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The adaptive significance of coloniality and harem polygyny in the sand tilefish, Malacanthus plumieri Baird, Troy Alan 1989

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THE ADAPTIVE SIGNIFICANCE OF COLONIALITY AND HAREM POLYGYNY IN THE SAND TILEFISH, MALACANTHUS PLUMIERI By TROY ALAN BAIRD B.S. San Diego State University, 1978 M.S. San Diego State University, 1980 A THESIS SUBMITTED IN PARTIAL FULFILLMENT THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOHY i n FACULTY OF GRADUATE STUDIES DEPARTMENT OF ZOOLOGY We accept t h i s t h e s i s as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA February, 1989 ©Troy Alan Baird, 1989 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department or by his or her representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of Z o o l o g y  The University of British Columbia Vancouver, Canada Date F e b r u a r y 19 f 1989 DE-6 (2/88) ABSTRACT The s o c i a l and r e p r o d u c t i v e b i o l o g y o f the sand t i l e f i s h , Malacanthus p l u m i e r i (Malacanthidae), was s t u d i e d i n the f i e l d a t G l o v e r ' s Reef, B e l i z e , C e n t r a l America. D i s c r e t e c o l o n i e s of i t i l e f i s h were h i g h l y clumped i n some sandy h a b i t a t s w i t h c o r a l r u b b l e used by t i l e f i s h i n burrow c o n s t r u c t i o n . Both females and males each occupied one "home burrow" as a re f u g e from p r e d a t o r a t t a c k s . T i l e f i s h were most abundant i n a channel through the f r i n g i n g r e e f . Smaller numbers of f i s h occupied s l o p e s a d j a c e n t t o i s o l a t e d patch r e e f s ( r e e f slopes) i n s i d e the lagoon. N e i t h e r l i m i t a t i o n o f h a b i t a t nor s o c i a l t r a n s f e r of f o r a g i n g cues appears t o e x p l a i n colony formation i n M. p l u m i e r i , because unoccupied h a b i t a t s were abundant and f i s h f o rage s o l i t a r i l y . The p r o x i m i t y o f unoccupied t o occupied h a b i t a t s a l s o suggests t h a t c o l o n i e s do not r e s u l t because l a r v a e a re t r a n s p o r t e d o n l y t o some patches. Rather, j u v e n i l e s appear t o s e t t l e p r e f e r e n t i a l l y near a d u l t s , perhaps because p r o x i m i t y t o c o n s p e c i f i c s reduces p r e d a t i o n r i s k . Contagious r e a c t i o n s t o p r e d a t o r s and experimental d i s t u r b a n c e support t h i s 1 h y p o t h e s i s . T i l e f i s h d isappeared more f r e q u e n t l y i n the channel than i n the r e e f s l o p e , perhaps because channel f i s h i n c u r r e d h i g h e r p r e d a t i o n r a t e s . T i l e f i s h e x h i b i t a harem polygynous mating system. Home range o v e r l a p among f i s h o f the same sex was low. Females and males defended e x c l u s i v e use of most of t h e i r home ranges a g a i n s t a l l c o n s p e c i f i c s except mates. Areas defended by males i i overlapped the t e r r i t o r i e s of up t o s i x females. Males maintained dominance over mates by a g g r e s s i o n . Females spawned as f r e q u e n t l y as every day, wit h the male whose t e r r i t o r y encompassed t h e i r t e r r i t o r i e s . H i s t o l o g i c a l and b e h a v i o r a l evidence i n d i c a t e t h a t M. p l u m i e r i i s capable o f f u n c t i o n a l protogynous hermaphroditism. Removal t e s t s and o b s e r v a t i o n s on f o r a g i n g i n d i c a t e d t h a t females defend burrows and f e e d i n g spaces. Male removals r e v e a l e d t h a t females mate wi t h whichever male occ u p i e s t h e i r f e e d i n g t e r r i t o r y , and do not p o s i t i o n t e r r i t o r i e s s o l e l y t o be near mates. Female removals confirmed t h a t i n t r a s e x u a l c o m p e t i t i o n r e s t r i c t s use of space by some females. Colony f o r m a t i o n suggests, however, t h a t c o m p e t i t i o n c o s t s are not so h i g h as t o prevent female o c c u p a t i o n o f adj a c e n t t e r r i t o r i e s . I n stead, j o i n i n g harems may promote spawning o p p o r t u n i t i e s f o r females t h a t are r e s t r i c t e d t o burrows f o r p r e d a t o r avoidance. Removal t e s t s i n d i c a t e d t h a t males p o s i t i o n t h e i r t e r r i t o r i e s t o defend female t e r r i t o r i e s and a c q u i r e mates. However, males d i d not prevent mates from moving t o oth e r harems when females were removed. Males a l s o d i d not abandon t h e i r t e r r i t o r i e s when mates were removed. A dichotomy between r e s o u r c e and female defense does not apply t o t i l e f i s h o r t o ot h e r g r o u p - l i v i n g f i s h e s where females are s i t e - r e s t r i c t e d and egg p r o d u c t i o n occurs year-round.. D i f f e r e n c e s i n t i l e f i s h d e n s i t y suggest t h a t r e e f s l o p e and channel h a b i t a t s may d i f f e r i n q u a l i t y . Channel females spawned tw i c e as f r e q u e n t l y as r e e f s l o p e females, but d a i l y b atch f e c u n d i t y and net y e a r l y mating success were s i m i l a r i n the two h a b i t a t s . By c o n t r a s t , net y e a r l y male mating success was h i g h e r i n the channel because harems were l a r g e r . A d u l t s d i d not move between r e e f s l o p e and channel h a b i t a t s . T h e r e f o r e , the dense c o n c e n t r a t i o n of a d u l t M. p l u m i e r i i n the channel, appears t o be a consequence of l a r v a l t r a n s p o r t by p r e v a i l i n g c u r r e n t s . Supplemental f e e d i n g i n c r e a s e d female f e c u n d i t y and growth i n both h a b i t a t s . D i f f e r e n t responses t o f e e d i n g by r e e f s l o p e and channel females i s c o n s i s t e n t w i t h the h y p o t h e s i s t h a t r e p r o d u c t i v e t a c t i c s are c o n d i t i o n a l upon the type of p r e d a t i o n r i s k t h a t f i s h experience i n l o c a l h a b i t a t s . i v TABLE OF CONTENTS Page A b s t r a c t i i Tabl e o f Contents v L i s t o f Ta b l e s x i L i s t o f F i g u r e s x i i Acknowledgements x i v Chapter 1. General I n t r o d u c t i o n 1 O b j e c t i v e s and O r g a n i z a t i o n o f the T h e s i s . . . 4 Chapter 2. General Methods 7 Study s i t e 7 General techniques 7 Mapping techniques and c o l l e c t i o n of b e h a v i o r a l data 10 S t a t i s t i c a l treatment of data 11 Chapter 3. Burrows and Burrowing Behavior 12 I n t r o d u c t i o n 12 Methods 12 R e s u l t s 13 Use o f burrows 13 Burrow d e s i g n and maintenance 16 D i s c u s s i o n 18 F u n c t i o n of burrows 18 Comparison with other burrowing t r o p i c a l marine f i s h e s 20 Chapter Summary 21 V Chapter 4. C o l o n i a l i t y and Predator Avoidance . . . 22 I n t r o d u c t i o n 22 Methods 24 D i s t r i b u t i o n of t i l e f i s h a t G l o v e r ' s Reef . . . 24 D e n s i t y of t i l e f i s h and burrows w i t h i n s i t e s . . 27 D i v e r approach experiments 27 E s t i m a t i o n of s u r v i v a l r a t e s 28 R e s u l t s 29 D i s t r i b u t i o n and abundance of t i l e f i s h and burrows 29 P r e d a t o r b e h a v i o r and t i l e f i s h avoidance responses 32 D i v e r approach experiments 33 Disappearance of tagged f i s h 35 D i s c u s s i o n 38 D i s t r i b u t i o n i n r e l a t i o n t o a v a i l a b l e h a b i t a t . 38 F u n c t i o n a l s i g n i f i c a n c e of c o l o n i a l i t y i n t i l e f i s h 38 I n f l u e n c e of p r e d a t o r b e h a v i o r on t i l e f i s h avoidance responses . 41 Chapter Summary 44 Chapter 5.- Reproductive B i o l o g y and S o c i a l O r g a n i z a t i o n W i t h i n C o l o n i e s . 45 I n t r o d u c t i o n 4 5 Methods 47 I n d i v i d u a l use of space 47 D i e t and l o c a t i o n of f o r a g i n g a c t i v i t i e s . . . . 49 A g o n i s t i c i n t e r a c t i o n s 49 y i Reproductive b i o l o g y 50 R e s u l t s 51 T e r r i t o r i a l b e h a v i o r of females 51 T e r r i t o r i a l b e h a v i o r of males 57 D i e t , l o c a t i o n o f f o r a g i n g , and i n t e r s p e c i f i c a g g r e s s i o n among food competitors 59 Reproductive behavior 59 S o c i a l and mating system 62 Evidence o f protogynous sex r e v e r s a l 66 D i s c u s s i o n 71 T e r r i t o r i a l i t y and harem polygyny 71 Protogynous hermaphroditism i n sand t i l e f i s h . . 72 Chapter Summary 76 Chapter 6. The F u n c t i o n a l S i g n i f i c a n c e o f Harem Polygyny 77 I n t r o d u c t i o n 77 Methods . 79 Techniques f o r removal experiments 79 S p e c i f i c T e s t s 80 F a c t o r s i n f l u e n c i n g the d i s t r i b u t i o n o f females 80 A. I n t r a s e x u a l c o m p e t i t i o n , . . 80 B. Males 81 C. Burrows 82 D. Food r e s o u r c e s 82 I n f l u e n c e o f i n t r a s e x u a l c o m p e t i t i o n and mates on the d i s t r i b u t i o n of males 84 v i i R e s u l t s 85 F a c t o r s i n f l u e n c i n g the d i s t r i b u t i o n o f females 85 A. I n f l u e n c e of i n t r a s e x u a l c o m p e t i t i o n . . . 85 B. I n f l u e n c e of Males on the d i s t r i b u t i o n o f females 87 G. I n f l u e n c e of burrows 87 D. D i s t r i b u t i o n and abundance of food . . . . 88 D i s t r i b u t i o n of males 88 A. I n f l u e n c e of i n t r a s e x u a l c o m p e t i t i o n and females 88 B. E f f e c t s of removing harems 94 D i s c u s s i o n 94 B e n e f i t s and c o s t s of harem formation t o males 94 D i s t r i b u t i o n of females 95 Costs and b e n e f i t s of harem formation t o females 97 Chapter Summary 100 Chapter 7. H a b i t a t D i f f e r e n c e s i n P o p u l a t i o n D e n s i t y and Reproductive E f f o r t 101 I n t r o d u c t i o n 101 Methods 105 Frequency of c o u r t s h i p and spawning 105 Body s i z e and growth r a t e s 106 Male harem s i z e 106 E s t i m a t e s of food abundance and female f o r a g i n g . 108 v i i i Female investment i n p r e s e n t r e p r o d u c t i o n . . . 108 E s t i m a t e s of female d a i l y batch f e c u n d i t y . . . 110 E s t i m a t e s of net y e a r l y mating success . . . . I l l Food supplementation experiments 113 R e s u l t s 115 H a b i t a t comparisons of body s i z e and growth r a t e s 115 Male spawning frequency 115 C o r r e l a t i o n s with male harem s i z e 120 Female spawning frequency 124 Female f o r a g i n g behavior and abundance of p o t e n t i a l prey 124 D a i l y female batch f e c u n d i t y 126 Net mating success of females and males . . . . 132 E f f e c t s of food supplementation . . . . . . . 134 D i s c u s s i o n 138 Male harem s i z e 138 Spawning frequency and f e c u n d i t y of females 14 0 I n f l u e n c e of food i n t a k e on female r e p r o d u c t i o n and growth 142 I n f l u e n c e of h a b i t a t s e l e c t i o n and l a r v a l s e t t l e m e n t on the d i s t r i b u t i o n of a d u l t s . . 143 Food a v a i l a b i l i t y and female spawning frequency 146 The r e l a t i o n s h i p between female r e p r o d u c t i v e e f f o r t and the behavior of p r e d a t o r s . . . . 147 Chapter Summary 150 ix Chapter 8. General D i s c u s s i o n . . . . 153 The r o l e of female t e r r i t o r i a l i t y i n marine f i s h harems 153 Harems i n pelagic-spawning marine f i s h e s : Female or r e s o u r c e defense? 155 Burrowing and c o l o n i a l i t y i n marine f i s h e s : P o s s i b l e a d a p t a t i o n s t o l i f e i n open seabed h a b i t a t s 158 The d i s t r i b u t i o n s of t r o p i c a l marine f i s h e s : A d u l t h a b i t a t s e l e c t i o n or consequence of l a r v a l settlement? 160 R e l a t i v e l i f e t i m e mating success of r e e f s l o p e and channel f i s h 162 H a b i t a t d i f f e r e n c e s i n female spawning r a t e s . 163 References C i t e d 166 x LIST OF TABLES Tabl e Page 1. Percentage of t i l e f i s h p r e s e n t 30 days a f t e r t a g g i n g 37 2. T e r r i t o r i a l i t y i n female and male t i l e f i s h . . . . 52 3. Stomach contents of female and male t i l e f i s h . . . 60 4. Male s o c i a l and r e p r o d u c t i v e m o n o p o l i z a t i o n of harems 63 5. D i s t r i b u t i o n of prey i n sediment samples . . . . . 89 6. E s t i m a t e s of average d a i l y mating success i n r e e f s l o p e and channel males 119 7. E s t i m a t e s of the average number of eggs spawned per day i n r e e f s l o p e and channel females 131 8. E s t i m a t e d net mating success i n s i m i l a r l y -s i z e d r e e f s l o p e and channel females 133 9. Estimated net mating success i n r e e f s l o p e and channel males 135 x i LIST OF FIGURES F i g u r e Page 1. Map of G l o v e r ' s Reef i n r e l a t i o n t o c o a s t a l B e l i z e and l o c a t i o n of study area 8 2. Diagram and photographs of sand t i l e f i s h burrows . . 15 3. Map of study area 26 4. T i l e f i s h and burrow d e n s i t y e stimates 31 5. G r e a t e s t d i s t a n c e t r a v e l e d from home burrows . . . . 34 6. Behavior of r e e f s l o p e and channel f i s h b e f o r e and a f t e r r a p i d approach by a d i v e r 3 6 7. Map of sand t i l e f i s h colony 54 8. I l l u s t r a t i o n of some aspects of s o c i a l and r e p r o d u c t i v e b ehavior i n sand t i l e f i s h 56 9. Male harem s i z e graphed as a f u n c t i o n of t e r r i t o r y area 65 10. Body s i z e d i s t r i b u t i o n of males, t r a n s i t i o n a l s , and females 67 11. Photomicrographs of t r a n s v e r s e s e c t i o n s of t i l e f i s h gonads 69 12. Frequency t h a t a female changed t e r r i t o r i e s and male mates spontaneously or f o l l o w i n g female removals 86 13. Frequency t h a t males changed t e r r i t o r i e s spontaneously or f o l l o w i n g male removals 90 14. Rates of i n t r a - and i n t e r s e x u a l male a g g r e s s i o n b e f o r e and a f t e r removal of one male 91 15. E f f e c t s of male mating s t a t u s on responses t o male removals 93 16. S i z e d i s t r i b u t i o n o f r e e f s l o p e and channel f i s h 116 17. Growth r a t e s of non-fed r e e f s l o p e and channel females 117 xdd 18. Spawning and d i s p l a y r a t e s i n r e e f s l o p e and channel males 118 19. Harem s i z e graphed as a f u n c t i o n of the d i s t a n c e between each female and her n e a r e s t female neighbor 121 20. D i s t a n c e between males and the s i x c l o s e s t females graphed as f u n c t i o n of female p r o x i m i t y rank . . . . 122 21. Mean harem s i z e w i t h i n c o l o n i e s graphed as a f u n c t i o n of the r a t i o of females t o males 123 22. D a i l y spawning frequency i n channel and r e e f s l o p e females 125 23. Comparison of f o r a g i n g b ehavior i n r e e f s l o p e and channel females 127 24. Percentage of r e e f s l o p e and channel female stomachs c o n t a i n i n g remains of p o l y c h a e t e s , mollusks, and crustaceans 128 25. Mass of i n v e r t e b r a t e s i n s u b s t r a t e samples 129 26. I n d i v i d u a l mass of i n v e r t e b r a t e s i n s u b s t r a t e samples 130 27. Growth r a t e s of non-fed and f e d r e e f s l o p e and channel females 13 6 28. Gonosomatic i n d i c e s of non-fed and fed r e e f s l o p e and channel females 137 29. E s t i m a t e s of the number of hydrated eggs i n non-fed and f e d r e e f s l o p e and channel females 139 x i i i ACKNOWLE DGEMENTS P a r t i a l f unding f o r t h i s r e s e a r c h was p r o v i d e d by gr a n t s from Sigma X i S o c i e t y , American Museum of N a t u r a l H i s t o r y Lerner Gray Fund, and the Marine Science Program and C o a s t a l Center of the U n i v e r s i t y o f Houston. Major funding was p r o v i d e d by a N a t u r a l S c i e n c e and E n g i n e e r i n g Research C o u n c i l Grant t o N.R. L i l e y . I thank the people o f B e l i z e f o r p e r m i s s i o n t o study i n t h e i r waters and f o r t h e i r warm h o s p i t a l i t y d u r i n g my s t a y . C a r l o s Brunet, George and Ralph Jackson, C h r i s Petersen, and John Steeves p r o v i d e d h e l p f u l t e c h n i c a l a s s i s t a n c e . I thank P e t e r Arcese, John Eadie, Doug Shapiro and the members of my committee, e s p e c i a l l y Robin L i l e y and Jamie Smith f o r t h e i r c o n s t r u c t i v e i n p u t and comments on the manuscript. I wish t o express my g r a t i t u d e t o Robin L i l e y f o r p r o v i d i n g me the o p p o r t u n i t y t o study a t the U n i v e r s i t y o f B r i t i s h Columbia and f o r h i s generous support and guidance. F i n a l l y , t h i s r e s e a r c h would not have been completed without the support o f my w i f e Teresa Davis B a i r d . She c o n t r i b u t e d g r e a t l y t o a l l phases of t h i s p r o j e c t , p a r t i c u l a r l y as an i n v a l u a b l e a s s i s t a n t and companion under r i g o r o u s , and a t times, t r y i n g f i e l d c o n d i t i o n s . To Teresa, I express my s p e c i a l a p p r e c i a t i o n . xiv. CHAPTER 1 GENERAL INTRODUCTION The study o f the e v o l u t i o n o f animal s o c i a l o r g a n i z a t i o n and r e p r o d u c t i v e behavior has blossomed i n the l a s t two decades. Undoubtedly, the concepts o f i n d i v i d u a l ( W i l l i a m s , 1966) and i n c l u s i v e f i t n e s s (Hamilton, 1964), have been fundamental t o pro g r e s s i n t h i s f i e l d . An even more important c o n t r i b u t i o n t o understanding the e v o l u t i o n of mating systems was T r i v e r s 1 (1972) f o r m a l i z a t i o n o f the n o t i o n t h a t females and males maximize f i t n e s s i n d i f f e r e n t ways. T h i s s e t the stage f o r Emlen and Oring's (1977) g e n e r a l e c o l o g i c a l model of the c o n d i t i o n s under which monogamous and polygamous s o c i a l o r g a n i z a t i o n s e v o l v e . Much of the r e s e a r c h progress i n the e v o l u t i o n o f s o c i a l systems has been made i n b i r d s and mammals (e.g. see Rubenstein and Wrangham, 1987 and papers c i t e d t h e r e i n ) , and r e s e a r c h on the s o c i a l systems of lower v e r t e b r a t e s l a g s behind t h a t o f h i g h e r v e r t e b r a t e s . F u r t h e r study of f i s h e s , amphibians, and r e p t i l e s i s needed t o expand the data base, and t o t e s t the g e n e r a l i t y of ideas from study o f oth e r t a x a . T r o p i c a l marine f i s h e s e x h i b i t s e v e r a l f e a t u r e s t h a t make them s u i t a b l e f o r r e s e a r c h on s o c i a l systems. A d u l t s are o f t e n sedentary and d i u r n a l ; t h i s allows d i r e c t o b s e r v a t i o n o f most b e h a v i o r s . Many of these s p e c i e s spawn d a i l y throughout the year d u r i n g s h o r t but p r e d i c t a b l e time p e r i o d s (reviewed by Thresher, 1984; Warner, 1984a). T h e r e f o r e , the d i s t r i b u t i o n and 1 frequency of matings can be observed d i r e c t l y (e.g. Warner and Hoffman, 