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Some factors affecting the development and expression of escape behavior in the guppy (Poecilia reticulata) Goodey, Wayne 1984

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FACTORS AFFECTING THE DEVELOPMENT AND EXPRESSION OF ESCAPE BEHAVIOR IN THE GUPPY (POECILIA RETICULATA) by WAYNE GOODEY B . S c , U n i v e r s i t y of B r i t i s h Columbia, 1980 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in THE FACULTY OF GRADUATE STUDIES (Department of Zoology) We accept t h i s t h e s i s as conforming to the r e q u i r e d standard THE UNIVERSITY OF BRITISH COLUMBIA A p r i l 1984 © Wayne Goodey, 1984 In p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f the requirements f o r an advanced degree a t the U n i v e r s i t y o f B r i t i s h Columbia, I agree t h a t the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and study. I f u r t h e r agree t h a t p e r m i s s i o n f o r e x t e n s i v e copying of t h i s t h e s i s f o r s c h o l a r l y purposes may be granted by the head o f my department o r by h i s o r her r e p r e s e n t a t i v e s . I t i s understood t h a t copying or p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l not be allowed without my w r i t t e n p e r m i s s i o n . Department o f Zoology  The U n i v e r s i t y o f B r i t i s h Columbia 1956 Main Mall Vancouver, Canada V6T 1Y3 Date 27 A p r i l 1984 DE-6 (3/81) i i ABSTRACT Adult guppies ( P o e c i l i a r e t i c u l a t a ) f r e q u e n t l y chase, but only i n f r e q u e n t l y capture and eat, young c o n s p e c i f i c s . On average, young i n p l a n t e d tanks c o n t a i n i n g 6-14 a d u l t s and 1-4 young experienced over 270 chases per i n d i v i d u a l per day. Does the experience of being chased a f f e c t escape behavior? I t e s t e d t h i s i n two experiments on i n d i v i d u a l guppies. In the f i r s t , the escape behavior of three groups of guppies - c o n t r o l f i s h (those chased by a d u l t s i n the f i r s t 48 hr of l i f e ) , p a r t i a l l y experienced f i s h (exposed to chemical cues from c h a s i n g a d u l t s , v i s u a l cues from chasing a d u l t s , or chemical cues from predatory f i s h ) , and inexperienced f i s h - was compared f o r t h e i r response to an a e r i a l predator s t i m u l u s . Response i n t e n s i t y v a r i e d among the treatments, but d e p r i v a t i o n had no e f f e c t on the appearance of s t e r e o t y p e d escape b e h a v i o r s . D e p r i v a t i o n had no i n f l u e n c e on the drop response e l i c i t e d by the a e r i a l s t i m u l u s , but i t caused a general i n c r e a s e i n the l e n g t h of time spent f r e e z i n g in response to the s t i m u l u s . F i s h exposed to chemical cues from a d u l t guppies, on the other hand, developed a n e a r - c o n t r o l response. In the second experiment, I exposed guppies from the same experience groups to p r e d a t i o n to see i f long f r e e z i n g times were s e l e c t e d a g a i n s t . C o n t r o l s were not a t t a c k e d with g r e a t e r l a t e n c y nor d i d they s u r v i v e longer than any d e p r i v e d group, but i t took more a t t a c k s to k i l l c o n t r o l f i s h than to k i l l any d e p r i v e d f i s h . I propose that chasing by a d u l t s i s an ontogenetic mechanism f o r c o n d i t i o n i n g the young to a v o i d p r e d a t i o n . T h i s i s s e l e c t e d f o r because guppies which are chased as j u v e n i l e s s u r v i v e b e t t e r than those not chased as j u v e n i l e s . TABLE OF CONTENTS ABSTRACT i i LIST OF TABLES v i i LIST OF FIGURES v i i i ACKNOWLEDGEMENTS ix General I n t r o d u c t i o n 1 General Methods 3 The chasing of young guppies by a d u l t s 4 I n t r o d u c t i o n 4 Methods 4 Re s u l t s 5 D e s c r i p t i o n of behavior 5 A n a l y s i s 5 D i s c u s s i o n 6 The e f f e c t of chasing d e p r i v a t i o n on the development and express i o n of guppy escape behavior 9 I n t r o d u c t i o n 9 Methods 10 Res u l t s 15 D e s c r i p t i o n of behavior 15 A n a l y s i s 15 D i s c u s s i o n 22 Sex and age d i f f e r e n c e s 22 Treatment d i f f e r e n c e s 23 Experience and pr e d a t i o n 24 V The e f f e c t of chasing d e p r i v a t i o n on the s u r v i v a l of guppies under f i s h p r e d a t i o n 27 I n t r o d u c t i o n 27 Methods 28 R e s u l t s 29 D i s c u s s i o n 31 An a l t e r n a t i v e e x p l a n a t i o n of sex d i f f e r e n c e s i n s u r v i v a l a b i l i t y 35 The e f f e c t of immediate s o c i a l d e p r i v a t i o n on the e x p r e s s i o n of escape behavior 37 I n t r o d u c t i o n 37 Methods 38 R e s u l t s 38 D i s c u s s i o n 40 General D i s c u s s i o n 42 P r e d a t i o n p r e s s u r e s o p e r a t i n g on guppies 42 The e f f e c t of e a r l y chasing experience on escape responses and s u r v i v a l under p r e d a t i o n 43 P o s s i b l e mechanisms through which chasing experience might a f f e c t escape behavior 44 The p o s s i b l e f u n c t i o n a l s i g n i f i c a n c e of chasing i n guppies 45 Suggestions f o r f u r t h e r r e s e a r c h 46 C o n c l u s i o n s 49 References 51 Appendix - Summary of d i s t a n c e - t i m e c o r r e l a t i o n t e s t s 56 D e p r i v a t i o n experiment 56 v i Immatures 56 Matures 57 Immediate s o c i a l d e p r i v a t i o n experiment 58 LIST OF TABLES Table I. Summary of c o n t r o l chasing experience 6 Table I I . Summary of experience given i n the d e p r i v a t i o n treatments 12 Table I I I . Summary of sample s i z e s of groups in the a e r i a l model response experiment 15 Table IV. Mean body lengths of f i s h i n the treatment groups. (standard lengths i n cm) 19 Table V. Summary of sample s i z e s f o r a l l treatment groups i n the p r e d a t i o n experiment 29 v i i i LIST OF FIGURES F i g u r e 1. D e r i v a t i o n of treatment groups : d e p r i v a t i o n s exper iment 11 Fi g u r e 2. Experimental apparatus 13 F i g u r e 3. A, stimulus model. B, model c a r r i e r d e t a i l 14 F i g u r e 4. Sex d i f f e r e n c e s i n escape response 16 F i g u r e 5. Age d i f f e r e n c e s i n escape response 18 F i g u r e 6. Treatment d i f f e r e n c e s i n males 20 F i g u r e 7. Treatment d i f f e r e n c e s i n females 21 Fi g u r e 8. I n i t i a l a t t a c k l a t e n c i e s f o r t r e a t e d groups under f i s h p r e d a t i o n 30 F i g u r e 9. T o t a l s u r v i v a l times f o r t r e a t e d groups under f i s h predat ion 32 Fi g u r e 10. Numbers of a t t a c k s per k i l l f o r t r e a t e d groups under f i s h p r e d a t i o n 33 F i g u r e 11. Group e f f e c t s on escape response 39 i x ACKNOWLEDGEMENTS A l l e n B i l l y , Pam McDonald, Jim Cardwell, and Doug Reid acted as in f o r m a l examiners f o r v a r i o u s p a r t s of my work. I am indebted to Ben Seghers and Don Kramer f o r background i n f o r m a t i o n , to Don Ingram f o r the Cren i c i c h l a used i n the p r e d a t i o n experiment, and to Dave Z i t t i n and Susan E r t i s f o r t h e i r computing s k i l l s and p a t i e n c e . Drs. J.N.M. Smith and R.W. Blake p o i n t e d out many problem areas d u r i n g the re s e a r c h , and helped me sol v e them. F i n a l l y , I thank Dr. N.R. L i l e y f o r many h e l p f u l suggestions and e s p e c i a l l y f o r h i s c r i t i c a l comments on the f i r s t two d r a f t s of the t h e s i s . 