l s - - p r e d a t i o n (Wolda, i963; 1965; 1969; Currey et a l . , 1964; Owen, 1965; P a r k i n , 1971; c f . Komai and Emura, 1955; C l a r k e , 1968). The i n c i d e n c e o f gray morphs of the p o e c i l i i d Brachyrhaphis e p i s c o p i i s h i g h e r i n the s i l t y water above a w a t e r f a l l than below i t ( D r e s s i e r , 1971) . The c o l o r s are not s e x - l i m i t e d , and males do not d i s c r i m i n a t e i n aggressive or c o u r t s h i p behaviour. The paper gives no i n f o r m a t i o n about predators. I t i s tempting to speculate t h a t underwater v i s i b i l i t y has been a f a c t o r i n the e v o l u t i o n of the Brachyrhaphis and guppy morphs. Species o f temperate fresh-water f i s h e s tend to be d u l l e r i n t u r b i d e n v i r o n - ments, but I could f i n d no evidence t h a t t h i s i s g e n e t i c . Though probably not important i n camouflage, the b r i g h t n e s s o f male guppies c o r r e l a t e s p o s i t i v e l y w i t h water c l a r i t y . Why have b r i g h t c o l o r s when they cannot be seen? This question im- mediately suggests the converse: why have b r i g h t c o l o r s when they can be seen? P l e i o t r o p i s m i s not a s a t i s f y i n g answer. An ada p t i v e , f u n c t i o n a l s o l u t i o n i s r e q u i r e d . For example, consider B a r t n i k ' s (1972) study o f two a l l o p a t r i c subspecies on longnose dace. The males o f the eastern sub- species (Rhinichthys cataractae cataractae) have b r i g h t crimson n u p t i a l 110 c o l o r a t i o n , which i s absent i n males o f the western subspecies (R_. c_. d u l c i s ) . R. c. cataractae males use the red c o l o r a t i o n f o r sex d i s - c r i m i n a t i o n , w h i l e R. c_. d u l c i s males appear to r e l y mostly on t a c t i l e s t i m u l i . Furthermore, the c o l o r e d subspecies spawns mostly d u r i n g day- l i g h t , and the uncolored subspecies spawns at n i g h t , p o s s i b l y i n response to a p r e d a t o r , which i s absent i n the East. Although naive guppy females o f at l e a s t the P and G races d i s c r i m i - nate i n f a v o r o f males o f t h e i r own race v i s u a l l y , I cannot r u l e out f a c t o r s other than c o l o r i n t h e i r choices ( i n c o n t r a s t to some b i r d s - - Mayr, 1963: 318-319). Haskins e;t al_. (1961: 387) have the impression that intra-male competition i s more important i n making more conspicuous males more a t t r a c t i v e t o females. Although I have found t h a t b r i l l i a n c e o f male c o l o r has l i t t l e to do w i t h aggression or a t t r a c t i v e n e s s to f e - males, I have the impression that c o l o r a t i o n i n f l u e n c e s i n t r a - m a l e be- haviour more than male-female behaviour, w i t h i n p o p u l a t i o n s . Consider, i n comparison, t h a t the t a i l - s p i k e o f the male s w o r d t a i l , Xiphophorus h e l l e r i , apparently f u n c t i o n s as a s i g n a l to other males only (Hemens, 1968; Franck and Hendricks, 1973). Higher r a n k i n g males have more c o l o r i n the r e l a t e d Gambusia h e t e r o c h i r (Warburton e_t a l _ . , 1957) and G_. h u r t a d o i ( M c A l i s t e r , 1958). Noble and C u r t i s (1935) and Haskins and Haskins (1949) consider the male's b r i g h t c o l o r s to be i n t i m i d a t i n g d e vices. Breder and Coates (1935) could not avoid concluding t h a t there was no sex recog- n i t i o n i n guppies, but t h i s i s now i m p o s s i b l e to accept. In support o f the m a l e - i n t i m i d a t i o n h y p o t h e s i s , Haskins et_ al_. (1961) suggest t h a t most mating i s performed by young males who are j u s t b eginning to show c o l o r . (I would be cautious i n extending t h i s statement to a l l guppy p o p u l a t i o n s , I l l however). Furthermore, i t seems that the b r i g h t e r P and UA males attend to one another f a r more than G males. A few cases have been s t u d i e d where h y b r i d zones and i n t r o g r e s s i o n occur between d i f f e r e n t l y c o l o r e d forms w i t h no obvious environmental c o r r e l a t e s (e.g., b i r d s : Short, 1965; Hubbard, 1969; l i z a r d s : Z w e i f e l , 1962; McKinney, 1971; salamanders: Stebbins, 1949). An intermediate h y b r i d may be adapted to an intermediate e c o l o g i c a l s i t u a t i o n (e.g., Hagen, 1967). O p p o r t u n i t i e s f o r e x p l o r i n g these kinds of d i f f e r e n c e s e x i s t w i t h i n the l a r g e r streams of T r i n i d a d . Guppies tend to form sub- populations w i t h r e l a t i v e l y l i t t l e gene flow between pools (Haskins et_ a l . , 1961; Seghers, 1973). C l i n e s i n morphological types o f a species can be more or l e s s steep, i n d i c a t i n g r e l a t i v e l y d i f f e r e n t amounts o f gene f l o w , and thereby r e l a t i v e degrees of d i s c r e t e n e s s o f p o p u l a t i o n s . D i f f e r e n c e s i n c o l o r are u s u a l l y responses to l o c a l c o n d i t i o n s , and represent a n t i p r e d a t o r adaptations (e.g., elephant shrews: Corbet, 1970; b i r d s : P i t e l k a , 1951; S i b l e y and West, 1959; Johnston and Selander, 1964; Johnston, 1966; f r o g s : Schaaf and Smith, 1970). Other cases e x i s t where the concommitants of c l i n a l c o l o r v a r i a t i o n are more obscure (e.g., b i r d s : M i l l e r , 1941; Mayr and Stresemann, 1950; D i c k i n s o n , 1952; G a l b r a i t h , 1956, 1969; V a u r i e , 1957; Banks, 1964; Berry and Davis, 1970; f i s h : Hubbs and M i l l e r , 1965). V a r i a t i o n i n c o l o r i s g e n e r a l l y l i n k e d to c r y p s i s . Some researchers have considered i n t r a s p e c i f i c s i g n a l i n g . A p o s s i b i l i t y which almost a l l i n v e s t i g a t o r s have neglected i s mimicry. Behaviour d i f f e r e n c e s a s s o c i a t e d w i t h geographical c o l o r d i f f e r e n c e s have been found only by McPhail (1969), 112 C o l l i a s and C o l l i a s (1971), McKinney (1971), and B a r t n i k (1972). Streams and Pimentel (1961) have s t a t e d , " S e l e c t i o n seldom acts on one c h a r a c t e r without a f f e c t i n g other c h a r a c t e r s " . The c u r r e n t s t a t e o f knowledge leads us to the c o n c l u s i o n that unexplained v a r i a t i o n s i n c o l o r are due l a r g e l y to p l e i o t r o p i s m s (Dobzhansky, Scudder, p e r s . comms.). I b e l i e v e t h i s to be a premature c o n c l u s i o n because i t e x p l a i n s nothing. Explanations f o r c o l o r v a r i a t i o n s have been sought mainly as adaptive mechanisms f o r a given animal's a s s o c i a t i o n w i t h o t h e r s p e c i e s , e s p e c i a l l y p redator avoidance and prey capture. The importance o f c o l o r s i n i n t r a - s p e c i f i c communication, emphasized by an animal's behaviour, must be given a t t e n t i o n . As I mentioned e a r l i e r , I i n i t i a l l y intended to study the s i g n a l value of guppy c o l o r a t i o n , but found that polymorphism i n a d d i t i o n to geographic v a r i a t i o n made the problem too complicated. The c o r r e l a t i o n s of black markings and behaviour, discussed i n Appendix 