1980a; 1980b; Hoffman, 1985). F e r t i l i z a t i o n occurs i n the water column i n many s p e c i e s , and a d u l t s do not p r o v i d e p a r e n t a l c a r e f o r the p l a n k t o n i c embryos and l a r v a e (reviewed by Thresher, 1984). In f i s h e s w i t h t h i s type of r e p r o d u c t i o n , f a c t o r s t h a t a f f e c t the s u r v i v a l of p l a n k t o n i c o f f s p r i n g are almost c e r t a i n l y s t o c h a s t i c (Barlow, 1981; Doherty e t a l . , 1985; V i c t o r , 1983), and not i n f l u e n c e d by the b e h a v i o r of a d u l t s . T h e r e f o r e , mating frequency i s an unbiased estimate of r e p r o d u c t i v e success (Warner and Hoffman, 1980a; 1980b). These f e a t u r e s , t o g e t h e r w i t h the c l e a r water i n t r o p i c a l marine h a b i t a t s , make i t p o s s i b l e t o r e c o r d much of the b e h a v i o r of known i n d i v i d u a l s and r e l a t e i t t o f i t n e s s . D e s p i t e the r e l a t i v e ease of o b s e r v i n g t r o p i c a l marine f i s h e s , t h r e e areas of r e s e a r c h are p a r t i c u l a r l y meager r e l a t i v e t o s t u d i e s on h i g h e r v e r t e b r a t e s . A major focus of s t u d i e s on t r o p i c a l f i s h e s has been the behavior of males i n s p e c i e s c h a r a c t e r i z e d by male c o m p e t i t i o n f o r mates, polygyny, and protogynous hermaphroditism (reviewed by Thresher, 1984; Warner, 1984a; 1988; Shapiro, 1987a). An understanding of f a c t o r s t h a t i n f l u e n c e the f i t n e s s of females i n such systems i s emerging more s l o w l y (e.g. Robertson, 1972; Robertson and Hoffman, 1977; Kuwamura, 1984; Hourigan, 1986; Shapiro, 1986). Even s t u d i e s t h a t document female behavior i n d e t a i l do so t o determine which mating t a c t i c s are s u c c e s s f u l f o r males, or t o ask how females i n c r e a s e t h e i r chances of changing sex and mating as males i n the f u t u r e . Few s t u d i e s have examined f a c t o r s t h a t c o n t r i b u t e t o f i t n e s s d u r i n g the female l i f e - h i s t o r y phase (but see Warner, 2 1987) . Secondly, workers have j u s t r e c e n t l y begun t o examine f a c t o r s t h a t may i n f l u e n c e the d i s t r i b u t i o n and abundance of l o c a l p o p u l a t i o n s o f t r o p i c a l marine f i s h e s (Shapiro and Boulon, 1987; Robertson, 1988; Shapiro e t a l . , 1988). The d i s t r i b u t i o n and abundance of l o c a l p o p u l a t i o n s almost c e r t a i n l y a f f e c t the type of a d u l t s o c i a l systems t h a t evolve because many s p e c i e s are c o n c e n t r a t e d i n i s o l a t e d patches of h a b i t a t (Warner, 1984a). Thus, the environmental p o t e n t i a l f o r polygamy (Emlen and Oring, 1977) i s h i g h . Settlement o f p l a n k t o n i c l a r v a e i s thought t o p l a y a s t r o n g e r r o l e than h a b i t a t s e l e c t i o n by p o s t - l a r v a l f i s h i n d e t e r m i n i n g the d i s t r i b u t i o n and abundance of a d u l t s (Doherty, 1983; Cowen, 1985; V i c t o r , 1986; Robertson, 1988). Grouping may occur on c o r a l r e e f s , because l a r v a l s e t t l e m e n t i s e p i s o d i c ( V i c t o r , 1983; 1984; Robertson, 1988), and p r e d a t i o n r i s k p r events s e t t l e d f i s h from d e p a r t i n g r e e f r e f u g i a t o choose h a b i t a t s (Robertson and Hoffman, 1977; Warner and Hoffman, 1980a; 1980b). A l t e r n a t i v e l y , i n d i v i d u a l s may a l s o choose from among a v a i l a b l e h a b i t a t s based upon the c o s t s of c o m p e t i t i o n and the q u a l i t y o f r e s o u r c e s ( F r e t w e l l and Lucas, 1969; F r e t w e l l , 1972). A l s o , t h e r e may be advantages t h a t f a v o r i n d i v i d u a l s t h a t s e t t l e near c o n s p e c i f i c s (Wittenberger, 1981). The formation of d i s c r e t e a ggregations has now been r e p o r t e d i n a number of r e e f and non r e e f s p e c i e s ( F r i c k e , 1970; C o l i n , 1973; C l a r k , 1983; Peter s e n and F i s c h e r , 1986; V i c t o r , 1987; Shapiro, 1987). F a c t o r s t h a t i n f l u e n c e the d i s t r i b u t i o n o f l o c a l p o p u l a t i o n s , 3 t h e r e f o r e , m e r i t f u r t h e r i n v e s t i g a t i o n i n a v a r i e t y o f s p e c i e s . F i n a l l y , s t u d i e s on the s o c i a l b e h a v i o r and l i f e - h i s t o r i e s o f t r o p i c a l marine f i s h e s too o f t e n focus on a few i n d i v i d u a l s occupying a s i n g l e type o f h a b i t a t . V a r i a t i o n i n the behavior and l i f e h i s t o r i e s o f i n d i v i d u a l s i n d i f f e r e n t h a b i t a t s has not been examined i n many marine f i s h e s . A few s p e c i e s , however, e x h i b i t marked d i f f e r e n c e s i n s o c i a l b e h a v i o r between separate l o c a t i o n s (Thresher, 1979; Robertson, 1981), or among groups w i t h i n one area (Warner, 1984a). Such environmental v a r i a t i o n i s a v a l u a b l e t o o l f o r examining the a d a p t i v e f u n c t i o n of be h a v i o r (Warner, 1984a), because i n d i v i d u a l s may be compared without confounding i n f l u e n c e s of d i f f e r e n t p h y l e t i c h i s t o r i e s ( C l u t t o n - B r o c k and Harvey, 1984) . O b j e c t i v e s and O r g a n i z a t i o n of the T h e s i s P o p u l a t i o n s o f the sand t i l e f i s h , Malacanthus p l u m i e r i ( B l o c h ) , a t G l o v e r ' s Reef, B e l i z e C e n t r a l America ( f o r m e r l y B r i t i s h Honduras), p r o v i d e d me an o p p o r t u n i t y t o conduct d e s c r i p t i v e and experimental f i e l d s t u d i e s on: 1) f a c t o r s t h a t i n f l u e n c e the f i t n e s s o f females as w e l l as males, 2) f a c t o r s t h a t i n f l u e n c e the d i s t r i b u t i o n o f groups, and 3) d i f f e r e n c e s i n the b e h a v i o r and l i f e - h i s t o r y t r a i t s of females and males i n d i f f e r e n t h a b i t a t s . Furthermore, I c o u l d study these f a c e t s of t i l e f i s h b i o l o g y under u n d i s t u r b e d c o n d i t i o n s because G l o v e r ' s Reef l i e s 26 m i l e s o f f mainland B e l i z e i n a remote l o c a t i o n , and t h i s s p e c i e s i s not f i s h e d commercially. F o l l o w i n g a g e n e r a l methods chapter (Chapter 2), t h e r e are f i v e data c h a p t e r s . Burrowing i s the most obvious f e a t u r e o f 4 t i l e f i s h b e h avior. In Chapter 3, I d e s c r i b e the s t r u c t u r e of burrows, burrow c o n s t r u c t i o n behavior, and the r o l e of burrows as r e f u g e s from p r e d a t o r s . I then compare sand t i l e f i s h burrows w i t h those of o t h e r marine f i s h e s . In Chapter 4, I document the c l u s t e r e d d i s t r i b u t i o n of t i l e f i s h and examine the extent t o which f o u r p o p u l a r hypotheses t h a t have been proposed t o e x p l a i n the e v o l u t i o n of group l i v i n g may apply t o t h i s s p e c i e s . In p a r t i c u l a r , I i n v e s t i g a t e the r o l e o f p r e d a t i o n r i s k i n group formation by r e p o r t i n g on p r e d a t o r a c t i v i t y , t i l e f i s h p r e d a t o r avoidance b e h a v i o r , and by e s t i m a t i n g s u r v i v a l r a t e s i n two types of h a b i t a t occupied by M. p l u m i e r i . I a l s o d e s c r i b e experiments t o examine contagious r e a c t i o n s t o t h r e a t e n i n g s t i m u l i . In Chapter 5, I document the s o c i a l o r g a n i z a t i o n w i t h i n t i l e f i s h groups, paying p a r t i c u l a r a t t e n t i o n t o the l o c a t i o n s of i n d i v i d u a l females and males i n r e l a t i o n t o burrows, food r e s o u r c e s , and mates. A l s o , I r e p o r t on experiments t o determine i f M. p l u m i e r i i s capable of protogynous sex r e v e r s a l . In Chapter 6, I i n v e s t i g a t e the f u n c t i o n of t e r r i t o r y defense and the harem s o c i a l o r g a n i z a t i o n of t i l e f i s h u s i n g a s e r i e s of f i s h and burrow removal experiments. These t e s t s were designed t o i n v e s t i g a t e the degree t o which male t i l e f i s h monopolize harems through r e s o u r c e defense or d i r e c t c o n t r o l of females. In Chapter 7, I compare estimates of mating success i n r e l a t i o n t o p r e d a t i o n r a t e s i n two types of h a b i t a t , and o b s e r v a t i o n s on f i s h l o c a t i o n i n r e l a t i o n t o the p h y s i c a l and b i o t i c environment. I then examine the extent t o which h a b i t a t s e l e c t i o n models ( F r e t w e l l and Lucas, 1969; F r e t w e l l , 1972) or 5 l a r v a l s e t t l e m e n t processes may e x p l a i n the d i s t r i b u t i o n of a d u l t t i l e f i s h . I conclude the t h e s i s w i t h a g e n e r a l d i s c u s s i o n (Chapter 8), i n which I examine r e s u l t s i n r e l a t i o n t o the g e n e r a l i s s u e s r a i s e d i n each data chapter. 6 CHAPTER 2 GENERAL METHODS Study S i t e G l o v e r ' s Reef (87°45' W, 16°45' N, F i g u r e 1) i s a c o r a l a t o l l w i t h a shallow (1.5-3 0 m depth) lagoon t h a t i s e n c l o s e d by a f r i n g i n g c o r a l r e e f ( F i g u r e 1, a f t e r Stoddart, 1962). The lagoon c o n t a i n s hundreds of patch r e e f s o f l i v i n g c o r a l i s o l a t e d from one another by expanses of deep ba r r e n sand i n t e r s p e r s e d w i t h beds of t u r t l e g r a s s ( T h a l l a s i a testudinum). My s t u d i e s were conducted w i t h i n a 15 km 2 area adjacent t o Long and Northeast Cays i n s i d e the lagoon and i n a channel through the f r i n g i n g r e e f t h a t connects the lagoon w i t h the Caribbean Sea (F i g u r e 1). General Techniques T i l e f i s h are d i u r n a l and occur over f l a t , r e l a t i v e l y b a r r e n s u b s t r a t e s where d i r e c t o b s e r v a t i o n o f s o c i a l b e h a v i o r among i n d i v i d u a l s i s unobstructed by p h y s i c a l f e a t u r e s o f the environment. T i l e f i s h h a b i t u a t e q u i c k l y t o a d i v e r s n o r k e l i n g q u i e t l y a few meters above and t o one s i d e . F i s h foraged, maintained burrows, i n t e r a c t e d , and spawned n e a r l y every day a p p a r e n t l y u n d i s t u r b e d by an observer's presence. Consequently, I c o u l d r e c o r d almost a l l aspects of t i l e f i s h b e h a v i o r . I n d i v i d u a l s w i t h i n s o c i a l groups each occupy a s p e c i f i c burrow s i t e . I t was a l s o p o s s i b l e , t h e r e f o r e , t o capture and mark f i s h e n a b l i n g me t o measure and monitor l i f e h i s t o r y components of known i n d i v i d u a l s f o r prolonged p e r i o d s . F i n a l l y , t i l e f i s h 7 F i g u r e 1. A. L o c a t i o n o f G l o v e r ' s Reef r e l a t i v e t o a d j a c e n t c o a s t a l r e g i o n s . B. Southern p o r t i o n (65%) o f G l o v e r ' s Reef ( a f t e r S t o d d a r t , 1962). Hatching i n d i c a t e s f r i n g i n g c o r a l r e e f . Shading i n d i c a t e s study a r e a . 8 o c c u r r e d i n two d i s t i n c t h a b i t a t s a t G l o v e r ' s Reef. T h i s a llowed comparisons o f be h a v i o r s adopted under d i f f e r e n t b i o t i c and p h y s i c a l environmental c o n d i t i o n s . I n i t i a l o b s e r v a t i o n s on s o c i a l and r e p r o d u c t i v e behavior were c a r r i e d out from May 14 t o June 20, 1983. A l l o t h e r s t u d i e s were conducted from February 7 through J u l y 8, 1984 and from A p r i l 1 through August 10 i n both 1985 and 1986. Data were c o l l e c t e d w h i l e s n o r k e l i n g 5-10 m from study f i s h . H o r i z o n t a l underwater v i s i b i l i t y i s u s u a l l y 20 m or more a t G l o v e r ' s Reef (measured by s i g h t i n g a submerged marker). Data were recorded on s l a t e s by the author and one other experienced observer. To f a c i l i t a t e i d e n t i f i c a t i o n of i n d i v i d u a l s , f i s h were tagged by sewing c o l o r e d p l a s t i c beads s t r u n g on monofilament l i n e through the e p a x i a l musculature 1-3 mm below the a n t e r i o r p o r t i o n o f the d o r s a l f i n . I n d i v i d u a l s were captured by chasing them i n t o t h e i r burrows ( d e s c r i b e d i n Chapter 3) and p l a c i n g a cage ( c o n s t r u c t e d from 1.5 cm mesh wire c l o t h ) w i t h a v e r t i c a l f u n n e l opening through the bottom over the burrow entrance. F i s h l e f t burrows w i t h i n 1 h and ascended through the f u n n e l i n t o the cage. When t a g g i n g s u b j e c t s of s t u d i e s on s o c i a l b e havior, cages were monitored c o n t i n u o u s l y so t h a t f i s h c o u l d be removed immediately t o minimize i n j u r y and trauma. Trapped f i s h were immediately taken t o a boat, measured (SL t o the ne a r e s t mm), tagged, and then c a r e f u l l y p l a c e d i n s i d e t h e i r home burrow. Tagging r e q u i r e d o n l y 5-10 min. A l l of these f i s h were behaving normally i n my presence w i t h i n a few hours of t a g g i n g . Some f i s h whose l o c a t i o n s were monitored f o r census purposes (Chapter 4) and f o r removal t e s t s (Chapter 6) were not 9 tagged. Untagged f i s h were i d e n t i f i e d by making d e t a i l e d drawings of the unique p a t t e r n s of spots and patches of b l a c k s k i n . These spots r e s u l t from d e p o s i t i o n of melanin around trematodes encysted i n the dermis (see F i g u r e 8, Chapter 5). The s i z e , l o c a t i o n and arrangement of spots was unique on each i n d i v i d u a l and d i d not change r a p i d l y . T h e r e f o r e spots c o u l d be used t o i d e n t i f y i n d i v i d u a l s f o r s e v e r a l months. Mapping Techniques and C o l l e c t i o n of B e h a v i o r a l Data Most data were recorded on s c a l e maps (lcm=lm, o r 0.8cm=lm). Study areas were mapped by r e c o r d i n g d i s t a n c e s and compass re a d i n g s between r e f e r e n c e p o i n t s t h a t c o n s i s t e d of prominent f e a t u r e s on the s u b s t r a t e (e.g., t i l e f i s h burrows, gorgonian c o r a l s ) or stakes, which were marked f o r easy v i s i b i l i t y . Reference markers were l o c a t e d such t h a t the p o s i t i o n of study f i s h c o u l d be determined i n r e l a t i o n t o a minimum of t h r e e known p o i n t s . C o l l e c t i o n o f s p a t i a l data i n v o l v e d t r a c i n g the swimming path of a f i s h onto a map f o r a 20 min p e r i o d . The l o c a t i o n of burrowing b e h a v i o r s , responses t o p o t e n t i a l p r e d a t o r s , and s o c i a l i n t e r a c t i o n s were recorded d i r e c t l y on these t r a c e s . A minimum of f o u r (and i n most i n s t a n c e s f i v e ) r e p l i c a t e t r a c e s , each recorded between 900 and 12 00h on separate days was obtained f o r a t o t a l of 54 females and 25 males. In a d d i t i o n , t r a c e s (4-5 r e p l i c a t e s / f i s h ) were recor d e d from 1630-1730h f o r these same 25 males and 16 o t h e r s . O v e r a l l , b e h a v i o r a l data recorded on maps t o t a l e d 13 0 h of f o c a l o b s e r v a t i o n s . A d d i t i o n a l f o c a l o b s e r v a t i o n s on males d u r i n g which s o c i a l and r e p r o d u c t i v e behavior was r e c o r d e d t o t a l l e d 415 S t a t i s t i c a l Treatment o f Data A l l b e h a v i o r a l f r e q u e n c i e s presented below are average v a l u e s f o r i n d i v i d u a l s c a l c u l a t e d by d i v i d i n g the t o t a l number of observed a c t s by the t o t a l f o c a l o b s e r v a t i o n time on t h a t f i s h . Data f o r oth e r r e s u l t s are e x p l a i n e d i n methods f o r each data chapter. I used standard s t a t i s t i c a l t e c h n i q u e s throughout (Sokal and Roh l f , 1969; Zar, 1974). T w o - t a i l e d p r o b a b i l i t i e s were used except i n a few i n s t a n c e s where a p r i o r i p r e d i c t i o n s j u s t i f i e d use of 1 - t a i l e d p r o b a b i l i t i e s . Some data were l o g -transformed t o homogenize sample v a r i a n c e s and improve the f i t t o n o r m a l i t y . The Mann-Whitney s t a t i s t i c was used i n one i n s t a n c e where the v a r i a n c e s o f log-transformed data were heterogeneous as determined by an F t e s t . Some q u e s t i o n s r e q u i r e d s t a t i s t i c a l examination o f the degree o f s p a t i a l clumping o f f i s h , prey organisms, o r f o r a g i n g b i t e s (Chapters 4 and 6). S p a t i a l clumping was examined by r e c o r d i n g the f r e q u e n c i e s of f i s h o r f o r a g i n g b i t e s , or the q u a n t i t y o f prey i n sampling quadrats and c a l c u l a t i n g the v a r i a n c e t o mean r a t i o of the r e s u l t a n t d i s t r i b u t i o n . T h i s a n a l y s i s i s based on the Poisson d i s t r i b u t i o n which r e q u i r e s t h a t the average d e n s i t y o f o b j e c t s o r events b e i n g sampled i s low r e l a t i v e t o d e n s i t i e s t h a t c o u l d p o t e n t i a l l y occur g i v e n the amount of a v a i l a b l e area (Cox, 1976; Grieg-Smith, 1983). In c l u s t e r e d d i s t r i b u t i o n s t h i s r a t i o i s s t a t i s t i c a l l y g r e a t e r than 1.0 ( t e s t e d u s i n g the t s t a t i s t i c ) , i n a random d i s t r i b u t i o n i t equals 1.0, and i s l e s s than 1.0 i n uniform d i s t r i b u t i o n s (Cox, 1976; Grieg-Smith, 1983). 