1 GENERAL INTRODUCTION "... i s o l a t e d f i s h o f t e n show exaggerated f r i g h t responses. I t would be i n t e r e s t i n g to i n v e s t i g a t e i f experience with c o n s p e c i f i c s i s important f o r the development of a normal e q u i l i b r i u m between the d i f f e r e n t b e h a v i o r a l systems ..." (Baerends 1971, p.326) When I began to i n v e s t i g a t e the e x p r e s s i o n of escape behavior i n the guppy, I turned to the work of Seghers (1973,1974a,b), who found d i f f e r e n c e s between i s o l a t e d n a t u r a l p o p u l a t i o n s of the guppy. He proposed that these d i f f e r e n c e s were due to the s e l e c t i v e e f f e c t s of d i f f e r e n t p r e d a t i o n regimes. I planned to b u i l d on Seghers' work, but i n order to do so I had to ensure that my f i s h and techniques resembled h i s . In the course of determining an e f f i c i e n t shape for a predator model to use i n a e r i a l s timulus t e s t s , I d i s c o v e r e d that I knew nothing about the i n f l u e n c e that e a r l y experience might have on the behavior of a d u l t guppies. I decided that unless I c o u l d determine the importance of e a r l y experience, I would be u n s a t i s f i e d with the data that c o u l d be gathered from experimental manipulation of a d u l t s of unknown background. I hypothesized that e x p e r i e n t i a l f a c t o r s i n f l u e n c e the development of guppy escape behavior, and that s u r v i v a l of a d u l t 2 guppies under p r e d a t i o n i s i n f l u e n c e d by these f a c t o r s . These hypotheses were suggested in p a r t by the work of Thompson (1966), who i n c r e a s e d the s u r v i v a l of j u v e n i l e P a c i f i c salmon r e l e a s e d from a hatchery by exposing them to an a v e r s i v e stimulus (an e l e c t r i f i e d t r o u t model). F i s h r a i s e d i n the absence of the stimulus ( i . e . i n the normal hatchery technique) s u f f e r e d g r e a t e r m o r t a l i t y when r e l e a s e d . I supposed that in guppies, e a r l y experience of being chased by a d u l t s c o u l d p r o v i d e analogous experience f o r the young. If t h i s i s so, then I c o u l d p o s t u l a t e a p o t e n t i a l l y s e l e c t i v e l y advantageous c o n d i t i o n i n g f u n c t i o n f o r e a r l y chasing experience. L i v e - b e a r i n g f i s h are good s u b j e c t s f o r e a r l y - e x p e r i e n c e experiments, because they are s m a l l , easy to maintain, and independent of the mother immediately a f t e r b i r t h (Stearns 1 9 8 3 ) . In mammals, e a r l y experience i s u s u a l l y d e f i n e d as post-weaning (e.g. Fox and S t e l z n e r 1966, Wilhelmsson amd Larsson 1973), but i n p o e c i l i i d f i s h l i k e the guppy the i d e a l t a b u l a  rasa i s more c l o s e l y approached. 3 GENERAL METHODS The guppies I used were bred from f i s h c o l l e c t e d at the Guayamare R i v e r , T r i n i d a d , W.I., i n the s p r i n g of 1980. The f i s h were shipped by a i r to Vancouver, where I e s t a b l i s h e d them in 37.5 1 aquaria at a d e n s i t y of 30 f i s h per tank. F i s h were maintained in aged water over sand (with submerged p l a n t s ) at a temperature of 23 i 1 degrees C. Each tank had a f i l t e r and a g l a s s l i d . The photoperiod was 10.5L:13.5D (short days to c o n t r o l algae) under cool-white f l u o r e s c e n t lamps. Young born i n a l l tanks of breeding a d u l t s were removed, between 24 and 48 hr a f t e r b i r t h , to unoccupied a q u a r i a . I added young to such new tanks u n t i l there were 35-40 pres e n t . By the end of my re s e a r c h , I had r a i s e d i n excess of 1600 f i s h , some as many as f i v e g e n e r a t i o n s removed from the founder group. With a few ex c e p t i o n s , a l l f i s h used in the experiments were t e s t e d only once each, then r e p l a c e d in tanks set a s i d e f o r used f i s h . Thus a l l f i s h were in e x p e r i e n c e d i n t e s t c o n d i t i o n s . The exce p t i o n s are c o n s i d e r e d l a t e r i n the t e x t . 4 THE CHASING OF YOUNG GUPPIES BY ADULTS I n t r o d u c t i o n In t h i s experiment I q u a n t i f i e d the c h a s i n g of young guppies by a d u l t s . I hypothesized that i f escape behavior i s developed through experience, then being chased by a d u l t s i s an important p a r t of that experience. I expected that i f chasing was important, i t should occur f r e q u e n t l y and be a p p l i e d to a l l young. I a l s o expected that c h a s i n g i n t e n s i t y would be a d i r e c t f u n c t i o n of a d u l t guppy d e n s i t y , and that chasing i n t e n s i t y would be an i n v e r s e f u n c t i o n of the amount of cover a v a i l a b l e . Methods I observed tanks of breeding a d u l t s with newborn young. I counted the numbers of a d u l t s and young present and estimated the p r o p o r t i o n of the tank volume occupied by p l a n t m a t e r i a l ( p o t e n t i a l c o v e r ) . I counted the number of chases o c c u r r i n g per 10 min f o r each tank ( i . e . one a d u l t chasing two young or two a d u l t s c hasing one young would each count as two c h a s e s ) . I d i d not score chases of i n d i v i d u a l young, because I observed no apparent p r e f e r e n c e by the a d u l t s f o r s p e c i f i c young. A given tank was observed no more o f t e n than once per day, and a l l young were removed immediately a f t e r the o b s e r v a t i o n was f i n i s h e d . 5 R e s u l t s D e s c r i p t i o n of behavior I found that s e v e r a l d i f f e r e n t a d u l t behaviors e l i c i t e d withdrawal or escape in the young guppy. A chase was d e f i n e d as an o b s e r v a t i o n of any one of these behaviors or any combination of these behaviors as long as i t e l i c i t e d a response. The behaviors were: s e v e r a l vigorous t a i l beats by the a d u l t moving i t i n the d i r e c t i o n of the young; course c o r r e c t i o n s by the a d u l t d u r i n g an approach to the young; and jaw snapping by the a d u l t at c l o s e approach to the young. I observed a l l three behaviors together in most cases, but o f t e n one or two of them were s u f f i c i e n t to e l i c i t a response. A n a l y s i s To show how I used some tanks more than once, I presented a l l the data i n Table I. I found no s i g n i f i c a n t c o r r e l a t i o n between the number of a d u l t s present and the i n t e n s i t y of chasing (Spearman r a n k - c o r r e l a t i o n c o e f f i c i e n t , df=l8, Rs=0.16, p>0.05) and no s i g n i f i c a n t c o r r e l a t i o n between the amount of cover present and the i n t e n s i t y of chasing (df=l8, Rs=-0.10, p>0.05) . 6 Table I. Summary of c o n t r o l c h asing experience. day(1) tank #adults #young #chases(2) chases/young %cover(3) 1 G4 6 2 6 3 5 1 G8R 1 4 2 10 5 1 5 1 G2R 8 2 1 1 5.5 25 2 G7R 10 1 5 5 20 3 G7R 10 2 1 2 6 20 3 G2R 8 2 6 3 25 4 G2R 8 4 5 1 .25 25 5 G1 5A 9 1 5 5 1 0 5 G2R 8 1 4 4 25 5 G4 6 1 4 4 5 8 G1 5A 9 1 1 1 1 1 10 8 G17 9 2 1 0 5 5 9 G1 0 1 2 2 3 1 .5 5 9 G2R 8 2 4 2 25 9 G1 3 1 1 1 7 7 1 0 1 0 G7R 10 2 3 1 .5 20 10 G8R 1 3 2 10 5 15 1 0 G1 4 1 0 3 6 2 1 5 1 0 G2R 8 2 6 3 25 1 1 G2R 8 1 8 8 25 N=20 mean= 9.3 1.8 6.8 4.4 16.5 Notes:(1) A f t e r t e s t , young removed. No young used more than once. (2) T o t a l chases= chases of a l l young by a l l a d u l t s . (3) Volumetric e s t i m a t e . P i s c u s s i o n The r e s u l t s i n d i c a t e d no i n f l u e n c e of cover on chasing i n t e n s i t y . I assumed f o r subsequent experiments that data taken from t e s t tanks without cover were e q u i v a l e n t to those from p l a n t e d tanks. I a l s o assumed that f i s h taken from tanks with d i f f e r e n t amounts of cover should not d i f f e r as a r e s u l t of any e f f e c t s of the amount of cover p r e s e n t . I expected chased young 7 to u t i l i z e cover , and that t h e r e f o r e chasing i n t e n s i t y would be reduced i n h e a v i l y p l a n t e d tanks. I cannot e x p l a i n why t h i s t r end d i d not appear. V a r i a t i o n in a d u l t d e n s i t y a l s o f a i l e d to produce s i g n i f i c a n t d i f f e r e n c e s i n chasing i n t e n s i t y . T h i s i s i n d i r e c t c o n t r a d i c t i o n to the r e s u l t s of Rose (1959) with the guppy and T h i b a u l t (1974) with the r e l a t e d s p e c i e s P o e c i l i o p s i s monacha . In Rose's study, chasing and c a n n i b a l i s m appeared only when ad u l t d e n s i t y exceeded 10 per 12 1. T h i s i s much higher than any of my d e n s i t i e s . T h i b a u l t , however, used d e n s i t i e s of from 0-20 f i s h per 75 1 ( e q u i v a l e n t to 0-10 f i s h i n my 37.5 1 tank s ) , and found a s i g n i f i c a n t p o s i t i v e r e l a t i o n between c a n n i b a l i s m and d e n s i t y (128 t r i a l s , p<0.00l, two-way a n a l y s i s of v a r i a n c e ) . P. monacha i s re p o r t e d by T h i b a u l t to be an extremely predaceous s p e c i e s ; the much l e s s frequent c a n n i b a l i s m that I observed i n guppies may be due simply to s p e c i e s d i f f e r e n c e s in predatory behavior. I found the mean number of chases per i n d i v i d u a l young per 10 min to be 4.4. E x t r a p o l a t e d to a 10.5 hr day, t h i s i s 277 chases per day. A l l young I used had at l e a s t t h i s much ch a s i n g experience. Those remaining in the n a t a l tank f o r 48 hr probably had more experience of c h a s i n g , but I d i d not separate the f i s h r e c e i v i n g t h i s a d d i t i o n a l experience from the o t h e r s . The c a l c u l a t e d f i g u r e may even be an underestimate of 24 hr experience, s i n c e I recorded chasing data i n the morning, and 8 c a s u a l o b s e r v a t i o n suggests that the hunger l e v e l (and presumably the a t t a c k readiness) of the a d u l t s i n c r e a s e s as l a t e - a f t e r n o o n feeding time approaches. F i e l d data on the yellow bass a l s o suggests that c o n s p e c i f i c young are a t t a c k e d only when the a d u l t s are short of t h e i r r e g u l a r d i e t ( B u l k l e y 1970) . Chasing was frequent and d i r e c t e d toward a l l young. It was i n s e n s i t i v e to a d u l t d e n s i t y and cover d e n s i t y . I conclude that i f e a r l y experience i s important in the development of the escape response, chasing by a d u l t s may be an important part of that experience. 