1, suggest f u r - t h e r work. Perhaps c e r t a i n c o l o r p a t t e r n s are l i n k e d q u a n t i t a t i v e l y w i t h behaviours. C e r t a i n l y enough i s known about guppy c o l o r i n h e r i - tance to begin (Winge, 1922a, b, 1923a, 1927, 1930; Winge and D i t l e v s e n , 1948; Haskins and Haskins, 1951, 1954; Haskins et^ a K , 1961; Haskins et a l . , 1970) , but the work would appear to r e q u i r e much space and many hours. N e v e r t h e l e s s , the guppy seems to me a l e a d i n g candidate f o r be- h a v i o u r g e n e t i c analyses, h o p e f u l l y u s i n g c o l o r s as marker genes. Some r e l a t e d work on behaviour-genetics and, s e p a r a t e l y , c o l o r , has begun on species o f the r e l a t e d genus Xiphophorus (Kallman and A t z , 1966; Kallman, 1970a, b; Franck, 1970). 113 B. Geographic v a r i a t i o n i n mating behaviour The probable consequence o f geographic v a r i a t i o n i n mating behaviour i s s exual i s o l a t i o n and s p e c i a t i o n . Therefore, most i n v e s t i g a t o r s who have looked at r a c i a l d i f f e r e n c e s i n mating have been s e a r c h i n g f o r s p e c i a t i o n i n a c t i o n , and not so much f o r the adaptive s i g n i f i c a n c e of the d i f f e r e n c e s . Obviously, r e i n f o r c e d sexual i s o l a t i o n i s adaptive, but the e v o l u t i o n of d i f f e r e n t mating p a t t e r n s or mate choices i n i s o l a t e d p o pulations where no secondary c o n t a c t has occurred i s p u z z l i n g . P l e i o - t r o p i s m may be a reason f o r many o f the cases on r e c o r d , b u t , as mentioned e a r l i e r , t h i s i s not a s a t i s f a c t o r y e x p l a n a t i o n to me. The r e p o r t o f McKenzie and Keenleyside (1970) i s the only study which I came across that o u t l i n e d d i r e c t environmental c o r r e l a t e s to geographic d i f f e r e n c e s i n mating behaviour, and here the s i g n i f i c a n c e o f the c o u r t s h i p d i f f e r e n c e s was not c l e a r . I n t r a s p e c i f i c v a r i a t i o n i n s o c i a l o r g a n i z a t i o n i n ungulates (Estes, 1966; K l o p f e r , 1972), rodents (Anderson, 1961), and primates ( G a r t l a n and B r i a n , 1968; Crook, 1970) i s l i k e l y to r e s u l t from the p h y s i c a l and s o c i a l environment, and i s not n e c e s s a r i l y g e n e t i c . S i m i l a r l y , geographical v a r i a t i o n i n some birdsongs (Marler and Tamura, 1964; T h i e l c k e , 1965, 1969) and n e s t i n g s i t e s and nest s t r u c t u r e (Walkinshaw and Zimmerman, 1961) show no i n d i c a t i o n o f a g e n e t i c b a s i s . In other s t u d i e s mate preferences (Godfrey, 1959) and c o u r t s h i p (Ferguson,", 1970; McKinney, 1971) d i f f e r , but environmental c o r r e l a t e s are not e v i d e n t . In g e n e r a l , members of one subspecies or race of D r o s o p h i l a succeed muhh more f r e q u e n t l y i n mating w i t h t h e i r own r a t h e r than another subspecies or race ( S t a l k e r , 1942; Dobzhansky, 1944; Dobzhansky and Mayr, 1944; Dobzhansky and S t r e i s i n g e r , 1944; Bateman, 1949; S p i e t h , 1951; Dobzhansky 114 and Spassky, 1959; Dobzhansky and Mather, 1961; Ehrman, 1961, 1964, 1965; Dobzhansky et^ a l _ . , 1964; Anderson and Ehrman, 1969; Baimai, 1970). This g e n e r a l i t y extends even to s t r a i n s w i t h i n races (Carmody et_ a l . , 1962). Laboratory s t u d i e s have demonstrated p o s s i b i l i t i e s o f how etho- l o g i c a l i s o l a t i o n evolves (Knight et_ a l _ . , 1956; Santibanez and Waddington, 