11 CHAPTER 3 BURROWS AND BURROWING BEHAVIOR INTRODUCTION Many t r o p i c a l marine f i s h e s l i v e on r e e f s t h a t p r o v i d e an abundance of h o l e s t h a t can be used as n o c t u r n a l s h e l t e r s o r t o evade p r e d a t o r a t t a c k s (Thresher, 1984). In c o n t r a s t , t h e r e are r e l a t i v e l y few s t r u c t u r e s t h a t can be used as r e f u g i a on the f l a t open s u b s t r a t e s juxtaposed w i t h r e e f s . T h e r e f o r e , s p e c i e s t h a t occur i n non-reef h a b i t a t s e x c l u s i v e l y , such as M. p l u m i e r i (see Chapter 4), may r e q u i r e an a l t e r n a t e means o f t a k i n g r e f u g e . The most conspicuous aspect o f sand t i l e f i s h b e h a v i o r i s i t s use of l a r g e mounded burrows as s h e l t e r s . Burrowing b e h a v i o r has been d e s c r i b e d p r e v i o u s l y f o r M_j_ p l u m i e r i i n the U.S. V i r g i n I s l a n d s ( C l i f t o n and Hunter, 1972), and i n the Bahamas ( C o l i n , 1973; C l a r k e e t a l . , 1977). These authors r e p o r t e d t h a t f i s h r e t r e a t t o burrows when d i s t u r b e d by d i v e r s . However, the des i g n , maintenance, and use of burrows f o r pr e d a t o r avoidance has not been examined i n d e t a i l . In t h i s chapter, I d e s c r i b e the des i g n and maintenance o f t i l e f i s h burrows, and examine the p o s s i b l e a n t i - p r e d a t o r f u n c t i o n o f burrowing b e h a v i o r . METHODS S i x t e e n burrows were dismantled t o examine t h e i r i n t e r n a l s t r u c t u r e . The extent t o which each f i s h uses one or more 12 burrows was examined by r e c o r d i n g the frequency, type, and l o c a t i o n o f bu r r o w - r e l a t e d a c t i v i t i e s on maps d u r i n g s p a t i a l t r a c e s . Burrows were marked wi t h p l a s t i c tags f i x e d t o pvc p o l e s pounded i n t o the s u b s t r a t e . The burrow s i t e s occupied a t dusk were recorded on a minimum of f i v e d a y s / f i s h . Three study s i t e s were examined wi t h a l i g h t between 2000 and 2200 h t o determine i f t i l e f i s h remain i n t h e i r burrows a t n i g h t . I n i t i a l o b s e r v a t i o n s suggested t h a t approach by l a r g e p i s c i v o r e s , p r i m a r i l y the barracuda (Sphvraena barracuda), sometimes caused one o r more t i l e f i s h t o r e t r e a t a b r u p t l y t o burrows. The occurrence o f such avoidance r e a c t i o n s t o barracuda was recorded d u r i n g f o c a l o b s e r v a t i o n s , and the g r e a t e s t d i s t a n c e ventured from burrows was estimated from mapped t r a c e s o f f i s h movements. RESULTS Use o f Burrows I n d i v i d u a l s of e i t h e r sex occupied a s i n g l e home burrow ( F i g u r e 2). F i s h s e a l e d the entrance t o t h e i r home burrow about 1 h b e f o r e sunset and l a t e r pushed t h e i r way i n s i d e (see below). T i l e f i s h were not s i g h t e d d u r i n g n i g h t examination o f study areas, and burrow entrances were c l o s e d . Home burrows were used d u r i n g the day as ref u g e s from p r e d a t o r s . Females responded t o the approach o f barracuda by r e t r e a t i n g t o and e n t e r i n g or ho v e r i n g above t h e i r home burrows. Males a l s o u s u a l l y r e t r e a t e d t o t h e i r home burrows. However, i f a male was f a r from i t s home s i t e when a p r e d a t o r approached the male sometimes swam t o a burrow occupied by another f i s h , 13 F i g u r e 2. Sand t i l e f i s h burrows. a. C r o s s - s e c t i o n a l diagram showing cavern ( c ) , foundation rock (f) , mounded r o o f o f c o r a l r u b b l e ( r ) , and sand p i t (p) l e a d i n g i n t o t u n n e l entrance ( t ) . b. Photograph of r o o f mound. c. Close-up o f t u n n e l entrance w i t h elongate c o r a l p i e c e s t h a t the occupant has p o s i t i o n e d as s u p p o r t i n g s t r u t s ( s ) . 14 u s u a l l y t h a t of a female mate. For f i s h i n a l l study areas pooled, females r e t r e a t e d t o t h e i r burrows i n response t o approach by barracuda, an average of 0.2 5 times/h (N=54 females, SE=0.10), w h i l e the average frequency of r e t r e a t s by males was 0.13/h (N=39 males, SE=0.04). Although the mean frequency of r e t r e a t s by females was almost double t h a t f o r males, f r e q u e n c i e s among females were' s u f f i c i e n t l y v a r i a b l e t h a t the d i f f e r e n c e between males and females i s not s t a t i s t i c a l l y s i g n i f i c a n t (t=0.67, p>0.05). Burrow Design and Maintenance A burrow c o n s i s t s of a cavern excavated beneath and a d j a c e n t t o a f l a t f o u n d a t i o n rock (Figure 2a). T i l e f i s h excavate the cavern by l y i n g prone on the s u b s t r a t e and u n d u l a t i n g l a t e r a l l y i n the sediment. When d i g g i n g i n t h i s manner, a f i s h sometimes grasps p a r t of the s u b s t r a t e w i t h i t s mouth, presumably f o r l e v e r a g e . Such movements of the v e n t r a l p a r t o f the body, the elongate anal f i n , and the caudal f i n push sand backward and outward removing i t from the cavern. F i s h moved r u b b l e out of the cavern by g r a s p i n g p i e c e s i n the mouth and c a r r y i n g or dragging them away. C o r a l r u b b l e , p a r t i c u l a r l y staghorn, Acropora c e r v i c o r n i s , i s arranged a d j a c e n t t o the f o u n d a t i o n rock i n a l a t t i c e w o r k of i n t e r - l o c k i n g p i e c e s t h a t covers the cavern ( F i g u r e 2a). A d d i t i o n a l r u b b l e i s p i l e d upon the r o o f , forming a r a i s e d mound (F i g u r e s 2a and b ) . The diameter of burrow mounds ranged from 0.75 t o 2.0 m. At l e a s t one t u n n e l , through which the f i s h e n t e r s and e x i t s the cavern head f i r s t , p e n e t r a t e s each mound at a downward (10-20°) angle. 16 Tunnel entrances are c h a r a c t e r i z e d by elongate p i e c e s of rubble t h a t the f i s h p o s i t i o n s as h o r i z o n t a l and v e r t i c a l s t r u t s s u p p o r t i n g the opening ( F i g u r e s 2a and c ) . An area of l o o s e sand i s u s u a l l y found d i r e c t l y i n f r o n t of and l e a d i n g i n t o burrow entrances ( F i g u r e 2 c ) . T i l e f i s h gathered new r u b b l e from throughout t h e i r t e r r i t o r i e s (see Chapter 5) and added i t t o the burrow or rearranged e x i s t i n g p a r t s of the burrow by g r a s p i n g and c a r r y i n g p i e c e s i n t h e i r mouths. F i s h sometimes c a r r i e d p i e c e s of rubble as l a r g e as o n e - f o u r t h of t h e i r body l e n g t h up t o 12 m t o t h e i r burrows. Burrow maintenance was a c o n t i n u i n g p r o c e s s . Caverns were maintained by removing p i e c e s of r u b b l e and by d i g g i n g w h i l e i n s i d e the burrow such t h a t sand was pushed out of the entrance. The bed of l o o s e sand and the s t r u t s s u p p o r t i n g the entrance were maintained m e t i c u l o u s l y . F i s h maintained the t u n n e l entrances by removing d e b r i s t h a t o b s t r u c t e d the opening or the sand p i t , and by l o o s e n i n g the sand by d i g g i n g w h i l e l y i n g prone. Females and males performed these burrow maintenance a c t s a t s i m i l a r r a t e s (X maintenance acts/h=10.5, N=54 females, SE=1.9; males X=11.3, N=39, SE=1.7). About 1 h b e f o r e sunset, f i s h began pushing l o o s e sand from the p i t backward i n t o the entrance by d i g g i n g w i t h t h e i r a n a l and caudal f i n s . Sometimes f i s h a l s o gathered b e n t h i c algae i n t h e i r mouths and p l a c e d i t i n burrow entrances. F i s h l a t e r d i v e d head f i r s t through the sand f i l l e d t u n n e l t o e n t e r the burrow f o r the n i g h t . 17 DISCUSSION F u n c t i o n of Burrows R e s u l t s show c l e a r l y t h a t each i n d i v i d u a l o f both sexes o c c u p i e s a p a r t i c u l a r "home burrow." Burrows are used as ref u g e s a t n i g h t and t o evade a t t a c k s by p r e d a t o r s d u r i n g the day. Burrows are not used e i t h e r as nests f o r l a y i n g eggs or as l a i r s from which t o ambush prey, as i m p l i e d p r e v i o u s l y ( C l i f t o n and Hunter, 1972; Dooley, 1978). Burrows do not serve e i t h e r of these purposes because f o r a g i n g occurs o u t s i d e o f ref u g e s , and gametes are broadcast p e l a g i c a l l y (Chapter 5 ) . Even though each f i s h occupied one home refuge, burrows or the c l a s t i c m a t e r i a l s used t o c o n s t r u c t them are common throughout G l o v e r ' s Reef. Old, unoccupied burrow mounds and c o r a l rock o f the type used i n c o n s t r u c t i o n o f burrows were abundant on a l l s i t e s (Chapter 4 ) . Why should i n d i v i d u a l s r e l y on a s i n g l e burrow f o r refuge when c l a s t i c m a t e r i a l s and unused burrows are abundant? One p o s s i b i l i t y i s t h a t r e l i a n c e on one burrow f a c i l i t a t e s p r e d a t o r avoidance because i n d i v i d u a l s become h i g h l y f a m i l i a r w i t h t h e i r home refuge s i t e . P o t e n t i a l p r e d a t o r s such as mutton snapper (Lutianus a n a l i s ) are abundant a t Gl o v e r ' s Reef. Stomach co n t e n t s c o n f i r m t h a t t h i s snapper preys on t i l e f i s h as l a r g e as 32.0 cm SL (Randall, 1967). The barracuda, however, i s proba b l y the major p r e d a t o r on t i l e f i s h a t G l o v e r ' s Reef. T i l e f i s h e x h i b i t e d obvious escape responses when barracuda approached, and numerous u n s u c c e s s f u l a t t a c k s were observed. Moreover, I witnessed one s u c c e s s f u l a t t a c k , and recorded 18 s e v e r a l i n s t a n c e s where known i n d i v i d u a l s a c q u i r e d wounds of the type l i k e l y t o be produced by the sharp c o n i c a l t e e t h o f t h i s p r e d a t o r . Barracuda, as w e l l as oth e r l a r g e p i s c i v o r e s s t r i k e t h e i r prey suddenly. Escape from such p r e d a t o r s may be enhanced by r e l i a n c e on one f a m i l i a r r e f u g e . Frequent and met i c u l o u s maintenance of home burrows suggests a l s o t h a t the c o n d i t i o n o f these s t r u c t u r e s i s important w i t h regard t o t h e i r s u i t a b i l i t y as r e f u g e s . The time and energy r e q u i r e d t o m a i n t a i n burrows may l i m i t use t o one s i t e . P a r t i c u l a r a t t e n t i o n i s d i r e c t e d t o the maintenance of t u n n e l entrances. A t u n n e l entrance t h a t can be ent e r e d r e a d i l y from s e v e r a l angles may i n c r e a s e the chance of escape. A l s o , frequent maintenance and defense (see Chapter 5) of one burrow ensures t h a t the refuge i s s u i t a b l e f o r immediate occupancy when r a p i d access i s c r u c i a l . The f u n c t i o n o f s e a l i n g burrow entrances a t n i g h t i s not obvious because known t i l e f i s h p r e d a t o r s are much too l a r g e t o e n t e r burrows. One p o s s i b i l i t y i s t h a t f i l l i n g the opening with sand and algae camouflages the exact l o c a t i o n o f the t u n n e l . D i s g u i s i n g the opening c o u l d make i t d i f f i c u l t f o r p r e d a t o r s t o l u r k near the entrance t o a t t a c k t i l e f i s h when they emerge i n the morning. The d e s i g n and maintenance of mounded burrow r o o f s p r o b a b l y a l s o d e t e r s p r e d a t o r s . Mounds of a b r a s i v e c o r a l fragments b u i l t up around a s t u r d y f o u n d a t i o n rock would c e r t a i n l y d e t e r most p i s c i v o r e s from d i g g i n g i n t o the burrow. 19 Comparison With Other T r o p i c a l Burrowing Marine F i s h e s Burrowing occurs i n s e v e r a l o t h e r marine f i s h e s t h a t occupy f l a t open seabeds. Other malacanthid and b r a n c h i o s t e g i d t i l e f i s h e s c o n s t r u c t burrows, but l a r g e mounded s h e l t e r s are unique t o malacanthids (Dooley, 1978; Able e t a l . , 1982; 1987). Three congeners c o n s t r u c t mounded burrows s i m i l a r i n s i z e and de s i g n t o those o f M. p l u m i e r i ( C l a r k and Ben-Tuvia, 1973; F r i c k e and Kacher, 1982). In some l o c a t i o n s the p e a r l y r a z o r f i s h , Hemipteronotus novacula, p i l e s c o r a l fragments on the r o o f o f i t s burrows (Bohlke and C h a p l i n , 1968), but t h i s s p e c i e s does not b u i l d mounded burrows a t Gl o v e r ' s Reef (pers. o b s e r v a t i o n s ) . Burrows of the yellow-headed j a w f i s h , Opistognathus a u r i f r o n s . l a c k mounded r o o f s but otherwise r i v a l those of t i l e f i s h i n complexity. J a w f i s h excavate a subterranean chamber t h a t i s connected w i t h the s u r f a c e by a narrow v e r t i c a l t u n n e l l i n e d with stones ( C o l i n , 1973). Some garden e e l s (Heterocongridae), a l s o c o n s t r u c t v e r t i c a l t u b e - l i k e burrows i n which the s i d e s are cemented wi t h mucous t o prevent c a v i n g - i n ( F r i c k e , 1970). Burrows t h a t are l i t t l e more than a h o l e under a rock are c h a r a c t e r i s t i c o f t o a d f i s h e s ( B a t r a c h o i d i d a e , Hoffman and Robertson, 1983). Perhaps the s i m p l e s t burrow d e s i g n i s t h a t of the s t r a i g h t - t a i l e d r a z o r f i s h , X y r i c h t y s m a r t i n i c e n s i s . Burrows i n t h i s s p e c i e s appear t o c o n s i s t o f o n l y a shallow d e p r e s s i o n i n the sand bed t h a t f i s h m a i n t a i n by removing d e b r i s and churning i n the sand ( V i c t o r , 1987; B a i r d , 1988). The mounded burrows of M. p l u m i e r i and ot h e r malacanthids, t h e r e f o r e , appear t o be the l a r g e s t and among the most e l a b o r a t e burrow s t r u c t u r e s b u i l t by marine f i s h e s . 20 CHAPTER SUMMARY 1. I n d i v i d u a l s o f each sex occupy home burrows t h a t serve as n o c t u r n a l r e t r e a t s and as refuges from p r e d a t o r a t t a c k s . 2. I n d i v i d u a l s m e t i c u l o u s l y maintained the c o n d i t i o n o f home burrows, paying p a r t i c u l a r a t t e n t i o n t o keeping t u n n e l entrances u n o b s t r u c t e d . 3. T i l e f i s h burrows are among the l a r g e s t and most e l a b o r a t e s t r u c t u r e s c o n s t r u c t e d by marine f i s h e s . 21 CHAPTER 4 COLONIALITY AND PREDATOR AVOIDANCE INTRODUCTION Four n o n - e x c l u s i v e hypotheses have been proposed t o e x p l a i n why some v e r t e b r a t e s form s o c i a l groups (reviewed by Wittenberger, 1981). 1) Groups r e s u l t because i n d i v i d u a l s p a s s i v e l y accumulate i n c e r t a i n areas as a r e s u l t o f c u r r e n t s i n a i r o r water: 2) S u i t a b l e h a b i t a t and/or r e s o u r c e s a re l i m i t e d and occur i n d i s c r e t e patches; 3) P r o x i m i t y t o c o n s p e c i f i c s a l l o w s some i n d i v i d u a l s t o u t i l i z e s o c i a l cues t o l o c a t e food r e s o u r c e s (Ward and Zahavi, 1973; Emlen and Demong, 1975); 4) L i v i n g i n groups reduces the t h r e a t of p r e d a t i o n by e n a b l i n g i n d i v i d u a l s t o u t i l i z e cues from c o n s p e c i f i c s t o d e t e c t p o t e n t i a l p r e d a t o r s and/or confuse o r d i s t r a c t p r e d a t o r s (reviewed by P u l l i a m and Caraco, 1984). S c h o o l i n g i s a common form of grouping b e h a v i o r among mobile f i s h e s , and p r o t e c t i o n from p r e d a t o r s i s one well-known f u n c t i o n o f such b e h a v i o r (Brock and R i f f e n b e r g , 1960; Shaw, 1970; 1978; P a r t r i d g e , 1982). The f u n c t i o n o f group l i v i n g i n sedentary bottom d w e l l i n g f i s h e s such as M. p l u m i e r i , however, i s understood l e s s w e l l . C l a r k e e t a l . , (1977) r e p o r t e d t h a t p o p u l a t i o n s o f M. p l u m i e r i i n the Bahamas were aggregated, and t i l e f i s h a l s o appeared t o be co n c e n t r a t e d i n c e r t a i n h a b i t a t s a t G l o v e r ' s Reef. The purpose of t h i s chapter i s t o document the d i s t r i b u t i o n of t i l e f i s h a t G l o v e r ' s Reef, and t o examine the ad a p t i v e s i g n i f i c a n c e o f group formation i n t h i s s p e c i e s . 22 S o c i a l f a c i l i t a t i o n of f e e d i n g (hypothesis 3) does not appear t o e x p l a i n the c l u s t e r e d d i s t r i b u t i o n of M. p l u m i e r i , because i n d i v i d u a l s forage s o l i t a r i l y (Chapter 5). Even though a d u l t t i l e f i s h can swim a g a i n s t c u r r e n t s , t h e i r d i s t r i b u t i o n may be i n f l u e n c e d by p a t t e r n s of o c e a n i c c u r r e n t s because l a r v a e f l o a t p a s s i v e l y i n the p l a n k t o n . Under t h i s h y p o t h e s i s , a d u l t t i l e f i s h may be most abundant i n areas where o c e a n i c c u r r e n t s flow onto s u i t a b l e h a b i t a t s because the l a r g e s t numbers of l a r v a e would be t r a n s p o r t e d t o these l o c a t i o n s . I estimated d e n s i t i e s of j u v e n i l e s and a d u l t s i n r e l a t i o n t o p r o x i m i t y t o p r e v a i l i n g o c e a n i c c u r r e n t s t o examine t h i s p o s s i b i l i t y . To examine the h y p o t h e s i s t h a t groups may r e s u l t because s u i t a b l e h a b i t a t i s patchy and l i m i t e d , I c h a r a c t e r i z e d the s u b s t r a t e s ( s ) occupied by M^ . p l u m i e r i . and determined the d i s t r i b u t i o n of f i s h i n r e l a t i o n t o these areas. I t seemed l i k e l y t h a t l i v i n g near c o n s p e c i f i c s might c o n f e r a n t i - p r e d a t o r advantages i n t i l e f i s h because t h i s s p e c i e s o c c u p i e s f l a t , two-dimensional s u b s t r a t e s w i t h few n a t u r a l h i d i n g p l a c e s . S i n c e I d i d not f i n d i s o l a t e d i n d i v i d u a l s , I c o u l d not compare the behavior of s o l i t a r y f i s h w i t h those l i v i n g i n groups t o examine t h i s p o s s i b i l i t y . For some group-l i v i n g s p e c i e s , however, i n d i v i d u a l s i n l a r g e or dense groups are l e s s v u l n e r a b l e then those i n s m a l l e r l e s s dense groups (reviewed by Wittenberger, 1981). I examined t h i s p o s s i b i l i t y i n t i l e f i s h by comparing r e a c t i o n s t o n a t u r a l p o t e n t i a l p r e d a t o r s and the f r e q u e n c i e s of disappearance of f i s h i n s m a l l (8-25 f i s h ) groups wi t h f i s h i n a s i n g l e l a r g e (>300 f i s h ) group. I a l s o compare the i n f l u e n c e of s i m u l a t e d p r e d a t o r a t t a c k s on the burrowing b e h a v i o r of f i s h i n l a r g e and s m a l l groups. METHODS D i s t r i b u t i o n of T i l e f i s h a t G l o v e r ' s Reef T i l e f i s h appeared t o occur e x c l u s i v e l y on sandy t e r r a i n w i t h exposed c o r a l base rock and l o o s e c l a s t i c m a t e r i a l ( r e f e r r e d t o below as sand-rubble s u b s t r a t e ) . An apron of sand-r u b b l e s u b s t r a t e surrounds a l l patch r e e f s l o c a t e d i n the lagoon and a l s o p a r a l l e l s the f r i n g i n g r e e f . Aprons d e c l i n e g r a d u a l l y (10-20 degrees) outward from the bases of r e e f s . I r e f e r t o these sand-rubble aprons as " r e e f s l o p e s . " Water depth on r e e f s l o p e s i n h a b i t e d by t i l e f i s h ranges from 1.5 t o 3 m. Reef s l o p e s v a r y i n s i z e , but a l l are demarcated by an abrupt t r a n s i t i o n t o deep sand and t u r t l e g r a s s bed, ( T h a l l a s s i a  testudinum, where exposed c o r a l rock and r u b b l e are absent. Areas of deep sand and g r a s s are not i n h a b i t e d by t i l e f i s h . Sand-rubble s u b s t r a t e i s a l s o p r e s e n t throughout the channel between Long and Northeast Cays t h a t connects the lagoon with the Caribbean Sea (Figure 1). The main body of t h i s channel i s 4-8 m deep. In 1986 the number of f i s h p r e s e n t i n each patch of sand-r u b b l e s u b s t r a t e w i t h i n the study area was recorded on maps t o determine the d i s t r i b u t i o n of t i l e f i s h i n more d e t a i l . Boundaries of t h i s study area were determined a r b i t r a r i l y by the amount of t e r r a i n t h a t I c o u l d survey. The r e l a t i v e l o c a t i o n of r e e f s l o p e s was estimated by s i g h t i n g patch r e e f s from a boat. 24 Areas between r e e f s l o p e s were surveyed thoroughly f o r t i l e f i s h . D i s t a n c e s s e p a r a t i n g adjacent sand r u b b l e aprons were estimated ( w i t h i n 2 0 m) from maps drawn w h i l e swimming around and between sepa r a t e r e e f s . Some patch r e e f s were s u f f i c i e n t l y c l o s e t o o t h e r s t h a t the surrounding sand-rubble aprons were continuous. Continuous r e e f - s l o p e s were c o n s i d e r e d s i n g l e s i t e s f o r census purposes, as was the l a r g e continuous expanse of sand-rubble s u b s t r a t e i n the channel ( F i g u r e 3 ). Between June 15 and August 10, 1986, the number of f i s h on r e e f s l o p e s i t e s and i n a sub-s e c t i o n of the channel was censused a t l e a s t once per week. At each census, spot p a t t e r n s were noted t o monitor i n d i v i d u a l s . To examine whether or not the d i s t r i b u t i o n of t i l e f i s h was s t a t i s t i c a l l y clumped, a g r i d of 78 quadrats (600 m2) was randomly superimposed over the study area map and the number of f i s h per quadrat was t a l l i e d . The v a r i a n c e t o mean r a t i o of f i s h / q u a d r a t was then determined as an index of clumping ( G r i e g -Smith, 1983). Because i n c l u s i o n of quadrats t h a t d i d not c o n t a i n sand-rubble h a b i t a t would b i a s t h i s a n a l y s i s towards clumping, these (N=14 quadrats) were e l i m i n a t e d . B i a s towards clumping c o u l d a l s o r e s u l t because more f i s h might occur i n quadrats w i t h l a r g e h a b i t a t patches. Up t o f o u r t i l e f i s h o c c u pied even the s m a l l e s t h a b i t a t patches. T h e r e f o r e , t o e l i m i n a t e t h i s source of b i a s , quadrats were t a l l i e d as c o n t a i n i n g 0 t o 4 f i s h even though some quadrats c o n t a i n e d many more than f o u r f i s h . 