9 THE EFFECT OF CHASING DEPRIVATION ON THE DEVELOPMENT AND EXPRESSION OF GUPPY ESCAPE BEHAVIOR Int r o d u c t ion Is the development and e x p r e s s i o n of escape behavior i n f l u e n c e d by the experience of being chased by a d u l t s ? If so, in what way i s the experience important? I assumed that c h a s i n g by a d u l t s was the only form of e a r l y predatory experience i n the l a b o r a t o r y . The extent of c h a s i n g i n the w i l d i s unknown, but there must be chasing t h e r e . I a l s o assumed that while a d u l t guppies may be subject to a e r i a l a t t a c k s , j u v e n i l e s are not. Based on these assumptions, I hypothesized that e a r l y chasing experience determines general escape responsiveness to a v e r s i v e s t i m u l i , e i t h e r a q u a t i c or a e r i a l . By a v e r s i v e I mean producing withdrawal; r a p i d l y approaching o b j e c t s i n the v i s u a l f i e l d have been shown to produce escape r e a c t i o n s i n f i s h ( D i l l 1974a,b). A l l the guppies i n my experiments had no p r e v i o u s exposure to the a e r i a l predator s t i m u l u s . The experimental groups I used d i f f e r e d only in t h e i r exposure to chasing by a d u l t s when young. I c o u l d not p r e d i c t how d i f f e r e n t types of experience might a f f e c t development. I c o u l d only p r e d i c t that those f i s h with no chasing experience (group n) would be the most d i f f e r e n t from c o n t r o l s (group c ) . I expected that i f d i f f e r e n t types of experience were a d d i t i v e i n t h e i r e f f e c t , then groups with p a r t i a l experience of being chased (through chemical cues from 10 a d u l t s [ g ] , v i s u a l cues from a d u l t s [ v ] , or chemical cues from predatory s p e c i e s [p]) would be intermediate i n response between n and c f i s h . . Methods I produced the experimental groups as f o l l o w s . I p l a c e d g r a v i d females i n net bags suspended i n unoccupied a q u a r i a . These females r e l e a s e d young which escaped through the meshes of the net. I removed spent females and r e p l a c e d them with more g r a v i d ones as r e q u i r e d . Young f i s h were not n e t t e d or otherwise d i s t u r b e d u n t i l t h e i r escape responses were measured. The v i s u a l cues group c o u l d see a group of a d u l t guppies i n the n e i g h b o r i n g tank. These a d u l t s c o u l d be observed chasing the young i n t h e i r tank. F i s h r e c e i v i n g guppy chemical cues had water from a tank of chasing a d u l t s pumped through t h e i r tank. Those r e c e i v i n g chemical cues from predatory f i s h had water from tanks of predatory f i s h added p e r i o d i c a l l y to t h e i r tank. F i n a l l y , guppies r e c e i v i n g no c h a s i n g cues were i s o l a t e d both v i s u a l l y and c h e m i c a l l y from t h e i r surroundings. The treatments are summarized in Table I I , and the apparatus used i s shown in F i g u r e 1. I t e s t e d f i s h at two ages: immature (10-15 wk, the time of e a r l i e s t appearance of m o r p h o l o g i c a l sex d i f f e r e n c e s ) and mature 11 w n te =0= t • od Figure 1. Derivation of treatment g r o u p s : deprivations experiment. groups: p - predator chemical cues n - no cues g - guppy chemical cues c - control (one of many) v - visual cues c od - opaque divider pw - water taken from predator tanks s - s iphons w - wall / - water flow v te •w 1 2 Table I I . Summary of experience given i n the d e p r i v a t i o n treatments treatment symbol c o n t r o l c no cues n v i s u a l cues v guppy chemical cues g predator chemical cues p experience with a d u l t s f u l l sensory c o n t a c t : 24-48 hr c h a s i n g none v i s u a l c o n t a c t with a d u l t s chemical (water) c o n t a c t with a d u l t s chemical c o n t a c t with predatory f i s h (20-25 wk, a f t e r breeding had been noted i n the t a n k ) . I used the apparatus i n F i g u r e 2 and the a e r i a l stimulus model in F i g u r e 3. I gave each i n d i v i d u a l f i s h 10 min a c c l i m a t i o n i n the t e s t tank. I then observed i t u n t i l i t was swimming w i t h i n 2.5 cm of the water s u r f a c e and at l e a s t 2 cm from the nearest w a l l , when I r e l e a s e d the model. I recorded the drop response by eye to the nearest 0.5 cm and the f r e e z i n g response by e l e c t r o n i c stopwatch to the nearest 0.1 sec. (These behaviors are d e s c r i b e d below.) Upon t e r m i n a t i o n of the escape response, I measured the standard l e n g t h to the nearest 0.1 cm. Sample s i z e s f o r a l l groups are presented i n Table I I I . A b b r e v i a t i o n s f o r treatment groups in a l l f i g u r e s and t a b l e s are r e i t e r a t e d i n in the c a p t i o n of F i g u r e 4. Figure 2 .Experimental apparatus. Views: A ,s ide ; B . top . (as - air supply ; fw - flight "window" for model ; gw - guide wire ; I - light source ; me - model ca r r ie r ; os - observat ion s l i t ; ps - plastic sheeting ; r - release mechan ism ; w - weight ) o 14 1 5 Table I I I . Summary of sample s i z e s of groups i n the a e r i a l model response experiment. sex aqe c a £ V n males immature 20 1 9 19 26 28 mature 20 9 1 9 24 24 females immature 20 1 7 20 19 22 mature 20 1 4 18 1 3 22 R e s u l t s D e s c r i p t i o n of behavior Exposure to the a e r i a l model e l i c i t e d two c h a r a c t e r i s t i c behaviors i n every guppy I t e s t e d . The f i r s t was the drop response, i n which the guppy a b r u p t l y descended through the water column a v a r i a b l e depth. The second behavior was the f r e e z i n g response. T h i s began immediately upon the t e r m i n a t i o n of the drop, and was c h a r a c t e r i z e d by immobility of the f i s h and by r a p i d , low-amplitude o s c i l l a t i o n s of the f i n s and o p e r c u l a . At the end of the fre e z e there was always a sudden r e t u r n to swimming behavior. A n a l y s i s I found s e v e r a l d i f f e r e n c e s when comparing the r e s u l t s f o r males with those f o r females ( F i g u r e 4). Males r e c e i v i n g only v i s u a l cues had a l a r g e r d i s t a n c e response than females (t t e s t , c m c g p v n Immatures-..distance. cm c g p v n Matures: d is tance. sec c g p v n Immatures: t ime. sec c g p v n Matures: t ime. F igure A . Sex differences in escape response . (Means and standard errors . ) ( c , c o n t r o l ; g, g u p p y c h e m i c a l c u e s ; p, p r e d a t o r c h e m i c a l c u e s ; v, v i s u a l c u e s ; n, no c u e s ) 1 7 p< 0 . 0 0 8 ) , but t h i s disappeared at m a t u r i t y . In the matures, females had a l a r g e r d i s t a n c e response among the c o n t r o l s (p=0.003) and longer f r e e z i n g times among the c o n t r o l s (p< 0 . 0 0 l ) , the group exposed to v i s u a l cues only (p< 0 . 0 4 ) , and the f i s h exposed to predator chemical cues only (p<0 .006) . I found a s l i g h t t r e n d toward l a r g e r responses i n the o l d e r f i s h of a given treatment (Figure 5 ) . Older males exposed to the guppy chemical cues had a l a r g e r d i s t a n c e response than younger ones (t t e s t , p< 0 . 