1958; Dobzhansky and Pavlovsky, 1971; a l s o see P o w e l l , 1971). A l l i n a l l , e i t h e r D r o s o p h i l a are unusual animals or i n v e s t i g a t o r s have examined a preponderance o f cases where races d i f f e r e d i n mating. Why should a mating system be so subject t o v a r i a t i o n ? Are other c h a r a c t e r i s t i c s o f f r u i t f l i e s as p l i a b l e ? Is p l e i o t r o p i s m so o f t e n expressed i n mating behaviour? Many s t u d i e s showing mating d i f f e r e n c e s and p r e f e r e n t i a l mate s e l e c - t i o n between c l o s e l y r e l a t e d species have been r e p o r t e d (e.g. c r i c k e t s : Hoy and P a u l , 1973; D r o s o p h i l a : Tan, 1946; Koopman, 1950, M e r r e l l , 1954; f i s h e s : C l a r k e , Aronson, and Gordon, 1954; H e i n r i c h , 1967; Nelson, 1968; Franck, 1969, 1970; P a r z e f a l l , 1969; G e r a l d , 1971; R u b i n o f f and R u b i n o f f , 1971; f r o g s : L i t t l e j o h n and L o f t u s - H i l l s , 1968; L i c h t , 1969; l i z a r d s : Gorman, 1969; b i r d s : Ramsay, 1961; Crook, 1964; Sharpe and Johnsgaard, 1966; Smith, 1966; Davies, 1970; mammals: B l a i r , 1953; F i s l e r , 1965). In many cases e t h o l o g i c a l i s o l a t i n g mechanisms may have evolved due to r e i n - f o r c i n g s e l e c t i o n . In other instances the d i f f e r e n c e s have evolved i n a l l o p a t r i c species and the s e l e c t i v e agents are not apparent. U s u a l l y no suggestions are given by i n v e s t i g a t o r s r e g a r d i n g the s i g n i f i c a n c e o f d i f f e r e n c e s between p o p u l a t i o n s . When concommitant v a r i a t i o n i n environmental parameters are g i v e n , they are only c o r r e l a t i o n s and not causal r e l a t i o n s h i p s , as Mayr (1963) suggests. I f we pursue 115 neo-Darwinian thought i n an e f f o r t to s u b s t a n t i a t e the adaptive s i g n i f i - cance of the phenotypic v a r i a t i o n s we see, we have the f o l l o w i n g s t a t e - ment o f Mayr w i t h which to contend: "Geographic v a r i a t i o n as a whole i s adaptive. I t adapts each p o p u l a t i o n to the l o c a l i t y i t occupies?*;,. How- ever, not a l l the phenotypic m a n i f e s t a t i o n s of t h i s genotypic adaptation are n e c e s s a r i l y adaptive"(e.g., Mayr, 1963; Dobzhansky, 1970). Dobzhansky s t a t e d t h a t the o r i g i n o f i s o l a t i o n i s a process d i f f e r - ent from the o r i g i n of other species d i f f e r e n c e s : "Race formation i s e s s e n t i a l l y the development o f genetic p a t t e r n s which are adapted to a d e f i n i t e environment. S p e c i a t i o n i s a process r e s u l t i n g i n f i x a t i o n o f these p a t t e r n s through the development of p h y s i o l o g i c a l i s o l a t i n g mechan- isms" (Dobzhansky, 1940). This l a t t e r sentence seems f i n e i n the case o f reinforcement, but i f two p o p u l a t i o n s are i s o l a t e d we must look t o e i t h e r t e l e o l o g y or p l e i o t r o p i s m i f s e l e c t i o n i s not working d i r e c t l y on mating behaviour or p h y s i o l o g y . There are no environmental f a c t o r s obvious to me which should i n - fluence guppy female s e l e c t i v i t y of males. The o p p o r t u n i t y f o r r e i n f o r c i n g s e l e c t i o n seems non-existent i n the absence of secondary contact. I could understand choices b i a s e d toward males w i t h more a t t r a c t i v e c o l o r s or d i s p l a y s , i f females had a s i m i l a r response t h r e s h o l d r e t a i n e d from an- c e s t