25 F i g u r e 3. Map of study area showing approximate l o c a t i o n and s i z e of sand-rubble patches and t i l e f i s h censused i n 1986. 26 D e n s i t y o f T i l e f i s h and Burrows W i t h i n S i t e s Because the i n h a b i t e d area i n the channel was too l a r g e t o map completely, d e n s i t i e s of a d u l t s (>15.0 cm) and burrows were est i m a t e d along t h i r t e e n t r a n s e c t s (50X20 m, LXW) taken a c r o s s the channel. D e n s i t y of j u v e n i l e s (<15.0 cm) was estimated a l o n g e i g h t t r a n s e c t s (30X20 m, LXW). Reef s l o p e s were s u f f i c i e n t l y s m a l l t o draw s c a l e maps of each s i t e , t a g a l l a d u l t s , and monitor the number of j u v e n i l e s . D i v e r Approach Experiments Two types of t e s t s were conducted t o examine responses of f i s h i n the l a r g e channel group and those i n s m a l l e r r e e f s l o p e groups t o the approach of a submerged d i v e r . F i s h used i n these t e s t s had not been handled or observed p r e v i o u s l y , except t o note t h e i r l o c a t i o n . T e s t s conducted on r e e f s l o p e f i s h were on s i t e s t h a t had not been used p r e v i o u s l y . T e s t s conducted on channel f i s h were i n areas separated by a t l e a s t 50 m from study areas. In 1985, "gradual approach" t e s t s were conducted. These c o n s i s t e d of a submerged scuba d i v e r approaching a f i s h a l o n g the bottom. The t e s t i n d i v i d u a l ' s i n i t i a l r e a c t i o n was recorded, and the l o c a t i o n of the d i v e r was marked when the f i s h e n t e r e d i t s burrow. The d i s t a n c e between the d i v e r and the burrow when the f i s h entered i t s refuge ( d i v e r approach d i s t a n c e ) c o u l d then be measured. The occurrence of abrupt r e t r e a t s t o burrows by one or more t i l e f i s h w i t h i n 10 m of the t e s t f i s h was a l s o noted. When t e s t s u b j e c t s d i d not r e t r e a t t o t h e i r burrows, the f i s h was pursued, and the amount of time 27 u n t i l i t e n t e r e d i t s burrow was recorded. Gradual approach t e s t s were conducted on 15 r e e f s l o p e and 15 channel f i s h r a n g i n g from 20.0 t o 30.0 cm SL. In 1986, t e s t s i n v o l v e d a more r a p i d l y approaching s t i m u l u s . Naive s u b j e c t s were observed from the s u r f a c e f o r a 2 0 min a c c l i m a t i o n p e r i o d d u r i n g which the l o c a t i o n o f the home burrow was determined. F o l l o w i n g a c c l i m a t i o n , the t o t a l amount of time spent i n s i d e the burrow was recorded and the d i s t a n c e of the f i s h from i t s burrow was estimated a t 10, one-minute i n t e r v a l s and summed (cumulative d i s t a n c e ) . Upon completion of t h i s c o n t r o l p e r i o d , the d i v e r submerged and swam r a p i d l y toward the t e s t f i s h f o r 15 seconds. The d i v e r then s u r f a c e d and record e d whether the t e s t f i s h had burrowed o r f l e d , i t s d i s t a n c e from burrows a t ten, 1 min i n t e r v a l s , and time spent i n s i d e burrows. Rapid approach t e s t s were conducted on 15 medium s i z e d (200-275 mm SL) f i s h i n both the channel and r e e f s l o p e study s i t e s . E s t i m a t i o n o f S u r v i v a l Rates Between A p r i l 1 and August 10 i n both 1985 and 1986, disappearance o f tagged f i s h was monitored t o es t i m a t e s u r v i v a l of a d u l t s i n the channel and r e e f s l o p e s i t e s . S u r v i v a l was monitored f o r 30 days a f t e r t a g g i n g by cen s u s i n g i n d i v i d u a l s every t h r e e t o f i v e days. F i s h t h a t were behaving normally ( i . e . , f o r a g i n g , defending t e r r i t o r i e s , see Chapter 5) i n my presence a t l e a s t one week a f t e r t a g g i n g were assumed t o have rec o v e r e d from t a g g i n g trauma. Only these f i s h were i n c l u d e d i n s u r v i v a l s t u d i e s . When a tagged f i s h was absent from i t s burrow 28 and t e r r i t o r y , a d jacent areas f o r a t l e a s t 50 m i n a l l d i r e c t i o n s were surveyed f o r s e v e r a l days t o determine i f the f i s h had moved. I assumed t h a t f i s h which were absent from t h e i r o r i g i n a l burrows and home ranges, and d i d not reappear i n surrounding areas, were v i c t i m s o f p r e d a t i o n . One-hundred twenty channel f i s h and 121 f i s h i n f i v e r e e f - s l o p e s i t e s were monitored. Observations were l i m i t e d t o a 30 day p e r i o d by the requirements o f oth e r experiments i n v o l v i n g removal o f tagged f i s h (see Chapters 6 and 7). F i s h almost always r e t a i n e d tags f o r 60 t o 90 days. F i s h t h a t l o s t tags were not m i s t a k e n l y counted as p r e d a t i o n v i c t i m s because they c o u l d be d i s t i n g u i s h e d by d i s t i n c t t a g g i n g s c a r s . F i s h were tagged throughout my study; t h e r e f o r e , censuses of tagged f i s h were not conducted over a s i n g l e c o n c u r r e n t p e r i o d . Sub-samples of channel and r e e f s l o p e f i s h were monitored c o n c u r r e n t l y t o reduce b i a s i n between h a b i t a t comparisons t h a t might r e s u l t from s p o r a d i c i n t e n s e p r e d a t i o n i n c e r t a i n s i t e s . I d i d not expect i n t e n s e e p i s o d i c p r e d a t i o n , because l a r g e p i s c i v o r e s were a c t i v e on a l l s i t e s throughout a l l study seasons. RESULTS D i s t r i b u t i o n and Abundance of T i l e f i s h and Burrows F i g u r e 3 maps the l o c a t i o n s o f a l l t i l e f i s h censused w i t h i n the study area i n 1986. M. p l u m i e r i was found o n l y where c o r a l base rock was exposed above the sand and where l o o s e c o r a l r u b b l e was abundant. S u b s t r a t e s o f deep sand and g r a s s were not 29 i n h a b i t e d . The v a r i a n c e t o mean r a t i o of f i s h per quadrat (S 2/X=1.71) was s t a t i s t i c a l l y g r e a t e r than 1.0 (t=3.99, N=64, p<0.001), i n d i c a t i n g t h a t the d i s t r i b u t i o n of f i s h w i t h i n the study area was s t a t i s t i c a l l y clumped. Numerous t i l e f i s h o c c u r r e d i n some patches of t h i s h a b i t a t w h i l e o t h e r s were not occupied. Even on i n h a b i t e d s i t e s , i n d i v i d u a l s were o f t e n clumped i n p a r t of the a v a i l a b l e s u b s t r a t e r a t h e r than being d i s p e r s e d over e n t i r e patches. Remnants of t i l e f i s h burrows on some unoccupied s i t e s i n d i c a t e d t h a t they had been i n h a b i t e d p r e v i o u s l y , s u g g e s t i n g t h a t these areas were s u i t a b l e f o r burrow c o n s t r u c t i o n . In both r e e f s l o p e s and the channel, n e i g h b o r i n g t i l e f i s h were always near enough t o one another (< 12 m) t h a t they were i n v i s u a l range of a t l e a s t one c o n s p e c i f i c . J u v e n i l e s (<150 mm SL) were a l s o observed o n l y i n areas adjacent t o those occupied by a d u l t s . T i l e f i s h o c c u r r e d c o n t i n u o u s l y a c r o s s the width o f the channel (500 m), and seaward f o r as f a r as I c o u l d survey (at l e a s t 700 m seaward from the edge of the lagoon, F i g u r e 3). The s u b s t r a t e occupied by M. p l u m i e r i i n the channel was demarcated on the lagoon s i d e by a dense gr a s s bed. The areas of r e e f s l o p e s i t e s t h a t were mapped ranged from 0.03 t o 0.44 ha. D e n s i t y of a d u l t s i n the channel was about 1.6 times (t=5.43, p<0.01) t h a t i n r e e f s l o p e s i t e s (N=12) and j u v e n i l e s were over 15 times more abundant i n the channel (t=14.35, p<0.01, F i g u r e 4) . Burrow d e n s i t y exceeded d e n s i t y of a d u l t s i n both r e e f s l o p e s and the channel ( F i g u r e 4), and abandoned burrow mounds were numerous on a l l s i t e s . The mean d e n s i t y of burrows i n the channel was a l s o h i g h e r (t=2.95, p<0.01) than t h a t on r e e f 30 2.0 F i g u r e 4. T i l e f i s h and burrow d e n s i t y e s t i m a t e s (X ± SEM) i n the r e e f s l o p e (open bars) and the channel (hatched b a r s ) . 31 s l o p e s . Rubble o f the type used t o c o n s t r u c t burrows (3-15 cm long) was abundant on a l l occupied and unoccupied s i t e s . The l o c a t i o n s o f c o l o n i e s censused weekly d i d not change throughout the 1986 study season. Although s y s t e m a t i c weekly censuses were l i m i t e d t o 1986, c o l o n i e s were a l s o r e c o r d e d i n most of these same l o c a t i o n s from 1984 through 1986. E x t i n c t i o n of known c o l o n i e s was not observed w i t h i n o r between seasons, nor d i d new c o l o n i e s appear i n areas t h a t were unoccupied d u r i n g p r e v i o u s surveys. P r e d a t o r Behavior and T i l e f i s h Avoidance Responses The h u n t i n g b e h a v i o r o f barracuda d i f f e r e d markedly i n r e e f s l o p e and channel h a b i t a t s . On r e e f s l o p e s , barracuda were f r e q u e n t l y seen, prone on the s u b s t r a t e , s t a l k i n g o r l y i n g i n wait f o r t i l e f i s h . S t a l k i n g barracuda swam s l o w l y , t o w i t h i n a few meters o f burrows where they waited f o r and lunged a t t i l e f i s h . Repeated s i g h t i n g s of barracuda w i t h unique markings suggested t h a t they sometimes remained near p a r t i c u l a r r e e f s l o p e s f o r s e v e r a l hours b e f o r e moving t o oth e r a r e a s . Barracuda were a l s o common i n the channel, but they were not observed t o s t a l k t i l e f i s h i n t h i s area. Instead, barracuda almost always swam h i g h i n the water column. The few r e t r e a t s t h a t were observed i n the channel o c c u r r e d when a barracuda d i v e d a b r u p t l y toward t i l e f i s h from above. R e t r e a t s i n response t o approaching barracuda were v e r y obvious i n r e e f s l o p e s i t e s . In s e v e r a l i n s t a n c e s , t i l e f i s h descended t o the s u b s t r a t e a b r u p t l y and swam r a p i d l y along the bottom t o t h e i r burrows i n response t o the approach o r an a t t a c k 32 by a barracuda. Even though barracuda were abundant i n the channel, such r e t r e a t s by channel f i s h were uncommon. Channel t i l e f i s h u s u a l l y responded t o barracuda swimming overhead by h o v e r i n g m o t i o n l e s s , but sometimes d i d not even stop t h e i r a c t i v i t i e s i f barracuda continued t o swim p a s t . The frequency of r e t r e a t s observed i n r e e f s l o p e f i s h (X r e t r e a t s / h = 0.09, N=52, SE=0.02) was about f o u r times h i g h e r (t=15.24, p<0.01) than i n channel f i s h (X=0.02, N=41, SE=0.01). The d i s t a n c e t r a v e l l e d away from burrows i n the two h a b i t a t s was compared s e p a r a t e l y f o r each sex because males had l a r g e r t e r r i t o r i e s than females (see Chapter 5). The mean g r e a t e s t d i s t a n c e t h a t channel females t r a v e l l e d from burrows was 2.4 m f a r t h e r (t=7.73, p<0.01) than t h a t of r e e f s l o p e females. The mean d i s t a n c e t h a t channel males swam from burrows was 6.2 m f a r t h e r (t=7.00, p<0.01) than t h a t of r e e f s l o p e males ( F i g u r e 5 ). D i v e r Approach Experiments Approach by a submerged d i v e r e l i c i t e d t i l e f i s h escape responses i n both h a b i t a t s . I n i t i a l responses t o d i s t u r b a n c e d i f f e r e d , (p<0.01, F i s h e r ' s Exact t e s t ) , however, between h a b i t a t s . In r e e f s l o p e s , t e s t s u b j e c t s and one or more n e i g h b o r i n g f i s h r e t r e a t e d immediately t o and hovered above t h e i r burrow entrances i n a l l t r i a l s . I n s tead of r e t r e a t i n g immediately t o t h e i r burrows, i n 9 of 15 t e s t s channel f i s h swam e r r a t i c a l l y f o r up t o 5 minutes (X time=1.55 min, range=0.5-5 min) b e f o r e e n t e r i n g t h e i r burrows. E r r a t i c swimming e l i c i t e d One or more nearby c o n s p e c i f i c s a l s o responded w i t h e r r a t i c swimming i n these nine t e s t s . The average d i v e r approach 33 CD O c D if) Q 25.0 20.0 15.0 10.0 5.0 0.0 A R S C H I A R S C H Females Males F i g u r e 5. G r e a t e s t d i s t a n c e t r a v e l l e d (X ± SEM) from home burrows i n channel (CH) and r e e f s l o p e (RS). f i s h . 34 d i s t a n c e a t burrowing i n r e e f s l o p e f i s h (&=7.6 m, SE=0.76) was c o n s i d e r a b l y g r e a t e r (t=5.67, p<0.01) than i n channel f i s h (X=2.5, SE=0.53). The i n i t i a l responses of f i s h i n r a p i d approach t e s t s was a l s o d i f f e r e n t (p<0.01, F i s h e r ' s Exact Test) i n the two h a b i t a t s . Reef s l o p e f i s h immediately entered t h e i r burrows i n 14 of 15 t e s t s . In c o n t r a s t , channel f i s h i n i t i a l l y f l e d away from the d i v e r i n 9 of 15 t e s t s . Two-way a n a l y s i s o f v a r i a n c e r e v e a l e d t h a t cumulative d i s t a n c e from burrows was lower (F=14.14, p<0.01, 2 - t a i l e d ) and time spent i n burrows was h i g h e r (F=11.27, p<0.01, 2 - t a i l e d ) i n r e e f s l o p e f i s h than i n channel f i s h both b e f o r e and a f t e r d i s t u r b a n c e ( F i g u r e 6). Disturbance i n c r e a s e d time spent i n burrows (F=23.50, p<0.01, 1 - t a i l e d ) and decreased cumulative d i s t a n c e (F=10.52,<0.01, 1 - t a i l e d ) i n both h a b i t a t s ( F i g u r e 6 ). 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 t e r a c t i o n s between h a b i t a t and both cumulative d i s t a n c e (F=4.49, p<0.05 1-t a i l e d ) and p e r c e n t time i n burrows (F=7.19, p<0.01 1 - t a i l e d ) i n d i c a t e f u r t h e r t h a t d i s t u r b a n c e caused r e e f s l o p e f i s h t o remain c l o s e r and spend more time i n s i d e burrows than channel f i s h . Disappearance of Tagged F i s h Only two tagged f i s h d isappeared from r e e f s l o p e s i t e s w h i l e 19 disappeared i n the channel (Table 1). The number of f i s h d i s a p p e a r i n g was not s i g n i f i c a n t l y d i f f e r e n t (p>0.05, F i s h e r ' s Exact or Chi-Square t e s t s ) among s i t e s o r years f o r r e e f s l o p e s , or between years i n the channel (Table 1). T h e r e f o r e , data were pooled t o compare the number of f i s h 35 6 0 CD O c o 00 5 0 4 0 3 0 2 0 1 0 0 7 / A 7-A T YA A 0 9 RS CH RS CH Cumulat ive d is tance % t ime burrowed 5 0 4 0 c CD 3 0 u 2 0 1 0 0 CD Q_ F i g u r e 6. Behavior (X ± SEM) of r e e f s l o p e (RS) and channel (CH) f i s h b e f o r e (open bars) and a f t e r (hatched bars) r a p i d approach by a submerged d i v e r . 36 T a b l e 1. Percentage o f t i l e f i s h p r e s e n t 30 days a f t e r t a g g i n g i n r e e f s l o p e and channel h a b i t a t s . S i t e Number of f i s h tagged Number of pre s e n t a t 30 f i s h days Percent disappearance Reef Slope S i t e s 1985 C 20 19 5 1986 C 10 10 0 1985 D 20 20 0 1986 D 10 10 0 1986 E 30 30 0 1986 G 18 17 5.5 1986 I 10 10 0 T o t a l Reef Slope 120 118 1.67 1985 Channel 40 36 10.0 1986 Channel 81 66 18.5 T o t a l Channel 121 102 15.7* * p<0.01 t h a t p e r c e n t disappearance i s independent o f h a b i t a t f o r a l l f i s h tagged i n the channel and a l l r e e f s l o p e s i t e s combined, Chi-square t e s t of a s s o c i a t i o n . 37 d i s a p p e a r i n g i n the channel w i t h t h a t o f a l l r e e f s l o p e s i t e s combined. O v e r a l l , the frequency o f disappearance was n e a r l y nine times h i g h e r (p<0.05, X 2=15.25) i n the channel than i n r e e f s l o p e s i t e s (Table 1). DISCUSSION D i s t r i b u t i o n i n R e l a t i o n t o A v a i l a b l e H a b i t a t At G l o v e r ' s Reef, t i l e f i s h occur o n l y on sand r u b b l e f l a t s where the exposed c o r a l rock and r u b b l e used f o r burrow c o n s t r u c t i o n are a v a i l a b l e . F u r t h e r , t i l e f i s h were co n c e n t r a t e d i n t o some of these h a b i t a t s , w h i l e o t h e r areas were not occupied. No s o l i t a r y i n d i v i d u a l s were encountered. Wittenberger (1981) d e f i n e d c o l o n i a l i t y as the occurrence o f d i s c r e t e and s i t e - a t t a c h e d groups, w i t h i n which i n d i v i d u a l s m a i n t a i n a w e l l - d e f i n e d and r e l a t i v e l y f i x e d s p a t i a l o r g a n i z a t i o n . T i l e f i s h occur i n s i t e - a t t a c h e d groups. W i t h i n groups each i n d i v i d u a l occupies a f i x e d home burrow s i t e and a t e r r i t o r y around the burrow (Chapter 5 ) . T i l e f i s h a t G l o v e r ' s Reef, t h e r e f o r e , are c o l o n i a l a c c o r d i n g t o t h i s d e f i n i t i o n . F u n c t i o n a l S i g n i f i c a n c e o f C o l o n i a l i t y i n T i l e f i s h 1) T r a n s f e r o f f o r a g i n g i n f o r m a t i o n : I t i s u n l i k e l y t h a t t i l e f i s h occur i n c o l o n i e s because p r o x i m i t y t o c o n s p e c i f i c s enhances the t r a n s f e r of i n f o r m a t i o n concerning the l o c a t i o n o f food patches (Ward and Zahavi, 1973). S i n c e both female and male t i l e f i s h forage s o l i t a r i l y w i t h i n e x c l u s i v e t e r r i t o r i e s (see Chapter 5), t h e r e i s l i t t l e o p p o r t u n i t y t o g a i n f o r a g i n g i n f o r m a t i o n from c o n s p e c i f i c s . 