0 0 l ) . Older females had l a r g e r d i s t a n c e responses i n the c o n t r o l (p< 0 . 0 0 l ) , v i s u a l cues (p< 0 . 0 2 ) , and predator chemical cues (p=0.04) groups. There were a l s o s i g n i f i c a n t i n c r e a s e s i n f r e e z i n g time with age i n some females ( v i s u a l and predator chemical cues groups, each p<0.002) . I conclude that these r e s u l t s i n d i c a t e l a r g e r responses from the l a r g e r f i s h i n a given comparison ( i . e . females i n sex comparisons, matures i n age comparisons; standard l e n g t h data are summarized i n Table I V ) . I found immature males to d i f f e r s i g n i f i c a n t l y by treatment i n t h e i r drop responses (one-way a n a l y s i s of v a r i a n c e , F= 7 . 2 5 , d f = 4 , l 0 7 , p< 0 . 0 0 l ) . T h i s was due mainly to the l a r g e d e p r e s s i o n in the response of the g group ( S c h e f f e ' s t e s t , g<c,n,v, P<0.001; g<p, p<0.02; see F i g u r e 6A ) . These d i f f e r e n c e s disappeared i n the mature males (F= 1 . 0 2 , d f = 4 , 9 l , p> 0 . 1 ; see F i g u r e 6B ) . I i n t e r p r e t t h i s change as evidence f o r an experience-independent maturation of the drop response i n males. 18 Males : distance. Females : distance. 50' 40-sec 30-20-C 175-1 [^Immature £ Mature c g p v Males : t ime n sec c g p v n Females : t ime. Figure 5 .Age d i f f e r e n c e s in escape response (Means and s tandard errors . ) A b b r e v i a t i o n s as in F i g u r e 4 . 19 Table IV. Mean body lengths of f i s h i n the treatment groups, (standard l engths i n cm) treatment males females immature mature immature mature c o n t r o l 1 .37 1 . 58 1 .61 2.35 no cues 1 .40 1 .56 1 .65 2.27 v i s u a l cues 1.41 1.61 1 .66 2. 35 guppy chemical cues 1 .37 1 .54 1 .64 2.32 predator 1 .43 1 .57 1 .70 2.25 chemical cues Immature males showed no d i f f e r e n c e s i n f r e e z i n g time among treatments (F=1.66, df=4,l07, p>0.1; see F i g u r e 6C), and mature males showed only one s i g n i f i c a n t d i f f e r e n c e i n t h i s parameter (n>c, p=0.05; see F i g u r e 6D). There appears to be l i t t l e e f f e c t of d e p r i v a t i o n on the f r e e z i n g response i n males. Immature females d i f f e r e d s i g n i f i c a n t l y by treatment i n t h e i r drop d i s t a n c e s (F=7.41, df=4,93, p<0.00l), due to a de p r e s s i o n i n the g group's response (g<c, p=0.04; g<n, p=0.003; g<p, p=0.002; see F i g u r e 7A). As i n the males, the d e p r e s s i o n disappeared by maturity (F=2.16, df=4,82, p=0.08; see Fig u r e 7B). In both sexes, then, there i s a l a r g e l y experience-independent maturation of the drop response. The n group among the immature females caused s i g n i f i c a n t d i f f e r e n c e s i n f r e e z i n g time (F=3.85, df=4,93, p=0.006; n>v, p=0.04; n>g, p=0.03; see 20 c m 6 51 4-i 3-1 2-1-0 ] A c g p v n Immatures: d istance. cm 6-5-4" 3-2-1: 0 B rh c g p v n Matures : d is tance. sec 50 40-30-20 10-0 c rfl rh rh c g p v n Immatures: t ime. sec 60-50 40 301 20-10-0 D rh r+T c g p v n Matures : t ime. Figure 6. Treatment di f ferences in males. ( M e a n s a n d s tandard errors. ) A b b r e v i a t i o n s a s in F i g u r e 4 . 6-1 A 8- B 4-cm 3-2-1-0 c g p v n Irnmatures: d istance. cm 4' 0 Ml rh c g p v n Matures: distance 100i 80-sec 60 40-I 20 0 C rh c g p v n Immatures: t ime . 175i 140-sec 105-70-35-j 0 D rh rh c g p v n Matures: t ime. F igure 7.Treatment dif ferences in females (Means and s tandard errors . ) A b b r e v i a t i o n s a s in F i g u r e 4 . 22 F i g u r e 7C). These s i g n i f i c a n t d i f f e r e n c e s disappeared i n the matures, a p p a r e n t l y due to v a r i a b i l i t y i n the r e s u l t s f o r the p, v, and n groups (F=2.45, df=4,82, p=0.052). The f r e e z i n g response i n females i s somewhat i n f l u e n c e d by d e p r i v a t i o n , but the trends are not very s t r o n g . In summary, both males and females showed a t r a n s i e n t d e p r e s s i o n i n d i s t a n c e response i f they were exposed only to guppy chemical cues. No groups responded more s t r o n g l y than c o n t r o l s . The constancy of drop depths was not simply an a r t i f a c t of constant tank depth. I a l s o t e s t e d f i s h i n tanks of 1.5 and 2 times the depth of t h i s t e s t tank and found no d i f f e r e n c e i n response (U t e s t , N=10 f i s h of each sex at each depth, a l l p>0.05). F r e e z i n g time d i f f e r e d l i t t l e i n e i t h e r sex in s p i t e of d e p r i v a t i o n , except f o r the t r e n d to i n f l a t e d responses among the n, p, and v groups. F i s h from the g group most c l o s e l y resembled c o n t r o l s i n the f r e e z i n g response. D i s c u s s i o n Sex and age d i f f e r e n c e s I found that three of four sex d i f f e r e n c e s were in the d i r e c t i o n of l a r g e r responses i n females. I found that a l l s i x of the s i g n i f i c a n t d i f f e r e n c e s by age were i n the d i r e c t i o n of l a r g e r responses i n the o l d e r f i s h . Females of a given age and matures of a given sex were l a r g e r than males and immatures 23 r e s p e c t i v e l y . Thus I cannot separate the e f f e c t s of sex, age, and body s i z e . Whichever of the three f a c t o r s may have caused d i f f e r e n c e s , I conclude that a l l f u r t h e r analyses should be separate by age and sex, i n order to a v o i d confounding the treatment d i f f e r e n c e s . F i e l d study of the i n f l u e n c e of sex and body s i z e on p r e d a t i o n i n Gambusia ( B r i t t o n and Moser 1982) suggested that the l a r g e r females were s e l e c t e d p r e f e r e n t i a l l y by herons. The females were a r i c h e r food source, but they were a l s o p r e f e r r e d because they were slower swimmers than the males and p r e f e r r e d shallower (warmer) water than the males. They r e q u i r e d only s l i g h t l y more h a n d l i n g than males. Confounded sex and s i z e e f f e c t s may a l s o e x p l a i n behavior d i f f e r e n c e s in the guppy (Seghers 1973), but cannot be d i s t i n g u i s h e d i n my experiments. Treatment d i f f e r e n c e s The f i s h exposed only to guppy chemical cues had reduced drop response when they were immature, but by m a t u r i t y they were not d i f f e r e n t from c o n t r o l s . I i n t e r p r e t t h i s as delayed maturation of the response. Guppy chemical cues were not s u f f i c i e n t to b r i n g about the normal t i m i n g of response maturation. These cues, and any other degree of experience, c o u l d not a f f e c t the eventual appearance of a p p a r e n t l y normal drop responses. The constancy i n drop response might be evidence f o r a f i x e d hunting depth i n a e r i a l p r e d a t o r s (found i n 24 k i n g f i s h e r s , Eastman 1969), but there i s i n s u f f i c i e n t data on the a e r i a l p r e d a t i o n of guppies to t e s t t h i s s p e c u l a t i o n . I found c h a s i n g d e p r i v a t i o n to have a d i f f e r e n t e f f e c t on the development of f r e e z i n g responses. Although the d i f f e r e n c e s were not always s i g n i f i c a n t , they showed a t r e n d f o r longer f r e e z i n g times i n the f i s h exposed to v i s u a l cues, predator chemical cues, or no cues. The f i s h exposed to guppy chemical cues developed a n e a r - c o n t r o l response. I conclude from these r e s u l t s that exposure to s p e c i f i c e a r l y experience (guppy chemical cues) i s necessary in order to a v o i d the development of e x c e s s i v e responses. (I w i l l d i s c u s s the disadvantage of long f r e e z i n g times a f t e r c o n s i d e r i n g the r e s u l t s of the p r e d a t i o n exper iment.) Experience and p r e d a t i o n The Guayamare stream i s i n h a b i t e d by s e v e r a l l a r g e c h a r a c i d and c i c h l i d p r e d a t o r s ( L i l e y and Seghers 1975). These s p e c i e s put guppies at c o n s i d e r a b l e r i s k of p r e d a t i o n , e s p e c i a l l y l a r g e guppies. Endler (1978,1980; Reznick and Endler 1982) has shown that there i s a s t r o n g i n f l u e n c e of p r e d a t i o n i n t e n s i t y on s e l e c t i o n f o r a d u l t s i z e . Guppies are smaller at maturity i n areas with heavy p r e