r a l p opulations ( c f . Selander, 1969; Oortmerssen, 1970). While t h i s type o f sexual s e l e c t i o n may take p l a c e w i t h i n p o p u l a t i o n s , the choice o f G females f o r t h e i r more d u l l y c o l o r e d , l e s s e l a b o r a t e l y performing males r e f u t e s t h i s hypothesis of Haskins et_ al_. (1961) . There i s good evidence to support the hypothesis that male guppy c o u r t s h i p d i f f e r e n c e s are the r e s u l t s of d i f f e r e n c e s i n s e l e c t i o n pressure o p e r a t i n g i n d i f f e r e n t 116 environments, (see Chpt. 5 ). The males do not appear t o d i s c r i m i n a t e between females o f d i f f e r e n t p o p u l a t i o n s - - t h e y respond t o females which respond to them. Could i t be that an a n c e s t r a l p o p u l a t i o n , b e l i e v e d to be s i m i l a r to the G r a c e , contained females which v a r i e d g e n e t i c a l l y i n response t h r e s h o l d to d i f f e r e n t males? Could the e v o l u t i o n of male conspicuousness i n i s o l a t e d p opulations have preceded female s e l e c t i v i t y ? Could the females more responsive to the type o f male now more p r e v a l e n t i n the po p u l a t i o n have l e f t more o f f s p r i n g , u n t i l most of the females possessed an innate "template" o f males of t h e i r race? Or would the g e n e t i c pre- ferences o f females prove i n c o n s e q u e n t i a l w i t h experience? This can be t e s t e d . Could the males transmit the genes f o r female b i a s toward t h e i r type? I f the a n c e s t r a l race were l i k e the Guayamare, perhaps the r a r e r , more conspicuous males i n the p o p u l a t i o n inseminated a h i g h e r p r o p o r t i o n o f females than expected due t o an advantage i n in t r a - m a l e competition (see Parsons, 1967; Ehrman and P e t i t , 1968; Ehrman, 1969, 1970). I have the impression that as many as 10% of G males f a l l w i t h i n the range o f " b r i g h t n e s s " v a r i a t i o n o f UA males. The male o f f s p r i n g would p o s s i b l y be at a disadvantage i n p r e d a t o r - i n f e s t e d waters, but the females would not. A balanced polymorphism could r e s u l t . In an i s o l a t e d p o p u l a t i o n w i t h r e - duced p r e d a t i o n , more conspicuous males would i n c r e a s e i n frequency, and more females would c a r r y t h e i r genes. This hypothesis i s t e s t a b l e , s i n c e a l l crosses are p o s s i b l e . Remember t h a t s e l e c t i o n by females i s j u s t t h a t : a choice must be presented. Choices w i t h i n a p o p u l a t i o n would be along a continuum, and genotype changes would evolve s t a t i s t i c a l l y . Now i n a p o p u l a t i o n w i t h conspicuous males, l e s s conspicuous ones could be maintained by a balanced polymorphism s i m i l a r l y to the reverse s i t u a t i o n . 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N a t u r a l p o p u l a t i o n s o f the polymorphic l a n d s n a i l Cepaea nemoralis ( L . ) . Factors a f f e c t i n g t h e i r s i z e and t h e i r g e netic c o n s t i t u t i o n . Arch. N e e r l . Zool. 15: 381-471. Wolda, H. 1965. Some p r e l i m i n a r y observations on the d i s t r i b u t i o n o f the v a r i o u s morphs w i t h i n n a t u r a l populations of the polymorphic l a n d s n a i l Cepaea nemoralis ( L . ) . Arch. N e e r l . Z o o l . 16: 280-292. Wolda, H. 1969. S t a b i l i t y o f a steep c l i n e i n morph frequencies o f the s n a i l Cepaea nemoralis ( L . ) . J . Anim. E c o l . 