38 2) L i m i t e d a v a i l a b i l i t y of s u i t a b l e h a b i t a t : C o l o n i a l i t y may a l s o e v o l v e because s u i t a b l e h a b i t a t i s l i m i t e d . C l a r k e e t a l . , (1977) suggested t h a t a shortage of c l a s t i c m a t e r i a l e x p l a i n e d the clumped d i s t r i b u t i o n of Mj_ p l u m i e r i i n the Bahamas. Sand r u b b l e s u b s t r a t e , however, i s not l i m i t e d a t G l o v e r ' s Reef. Unoccupied r e e f s l o p e s i t e s were common i n the lagoon. Some unused s u b s t r a t e was a v a i l a b l e even w i t h i n the channel where the l a r g e s t and most dense c o n c e n t r a t i o n of t i l e f i s h was l o c a t e d . Old burrow mounds on both unoccupied r e e f s l o p e s , and i n unoccupied areas of the channel confirmed t h a t these h a b i t a t s were s u i t a b l e f o r c o n s t r u c t i o n o f burrows. I d i d not measure the a v a i l a b i l i t y of t i l e f i s h prey ( b e n t h i c i n v e r t e b r a t e s , see Chapter 5) on unoccupied s i t e s q u a n t i t a t i v e l y . However, o b s e r v a t i o n s suggested t h a t food was a v a i l a b l e on s i t e s not occupied by M. p l u m i e r i . T i l e f i s h sometimes chase g o a t f i s h e s , Pseudupeneus maculatus; wrasses, H a l i c h o r e s spp.; j a c k s , Caranx spp. away from t h e i r t e r r i t o r i e s , and p i l f e r food items from them. These s p e c i e s a l s o feed on b e n t h i c i n v e r t e b r a t e s , and may compete wi t h t i l e f i s h f o r food r e s o u r c e s . These probable competitors foraged on s i t e s t h a t were not occupied by t i l e f i s h , s u g g e s t i n g t h a t b e n t h i c i n v e r t e b r a t e s were a v a i l a b l e on these l o c a t i o n s . Thus, i t seems u n l i k e l y t h a t the d i s t r i b u t i o n of t i l e f i s h i s e x c l u s i v e l y a response t o the d i s t r i b u t i o n of p o t e n t i a l prey. 3) C o n c e n t r a t i o n by c u r r e n t s : P r e v a i l i n g c u r r e n t s may p l a y a r o l e i n colony l o c a t i o n and d e n s i t y . The p r e v a i l i n g o c e a n i c c u r r e n t s flow north-westwardly a c r o s s the Caribbean towards 39 G l o v e r ' s Reef (Stoddart, 1962). The channel s i t e i s one of two east-west passages on the e a s t e r n s i d e of the a t o l l t h a t connects the lagoon w i t h the Caribbean ( F i g u r e 2). As a consequence of the p r e v a i l i n g c u r r e n t s , a l a r g e volume of o c e a n i c water passes through the channel and the d i r e c t i o n of flow a c r o s s G l o v e r ' s Reef i s u s u a l l y from the e a s t t o west (Stoddart, 1962). The h i g h d e n s i t i e s of a d u l t s and j u v e n i l e s i n the channel r e l a t i v e t o r e e f s l o p e s , t h e r e f o r e , are c o n s i s t e n t w i t h the h y p o t h e s i s t h a t l a r g e s c a l e c u r r e n t p a t t e r n s may i n f l u e n c e the r e l a t i v e abundance of M. p l u m i e r i i n d i f f e r e n t h a b i t a t s . I d i d not measure s m a l l e r s c a l e c u r r e n t p a t t e r n s w i t h i n the lagoon. Shallow lagoons l i k e the one a t G l o v e r ' s Reef are f l u s h e d f r e q u e n t l y , p a r t i c u l a r l y i n areas a d j a c e n t t o passages, and c u r r e n t p a t t e r n s change wi t h wind d i r e c t i o n (Shapiro e t a l . , 1988). Thus, i t seems u n l i k e l y t h a t t i l e f i s h c o l o n i e s occur merely because l o c a l c u r r e n t s c o n c e n t r a t e p l a n k t o n i c l a r v a e on some r e e f s l o p e s w h i l e r e c r u i t s do not r each a d j a c e n t s i t e s w i t h i n 3 0 m. 4) P r e d a t o r avoidance: Contagious alarm responses t o both n a t u r a l p r e d a t o r s and experimental s t i m u l i suggest t h a t l i v i n g w i t h i n v i s u a l range of c o n s p e c i f i c s enhances d e t e c t i o n and e v a s i o n of p r e d a t o r s . In r e e f s l o p e h a b i t a t s , an abrupt r e t r e a t t o the burrow u s u a l l y e l i c i t e d s i m i l a r b e h a v i o r by a t l e a s t one neighbor. In the channel colony, e r r a t i c f l i g h t b e h a v i o r by t e s t f i s h b e f o r e r e t r e a t i n g t o t h e i r burrows caused s e v e r a l nearby c o n s p e c i f i c s t o r e a c t s i m i l a r l y . E a r l y d e t e c t i o n of would-be p r e d a t o r s would almost c e r t a i n l y f a c i l i t a t e e v a s i o n of a t t a c k s e i t h e r by an immediate escape or by f l e e i n g i n i t i a l l y 40 and then r e t r e a t i n g i n t o a burrow. N a t u r a l h i d i n g p l a c e s are s c a r c e on sand r u b b l e f l a t s r e l a t i v e t o those a v a i l a b l e on r e e f s . Furthermore, p r e d a t o r s can s t r i k e from s e v e r a l d i r e c t i o n s . Under these c o n d i t i o n s , s e t t l e m e n t i n c o l o n i e s very l i k e l y enhances escape from a t t a c k s , and s e l e c t i o n may f a v o r i n d i v i d u a l s t h a t s e t t l e near c o n s p e c i f i c s . I n f l u e n c e o f Predator Behavior on T i l e f i s h Avoidance Responses The s a f e t y o f i n d i v i d u a l prey may i n c r e a s e w i t h the a b s o l u t e s i z e o r d e n s i t y o f groups (e.g., Brock and R i f f e n b u r g , 1960; Hoogland, 1979, 1980). On the oth e r hand, l a r g e c o n c e n t r a t i o n s o f prey may a c t u a l l y a t t r a c t more p r e d a t o r s (reviewed by Wittenberger, 1981; Alc o c k , 1984) t o the extent t h a t t h i s counters p o t e n t i a l b e n e f i t s o f group l i v i n g . My r e s u l t s do not support the proposed p o s i t i v e r e l a t i o n s h i p between i n d i v i d u a l s a f e t y and e i t h e r colony s i z e o r d e n s i t y . The percentage o f f i s h d i s a p p e a r i n g was much g r e a t e r i n the channel, even though r e e f s l o p e c o l o n i e s are s m a l l e r and f i s h a re l e s s dense. Although I cannot be c e r t a i n of the f a t e s of f i s h t h a t disappeared, i t i s ve r y l i k e l y t h a t these i n d i v i d u a l s were taken by p r e d a t o r s . T i l e f i s h are s t r o n g l y a t t a c h e d t o t h e i r home s i t e s (Chapter 5). F i s h r a r e l y change l o c a t i o n s u n l e s s neighbors are removed, and even then move o n l y i n t o a d j a c e n t t e r r i t o r i e s (Chapter 6). None of the tagged f i s h t h a t disappeared from t h e i r o r i g i n a l l o c a t i o n s subsequently appeared i n a d j a c e n t areas. Higher disappearance r a t e s suggest, t h e r e f o r e , t h a t the i n t e n s i t y of p r e d a t i o n i s h i g h e r i n the channel than i n r e e f s l o p e h a b i t a t s . 41 Responses by t i l e f i s h to both natural predators and simulated attacks indicate that f i s h i n reef slope and channel colonies adopt d i f f e r e n t behavior with regard to avoidance of predators. Furthermore, differences i n t i l e f i s h behavior and frequencies of disappearance may be related to differences i n predator a c t i v i t y . The channel i s a primary route for d a i l y f i s h migrations including large piscivores that follow prey swimming through t h i s passage. Piscivores are p a r t i c u l a r l y active i n the channel at dusk when t i l e f i s h are courting and spawning (Chapter 5) and hence conspicuous. Channel t i l e f i s h , therefore, are exposed to large numbers of mobile pi s c i v o r e s . By contrast, the primary threat to t i l e f i s h on reef slopes appears to be s o l i t a r y barracuda u t i l i z i n g s t a l k i n g type hunting techniques. T i l e f i s h might be expected to remain closer and retreat more r e a d i l y to t h e i r burrows where a c t i v i t y by predators i s high. My r e s u l t s show, however, that t h i s was not the case. Even though both channel and reef slope f i s h r e l i e d on home burrows, channel f i s h were less c l o s e l y attached to and retreated less r e a d i l y . One possible explanation of t h i s behavior i s that channel t i l e f i s h do not r e a d i l y detect predators swimming high above them. Perhaps as a r e s u l t , retreats occur infrequently, and, as the high frequency of disappearance suggests, threat of predation to channel f i s h i s high. An al t e r n a t i v e explanation i s that immediate retreat to burrows may not be an e f f e c t i v e defense given the hunting 42 t e c h n i q u e s employed by barracuda i n the channel. The channel i s deep r e l a t i v e t o r e e f s l o p e s , and barracuda u s u a l l y swim h i g h above. A t i l e f i s h t h a t i s undetected by a p r e d a t o r swimming h i g h above might be conspicuous i f i t r e t r e a t e d a b r u p t l y . To a v o i d d e t e c t i o n by p r e d a t o r s overhead, i t may be most e f f e c t i v e t o remain m o t i o n l e s s . When att a c k e d , e r r a t i c swimming t h a t evokes s i m i l a r b e h a v i o r by nearby c o n s p e c i f i c s may then become the b e s t means of escape i f such r e a c t i o n s d i s t r a c t or confuse a would-be p r e d a t o r . By c o n t r a s t , remaining c l o s e r t o the burrow and m a i n t a i n i n g a h i g h l e v e l of v i g i l a n c e should be a more e f f e c t i v e means of a v o i d i n g a t t a c k s where p r e d a t o r s s t a l k t i l e f i s h a l ong the s u b s t r a t e . Infrequent disappearance suggests t h a t these t a c t i c s may be more e f f e c t i v e than those adopted by channel f i s h . 43 CHAPTER SUMMARY 1. T i l e f i s h are h i g h l y clumped on sand-rubble f l a t s a djacent t o i s o l a t e d p a tch r e e f s ( r e e f slopes) and i n a s i n g l e l a r g e a g g r e g a t i o n w i t h i n the channel. 2. The f i x e d l o c a t i o n s of t i l e f i s h groups and of i n d i v i d u a l s w i t h i n groups i s c o n s i s t e n t w i t h Wittenberger's (1981) d e f i n i t i o n of c o l o n i a l i t y . 3. T i l e f i s h c o l o n i e s do not r e s u l t because h a b i t a t i s l i m i t e d , or because i n d i v i d u a l s b e n e f i t from s o c i a l t r a n s f e r of f o r a g i n g i n f o r m a t i o n . The r e l a t i v e abundance of f i s h i n r e e f s l o p e and channel h a b i t a t s may be a consequence of the i n f l u e n c e on l a r v a l t r a n s p o r t of l a r g e - s c a l e water c i r c u l a t i o n p a t t e r n s . However, i t i s u n l i k e l y t h a t r e e f s l o p e c o l o n i e s r e s u l t merely because l o c a l i z e d c u r r e n t s c o n c e n t r a t e p l a n k t o n i c l a r v a e o n l y i n some patches. 4. Contagious r e a c t i o n s t o barracuda and experimental d i s t u r b a n c e s suggest t h a t p r o x i m i t y t o c o n s p e c i f i c s may reduce p r e d a t i o n r i s k t o i n d i v i d u a l s . 5. Barracuda hunt t i l e f i s h on r e e f s l o p e s by s t a l k i n g along the s u b s t r a t e , whereas i n the channel barracuda a t t a c k from above. Perhaps as a r e s u l t , r e e f s l o p e f i s h remain c l o s e r t o burrows, burrow more r e a d i l y , and d i s a p p e a r l e s s f r e q u e n t l y than channel f i s h . By c o n t r a s t , channel f i s h venture f a r t h e r from burrows, r e t r e a t l e s s r e a d i l y and disappeared more f r e q u e n t l y . 44 CHAPTER 5 REPRODUCTIVE BIOLOGY AND SOCIAL ORGANIZATION WITHIN COLONIES INTRODUCTION Polygynous mating systems are w e l l documented i n t r o p i c a l marine f i s h e s t h a t i n h a b i t c o r a l o r rocky r e e f s (reviewed by Thresher, 1984; Warner, 1984a). Because r e e f f i s h e s are o f t e n sedentary and spawning i s i t e r a t e d , s p a c i n g of i n d i v i d u a l s i n r e l a t i o n t o food r e s o u r c e s , p o t e n t i a l mates, spawning and refuge s i t e s , o r a l l of these, may i n f l u e n c e the type of mating system t h a t e v o l v e s (e.g., Robertson and Hoffman, 1977; Moyer and Nakazono, 1978; Jones, 1981; Robertson, 1981; Thresher, 1984; Warner, 1984a; Shapiro, 1986). In p a r t i c u l a r , the b e h a v i o r and d i s t r i b u t i o n o f females d u r i n g spawning p e r i o d s may i n f l u e n c e the mating t a c t i c s t h a t are s u c c e s s f u l f o r males. For example, i n some s p e c i e s females l e a v e t h e i r f e e d i n g ranges and congregate i n f a v o r a b l e spawning s i t e s where a few males are ab l e t o garner numerous matings by defending temporary t e r r i t o r i e s (e.g., Warner, 1984a; 1987; Hoffman, 1985). In c o n t r a s t , polygyny may a l s o i n v o l v e male defense of permanent, a l l - p u r p o s e t e r r i t o r i e s and m o n o p o l i z a t i o n of spawnings w i t h a sma l l group of the same females ( i . e . , harem-polygyny) . Male defense of permanent t e r r i t o r i e s and harem polygyny sometimes ev o l v e s when females do not migrate away from t h e i r u s u a l f e e d i n g ranges i n order t o spawn (e.g., Robertson and Hoffman, 1977; Robertson, 1981; Hoffman, e t a l . , 1985). Protogynous hermaphroditism i s common i n s p e c i e s w i t h both types 45 of polygynous mating system (reviewed by Thresher, 1984; Warner, 1984a; Shapiro, 1987a). Although the importance of female b e h a v i o r i n the e v o l u t i o n of t r o p i c a l marine f i s h mating systems seems e v i d e n t , behavior of females has been s t u d i e d much l e s s than t h a t o f males (but see Shapiro, 1986; Warner, 1987). Kuwamura (1984) p o i n t s out f o r harem s p e c i e s i n p a r t i c u l a r , t h a t few s t u d i e s have examined i n d e t a i l the sp a c i n g and s o c i a l o r g a n i z a t i o n o f females. F i s h e s t h a t occupy f l a t open areas are p a r t i c u l a r l y w e l l s u i t e d f o r study o f the use of space because these h a b i t a t s a l l o w u n o b s t r u c t e d o b s e r v a t i o n of the l o c a t i o n o f spawning a c t i v i t i e s , r e f u g e s i t e s , r e s o u r c e s , and mates. In M. p l u m i e r i , the p o t e n t i a l f o r the e v o l u t i o n o f polygamy i s h i g h because i n d i v i d u a l s aggregate i n c o l o n i e s . I n t r a s p e c i f i c a g o n i s t i c behavior and d i s p l a y s g i v e n t o models l e d C l i f t o n and Hunter (1972) and C l a r k e e t a l . (1977) t o suggest t h a t M. p l u m i e r i i s t e r r i t o r i a l . The o n l y o t h e r i n f o r m a t i o n on the s o c i a l b i o l o g y of t h i s s p e c i e s are o b s e r v a t i o n s t h a t t i l e f i s h sometimes spawn i n p a i r s and r e l e a s e p e l a g i c gametes ( C o l i n and C l a v i j o , i n p r e s s ) . The o b j e c t i v e o f t h i s chapter i s t o d e s c r i b e the s o c i a l o r g a n i z a t i o n w i t h i n t i l e f i s h c o l o n i e s . In p a r t i c u l a r , I i n v e s t i g a t e the extent t o which females and males defend t e r r i t o r i e s , and the s o c i a l and mating r e l a t i o n s h i p s among i n d i v i d u a l s . Because the d i s t r i b u t i o n of necessary r e s o u r c e s may have an important i n f l u e n c e on sp a c i n g and mating b e h a v i o r of p e l a g i c a l l y spawning f i s h e s , the l o c a t i o n s o f f o r a g i n g and mating a c t i v i t i e s were examined i n d e t a i l . L a s t l y , because 46 hermaphroditism i s an important component of the r e p r o d u c t i v e b i o l o g y o f many t r o p i c a l marine s p e c i e s , and has been suggested f o r o t h e r t i l e f i s h e s (Dooley, 1978; Ross and M e r r i n e r , 1982), the s e x u a l ontogeny of M. p l u m i e r i was a l s o i n v e s t i g a t e d . METHODS I n d i v i d u a l Use of Space The use of space by i n d i v i d u a l s was i n v e s t i g a t e d by c o n t i n u o u s l y t r a c i n g the swimming path o f a f i s h onto a map f o r 20 min. The slow r a t e o f movement (5-13m/min) and s t r o n g a f f i n i t y o f i n d i v i d u a l s f o r home burrows f a c i l i t a t e d r e c o r d i n g of movements. R e p l i c a t e t r a c e s were then o v e r l a y e d , and the maximum peri m e t e r o f combined t r a c e s was drawn t o estimate the home range o f each i n d i v i d u a l . The composite t r a c e o f each f i s h was then drawn on a master map of the e n t i r e study s i t e . I n i t i a l c o l l e c t i o n o f t e n r e p l i c a t e t r a c e s per i n d i v i d u a l (N=4 females and 4 males) i n d i c a t e d t h a t f o u r , 20 min t r a c e s taken on separate days y i e l d e d a r e l i a b l e estimate of the s i z e and l o c a t i o n of an i n d i v i d u a l ' s home range. A d d i t i o n a l t r a c e s changed the composite estimate o f home range by l e s s than 5%. To determine i f i n d i v i d u a l s occupied the same home ranges f o r l o n g p e r i o d s , I recorded the l o c a t i o n s o f f i s h f o r which s p a t i a l t r a c e s were mapped, as w e l l as oth e r tagged f i s h (N=73 females, 16 males) every few days f o r 1-4 months. Most f i s h l o s t tags from one season t o the next, t h e r e f o r e , o b s e r v a t i o n s were terminated a t the end of each f i e l d season on 47 a l l but a few f i s h . The d u r a t i o n o f p e r i o d s over which l o c a t i o n was monitored v a r i e d because f i s h were tagged throughout my st a y . Disappearance of f i s h due t o p r e d a t i o n and removal f o r ot h e r s t u d i e s (Chapter 6) a l s o c o n t r i b u t e d t o v a r i a t i o n i n the l e n g t h o f o b s e r v a t i o n p e r i o d s . To determine i f t i l e f i s h defend p a r t or a l l o f t h e i r home range as a t e r r i t o r y , I recorded the location-dependent s o c i a l b e h a v i o r o f i n d i v i d u a l s . I used " e x c l u s i v e occupancy o f space by i n d i v i d u a l s (excepting mates, see below) by means of o v e r t a g g r e s s i o n and/or advertisement" (Brown, 1975; Wilson, 1975) as my working d e f i n i t i o n o f t e r r i t o r i a l i t y . The l o c a t i o n s , i d e n t i t y o f p a r t i c i p a n t s , and outcomes of a g o n i s t i c s o c i a l i n t e r a c t i o n s (see below) were recorded d u r i n g s p a t i a l t r a c e s . These were then p l o t t e d onto the master map of the study s i t e t o examine whether or not i n d i v i d u a l s r e p e l l e d o r y i e l d e d t o c o n s p e c i f i c s depending on t h e i r l o c a t i o n s . A g o n i s t i c i n t e r a c t i o n s o