d a t i o n . I assume t h e r e f o r e that small guppies are r e l a t i v e l y l e s s s u b j e c t to p r e d a t i o n from these l a r g e s p e c i e s . I made a c a s u a l o b s e r v a t i o n which supports t h i s . While a d u l t guppies s u r v i v e d f o r only a few minutes in the 25 presence of l a r g e c i c h l i d s ( d e t a i l e d r e s u l t s below), j u v e n i l e s were a l i v e even s e v e r a l days or weeks a f t e r i n t r o d u c t i o n . As I found i n the present experiment, f i s h exposed to predator chemical cues f a i l e d to respond i n the same way as c o n t r o l s . T h i s suggests that the young lack the a b i l i t y to a l t e r t h e i r escape responses when exposed to predator chemicals i n the environment. T h e r e f o r e I assume that d e s p i t e the presence of l a r g e p r e d a t o r s i n the stream, young guppies do not r e c e i v e s i g n i f i c a n t experience from them. The only cues s u f f i c i e n t to form a c o n t r o l response when presented alone were the guppy chemical cues. Since chemical cues from a v a r i e t y of predator s p e c i e s were i n e f f e c t i v e , I conclude that there i s a s p e c i e s - s p e c i f i c chemical cue i n the guppy which b r i n g s about a normal f r e e z i n g response. T h i s might be c a l l e d a "chasing pheromone". No pheromones have been i s o l a t e d i n f i s h ( L i l e y 1982). If there i s a pheromone i n v o l v e d in the development of escape behavior, i t might be p o s s i b l e to i s o l a t e i t by t a k i n g a v a r i e t y of e x t r a c t s from water i n which a d u l t s have been chasing young and then exposing young to these e x t r a c t s and t e s t i n g t h e i r escape responses l a t e r . The f i n a l step would be the a n a l y s i s of the a p p r o p r i a t e e x t r a c t and the c h a r a c t e r i z a t i o n of the c h e m i c a l ( s ) i n v o l v e d . I have not c o n s i d e r e d a more d e t a i l e d scheme. I found the guppy chemical cues to have a priming e f f e c t , s i n c e e a r l y a d m i n i s t r a t i o n r e s u l t e d i n the l a t e r response 26 i n t e n s i t y . There might a l s o be a r e l e a s i n g e f f e c t , but I cannot say because I d i d not give l a t e treatments. Seghers (1973) observed no overt r e a c t i o n i n guppies to water taken from tanks of predatory f i s h . Rose (1959) showed that water from tanks with a high d e n s i t y of a d u l t guppies e l i c i t e d slower r e a c t i o n s from the young than d i d water from tanks with fewer a d u l t s p r e s e n t . I d i d not observe such an e f f e c t , p o s s i b l y because the a d u l t d e n s i t i e s I used were lower than those Rose used. A l l the f i s h i n the treatments I used responded i n q u a l i t a t i v e l y the same way. I conclude that as i n Gasterosteus and other s p e c i e s d i s c u s s e d by G i l e s (1984), guppy escape responses appear independently of experience with r e a l or p o t e n t i a l p r e d a t o r s , but the i n t e n s i t y of the response i s a f f e c t e d by experience. 27 THE EFFECT OF DEPRIVATION FROM CHASING ON THE SURVIVAL OF GUPPIES UNDER FISH PREDATION I n t r o d u c t i o n I found i n the preceding experiment that f i s h d e p r i v e d of chasing by a d u l t s develop l a r g e r escape responses than those developed by chased guppies. If chasing i s v i t a l to the normal development of the response, I hypothesized that the l a r g e escape responses would be disadvantageous. In t h i s experiment, I t e s t e d f i s h with v a r i o u s e a r l y chasing experiences by s u b j e c t i n g them to p r e d a t i o n ; I expected that i f l a r g e escape responses were d e l e t e r i o u s , then the f i s h showing these responses should not s u r v i v e as w e l l as c o n t r o l s . I expected that c o n t r o l f i s h would be more e f f i c i e n t at a v o i d i n g p r e d a t i o n . As I c o u l d not p r e d i c t i n what way they might be more e f f i c i e n t , I recorded s e v e r a l measures of avoidance. I s p e c u l a t e d that i f the c o n t r o l s l i v e d longer, i t would suggest that being chased when young i s advantageous f o r guppies. Circumstances d i c t a t e d the use of d i f f e r e n t p redators on the male and female guppies. T h i s may have had the f o r t u i t o u s e f f e c t of i n c r e a s i n g the g e n e r a l i t y of the experiment. I f two types of a q u a t i c predator produce the same e f f e c t in guppies, the e f f e c t i s u n l i k e l y to be an a r t i f a c t . I hope that f u t u r e p r e d a t i o n experiments w i l l adhere more c l o s e l y to the g u i d e l i n e s of Hu n t i n g f o r d (1984), who has suggested 28 design improvements to maximize the i n f o r m a t i o n gained from such s t u d i e s . Methods I used the t r e a t e d f i s h from the preceding ( d e p r i v a t i o n ) experiment as s u b j e c t s . I a c q u i r e d one C r e n i c i c h l a sp. ( C i c h l i d a e ; standard l e n g t h 22 cm) and one Pseudotropheus sp. ( C i c h l i d a e ; s . l . 9 cm) to use as p r e d a t o r s on the female guppies. I a c q u i r e d three Cichlasoma n i q r o f a s c iatum ( C i c h l i d a e ; s . l . 9 cm each) to use as p r e d a t o r s on the male guppies. The t e s t tank f o r females measured 45x110x30 cm, and the one f o r males measured 45x90x15 cm. I i n t r o d u c e d the guppies s i n g l y to the t e s t tanks by g e n t l y decanting them from small b o t t l e s of water. I presented no more than two guppies of a given treatment c o n s e c u t i v e l y . I d e f i n e d time zero as the time of i n t r o d u c t i o n , and measured a t t a c k times as seconds el a p s e d s i n c e time zer o . I analyzed time to f i r s t a t t a c k ( i n i t i a l a t t a c k l a t e n c y ) , time to l a s t a t t a c k ( i . e . the k i l l ; t o t a l s u r v i v a l time), and the number of a t t a c k s per k i l l . Sample s i z e s f o r a l l treatments are summarized in Table V. 29 Table V. Summary of sample s i z e s f o r a l l treatment groups i n the p r e d a t i o n experiment. sex c a E V n males 1 5 7 18 7 1 1 females 1 5 7 1 7 7 1 1 R e s u l t s I found that a l l the escape behaviors known to be e l i c i t e d i n guppies by aq u a t i c p r e d a t o r s (Seghers 1973) appeared i n a l l my t r e a t e d groups. In males, the i n i t i a l a t t a c k l a t e n c y scores d i f f e r e d s i g n i f i c a n t l y among treatments (one-way a n a l y s i s of v a r i a n c e , F=3.65, df=4,53, p=0.0l; see F i g u r e 8A). I d i d not expect such a d i f f e r e n c e because i n a s m a l l , bare tank a l l guppies should have been about e q u a l l y v i s i b l e to p r e d a t o r s . The females d i d not d i f f e r i n i n i t i a l a t t a c k l a t e n c y (F=1.05, df=4,52, p>0.1; see F i g u r e 8B). Since the r e s u l t s are d i f f e r e n t f o r the two sexes, I i n t e r p r e t i n i t i a l a t t a c k l a t e n c y to be r e l a t i v e l y independent of guppy experience. I found that t o t a l s u r v i v a l time d i f f e r e d s i g n i f i c a n t l y among the t r e a t e d males (F=2.55, df=4,53, p=0.05; see F i g u r e 9A), but no two groups d i f f e r e d by S c h e f f e ' s t e s t . The trend was f o r c o n t r o l males to l i v e longer, but there was too much va r i a n c e to allow a f i r m c o n c l u s i o n . The females d i d not d i f f e r 30 2001 sec . 100-0 m rh c g p v n M a l e s 2001 sec . 