38: 623-633. Z w e i f e l , R. G. 1962. A n a l y s i s o f h y b r i d i z a t i o n between two subspecies o f the desert w h i p t a i l l i z a r d , Cnemidophorus t i g r i s . Copeia. 1962: 749-766. 131 Appendix 1. Some Sp e c u l a t i o n and Findings About Black Markings o f the Male Guppy A. I n t r o d u c t i o n As c o u r t s h i p proceeds, the bl a c k markings o f the d guppy become more and more prominent, although no s p e c i a l " a g g r e s s i v e " or " s e x u a l " melanophore systems were noted ( c f : Baerends et a l . , 1955). Because the black seems to be an ar o u s a l s i g n a l , I hypothesized t h a t dd of the race which courted most should have the most b l a c k ; i . e . , P a r i a and Upper A r i p o should have more black than Guayamare. In a d d i t i o n i t i s p o s s i b l e that the black markings a l s o have some appeasement f u n c t i o n (see Barlow, 1970, on the appeasement and arou s a l hypothesis o f Tinbergen). When dd are engaged i n aggressive a c t i v i t i e s , v i r t u a l l y a l l the black on the body blanches. Furthermore, when the d d i s p l a y s i n f r o n t o f the * , he i s i n a p o s i t i o n to be charged. Males do o c c a s i o n a l l y d i s p l a y to other dd , and the p o s s i b i l i t y remains t h a t t h i s behaviour i s not j u s t misguided s e x u a l i t y , but has a component o f appeasement. Since P f i s h are much more aggressive than e i t h e r of the other r a c e s , I p r e d i c t e d that P dd should have the most b l a c k . The hypothesized order f o r the most t o the l e a s t amount o f black pigment, then, was P--UA--G. B. Method o f a n a l y s i s F o r t u n a t e l y , the a n e s t h e t i c MS 222 expands melanophores so th a t an ane s t h e t i z e d d has much the same appearance as a h i g h l y motivated c o u r t - i n g d . The sketches of 32 P, 32 UA, and 30 G dd a s s o c i a t e d w i t h Experiment 3 were employed to score b l a c k markings by e s t i m a t i n g the amount 132 of black i n each of eleven s e c t i o n s o f the guppy's l a t e r a l s u rface ( F i g . 31). 0 - 25% of the area b l a c k gave a score o f 1, 26 - 50% = 2, 51 - 75% = 3, and 76 - 100% = 4 ) . The use of s t e n c i l e d o u t l i n e s of the same s i z e a u t o m a t i c a l l y c o r r e c t e d scores f o r s i z e d i s c r e p a n c i e s between the races. An independent a n a l y s i s was performed i n a d d i t i o n to my own because o f the s u b j e c t i v i t y i n v o l v e d i n the s c o r i n g . C. R e s u l t s The two analyses y i e l d e d v i r t u a l l y i d e n t i c a l r e s u l t s . The d i f f e r - ences i n the amount of black were s i g n i f i c a n t as p r e d i c t e d (P had an average score o f 1.25 per body s e c t i o n , UA = 1.08, and G = .93; P t o G comparison, p <.00023; UA-G, p<.0054; P-UA, p< .0329; Mann-Whitney U t e s t ) . No c o r r e l a t i o n s e x i s t e d between amount o f b l a c k and the dd who courted most w i t h i n a r a c e , however. In comparison, see Warburton et a l _ . , (1957) , where dominant dd of Gambusia h e t e r o c h i r may be recog- n i z e d by in c r e a s e d i n t e n s i t y o f black c o l o r a t i o n . These r e s u l t s are perhaps not as o b j e c t i v e as i s d e s i r a b l e , but they do suggest f u r t h e r experiments on the value of b l a c k as a s i g n a l i n c o u r t s h i p and aggression. 133 F i g . 31. Areas of the <S guppy's l a t e r a l surface used t o q u a n t i f y black markings. 