c c u r r e d p r i m a r i l y near borders of n e i g h b o r i n g home ranges. However, f i s h o c c a s i o n a l l y ventured i n t o areas defended by neighbors. Such f o r a y s e l i c i t e d a g g r e s s i o n from neighbors, c a u s i n g i n t r u d e r s t o r e t r e a t . T h e r e f o r e , area t r a v e l l e d over d u r i n g such i n t r u s i o n s was not c o n s i d e r e d p a r t o f the t e r r i t o r y o f the f i s h t h a t was chased away by a c o n s p e c i f i c . Only the space t h a t each i n d i v i d u a l o c c upied without evoking a g g r e s s i o n from i t s neighbors, and from which i t c o n s i s t e n t l y r e p e l l e d a l l i n t r u d e r s , was c o n s i d e r e d i t s t e r r i t o r y . Where the maximum peri m e t e r o f one home range was adjacent 48 t o o r overlapped t h a t o f a neighbor, defended borders were est i m a t e d u s i n g the location-dependent outcome of a g o n i s t i c s o c i a l i n t e r a c t i o n s between n e i g h b o r i n g f i s h . Borders o f ne i g h b o r i n g t e r r i t o r i e s were determined by p l o t t i n g the outermost segments of t r a c e s from where each f i s h chased away i t s neighbors, and by e x c l u d i n g p o r t i o n s o f swimming paths from which t h a t f i s h was i t s e l f chased away. On s i d e s where t h e r e were no n e i g h b o r i n g c o n s p e c i f i c s , t e r r i t o r y borders were c o n s i d e r e d t o be the maximum peri m e t e r o f the home range. A map of each t e r r i t o r y was then c o n s t r u c t e d u s i n g these c r i t e r i a , and the areas of both home ranges and t e r r i t o r i e s were measured u s i n g a p l a n i m e t e r . Areas were measured i n the h o r i z o n t a l plane because t i l e f i s h l i v e near the bottom (Chapter 4). However, t i l e f i s h home ranges and t e r r i t o r i e s i n c l u d e the water column between the s u b s t r a t e and the s u r f a c e . D i e t and L o c a t i o n of For a g i n g A c t i v i t i e s D i e t s were estimated by examining the p r e s e r v e d gut contents o f 25 females and 25 males. I c o u l d a l s o observe the prey eaten by M. p l u m i e r i because t i l e f i s h o f t e n r e p e a t e d l y grasped and spat out prey p r i o r t o i n g e s t i n g them, a p p a r e n t l y t o break prey a p a r t . To examine the extent t o which t i l e f i s h f oraged w i t h i n t h e i r home ranges, the l o c a t i o n s o f b i t e s were recor d e d d u r i n g s p a t i a l t r a c e s . A g o n i s t i c I n t e r a c t i o n s A g o n i s t i c i n t e r a c t i o n s i n which the f o c a l i n d i v i d u a l s p a r t i c i p a t e d were recorded d u r i n g s p a t i a l t r a c e s . I n t e r a c t i o n s i n v o l v e d one or s e v e r a l a g o n i s t i c a c t s (see r e s u l t s ) d i r e c t e d toward and e l i c i t i n g a response from a nearby c o n s p e c i f i c . E i t h e r or both f i s h i n i t i a t e d a g g r e s s i v e a c t s d u r i n g these exchanges. I n t e r a c t i o n s were recorded as "bouts," d e f i n e d as a g o n i s t i c exchanges between two f i s h t h a t were separated by a t l e a s t 1 min d u r i n g which these f i s h d i d not i n t e r a c t w i t h one another. A g o n i s t i c i n t e r a c t i o n s by males were a l s o recorded throughout f o c a l o b s e r v a t i o n s d u r i n g f i v e spawning p e r i o d s per male. Reproductive B i o l o g y Observations made throughout d a y l i g h t hours suggested t h a t r e p r o d u c t i v e b e h a v i o r M. p l u m i e r i i s r e s t r i c t e d t o a 2 h p e r i o d p r i o r t o sunset. To d e s c r i b e c o u r t s h i p and mating b e h a v i o r and document the d i s t r i b u t i o n of d a i l y matings w i t h i n c o l o n i e s , f o c a l o b s e r v a t i o n s were conducted on 39 tagged males f o r a minimum of f i v e spawning p e r i o d s each. Throughout these p e r i o d s , the f r e q u e n c i e s of r e p r o d u c t i v e b e h a v i o r and the i d e n t i t y of the p a r t i c i p a n t s were recorded. To examine whether i n d i v i d u a l s p r e f e r r e d c e r t a i n s i t e s f o r spawning, l i n e a r h o r i z o n t a l d i s t a n c e along the bottom between each female's burrow and the spawning s i t e was a l s o estimated f o r 60% of observed spawnings. To examine the s i z e d i s t r i b u t i o n of male and female t i l e f i s h , 316 i n d i v i d u a l s r anging from 14.8 t o 41.9 cm SL were sexed. Sex was determined by o b s e r v a t i o n s of spawning, and d i s s e c t i o n and h i s t o l o g y of gonads, or both. Specimens were c o l l e c t e d by spear or t r a p and measured. Gonads were d i s s e c t e d from f r e s h specimens and p r e s e r v e d i n Bouin's f i x a t i v e . These 50 were l a t e r embedded i n p a r a f f i n , s e c t i o n e d (10-15 u ) , and s t a i n e d w i t h haematoxylin and e o s i n . I attempted t o induce sex change by removing i n d i v i d u a l males (N=20) t h a t had been p r e v i o u s l y observed t o spawn on s u c c e s s i v e days w i t h a t l e a s t one female. Observations were conducted d u r i n g spawning p e r i o d s f o r a minimum of t h r e e days f o l l o w i n g removal of males and i n t e r m i t t e n t l y t h e r e a f t e r t o examine the b e h a v i o r of females whose mate was removed. In one t e s t , a l l f i v e males were removed from a colony on J u l y 15, 1985. The remaining nine f i s h had p r e v i o u s l y spawned as females d u r i n g a t l e a s t f i v e spawning p e r i o d s . These i n d i v i d u a l s were marked wi t h two tags t o d i s t i n g u i s h them from a l l o t h e r f i s h tagged a t G l o v e r ' s Reef. Loss of t a g s produced d i s t i n c t s c a r s where the s k i n was punctured. T h e r e f o r e , even when tags were l o s t , these f i s h c o u l d be i d e n t i f i e d 8 months l a t e r when I r e t u r n e d i n 1986 u s i n g double t a g s c a r s . Unique p a t t e r n s of b l a c k s k i n spots were a l s o r e c o r d e d t o a i d i n the i d e n t i f i c a t i o n of these i n d i v i d u a l s . These f i s h were monitored d u r i n g spawning p e r i o d s f o r 15 days f o l l o w i n g removal of males. In A p r i l 1986 t h i s s i t e was censused again, and the r e p r o d u c t i v e a c t i v i t y of f i s h s u r v i v i n g from 1985 was recorded. RESULTS T e r r i t o r i a l Behavior of Females R e p l i c a t e t r a c e s of f i s h movements r e v e a l e d t h a t females each occupied a home range surrounding t h e i r home burrow s i t e s . Overlap between adjacent female home ranges was low (Table 2). 51 T a b l e 2. T e r r i t o r i a l i t y i n female and male t i l e f i s h . SL(mm) T e r r i t o r y area(m ) P e r c e n t 1 i n t r a s e x u a l home range o v e r l a p Frequency of i n t r a s e x u a l i n t e r a c t i o n s (bouts/h) Females N 54 54 66 54 X (SE) 233.5 (4.37) 140 (9.7) 2.15 (0.35) 1.75 (0.67) * * * * Males N 39 41 30 39 ~X (SE) 333.1 (6.15) 411 (33) 7.45 (1.24) 1.06 (0.15) I n t r a s e x u a l home range o v e r l a p i s expressed as a percentage of the combined area o f the two adj a c e n t home ranges. * p<0.01 Student t - t e s t comparisons between females and males. 52 Ninety-one p e r c e n t (96 of 106) of the a g o n i s t i c i n t e r a c t i o n s (see below) between females t h a t were mapped, began w i t h i n 2 m of the o v e r l a p of the maximum per i m e t e r s of two n e i g h b o r i n g female home ranges. Each female r e p e l l e d i n t r u d e r s a g g r e s s i v e l y from much of her home range (X percentage o f home range area t h a t was defended=90.8, SE=1.7, range=47.4-100.0, N=54 females). The l o c a t i o n , s i z e , and shape of female t e r r i t o r i e s i s shown f o r one colony i n F i g u r e 7. Borders of a b u t t i n g t e r r i t o r i e s were d e f i n e d c l e a r l y by the location-dependent outcome of a g o n i s t i c i n t e r a c t i o n s . In 87% of i n t e r a c t i o n s observed, i n t r u d e r s were i n t e r c e p t e d and r e p u l s e d b e f o r e they had encroached f a r t h e r than 1 m i n s i d e the border of a neighbor's t e r r i t o r y . Less o f t e n (13% of i n t e r a c t i o n s ) , i n t r u d e r s had p e n e t r a t e d deeper than 1 m (range=1.5-8 m) i n t o a neighbor's t e r r i t o r y , whereupon they were i n t e r c e p t e d and r e p e l l e d by the owner. Disputes were u s u a l l y t erminated when the i n t r u d e r was chased or e s c o r t e d o f f the t e r r i t o r y . I n truder/occupant r o l e s were r e v e r s e d i f , w h i l e e s c o r t i n g an i n t r u d e r , the occupant encroached onto i t s opponent's t e r r i t o r y . A g o n i s t i c encounters, t h e r e f o r e , ended between n e i g h b o r i n g borders or on borders t h a t were contiguous, and i n v a r i a b l y ended i n a " s t a n d - o f f " without the p a r t i c i p a n t s a c q u i r i n g space c u r r e n t l y o c c upied by the ot h e r f i s h . During a g o n i s t i c i n t e r a c t i o n s between females, each f i s h performed one or more of the f o l l o w i n g b e h a v i o r s : d i s p l a y s , i n v o l v i n g e r e c t i o n o f the medial or p e l v i c f i n s ; abrupt upward "jumps" w h i l e the p e l v i c and medial f i n s were h e l d e r e c t ; s h o r t (<1 m) displacements of the opponent; long (>lm) chases; and 53 Figure 7. Map of one t i l e f i s h colony consisting of four harems ranging in size from 1 to 6 females. Female t e r r i t o r i e s are enclosed by s o l i d lines, and male t e r r i t o r i e s are distinguished by lines composed of different symbols. Male burrows are indicated by squares containing capital l e t t e r s . Burrows occupied by each female are c i r c l e s labeled with lower case le t t e r s that correspond to their male mate. Burrows are not drawn to scale. Male E was unmated. 54 v i o l e n t b i t e s on the opponent's t a i l and f i n s . I n t e r a c t i o n s a l s o i n c l u d e d " c i r c l e d i s p l a y s " i n which two opponents p o s i t i o n e d themselves l a t e r a l l y t o one another, h e a d - t o - t a i l , w i t h medial and p e l v i c f i n s f l a r e d and mouths and o p e r c u l a h e l d s t i f f l y open ( F i g u r e 8a). While i n t h i s p o s i t i o n , each f i s h swam r a p i d l y i n the same d i r e c t i o n i n a sm a l l (~1 body l e n g t h diameter) c i r c l e . T e r r i t o r i a l d i s p u t e s v a r i e d both i n t h e i r i n t e n s i t y and d u r a t i o n . Some i n v o l v e d o n l y the exchange of f i n d i s p l a y s , w h i l e o t h e r s e s c a l a t e d i n t o l o n g e r and more v i o l e n t exchanges. Females p a r t i c i p a t e d i n i n t r a s e x u a l a g g r e s s i o n a t d i f f e r e n t r a t e s (Table 2). Frequencies o f a g g r e s s i o n were not c o r r e l a t e d w i t h female body s i z e (r=-0.25, N=54 females, NS), and t e r r i t o r y occupants r e p e l l e d i n t r u d e r s r e g a r d l e s s o f t h e i r r e l a t i v e s i z e . Females a l s o r e a c t e d a g g r e s s i v e l y toward i n t r u d e r males other than t h e i r mates (see below). These o c c u r r e d more than 12 times l e s s f r e q u e n t l y , (t=7.87, p<0.01, X=0.14/h, N=54 females, SE=0.04) than i n t r a s e x u a l d i s p u t e s , perhaps because male i n t r u d e r s were u s u a l l y i n t e r c e p t e d by male t e r r i t o r y occupants (see below). The s i z e of female t e r r i t o r i e s was h i g h l y v a r i a b l e (range= 43-309 m2. There was no c o r r e l a t i o n between female s i z e and t e r r i t o r y area (r=-0.04, N=54 females, NS), nor was the s i z e of female defended areas r e l a t e d t o the t o t a l number of females t h a t were spawning wi t h the same male (r=0.16, N=54 females, NS). The p o s i t i o n s o f female t e r r i t o r i e s remained s t a b l e , p r o v i d i n g t h a t a d j a c e n t females were not removed (see Chapter 6). None of the females whose l o c a t i o n was monitored ( t o t a l N=127), s h i f t e d 55 F i g u r e 8 . A s p e c t s o f s o c i a l and r e p r o d u c t i v e b e h a v i o r i n sand t i l e f i s h . A. c i r c l e d i s p l a y . B. Male advertisement d i s p l a y . C. Female a r c d i s p l a y . D. Male and female a t apex of spawning a s c e n t . B l a c k spots on f i s h a r e m e l a n i z a t i o n o f e n c y s t e d trematodes. 56 t h e i r burrows or t e r r i t o r i e s spontaneously over p e r i o d s ranging from one t o f o u r months. Moreover, t h r e e females t h a t r e t a i n e d tags over two study seasons occupied the same t e r r i t o r y f o r a t l e a s t n ine months. T e r r i t o r i a l Behavior o f Males Tra c e s of f i s h movements a l s o r e v e a l e d t h a t males each occupied a s t a b l e home range around t h e i r home burrow. I n t r a s e x u a l o v e r l a p between adjacent male home ranges was about 3.5 times (t=3.65, p<0.01) l a r g e r than t h a t o f females (Table 2). N i n e t y - t h r e e p e r c e n t (84 of 90) of a g o n i s t i c encounters between males began w i t h i n 2 m of where the maximum p e r i m e t e r s o f two ne i g h b o r i n g male home ranges overlapped. Male-male a g o n i s t i c i n t e r a c t i o n s i n v o l v e d the same be h a v i o r s d e s c r i b e d above f o r females. Males a l s o each defended e x c l u s i v e occupancy (ex c e p t i n g t h e i r mates, see below) of most of t h e i r home ranges (X % of home range t h a t was defended=80.3, SE=4.2, range=50-100%, N=39 males) from i n t r u d e r males. In 80% of a l l a g o n i s t i c i n t e r a c t i o n s , male i n t r u d e r s were r e p u l s e d w i t h i n 1 m o f t e r r i t o r y borders, w h i l e i n 20% of encounters an i n t r u d e r p e n e t r a t e d 2-10 m be f o r e he was d e t e c t e d and chased. The frequency w i t h which males p a r t i c i p a t e d i n a g o n i s t i c d i s p u t e s was not c o r r e l a t e d w i t h male s i z e (r=0.09, N=39, NS). Male d i s p u t e s w i t h n e i g h b o r i n g females ( i . e . , females mating w i t h a d j a c e n t males) a l s o occurred, but were l e s s f r e q u e n t (X=0.32 i n t e r a c t i o n s / h , SE=0.08, t=3.29, p<0.001, N=39 males) than with neighbor males. The s i z e o f male t e r r i t o r i e s was a l s o h i g h l y v a r i a b l e (range=73-950 m 2), but t e r r i t o r y area was not 57 c o r r e l a t e d w i t h male s i z e (r=-o.l8, N=39 males, NS). Though males o c c a s i o n a l l y went on e x t r a - t e r r i t o r i a l e x c u r s i o n s (see below), o n l y 1 of 57 males s h i f t e d the l o c a t i o n o f h i s t e r r i t o r y over one t o f o u r month o b s e r v a t i o n p e r i o d s . Furthermore, s i x males t h a t r e t a i n e d tags between two study seasons occupied the same areas nine months l a t e r . Although male t e r r i t o r i e s were l a r g e r (t=6.69, p<0.01) than those o f females, females p a r t i c i p a t e d i n i n t r a s e x u a l a g g r e s s i o n more f r e q u e n t l y than males (t=2.68, p<0.01, Tab l e 2). Home range o v e r l a p between adjacent males was g r e a t e r than t h a t of females, because males sometimes swam f a r t h e r than 5 m beyond t h e i r defended borders without being e l i c i t e d by an i n t r u d i n g c o n s p e c i f i c . E x t r a - t e r r i t o r i a l e x c u r s i o n s were r a p i d f o r a y s i n t o t e r r i t o r i e s defended by adjacent males, and o c c a s i o n a l l y a c r o s s more than one n e i g h b o r i n g t e r r i t o r y . Such e x c u r s i o n s were i n f r e q u e n t (X excursions/h=0.26, N=39 males, SE=0.05)> and accounted f o r l e s s than 1% of the t o t a l o b s e r v a t i o n time. Behavior o f males was c l e a r l y d i f f e r e n t d u r i n g these e x c u r s i o n s . Males e i t h e r swam ve r y f a s t or swam more s l o w l y on the bottom as i f t o a v o i d d e t e c t i o n . However, i n t r u d i n g males were almost always d e t e c t e d and chased away by t e r r i t o r y occupants o f both sexes. Although e s c a l a t e d border d i s p u t e s sometimes took females onto neighbor t e r r i t o r i e s , they d i d not make l o n g e x t r a - t e r r i t o r i a l e x c u r s i o n s l i k e those o f males. 