100 0 c g p v n F e m a l e s F i g u r e 8 . In i t ial a t t a c k l a t e n c i e s for t r e a t e d g r o u p s u n d e r f i s h p r e d a t i o n . ( M e a n s a n d s t a n d a r d e r ro rs . ) A b b r e v i a t i o n s a s in F i g u r e 4 31 in s u r v i v a l time (F=0.94, df=4,52, p>0.1; see F i g u r e 9B), and there were no t r e n d s . I conclude that there i s evidence of a weak trend f o r longer s u r v i v a l by c o n t r o l f i s h . I found a s i g n i f i c a n t e f f e c t of treatment on the number of a t t a c k s r e q u i r e d f o r a k i l l i n both sexes (males, F=4.61, df=4,53, p=0.003; see F i g u r e 10A; females, F=3.57, df=4,52, P=0.012; see F i g u r e 10B). The d i f f e r e n c e s were due to the l a r g e r number of a t t a c k s r e q u i r e d to k i l l c o n t r o l f i s h ( S c h e f f e ' s t e s t : males, o n , p=0.08; c>g, p=0.04; o p , p=0.02; females, o n , g , p<0.05). These r e s u l t s are the s t r o n g e s t evidence of a d e f i c i t i n s u r v i v a l a b i l i t y among the f i s h d e p r i v e d of f u l l c hasing experience when young. D i s c u s s i o n Although the i n i t i a l a t t a c k l a t e n c y was s i g n i f i c a n t l y d i f f e r e n t among the males, I conclude that s i n c e the females showed no e f f e c t at a l l (not even a t r e n d ) , evading the p r e d a t o r ' s i n i t i a l a t t e n t i o n was not a key f a c t o r i n p r e d a t i o n avoidance. A l s o , s i n c e no two groups of males d i f f e r e d i n s u r v i v a l time, and s i n c e there was no t r e n d among the females, I conclude that t o t a l s u r v i v a l time was not a f f e c t e d by the e a r l y experience of being chased by a d u l t s . I found that the d e p r i v e d groups took s i g n i f i c a n t l y fewer a t t a c k s to k i l l than d i d the c o n t r o l s . The only d i f f e r e n c e 800- 800-sec sec 400i 400-0 c g p v M a l e s n 0 c g p v n F e m a l e s F i g u r e 9 . Total s u r v i v a l t i m e s for t r e a t e d g r o u p s under f i s h p r e d a t i o n . ( M e a n s a n d s t a n d a r d e r r o r s . ) A b b r e v i a t i o n s as in F i g u r e 4 . 33 81 a t t a c k s / k i l l 4-0 rh rh c g p v n M a l e s 8 a t t a c k s / . k i l l 0 c g p v n F e m a l e s F i g u r e 10 . N u m b e r s of a t t a c k s per k i l l for t r e a t e d g r o u p s under f i s h p r e d a t i o n . ( M e a n s and s t a n d a r d e r r o r s . ) A b b r e v i a t i o n s a s in F i g u r e 4 . 34 between c o n t r o l s and the d e p r i v e d f i s h was the experience of being chased by a d u l t s . I t h e r e f o r e conclude that the experience of being chased by a d u l t s enhanced the l i k e l i h o o d that a c o n t r o l guppy would s u r v i v e a predatory a t t a c k . I p r e d i c t e d that l a r g e escape responses would prove to be disadvantageous. Indeed, d e p r i v e d guppies responded s t r o n g l y and took few a t t a c k s to k i l l . E xperience improves the l i k e l i h o o d of s u r v i v a l of the young i n two ways. F i r s t , by moderating the response i n t e n s i t y , chasing experience l e s s e n s the p r o b a b i l i t y of a guppy d i v i n g too f a r i n t o deeper water (where pre d a t o r s l i v e ) or s t a y i n g there f o r long. Second, by enhancing the a b i l i t y to evade each a t t a c k , chasing experience i n c r e a s e s the p r o b a b i l i t y that the guppy w i l l s u r v i v e a predatory encounter. Both of these mechanisms would operate to keep the guppy i n " s a f e " areas and away from "unsafe" ones. Safe areas f o r guppies are probably l i m i t e d to stream edges, s i n c e there i s l i t t l e submerged v e g e t a t i o n i n the Guayamare R i v e r (B.H. Seghers, p e r s . comm.). Shallow edges are known to be refuges f o r Gambusia ( P o e c i l i i d a e ; Goodyear 1973). Under t h i s model, the guppy would appear to use a couple of simple r u l e s to a v o i d p r e d a t o r s , and there would be no need to know what the p r e d a t i o n r i s k was i n order to apply these r u l e s . 35 An a l t e r n a t ive explanat ion of sex d i f ferences in s u r v i v a l  a b i l i t y I have thought of at l e a s t one other i n t e r p r e t a t i o n of the r e s u l t s . The p r e d a t o r s I used on the male guppies were u n f a m i l i a r with l i v e food. The predator ( C r e n i c i c h l a ) I used on the female guppies was r a i s e d with l i v e food only. I t i s p o s s i b l e that the male guppies d e r i v e d c o n s i d e r a b l e advantages from small d i f f e r e n c e s i n s u r v i v a l a b i l i t y because t h e i r p r e d a t o r s were e a s i e r to a v o i d . I f t h i s were so, then the d i f f e r e n c e s among the males for i n i t i a l a t t a c k l a t e n c y and t o t a l s u r v i v a l time, which I minimized above, c o u l d be r e a l d i f f e r e n c e s . C r e n i c i c h l a i s an extremely e f f i c i e n t p r e d a t o r . In an experiment r e p o r t e d by L i l e y and Seghers (1975), t h i s predator took female guppies of 1.9 cm standard l e n g t h ( s m a l l e r than the f i s h I used) on the f i r s t a t t a c k , but r e q u i r e d more a t t a c k s to k i l l s m aller f i s h . I t i s p o s s i b l e , then, that small d i f f e r e n c e s in s u r v i v a l a b i l i t y among the females were obscured by the r e l a t i v e l y high e f f i c i e n c y of the p r e d a t o r . If t h i s were the case, I would expect that the l a c k of d i f f e r e n c e i n my r e s u l t s f o r i n i t i a l a t t a c k l a t e n c y and t o t a l s u r v i v a l time in females was due to type II e r r o r . In e i t h e r i n t e r p r e t a t i o n made above, there was a s u b s t a n t i a l e f f e c t of e a r l y chasing experience on s u r v i v a l . The 36 i n t e r p r e t a t i o n s I gave are probably not mutually e x c l u s i v e , and are c e r t a i n l y not the only i n t e r p r e t a t i o n s p o s s i b l e . The f i r s t i n t e r p r e t a t i o n i s the more c o n s e r v a t i v e , but even i t i s s t i l l c l e a r l y i n t h i s d i r e c t i o n : c o n t r o l guppies avoided p r e d a t i o n b e t t e r than d e p r i v e d ones. 37 THE EFFECT OF IMMEDIATE SOCIAL DEPRIVATION ON THE EXPRESSION OF ESCAPE BEHAVIOR I n t r o d u c t i o n Guppies l i v e i n groups. I t e s t e d i n d i v i d u a l guppies i n the a e r i a l response and p r e d a t i o n experiments. Could t e s t i n g s o c i a l f i s h i n d i v i d u a l l y have a f f e c t e d the r e s u l t s ? In t h i s experiment, I looked f o r response d i f f e r e n c e s in f i s h t e s t e d both alone and i n groups. I c o u l d not p r e d i c t what the d i f f e r e n c e might be, but any d i f f e r e n c e would cause me to q u e s t i o n my i n t e r p r e t a t i o n s of the r e s u l t s from these experiments on s o l i t a r y f i s h . L i v i n g i n groups has been i n t e r p r e t e d as advantageous, e s p e c i a l l y f o r the p r e v e n t i o n of p r e d a t i o n i n f i s h (review i n Burgess and Shaw 1979). In the guppy congener P o e c i l i a v i v i p a r a , grouping lowers predator hunting success i n the l a b o r a t o r y ( N e i l l and C u l l e n 1974). The e x p l o r a t o r y behavior of guppies i s enhanced i n groups (Amouriq 1969); presumably t h i s r e f l e c t s reduced r i s k that guppies in groups may p e r c e i v e . Seghers (1974b) found that t i g h t l y s c h o o l i n g guppies ( i n c l u d i n g the Guayamare R i v e r p o p u l a t i o n ) s u r v i v e b e t t e r under p r e d a t i o n than those which school l o o s e l y . For these reasons, I expected that guppies t e s t e d i n groups might respond d i f f e r e n t l y from those t e s t e d alone. 38 Although a lack of d i f f e r e n c e would not prove that t e s t i n g f i s h alone was the same as t e s t i n g them i n groups, i t would i n d i c a t e that f o r the purposes of my experiments, the number of f i s h t e s t e d was unimportant. Methods I used a tank i d e n t i c a l in s i z e , shape, and water depth to the tank used i n the a e r i a l response experiment ( F i g u r e 2). I i n s t a l l e d a two-part d i v i d e r a c r o s s the c e n t r e of the tank. One l a y e r was t r a n s p a r e n t , p e r f o r a t e d , and f i x e d i n p o s i t i o n . The second l a y e r was opaque and removable. On one s i d e of the d i v i d e r , I e s t a b l i s h e d a stimulus group of guppies. I p l a c e d t e s t i n d i v i d u a l s s i n g l y i n the c e l l on the other s i d e of the d i v i d e r . Test c r i t e r i a were i d e n t i c a l to those i n the a e r i a l response experiment. Each t e s t e d f i s h was s t i m u l a t e d twice with the a e r i a l model: once alone (opaque d i v i d e r i n place) and once in the presence of the group (opaque d i v i d e r removed). R e s u l t s I found no d i f f e r e n c e between group and alone treatments for males or females i n drop d i s t a n c e or f r e e z i n g time (Wilcoxon matched-pairs signed-rank t e s t , N=20, a l l p>0.05; see F i g u r e 11). I found a h i g h l y s i g n