134 Appendix 2. A D e s c r i p t i o n of Guppy Behaviour Patterns P e r t a i n i n g t o C ourtship The f o l l o w i n g d e s c r i p t i o n s f o l l o w L i l e y (1966). A. Male c o u r t s h i p O r i e n t a t i n g . The <t attends to the ¥ , u s u a l l y watching her. He g e n e r a l l y f o l l o w s her when she moves, and attempts to maintain an optimal p o s i t i o n o f o b s e r v a t i o n . He may o r i e n t a t e from p o s i t i o n s above, below, or l e v e l w i t h the ? . Gonopodial swinging. The gonopodium i s moved forward on one s i d e of the m i d l i n e , accompanied by an arching i n the v e r t i c a l plane and o f t e n a sigmoid bending i n the h o r i z o n t a l plane. This may occur at p r a c t i c a l l y any time during c o u r t s h i p . Sigmoid d i s p l a y . The <S bends h i s body i n t o an S shape and q u i v e r s , w i t h the p e c t o r a l f i n s working r a p i d l y . Often the c/ rocks back and f o r t h . This posture i s u s u a l l y h e l d f o r a few seconds. Leap. As i f s p r i n g - l o a d e d , the d* shoots away from the % along a s t r a i g h t or curved path f o r 10 cm or more. He then o f t e n resumes o r i e n - t a t i n g , sometimes a f t e r a s h o rt p e r i o d of i m m o b i l i t y . Leaps may f o l l o w sigmoid d i s p l a y s , and are always preceded by them. Thrust. The <f approaches the ? from behind, below, and s l i g h t l y to one s i d e , and b r i n g s h i s gonopodium forward and t h r u s t s i t at the S 's g e n i t a l opening w i t h an upwards and forward movement. Jer k . A <f may make a s e r i e s o f s h o r t , sharp, forward and upward movements w i t h h i s whole body f o l l o w i n g a gonopodial c o n t a c t . His body moves no more than a few mm and he u s u a l l y continues o r i e n t a t i n g . 135 Copulation and C o p u l a t i o n Attempt. While d i s p l a y i n g , a d" moves i n t o a p o s i t i o n p a r a l l e l to one s i d e and j u s t below the ? . He then stops d i s p l a y i n g , swims to l i n e h i m s e l f up w i t h her, then d i r e c t s h i s gonopodium as i n t h r u s t i n g . I f he makes contact w i t h the $ 's g e n i t a l pore, he r o l l s over on h i s s i d e . The p a i r may swim i n one or two small c i r c l e s depending on the d i f f i c u l t y o f gonopodial i n s e r t i o n . Contact i s maintained f o r o n l y a f r a c t i o n of a second, a f t e r which the d* jumps away and performs a s e r i e s o f j e r k s . The o n l y d i f f e r e n c e between copu- l a t i o n and c o p u l a t i o n attempt i s whether or not i n s e m i n a t i o n has taken p l a c e . B. Male a g o n i s t i c behaviour S p a r r i n g . Males l i n e up p a r a l l e l or a n t i - p a r a l l e l , .5 t o 1 cm a p a r t , w i t h s t r a i g h t , q u i v e r i n g bodies and median f i n s spread. T a i l - b e a t i n g . From the s p a r r i n g p o s i t i o n , a <S lashes h i s t a i l toward the other d*. C. Female c o u r t s h i p G l i d e . A r e c e p t i v e % may g l i d e i n response to a d i s p l a y or Leap. The g l i d i n g % seems r i g i d i n motion, u s i n g her trunk l i t t l e and r e l y i n g mainly on her p e c t o r a l and caudal f i n s . Her a t t e n t i o n i s " f i x e d " on the d". , Arch. F o l l o w i n g g l i d i n g the % may stop and r a i s e her t a i l and head s l i g h t l y , o f t e n moving the t a i l s l i g h t l y to one s i d e away from the d" . She thus makes her g e n i t a l pore q u i t e a c c e s s i b l e to the <£ , who u s u a l l y attempts c o p u l a t i o n . Wheel. The $ moves i n a t i g h t c i r c l e , a s s i s t i n g the d i n a c o p u l a t i o n attempt.

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