58 D i e t , L o c a t i o n of Foraging, and I n t e r s p e c i f i c A g g r e s s i o n With  Food Competitors T i l e f i s h foraged w i t h i n t h e i r t e r r i t o r i e s p r i m a r i l y on b e n t h i c i n v e r t e b r a t e s . At l e a s t 60% of the stomachs of both females and males c o n t a i n e d gastropod and b i v a l v e mollusks, c r u s t a c e a n s , and p o l y c h a e t e a n n e l i d s (Table 3). I a l s o observed both sexes c a p t u r i n g and e a t i n g these i n v e r t e b r a t e s . Maps of f o r a g i n g b i t e s r e v e a l e d t h a t an average of 97.5% of f o r a g i n g b i t e s by females (N=54, SE=0.57) and 97.0% of f o r a g i n g b i t e s by males (N=25, SE=1.24) were taken w i t h i n the boundaries o f t h e i r defended areas. Both sexes a l s o chased o t h e r f i s h s p e c i e s t h a t were f e e d i n g on b e n t h i c i n v e r t e b r a t e s w i t h i n t h e i r t e r r i t o r i e s , a l though these s p e c i e s were too numerous t o be excluded completely. Females a t t a c k e d h e t e r o s p e c i f i c s more f r e q u e n t l y (t=3.46, p<0.01, X=1.28 chases/h, N=54 females, SE=0.23) than males (X=0.32 chases/h, N=23 males, SE=0.07). Reproductive Behavior Sand t i l e f i s h spawned d u r i n g a l l months t h a t I was p r e s e n t a t G l o v e r ' s Reef (February through August). Spawning has been r e p o r t e d from October t o A p r i l i n Puerto R i c o ( C o l i n and C l a v i j o , i n press) , s u g g e s t i n g t h a t M^_ p l u m i e r i may reproduce throughout the year. Observations conducted throughout the day confirmed t h a t spawning o c c u r r e d e x c l u s i v e l y from 1630 t o 1830h. A l l 541 spawnings observed i n unmanipulated f i s h o c c u r r e d d u r i n g t h i s time p e r i o d , as d i d an a d d i t i o n a l 150 spawns observed i n v a r i o u s experiments (see Chapters 6 and 7 ) . Spawning males were l a r g e r than t h e i r mates and almost always l a r g e r than o t h e r 59 T a b l e 3. Stomach contents o f female and male sand t i l e f i s h . Percentage o f T o t a l Guts C o n t a i n i n g Crustaceans M o l l u s k s P o l y c h a e t e s Females 60 76 80 (N=25) Males 67 76 67 (N=25) 60 females w i t h i n the colony. Female and male t i l e f i s h are otherwise monomorphic. T i l e f i s h mating was e x c l u s i v e l y pair-spawning i n v o l v i n g a s i n g l e male and female. The r e p r o d u c t i v e p e r i o d was c h a r a c t e r i z e d by males swimming about t h e i r t e r r i t o r i e s p e r f o r m i n g "advertisement" d i s p l a y s . T h i s c o n s i s t e d o f a s e r i e s o f upward jumps a t a 30-45 degree angle ( F i g u r e 8b), each f o l l o w e d by a downward g l i d e . The white p e l v i c f i n s were a l t e r n a t e l y h e l d e r e c t and outward from the body w h i l e ascending, and r e l a x e d d u r i n g downward g l i d e s . Males performed advertisement d i s p l a y s throughout t h e i r t e r r i t o r i e s , whether or not females were nearby. Pair-spawning was i n i t i a t e d by females. When ready t o spawn, a female ascended 1-3 m above the bottom w h i l e p r o t r u d i n g her abdomen i n an exaggerated manner. As she ascended, the snout and caudal f i n were a l s o p o i n t e d upward, forming her body i n t o a shallow i n v e r t e d a r c (Fi g u r e 8 c ) . I f the d i s p l a y a t t r a c t e d her mate, the two f i s h " p a i r e d " s i d e - b y - s i d e and remained i n t h i s p o s i t i o n o f t e n rubbing bodies f o r 5 t o 60 sec. P a i r e d f i s h o f t e n p a r t e d and then r e - p a i r e d 1 t o 10 or more times p r i o r t o a spawning ascent. An ascent began when the male swam l a t e r a l l y t o but s l i g h t l y above and behind the female. While i n t h i s p o s i t i o n , the p a i r ascended 2-4 m a t a 30 t o 40 degree angle above the h o r i z o n t a l . During the l a s t o n e - t h i r d of the ascent, the abdomen of each f i s h q u i v e r e d and gametes were r e l e a s e d e x t e r n a l l y ( F i g u r e 8d). F o l l o w i n g gamete r e l e a s e , both a d u l t s r e t u r n e d immediately t o the bottom. Each female spawned above her t e r r i t o r y near t o her burrow (X d i s t a n c e from burrow 61 t o spawning site=3.8m, N=401 spawns, SE=1.0). S o c i a l and Mating System Data on s o c i a l i n t e r a c t i o n s , the l o c a t i o n o f male t e r r i t o r i e s i n r e l a t i o n t o those of t h e i r mates, and the d i s t r i b u t i o n o f spawnings (Table 4) r e v e a l e d t h a t t i l e f i s h have a mating system c h a r a c t e r i z e d by male m o n o p o l i z a t i o n of one or more females ( i . e . , harem polygyny). Male t e r r i t o r i e s encompassed the burrow and most of the t e r r i t o r y o c c u p i e d by each mate ( F i g u r e 7, Table 4) i n a l l f i s h f o r which s p a t i a l t r a c e s were recorded. For females whose t e r r i t o r i e s were not mapped, but whose mate and burrow l o c a t i o n were known (N=73), the male's t e r r i t o r y a t l e a s t encompassed the burrows of a l l mates. Males i n i t i a t e d a g g r e s s i v e i n t e r a c t i o n s w i t h each female w i t h i n t h e i r t e r r i t o r i e s (Table 4 ). A g g r e s s i v e i n t e r a c t i o n s by males wi t h t h e i r mates were the same as those d e s c r i b e d f o r i n t r a s e x u a l d i s p u t e s , except t h a t they d i d not i n v o l v e c i r c l e d i s p l a y s . In some i n s t a n c e s , males a t t a c k e d or chased females i n response t o female t e r r i t o r i a l d i s p u t e s (Table 4 ). Such i n t e r v e n t i o n was u s u a l l y (86% of a l l i n t e r v e n t i o n s observed, N=39 males) e l i c i t e d from a male when two of h i s mates entered i n t o a d i s p u t e . The other i n t e r v e n t i o n s o c c u r r e d when one mate was i n t e r a c t i n g w i t h a female from a n e i g h b o r i n g harem. Although d i s p u t e s between females were common, females d i d not i n i t i a t e a g g r e s s i o n w i t h the male whose defended area encompassed t h e i r t e r r i t o r i e s . In response t o a g g r e s s i o n from mates, females e i t h e r f l e d , lowered t h e i r head and swam 62 T a b l e 4. Male s o c i a l and r e p r o d u c t i v e m o n o p o l i z a t i o n of harems. P e r c e n t 1 Male Percent male female i n t e r a c t i o n s / i n t e r v e n t i o n t e r r i t o r y Pair-spawns mate/h responses/mate overlapped /female/day Number of 94 94 54 94 females Mean(SE) 1.09(0.08) 13.25(2.18) 72.9(2.77) 0.91(0.05) •'•Percentage of male i n t e r v e n t i o n responses i s the p r o p o r t i o n o f each male's i n t e r a c t i o n s w i t h h i s mates t h a t was e l i c i t e d by i n t r a s e x u a l a g g r e s s i o n i n v o l v i n g those females. 63 beneath the approaching male, or b r i e f l y (1-10 sec) e x h i b i t e d an a r c d i s p l a y . Females maintained almost e x c l u s i v e spawning f i d e l i t y with one male. F o c a l o b s e r v a t i o n s on 10 females f o r e n t i r e spawning p e r i o d s r e v e a l e d t h a t these f i s h mated o n l y w i t h the males t h a t defended areas which encompassed each of t h e i r t e r r i t o r i e s . In o n l y 3 o f 691 pair-spawns (0.4%) d i d a female (N=94) mate with a p a r t n e r o t h e r than the male whose t e r r i t o r y overlapped her burrow and t e r r i t o r y . In each i n s t a n c e of i n f i d e l i t y , the female's u s u a l mate was i n s i d e h i s burrow f o r a l a r g e p a r t of the spawning p e r i o d , and she spawned wit h a male t h a t occupied an a d j a c e n t t e r r i t o r y . Females sometimes spawned as many as t h r e e times d u r i n g a s i n g l e d a i l y r e p r o d u c t i v e p e r i o d , but d i d not spawn d u r i n g 22.5% of the t o t a l r e p r o d u c t i v e o b s e r v a t i o n p e r i o d s (see Chapter 7). Males spawned as many as 10 times/day, and the number of mates (harem s i z e ) of males ranged from 1 t o 6. There was no c o r r e l a t i o n between male s i z e and harem s i z e (N=39 males, r=-0.18, NS), nor d i d spawning frequency per female v a r y c o n s i s t e n t l y w i t h harem s i z e . Because male t e r r i t o r i e s encompassed much of each female's t e r r i t o r y (Table 4), harem s i z e was p o s i t i v e l y c o r r e l a t e d (p<0.001) wit h male t e r r i t o r y area ( F i g u r e 9). A l l c o l o n i e s a l s o c o n t a i n e d i n d i v i d u a l s t h a t were not observed t o spawn. The s i z e of these f i s h ranged from 19.0 t o >29.0 cm SL. S p a t i a l t r a c e s and o b s e r v a t i o n s on s o c i a l i n t e r a c t i o n s of 10 non-mating f i s h showed t h a t they each occupied a home burrow and were a g g r e s s i v e t o nearby mating and 64 CD N if) 6 r 4 E ^ CD 2 0 • • • • M / l 3 4 7 8 1 0 Male territory area (m 2 x 100) F i g u r e 9. Male harem s i z e (number of female mates) as a f u n c t i o n o f the t e r r i t o r y areas (m2 x 100) of 41 males. L i n e i s l e a s t squares r e g r e s s i o n d e s c r i b e d by the equation, harem s i z e = 0.626 + 0.47 t e r r i t o r y area, r=0.75, p<0.001. 65 non-mating c o n s p e c i f i c s . H i s t o l o g i c a l examination of s i x non-spawning i n d i v i d u a l s (24.4-29.2 mm SL) r e v e a l e d t h a t these f i s h were males. L o c a t i o n and outcome of s o c i a l i n t e r a c t i o n s r e v e a l e d t h a t l a r g e unmated males defended t e r r i t o r i e s from n e i g h b o r i n g males. Unmated males were ad j a c e n t t o one or more harems but t h e i r t e r r i t o r i e s d i d not encompass t e r r i t o r i e s o c c u pied by females. T e r r i t o r i e s of these males u s u a l l y encompassed one or more s m a l l e r non-mating f i s h . D i s s e c t i o n and h i s t o l o g y of two s m a l l specimens r e v e a l e d t h a t they had immature gonads. Although I mapped i n t e r a c t i o n s of o n l y f o u r s m a l l non-mating f i s h , they d i d not appear t o defend e x c l u s i v e t e r r i t o r i e s . Areas occupied by these f i s h o verlapped c o n s i d e r a b l y (20 t o 70%) w i t h one or more s i m i l a r l y s i z e d c o n s p e c i f i c s , and the outcome of s o c i a l i n t e r a c t i o n s was not c l e a r l y r e l a t e d t o l o c a t i o n . Evidence of Protocrynous Sex R e v e r s a l F i g u r e 10 shows the s i z e d i s t r i b u t i o n of the sexes f o r 316 f i s h c o l l e c t e d from 2 0 c o l o n i e s . There i s a l a r g e s i z e o v e r l a p between the sexes, however, females and males predominate i n s m a l l and l a r g e s i z e c l a s s e s r e s p e c t i v e l y . S e v e r a l a s p e c t s of gonad m i c r o s t r u c t u r e i n d i c a t e t h a t M. p l u m i e r i i s a protogynous hermaphrodite. Twelve specimens r a n g i n g from 19.1 t o 24.3 cm SL had gonads t h a t appeared t o be t r a n s f o r m i n g from ovary t o t e s t i s . T r a n s i t i o n a l gonads c o n t a i n e d spermatogenic c r y p t s a d j a c e n t t o degenerating ova ( F i g u r e 11a & b ) . Although l a t e stage t r a n s i t i o n a l gonads are s i m i l a r t o t e s t e s , they are d i s t i n g u i s h e d from f u n c t i o n a l t e s t e s by the absence of f r e e 66 00 o CD 35 30 h 25 20 15 10 5 h 0 10 5 0 15 10 Females Transitionals j i i i—i ' i * i i i i ' ' Males 5 -Q n 1 1 1 1 1 i • 1 1 1 1 1 1 1 1 1 1 1 1 5 10 15 20 25 30 35 40 Standard length (cm) F i g u r e 10. Body s i z e d i s t r i b u t i o n o f males (N=104), t r a n s i t i o n a l s (N=12) and mature females (N=200). 67 F i g u r e 11. Photomicrographs of t r a n s v e r s e s e c t i o n s of t i l e f i s h gonads. Black bars g i v e s c a l e f o r each p a n e l , a. and b. T r a n s i t i o n a l gonads showing d e v e l o p i n g spermatogenic c r y p t s a d j a c e n t t o s e v e r a l degenerating ova. c. and d. Male t e s t e s showing sperm s i n u s e s c o n t a i n i n g spermatozoa, a t r e t i c ova i n c, and a narrow c a v i t y t h a t may be a remnant of the o v a r i a n lumen i n d. SC-spermatogenic c r y p t s , DO-degenerating ova, SS-sperm s i n u s e s , SZ-spermatozoa, OL-remnant of o v a r i a n lumen. 68 spermatozoa w i t h i n sperm s i n u s e s (see below). A t r e t i c , p r e v i t e l l e g e n i c ova were most pronounced i n t r a n s i t i o n a l gonads. However, t r a n s i t i o n a l specimens a l s o c o n t a i n e d degenerating ova t h a t appear t o have a t t a i n e d l a t e r stages of v i t e l l o g e n e s i s , s u g g e s t i n g t h a t these f i s h had f u n c t i o n e d p r e v i o u s l y as females. The s t r u c t u r e of a l l t e s t e s examined h i s t o l o g i c a l l y (N=79) a l s o suggests protogyny. A l l t e s t e s c o n t a i n e d s e v e r a l s i n u s e s a d j a c e n t t o the medial w a l l of the gonad and between i n t e r n a l membranes ( F i g u r e 11c & d ) . These s i n u s e s ran the l e n g t h of the gonad and always c o n t a i n e d f r e e spermatozoa. Sperm s i n u s e s of t h i s type are o f t e n c h a r a c t e r i s t i c of sex-changing s p e c i e s because they form as s e p a r a t i o n s i n t h i c k e n e d areas of the former o v a r i a n w a l l and membranes (Sadovy and Shapiro 1987). Many t e s t e s a l s o c o n t a i n e d degenerating ova, p a r t i c u l a r l y on the l a t e r a l edge of the gonad o p p o s i t e t o sperm s i n u s e s ( F i g u r e 11c). F i f t y - f o u r t e s t e s (68%) c o n t a i n e d a t r e t i c p r e v i t e l l o g e n i c ova and l a t e r - s t a g e y o l k y ova were e v i d e n t i n 33 specimens (42%). A few t e s t e s a l s o c o n t a i n e d a narrow membrane-lined c a v i t y t h a t may be a remnant of the o v a r i a n lumen ( F i g u r e l i d ) . T h i s c a v i t y was not apparent i n most t e s t e s however, perhaps because i t was occluded by densely packed spermatogenic t i s s u e s . B e h a v i o r a l sex change was observed i n one f i s h f o l l o w i n g the removal of a l l males from t h a t colony. By c o n t r a s t , i n a l l s i n g l e male removals, females d i d not change sex and resumed spawning w i t h a male t h a t moved t o encompass t h e i r t e r r i t o r i e s (Chapter 6). F o l l o w i n g removal of a l l males from a c o l o n y i n 1985, a l l females remained on the s i t e a t l e a s t u n t i l my d e p a r t u r e (15 d a y s ) . No b e h a v i o r a l evidence of sex change was 70 observed d u r i n g t h i s p e r i o d . In A p r i l 1986, one f i s h was i d e n t i f i e d as a s u r v i v o r from 1985 u s i n g d i s t i n c t i v e double t a g s c a r s t o g e t h e r w i t h r e c o r d s of her s p o t s . The other e i g h t tagged females were not p r e s e n t on the experimental s i t e o r i n ot h e r c o l o n i e s w i t h i n a t l e a s t a 100 m r a d i u s . The 1985 s u r v i v o r was observed t o c o u r t and spawn wi t h two s m a l l e r i n d i v i d u a l s t h a t had r e c r u i t e d d u r i n g my absence. D i s s e c t i o n r e v e a l e d t h a t both s m a l l e r f i s h were females and the 1985 s u r v i v o r was now a male. H i s t o l o g i c a l examination showed t h a t the gonads of t h i s f i s h were sma l l but f u n c t i o n a l t e s t e s c o n t a i n i n g a few a t r e t i c ova. The on l y o t h e r t i l e f i s h p r e s e n t on t h i s s i t e were two s m a l l j u v e n i l e r e c r u i t s . DISCUSSION T e r r i t o r i a l i t y and Harem Polygyny Female and male t i l e f i s h a g g r e s s i v e l y excluded a l l c o n s p e c i f i c s except t h e i r mate(s) from areas surrounding t h e i r home burrows. T h e r e f o r e , t i l e f i s h are t e r r i t o r i a l (sensu Brown, 1975; Wilson, 1975; reviewed by Searcy, 1986). I n d i v i d u a l s each foraged, spawned and burrowed w i t h i n these " a l l - p u r p o s e " t e r r i t o r i e s . The defense of t e r r i t o r i e s by each sex r e s u l t s i n a w e l l d e f i n e d s p a t i a l s t r u c t u r e w i t h i n c o l o n i e s . T e r r i t o r i e s o f females were adjacent t o female neighbors on one or more s i d e s . The l a r g e r t e r r i t o r i e s of spawning males were arranged as a mosaic, w i t h each t e r r i t o r y b e i n g superimposed over those of one or more females ( F i g u r e 7 ) . Males were l a r g e r and maintained s o c i a l dominance over the females w i t h i n t h e i r 71 t e r r i t o r i e s by means of a g g r e s s i o n . Spawning data confirmed almost e x c l u s i v e female mating f i d e l i t y w i t h dominant males. T h e r e f o r e , c o l o n i e s each c o n s i s t e d of adjacent s o c i a l and mating u n i t s t h a t are a p p r o p r i a t e l y r e f e r r e d t o as harems (sensu Robertson and Hoffman, 1977). Protogynous Hermaphroditism i n Sand T i l e f i s h H i s t o l o g i c a l and b e h a v i o r a l evidence i n d i c a t e t h a t M. p l u m i e r i i s capable of f u n c t i o n a l sex change from female t o male. Sperm s i n u s e s t h a t are d e r i v e d as s e p a r a t i o n s between o v a r i a n membranes, a t r e t i c ova i n t e s t e s , and o b s e r v a t i o n s on a known i n d i v i d u a l spawning f i r s t as a female and l a t e r as a male t o g e t h e r are s t r o n g evidence of protogyny (Sadovy and Shapiro, 1987). To my knowledge, these r e s u l t s are the f i r s t evidence of f u n c t i o n a l hermaphroditism i n the Malacanthidae. The presence o f a t l e a s t one m o r p h o l o g i c a l i n d i c a t i o n of gonad r e o r g a n i z a t i o n i n a l l t e s t e s suggests t h a t a l l male t i l e f i s h a re d e r i v e d through sex change (monandry). Monandry i s common among s p e c i e s w i t h harem mating systems. Presumably sma l l males without t e r r i t o r i e s a re unable t o breed because l a r g e r sex-changed t e r r i t o r i a l males are a b l e t o monopolize a l l a v a i l a b l e females (Warner, 1984a). Male r e p r o d u c t i v e t a c t i c s o t h e r than e x c l u d i n g competitors from t e r r i t o r i e s o ccupied by female mates were not observed. Although my r e s u l t s show t h a t M. p l u m i e r i i s capable of f u n c t i o n a l protogynous sex r e v e r s a l , the f a c t o r s t h a t c o n t r o l the onset of sex change and the e v o l u t i o n a r y s i g n i f i c a n c e of when i n d i v i d u a l s t r a n s f o r m are not y e t c l e a r . Protogyny may 72 e v o l v e when l a r g e males are a b l e t o mate w i t h a d i s p r o p o r t i o n a t e l y h i g h number of the females i n l o c a l p o p u l a t i o n s . Under these c o n d i t i o n s , i n d i v i d u a l s may maximize t h e i r l i f e t i m e r e p r o d u c t i v e success by f u n c t i o n i n g as females when s m a l l , and then changing sex when they are l a r g e enough t o compete as males (the size-advantage h y p o t h e s i s , G h i s e l i n , 1969; Warner e t a l . , 1975). Among the b e s t support f o r the s i z e advantage h y p o t h e s i s are harem-forming s p e c i e s i n which sex change occurs a c c o r d i n g t o l i n e a r s o c i a l h i e r a r c h i e s t h a t are based on the r e l a t i v e s i z e of f i s h w i t h i n each mating u n i t (e.g., Robertson, 1972; Moyer and Nakazono, 1978; Hoffman e t a l . , 1985). In such s p e c i e s , l a r g e females r e p o r t e d l y change sex o n l y when the dominant male i s removed, and sex r e v e r s a l u s u a l l y occurs over a r e l a t i v e l y s h o r t time p e r i o d . There are a p p a r e n t l y no unmated "bachelor males" i n these s p e c i e s , and sex-changing f i s h s u f f e r few l o s t mating o p p o r t u n i t i e s d u r i n g the t r a n s f o r m a t i o n (Hoffman e t a l . , 1985) . T i l e f i s h d i f f e r from these harem-forming s p e c i e s . Female t i l e f i s h d i d not change sex i n response t o removal of one male. One female u l t i m a t e l y transformed f o l l o w i n g removal of a l l males from her colony. However, onl y l i m i t e d c o n c l u s i o n s can be drawn r e g a r d i n g the proximate cues t h a t t r i g g e r e d sex change i n t h i s i n s t a n c e . F i s h were not observed f o r e i g h t months d u r i n g which time a t l e a s t one female changed sex but e i g h t o t h e r s d i s a p p e a r e d f o r reasons unknown. No b e h a v i o r a l changes by any of these females were e v i d e n t d u r i n g the two week o b s e r v a t i o n 73 p e r i o d immediately f o l l o w i n g removals. These r e s u l t s suggest t h a t gonad r e o r g a n i z a t i o n i n t i l e f i s h may take l o n g e r than two weeks, i f i t was t r i g g e r e d i n t h i s female by removal of males. There i s a l s o no evidence t h a t female t i l e f i s h a re arranged i n s o c i a l h i e r a r c h i e s , w i t h i n harems or c o l o n i e s , t h a t determine the sequence of female sex change should i t sometimes occur i n response t o male removals. The outcome of s o c i a l i n t e r a c t i o n s among females was not determined by r e l a t i v e s i z e as i s r e p o r t e d f o r some o t h e r harem s p e c i e s (Hoffman, 1985). F i n a l l y , the presence i n a l l c o l o n i e s o f e i t h e r s m a l l t r a n s i t i o n a l f i s h or l a r g e sex-changed but unmated males i n d i c a t e s t h a t some i n d i v i d u a