i f i c a n t d i f f e r e n c e between the males and females i n the group c o n d i t i o n f o r f r e e z i n g time (t t e s t , df=39, p<<0.00l). T h i s d i f f e r e n c e was much g r e a t e r than that i n Dis tance . Time. F igure 11 . G r o u p effects on escape response (Means and s tandard errors. ) 40 the sex comparison of alone f i s h or i n the e q u i v a l e n t comparison in the a e r i a l response experiment (p<0.02 , p<0.00l r e s p e c t i v e l y ) . T h i s d i f f e r e n c e may i n d i c a t e t hat females i n a group responded more, but s i n c e the p a i r e d comparison showed no d i f f e r e n c e I w i l l ignore i t . D i s c u s s i o n I found that there was no d i f f e r e n c e i n response between f i s h t e s t e d alone and those t e s t e d i n groups. T h i s does not prove the absence of a group i n f l u e n c e on escape behavior. I t does show t h a t , f o r the purposes of my experimental design and techniques, I do not have to worry about the t e s t i n g of lone f i s h being u n n a t u r a l . I found that f i s h separated by a t r a n s p a r e n t , p e r f o r a t e d d i v i d e r responded s o c i a l l y to each other. I saw o r i e n t a t i o n s and c o u r t s h i p behaviors e l i c i t e d by and e l i c i t e d i n the t e s t i n d i v i d u a l s . Pinckney and Anderson (1967) showed that guppies co u l d r e c o g n i z e and d i r e c t s o c i a l behavior toward c o n s p e c i f i c s in g l a s s e n c l o s u r e s ; indeed, there may not have been any need to p e r f o r a t e the transparent d i v i d e r i n the t e s t tank. My r e s u l t s a p p a r e n t l y c o n t r a d i c t many experiments that show a reduced i n d i v i d u a l response i n groups. Examples range from mammals ( c e r v i d s , Altmann 1958; bighorn sheep, Berger 1978; p r a i r i e dogs, Hoogland 1 979) and b i r d s (penguins, M i i l l e r -41 Schwarze and Mliller-Schwarze 1970; s t a r l i n g s , Powell 1 974 ; weaverbirds, Lazarus 1979; o s t r i c h e s , Bertram 1980) to f i s h (zebra danios, Gleason et a l . 1977) and i n s e c t s (ocean s k a t e r s , Treherne and F o s t e r 1980,1981). I cannot account f o r the c o n t r a d i c t i o n ; I have i n s u f f i c i e n t data to e s t a b l i s h the cause, but from my r e s u l t s there seems to be no i n f l u e n c e of grouping on responses to the a e r i a l s t i m u l u s . 42 GENERAL DISCUSSION Pre d a t i o n p r e s s u r e s o p e r a t i n q on guppies Guppies l i v i n g i n lowland streams l i k e the Guayamare are exposed to a v a r i e t y of l a r g e predatory f i s h ( L i l e y and Seghers 1975). Predation by these f i s h has been i m p l i c a t e d i n the e v o l u t i o n of d i f f e r e n c e s between guppy p o p u l a t i o n s i n morphology, behavior, and l i f e h i s t o r y s t r a t e g y ( L i l e y and Seghers 1975; Endler 1978, 1980; Reznick and Endler 1982), although f a c t o r s such as temperature and t u r b i d i t y are l i k e l y to be i n v o l v e d as w e l l ( L i l e y and Seghers 1975). I found l i m i t e d c a n n i b a l i s m i n the l a b o r a t o r y , and there seems to be l i t t l e i n the w i l d (D.L. Kramer, p e r s . comm.). Adult guppies chase t h e i r young, but seldom c a t c h and eat them. P o p u l a t i o n d i f f e r e n c e s i n response to an a e r i a l stimulus have been a s c r i b e d to d i f f e r e n c e s i n a q u a t i c p r e d a t i o n i n t e n s i t y between streams (Seghers 1974a). Thus guppies appear to set response i n t e n s i t y to one type of stimulus by using input from another type of stimulus i n the course of n a t u r a l s e l e c t i o n . I propose that the e a r l y chasing of the young by a d u l t guppies enables the young to set t h e i r f u t u r e escape responses to other stimulus types i n the course of i n d i v i d u a l ontogeny. 43 The e f f e c t of e a r l y chasing experience on escape responses and  s u r v i v a l under p r e d a t i o n E a r l y experience of being chased by a d u l t s had l i t t l e e f f e c t on the s p a t i a l extent of the escape response e l i c i t e d by an a e r i a l model. I i n t e r p r e t the u n i f o r m i t y of the response as a predetermined escape r e a c t i o n , which matures r e g a r d l e s s of environmental i n p u t . The amount of time a guppy spent f r e e z i n g in response to the model seemed to be determined by e a r l y exposure to guppy chemical s e c r e t i o n s . A l a r g e f r e e z i n g response was d e l e t e r i o u s i n the presence of predatory f i s h , so the r e d u c t i o n i n response caused by the guppy chemical cues was c l e a r l y a p o s i t i v e a d a p t a t i o n to predatory c o n d i t i o n s . Chased guppies were s u p e r i o r to d e p r i v e d ones in the number of a t t a c k s r e q u i r e d f o r a k i l l . E a r l y c h asing experience a p p a r e n t l y enables the guppy to a v o i d predatory a t t a c k s more e f f e c t i v e l y . I conclude that under n a t u r a l c o n d i t i o n s , f i s h e i t h e r do not venture f a r i n t o p r e d a t o r - i n f e s t e d areas or do not get taken e a s i l y by p r e d a t o r s i f they do. I t i s c l e a r that the procedures i n v o l v e d i n r a i s i n g and m a i n t a i n i n g guppies may have a c o n s i d e r a b l e e f f e c t on the e x p r e s s i o n of behavior. I f a r e s e a r c h e r cannot d e f i n e the e a r l y experience of h i s f i s h , any c o n c l u s i o n s he may draw about behavior should be viewed s k e p t i c a l l y . 44 P o s s i b l e mechanisms through which chasing experience might  a f f e c t escape behavior The f i s h t e l e n c e p h a l o n i s the most l i k e l y l o c a t i o n f o r n e u r a l pathways c o n t r o l l i n g escape and avoidance r e a c t i o n s . T h i s region of the b r a i n i s a l s o concerned with o l f a c t i o n . (For a recent review of the i n t e r a c t i o n among t e l e n c e p h a l i c f u n c t i o n s , see Flood et a l . 1976.) In mammals, the hippocampus i s an a r c h i p a l l i a l s t r u c t u r e which i n t e g r a t e s o l f a c t o r y input and c o n t r o l s emotional behavior (Ewert 1980); i t i s a l s o the only s u b c o r t i c a l s t r u c t u r e which shows f u n c t i o n a l d e f i c i t s under d e p r i v a t i o n . The f i s h b r a i n i s mostly a r c h i p a l l i u m (Romer and Parsons 1977). T h e r e f o r e , on analogy, I propose that guppy chemical cues act through the t e l e n c e p h a l o n to c o n t r o l the e x p r e s s i o n of escape behavior. The behavior cannot be expressed p r o p e r l y i n the absence of these cues. Guppy chemical cues were not s u f f i c i e n t to produce c o n t r o l -l e v e l a b i l i t y to escape from p r e d a t o r s . There must be some a d d i t i o n a l f a c t o r i n v o l v e d here ( p o s s i b l y t a c t i l e ) which i s a l s o gained through c o n t a c t with a d u l t guppies. I found that there was no c o r r e l a t i o n between the i n t e n s i t i e s of the two p a r t s of the escape response (see Appendix). These two p o i n t s suggest that d i f f e r e n t p a r t s of the b r a i n , i n t e g r a t i n g input from d i f f e r e n t sensory sources, may be i n v o l v e d i n the development of escape behavior. Walsh (1981) has shown that d i f f e r e n t p a r t s of the mammal b r a i n are d i f f e r e n t i a l l y s u b j e c t to the e f f e c t s of 45 d e p r i v a t i o n . The p o s s i b l e f u n c t i o n a l s i g n i f icance of chasing i n guppies Adult guppies chase the young but very seldom c a t c h and eat them. I found a s u b s t a n t i a l advantage for chased f i s h under p r e d a t i o n . I propose that chasing by a d u l t s i s a p a r e n t a l behavior evolved through s e l e c t i o n f a v o r i n g the improved s u r v i v a l (and presumably subsequent rep r o d u c t i o n ) of chased f i s h . T h i s hypothesis does not c o n t r a d i c t the n o t i o n that c a n n i b a l i s m i s a disadvantageous t r a i t (reviews in Fox 1975, P o l i s 1981). Attempted c a n n i b a l i s m , or what looks to us l i k e attempted c a n n i b a l i s m , i s the process i n v o l v e d . If the s e l e c t i v e pressure i s severe enough, a g g r e s s i v e p a r e n t a l behaviors c o u l d be s e l e c t e d f o r . Keenleyside (1978) d e f i n e s p a r e n t a l care behavior as "..any behavior, performed a f t e r breeding, by one or both p a r e n t s , that c o n t r i b u t e s to the s u r v i v a l of t h e i r o f f s p r i n g . " Given the advantages I have demonstrated f o r p a r e n t a l c h a s i n g , i t seems reasonable to d e f i n e i t as a form of p a r e n t a l c a r e . Even c a n n i b a l i s m i t s e l f can be a s t a b l e s t r a t e g y i n some circumstances (e.g. p r o v i d e d l i f e t i m e net r e p r o d u c t i v e r a t e of the p o p u l a t i o n i s g r e a t e r than one; G u r t i n and Levine 1982). I propose that chasing a d u l t s would have increased i n c l u s i v e f i t n e s s r e l a t i v e to non-chasing a d u l t s . A problem with t h i s hypothesis i s that a d u l t s are not n e c e s s a r i l y chasing 46 only t h e i r own young. I observed that a l l a d u l t s chased a l l young. Guppies l i v e in groups which are r e l a t i v e l y i s o l a t e d in s t r e t c h e s of streams. During the wet season, f l o o d i n g can cause mixing between groups (Seghers, p e r s . comm.). Under these c o n d i t i o n s , n a t u r a l s e l e c t i o n can favor the e v o l u t i o n of t r a i t s which maximize i n d i v i d u a l f i t n e s s through maximizing group f i t n e s s (Wilson 1980). Any r e l a t e d n e s s of the i n d i v i d u a l s i n a group would enhance t h i s s e l e c t i o n , but kin s e l e c t i o n i s not necessary; the frequency of genes coding f o r the t r a i t of chasing c o u l d i n c r e a s e through the feedback e f f e c t s of s e l e c t i o n in s t r u c t u r e d demes. In c o n c l u s i o n , I propose that chasing by a d u l t s has an analogous e f f e c t i n the ontogeny of escape behavior to that of p r e d a t i o n i n the phylogeny of escape behavior. A d u l t s c o n d i t i o n t h e i r young to d i s p l a y a p p r o p r i a t e behavior. Suggest ions f o r f u r t h e r r e s e a r c h The d e t a i l s of escape behavior are d i f f i c u l t to d i s c e r n with unaided o b s e r v a t i o n . Therefore I do not know i f the behavior employed by a d u l t guppies i n escaping from p r e d a t o r s i s the same as that employed by j u v e n i l e guppies i n escaping from a d u l t chases. I a l s o do not know i f guppies d e p r i v e d of chasing use the same method to escape from p r e d a t o r s that chased guppies use. If chased guppies use the same behavior as a d u l t s that they l e a r n e d as young, t h i s would argue f o r d i r e c t p a r e n t a l 47 c o n d i t i o n i n g of the young. If chased and unchased guppies use d i f f e r e n t escape t a c t i c s , t h i s would a l s o be strong evidence f o r p a r e n t a l c o n d i t i o n i n g . I t would a l s o be i n t e r e s t i n g to compare the attack method used by a d u l t s in chasing to the normal a d u l t guppy feeding behavior and to the a t t a c k method of guppy p r e d a t o r s . If a d u l t a t t a c k s were s u b s t a n t i a l l y d i f f e r e n t from normal guppy feeding behavior, i t would suggest that chasing evolved not simply as a s i d e e f f e c t of normal fee d i n g or c a n n i b a l i s m , but r a t h e r s p e c i f i c a l l y f o r the c o n d i t i o n i n g of the young. If guppy chasing behavior a l s o resembled the a t t a c k t a c t i c s of p r e d a t o r s , t h i s would be s t i l l s t r o n ger evidence f o r a c o n d i t i o n i n g f u n c t i o n of a d u l t c h a s i n g . A l l these hypotheses and s p e c u l a t i o n s c o u l d be t e s t e d by high-speed cinematography of the behaviors i n v o l v e d . P r e d a t i o n pressure (and presumably the s e l e c t i o n f a v o r i n g a d u l t chasing as I have d e s c r i b e d i t ) v a r i e s i n d i f f e r e n t h a b i t a t s . For example, guppies in h i g h l a n d streams are subject to p r e d a t i o n only from the small c y p r i n o d o n t i d R i v u l u s h a r t i i , and as a r e s u l t the morphology, behavior, and l i f e h i s t o r y s t r a t e g i e s of guppies in these streams are c o n s i d e r a b l y d i f f e r e n t from those i n lowland streams ( L i l e y and Seghers 1975). I would expect that the a c q u i s i t i o n of escape behavior in these h a b i t a t s would d i f f e r i f c o n d i t i o n i n g f o r p r e d a t i o n avoidance i s an important f a c t o r i n the e v o l u t i o n of guppy 48 behavior. 49 CONCLUSIONS 1. Young f i s h are chased by a d u l t s ; the average number of chases i s 277 per i n d i v i d u a l per day. 2. The amount of cover or number of a d u l t s present has no e f f e c t on chasing i n t e n s i t y . 3. Escape responses are q u a l i t a t i v e l y i d e n t i c a l i n s p i t e of e a r l y c h asing d e p r i v a t i o n , immediate s o c i a l i s o l a t i o n , and changes i n the a b i o t i c environment. 4. Response d i f f e r e n c e s based on body s i z e can not be separated from those based on sex and age d i f f e r e n c e s . 5. A "chasing pheromone" i s proposed to account f o r the p a t t e r n of development of escape responses i n p a r t i a l l y d e p r i v e d f i s h . 6. S u b s t a n t i a l independence of the two p a r t s of the response suggests independent c o n t r o l of dropping and f r e e z i n g b e h aviors. 7. B r a i n c e n t r e s f o r o l f a c t o r y i n t e g r a t i o n are l i k e l y s i t e s f o r the c o n t r o l of escape response development. 8. A l l a q u a t i c escape response types known to e x i s t i n guppies develop independently of e a r l y c h a s i n g experience. 50 9. The a b i l i t y to a v o i d predatory a t t a c k s , at which the chased f i s h are s u p e r i o r , may be l e a r n e d from a d u l t s i n the course of j u v e n i l e c h a s i n g . 10. The enhanced s u r v i v a l and moderated r e a c t i v i t y of chased f i s h may be the r e s u l t of s e l e c t i o n f o r chasing by a d u l t s as an a g g r e s s i v e p a r e n t a l s t r a t e g y . 11. Grouping has no e f f e c t on the i n t e n s i t y of guppy escape responses. 12. The o r i g i n and experience of guppies used as experimental s u b j e c t s must be d e f i n e d i f c o n c l u s i o n s are drawn about e f f e c t s on behavior. 51 REFERENCES Altmann, M. 1958. 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The e v o l u t i o n and dynamics of i n t r a s p e c i f i c p r e d a t i o n . Annual Review of Ecology and Systematics' 12: 225-251. 54 Powell, G.V.N. 1974. Experimental a n a l y s i s of the s o c i a l value of f l o c k i n g by s t a r l i n g s ( Sturnus v u l g a r i s ) i n r e l a t i o n to p r e d a t i o n and f o r a g i n g . Animal Behavior 22:501-505. Reznick, D., and J.A. E n d l e r . 1982. The impact of pr e d a t i o n on l i f e h i s t o r y e v o l u t i o n i n T r i n i d a d i a n guppies ( P o e c i l i a r e t i c u l a t a ). E v o l u t i o n 36:160-177. Romer, A.S., and T.S. Parsons. 1977. The V e r t e b r a t e Body. W.B. Saunders Co., P h i l a d e l p h i a , PA. Rose, S.M. 1959. P o p u l a t i o n c o n t r o l i n guppies. American Midland N a t u r a l i s t 62:474-481. Seghers, B.H. 1973. 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APPENDIX - SUMMARY OF DISTANCE-TIME CORRELATION TESTS D e p r i v a t i o n experiment Immatures sex treatment coef £ i c i e n t d i r e c t ion males c o n t r o l -0.15 NS no cues 0.52 + v i s u a l cues 0.03 NS guppy chemical cues 0.23 NS predator chemical cues 0.10 NS females c o n t r o l 0.02 NS no cues 0.33 NS v i s u a l cues 0.14 NS guppy chemical cues 0.27 NS predator chemical cues 0.12 NS t o t a l s - "+"=9, "-"=1 NS=9, S=1 Matures sex treatment coef f i c i e n t d i r e c t i o n males c o n t r o l 0.15 NS no cues 0.16 NS v i s u a l cues 0.30 NS guppy chemical cues -0.20 NS predator chemical cues 0.20 NS females c o n t r o l -0.10 NS no cues 0.33 NS v i s u a l cues 0.43 NS guppy chemical cues 0.55 + predator chemical cues 0.06 NS t o t a l s = +"=8, "-"=2 NS=9, S=1 sex Immediate soc i a l depr i v a t ion experiment treatment c o e f f i c i e n t d i r e c t i o n males alone 0.17 NS group 0.35 NS females alone 0.24 NS group 0.35 NS t o t a l s = " + " = 4 " - " = 0 NS=4, S=0 

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