l s change sex without t h e r e b e i n g immediate o p p o r t u n i t i e s t o a c q u i r e females. F i f t e e n unmated t i l e f i s h males occupied t e r r i t o r i e s without r e s i d e n t females f o r 2 t o 4.5 months. These r e s u l t s suggest t h a t some female t i l e f i s h change sex but do not spawn as males f o r long p e r i o d s u n t i l a vacancy o c c u r s . S i m i l a r o b s e r v a t i o n s r e g a r d i n g the onset o f sex r e v e r s a l have been r e p o r t e d f o r ot h e r s p e c i e s w i t h harems ( C l a v i j o , 1982; Moyer and Z a i s e r , 1984; Aldenhoven, 1986; Shapiro, 1987a). Aldenhoven (1986) proposed a model f o r harem mating systems t h a t compares t h e , r e p r o d u c t i v e v a l u e of changing sex and becoming a b a c h e l o r male b e f o r e t h e r e i s an o p p o r t u n i t y t o a c q u i r e mates, w i t h t h a t o f remaining female u n t i l t h e r e i s an immediate male vacancy c r e a t e d by the death of a male. At c e r t a i n p o p u l a t i o n d e n s i t i e s , " e a r l y sex-changed b a c h e l o r male" and "remain female" phenotypes may e x i s t i n a frequency-74 dependent e q u i l i b r i u m t h a t i s e v o l u t i o n a r i l y s t a b l e (Aldenhoven, 1986). I f the chance of o b t a i n i n g a harem i s h i g h e r f o r i n d i v i d u a l s t h a t change sex b e f o r e a male d i e s than those i n d i v i d u a l s t h a t c ontinue t o spawn as females u n t i l a vacancy oc c u r s , than t h e r e may be s e l e c t i o n f o r some i n d i v i d u a l s t o change sex when they are r e l a t i v e l y s m a l l . P o t e n t i a l r e p r o d u c t i v e rewards f o r such b a c h e l o r males almost c e r t a i n l y would d i m i n i s h as they become more abundant i n l o c a l p o p u l a t i o n s . T h e r e f o r e , s e l e c t i o n may a l s o f a v o r o t h e r i n d i v i d u a l s t h a t remain female as long as male mates are p r e s e n t . S e v e r a l o b s e r v a t i o n s on M. p l u m i e r i are c o n s i s t e n t w i t h the h y p o t h e s i s t h a t some i n d i v i d u a l s change sex when they are r e l a t i v e l y s m a l l and do not mate u n t i l a male vacancy o c c u r s . Unmated males and/or t r a n s i t i o n a l i n d i v i d u a l s t h a t were s m a l l e r than nearby females were common i n t i l e f i s h c o l o n i e s . F o r t y -f o u r p e r c e n t (11 of 25) of experimental male removals r e s u l t e d i n an unmated male moving i n t o vacant harems (Chapter 6). A l s o , the disappearance of a s u b s t a n t i a l percentage of tagged f i s h , presumably due t o p r e d a t i o n (Chapter 4), suggests t h a t n a t u r a l v a c a n c i e s may occur f r e q u e n t l y enough t h a t the f u t u r e p o t e n t i a l f o r unmated males t o a c q u i r e harems may be s u f f i c i e n t l y h i g h t o f a v o r e a r l y sex change. Together, these r e s u l t s suggest t h a t a frequency-dependent balance between b a c h e l o r males t h a t changed sex e a r l y , and f i s h t h a t remain female u n l e s s male v a c a n c i e s are not f i l l e d , may be a t l e a s t p l a u s i b l e i n sand t i l e f i s h . 75 CHAPTER SUMMARY 1. Both females and males occupy a l l - p u r p o s e home ranges s u r r o u n d i n g t h e i r home burrows. Home range o v e r l a p among ad j a c e n t f i s h of the same sex i s low and i n d i v i d u a l s defend e x c l u s i v e use of much of t h e i r home range a g a i n s t a l l c o n s p e c i f i c s except mates ( i . e . , t e r r i t o r i a l i t y ) . 2. Areas defended by males o v e r l a p the t e r r i t o r i e s of up t o 6 females, and male t e r r i t o r y area i s p o s i t i v e l y c o r r e l a t e d w i t h the number of female r e s i d e n t s . 3. Males m a i n t a i n dominance over females w i t h i n t h e i r t e r r i t o r i e s by a g g r e s s i o n , i n c l u d i n g i n t e r v e n t i o n i n t o some female d i s p u t e s . 4. Females spawn p e l a g i c a l l y - d i s p e r s e d eggs as f r e q u e n t l y as every day. Each female spawns almost e x c l u s i v e l y w i t h the male whose defended area encompasses her t e r r i t o r y (harem polygyny). Some males have up t o s i x female r e s i d e n t s w i t h i n t h e i r t e r r i t o r i e s 5. M. p l u m i e r i i s capable of f u n c t i o n a l protogynous sex r e v e r s a l , however, sex change i s c o n t r o l l e d by f a c t o r s o t h e r than s i z e - r e l a t e d s o c i a l h i e r a r c h i e s w i t h i n harems or c o l o n i e s . 76 CHAPTER 6 THE FUNCTIONAL SIGNIFICANCE OF HAREM POLYGYNY INTRODUCTION Two hypotheses have been proposed t o e x p l a i n the e v o l u t i o n of harem polygynous mating systems l i k e t h a t o f M. p l u m i e r i . The r e s o u r c e defense h y p o t h e s i s proposes t h a t an uneven d i s t r i b u t i o n of c r i t i c a l r e s o u r c e s f o r females a l l o w s some males to monopolize more than one mate (Emlen and Oring, 1977). The female defense h y p o t h e s i s proposes t h a t males are a b l e t o c o n t r o l groups of mates d i r e c t l y because females aggregate f o r reasons t h a t are u n r e l a t e d t o the a c q u i s i t i o n of r e s o u r c e s necessary f o r r e p r o d u c t i o n , f o r example t o reduce the t h r e a t of p r e d a t i o n (Emlen and Oring, 1977). There are u s u a l l y obvious advantages t o males of o b t a i n i n g more than one mate. The e v o l u t i o n of harem polygyny, however, must a l s o depend on the consequences t o females of s h a r i n g a male and l i v i n g i n groups t h a t can be monopolized by a male. In s p e c i e s t h a t n u r t u r e o f f s p r i n g , the c o s t s t o females of mating i n a harem and l i v i n g c l o s e t o c o n s p e c i f i c s may i n c l u d e both reduced p a t e r n a l care and i n c r e a s e d c o m p e t i t i o n f o r r e s o u r c e s (Wittenberger, 1979). S e l e c t i o n should f a v o r females t h a t j o i n harems, p r o v i d e d t h a t these c o s t s are more than o f f s e t by compensating advantages. Advantages may i n v o l v e access e i t h e r t o a b e t t e r q u a l i t y male and/or r e s o u r c e s (Verner and Wilson, 1966; O r i a n s , 1969; Altmann e t a l . , 1977; Wittenberger, 1979), or a r e d u c t i o n i n p r e d a t i o n from group l i v i n g (Altmann e t a l . , 77 1977; Wittenberger, 1979). Harem mating systems have a l s o been documented i n marine f i s h e s o t h e r than M. p l u m i e r i t h a t spawn p l a n k t o n i c gametes (reviewed by Kuwamura 1984; Thresher 1984). O b v i o u s l y t h e r e i s no c o s t t o females a r i s i n g from a r e d u c t i o n i n p a t e r n a l c a r e i n such s p e c i e s . However, female defense of e x c l u s i v e t e r r i t o r i e s or a g g r e s s i o n toward consexuals t h a t occupy f i x e d but o v e r l a p p i n g home ranges (Robertson and Hoffman, 1977; Moyer and Nakazono, 1978; Stroud, 1981; C l a r k , 1983; Hoffman, 1985; Nemtzov, 1985; V i c t o r , 1987; B a i r d , 1988) suggests t h a t females may compete f o r r e s o u r c e s i n these systems. S i t e - s p e c i f i c i t y by females appears t o promote male m o n o p o l i z a t i o n of m u l t i p l e mates. Understanding f a c t o r s t h a t shape female s p a t i a l behavior, t h e r e f o r e , i s c e n t r a l t o the q u e s t i o n of whether males monopolize d a i l y spawnings w i t h m u l t i p l e mates through c o n t r o l of r e s o u r c e s , females, or both. The e v o l u t i o n of harems i n p e l a g i c a l l y - s p a w n i n g t r o p i c a l marine f i s h e s has been a t t r i b u t e d t o both male defense of r e s o u r c e s (Robertson and Hoffman, 1977), and t o d i r e c t defense of females (Hourigan, 1986; V i c t o r , 1987). In o t h e r s p e c i e s , t h i s i s s u e appears t o be u n r e s o l v e d (Moyer and Nakazono, 1978; Moyer, 1979; Kuwamura, 1984; Kobayashi, 1986). Few i f any s t u d i e s , however, have examined e m p i r i c a l l y the f a c t o r s t h a t i n f l u e n c e the l o c a t i o n and d i s t r i b u t i o n of females i n harem-type mating systems. I documented the t e r r i t o r i a l b e havior of females and males and the mating system of M. p l u m i e r i i n Chapter 5. The o b j e c t i v e of the p r e s e n t chapter i s t o i n v e s t i g a t e the i n f l u e n c e 78 of c o n s p e c i f i c s and re s o u r c e s on the l o c a t i o n s o f females and males t o examine the e v o l u t i o n a r y s i g n i f i c a n c e o f harem polygyny i n t i l e f i s h . The extent t o which female and male t i l e f i s h are a t t r a c t e d t o p o t e n t i a l mates, and t h a t the l o c a t i o n s o f i n d i v i d u a l s are r e s t r i c t e d by i n t r a s e x u a l c o m p e t i t i o n was examined i n a s e r i e s o f removal experiments. Whether or not females occupy and defend c e r t a i n l o c a t i o n s may a l s o be i n f l u e n c e d by the d i s t r i b u t i o n and abundance of food and oth e r l i m i t e d r e s o u r c e s (reviewed by Davies and Houston, 1984; Vehrencamp, and Bradbury, 1984). The s p a t i a l d i s t r i b u t i o n of food r e s o u r c e s and female f o r a g i n g was examined by o b s e r v a t i o n of f e e d i n g b e h a v i o r and q u a n t i t a t i v e assessment o f p o t e n t i a l i n v e r t e b r a t e prey i n s u r f a c e sediments. The importance t o females o f s p e c i f i c burrows was i n v e s t i g a t e d by r e c o r d i n g responses t o removal o f these s t r u c t u r e s . METHODS Techniques For F i s h Removal Experiments Experiments i n v o l v i n g removal of f i s h ( s i n g l y o r i n groups) were conducted t o examine the i n f l u e n c e o f c o n s p e c i f i c s on the l o c a t i o n s and beh a v i o r o f remaining f i s h . More than one t e s t was o f t e n conducted w i t h i n l a r g e c o l o n i e s . When m u l t i p l e t e s t s were performed, r e p l i c a t e s were begun no sooner than two weeks a f t e r p r e v i o u s t e s t s , w e l l a f t e r f i s h l o c a t i o n s had s t a b i l i z e d (see below). Responses t o removals were measured by d a i l y o b s e r v a t i o n s on a l l f i s h near experimental s i t e s f o r a minimum of two weeks (range = 2-8 weeks) b e f o r e and a f t e r each t e s t . A 79 two week minimum p e r i o d between m u l t i p l e t e s t s and f o r o b s e r v a t i o n of responses was adequate because changes i n l o c a t i o n s of a d j a c e n t f i s h o c c u r r e d w i t h i n two days (see R e s u l t s ) . Because t i l e f i s h occur on f l a t open s u b s t r a t e s and are each r e s t r i c t e d t o s p e c i f i c burrows and t e r r i t o r i e s , the l o c a t i o n s of i n d i v i d u a l s b e f o r e and a f t e r removals c o u l d be r e c o r d e d r e a d i l y . Most f i s h occupying t e r r i t o r i e s next t o removal s i t e s were tagged. Untagged f i s h were i d e n t i f i e d by n o t i n g unique spot p a t t e r n s . F i s h were removed e i t h e r by spear or by t r a p p i n g them i n burrows. The l o c a t i o n s of i n d i v i d u a l s were monitored f o r a t l e a s t two weeks p r i o r t o each removal t o c o n t r o l f o r the p o s s i b i l i t y o f spontaneous changes i n l o c a t i o n (pre-removal c o n t r o l s ) . For t e s t s i n v o l v i n g removal of one f i s h , a second c o n t r o l c o n s i s t e d of m o n i t o r i n g another s i m i l a r l y s i z e d f i s h o f the same sex d u r i n g the p e r i o d when the t e s t f i s h was removed (non-removal c o n t r o l s ) . Non-removal c o n t r o l s r e s i d e d i n the same colony, but on a t e r r i t o r y not adjacent t o t h a t of the removed f i s h . Observed and p r e d i c t e d f r e q u e n c i e s under n u l l hypotheses f o r each type of experiment (see below) were compared u s i n g Binomial t e s t s . Responses t o removals were compared t o c o n t r o l s w i t h the Chi-squared s t a t i s t i c . SPECIFIC TESTS F a c t o r s I n f l u e n c i n g the D i s t r i b u t i o n of Females A. I n t r a s e x u a l Competition Defense of e x c l u s i v e t e r r i t o r i e s suggests t h a t i n t r a s e x u a l 80 c o m p e t i t i o n may r e s t r i c t use of space by females. To examine t h i s h y p o t h e s i s , i n d i v i d u a l females (N=38) were removed from t e r r i t o r i e s t h a t were adjacent t o female neighbors on s e v e r a l s i d e s . Assuming t h a t males do not r e s t r i c t female m o b i l i t y (see R e s u l t s ) , and i f females do not compete f o r space, then each f i s h s h ould occupy a p r e f e r r e d l o c a t i o n and removal o f one female should not r e s u l t i n s p a t i a l s h i f t s by her neighbors. A l t e r n a t i v e l y , i f c o m p e t i t i o n r e s t r i c t s the l o c a t i o n o r s i z e of female t e r r i t o r i e s , removal of one female should r e s u l t i n s p a t i a l changes by adjacent f i s h . B. Males Movement by females may a l s o be r e s t r i c t e d by dominant males. Removal of one female o f t e n r e s u l t e d i n movement by female neighbors (see R e s u l t s ) . T h e r e f o r e , female removals c o u l d a l s o be used t o t e s t whether males are not a b l e t o c o n t r o l movement by t h e i r mates. I f females move t o t e r r i t o r i e s defended by o t h e r males when a female neighbor i s removed, then the h y p o t h e s i s of male c o n t r o l can be r e j e c t e d . Females may a l s o choose l o c a t i o n s on the b a s i s of p r o x i m i t y t o male mates. I f t h i s i s t r u e , then females should attempt t o move c l o s e r t o a d j a c e n t males when the mates of these females are removed. Neighboring females may r e s i s t encroachment by females attempting t o move c l o s e r t o o t h e r mates. However, females c o u l d move c l o s e r t o adjacent males by d i g g i n g new burrows or by occupying unused burrows c l o s e r t o the edges of t h e i r e x i s t i n g t e r r i t o r i e s . The p o s s i b i l i t y t h a t females choose l o c a t i o n s near males was examined by comparing the burrow 81 l o c a t i o n s o f females (N=54) b e f o r e and a f t e r removal of t h e i r mates (N=2 9). The i d e n t i t y of males w i t h which females resumed spawning was determined i n 25 t e s t s . C. Burrows E x c l u s i v e use of s p e c i f i c home burrows, even though unused burrows are abundant, suggests a s t r o n g p r e f e r e n c e f o r c e r t a i n l o c a t i o n s over o t h e r p o t e n t i a l s i t e s . The i n f l u e n c e o f home burrows on female l o c a t i o n was examined by removing the s t r u c t u r e s o c cupied by " t e s t " females (N=12) whose t e r r i t o r i e s c o n t a i n e d a t l e a s t one unused burrow. Burrow removals i n v o l v e d d i s m a n t l i n g these s t r u c t u r e s and moving a l l m a t e r i a l s away from the t e s t s u b j e c t ' s t e r r i t o r y . Because o c c u p a t i o n of burrows on ad j a c e n t t e r r i t o r i e s would probably be r e s i s t e d by neighbors, t e s t females must e i t h e r 1) excavate ot h e r burrows w i t h i n t h e i r t e r r i t o r i e s , 2) r e c o n s t r u c t t h e i r o r i g i n a l burrows, or, 3) do without burrows. R e f u r b i s h i n g unused burrows should r e q u i r e l e s s time and energy than r e c o n s t r u c t i n g removed burrows. T h e r e f o r e , females were expected t o r e f u r b i s h unused refuges u n l e s s o r i g i n a l burrow s i t e s are p r e f e r r e d . D. Food Resources Even i f females p r e f e r p a r t i c u l a r burrow s i t e s , t e r r i t o r i e s o f t i l e f i s h females are much l a r g e r (X area = 140 m2, Table 2) than necessary t o ensure access t o burrows alone. The s i z e o f female t e r r i t o r i e s suggests t h a t females may a l s o defend other r e s o u r c e s , such as food. Rates of egg p r o d u c t i o n and growth are o f t e n i n f l u e n c e d by food i n t a k e i n female f i s h e s ( S c o t t , 1962; Bagenal, 1969; Wootton, 1973; 1977; H i s l o p , e t a l . 1978). 82 Furthermore, p r o d u c t i o n of eggs each day almost c e r t a i n l y c a r r i e s h i g h e n e r g e t i c c o s t s (Hoffman, 1983). Thus, i f the d i s t r i b u t i o n of prey i s such t h a t defense of a food supply i s f e a s i b l e , female t i l e f i s h may defend t e r r i t o r i e s t o ensure access t o food r e s o u r c e s near burrows. To estimate the d i s t r i b u t i o n of the b e n t h i c i n v e r t e b r a t e s found i n t i l e f i s h stomachs (Chapter 5), samples of s u r f a c e sediment were c o l l e c t e d a t pre-determined g r i d p o i n t s spaced evenly (10 m apart) throughout f i v e c o l o n i e s . Each sample was c o l l e c t e d by scooping 2.5 l i t e r s of sediment from a quadrat (0.25 m2) t o a depth of 5-7 cm. Organisms were s i f t e d w i t h a 2 mm mesh scree n and p r e s e r v e d i n 10% s e a w a t e r - f o r m a l i n . I n v e r t e b r a t e s were l a t e r b l o t t e d dry and weighed t o the n e a r e s t 0.01 g. Organisms were weighed whole, except f o r mollusks, from which the s h e l l was removed. The s p a t i a l d i s t r i b u t i o n of i n v e r t e b r a t e s w i t h i n c o l o n i e s was analyzed by c a l c u l a t i n g the v a r i a n c e t o mean r a t i o of biomass per sample. S p a t i a l d i s t r i b u t i o n of f o r a g i n g was a l s o a n alyzed f o r 54 females. The l o c a t i o n s of a l l b i t e s were recorded on t e r r i t o r y maps. A g r i d of quadrats was then superimposed haphazardly over female t e r r i t o r y maps and the v a r i a n c e t o mean r a t i o of the number o f b i t e s t h a t o c c u r r e d i n each quadrat was c a l c u l a t e d . A quadrat area was chosen f o r each f i s h so t h a t the t o t a l number of b i t e s t a l l i e d , d i v i d e d by the t o t a l number of quadrats i n ' each t e r r i t o r y was approximately 1.0. S c a l i n g of quadrat area t o the frequency of b i t e s a voids b i a s towards or a g a i n s t a clumped d i s t r i b u t i o n (see s i m i l a r l y , Kramer and Graham, 1976; 83 B a i r d , 1983), so long as quadrats are l a r g e enough t o i n c l u d e numerous b i t e s should they be co n c e n t r a t e d . Quadrats ranged i n s i z e from 1-2 m which were s u f f i c i e n t l y l a r g e t o i n c l u d e numerous b i t e s . I n f l u e n c e of I n t r a s e x u a l Competition and Mates on the  D i s t r i b u t i o n o f Males A c o r r e l a t i o n between male t e r r i t o r y area and harem s i z e , s p a t i a l o v e r l a p of male t e r r i t o r i e s w i t h those o f mates, and a h i g h degree of female spawning f i d e l i t y w i t h the n e a r e s t male (Chapter 5) a l l suggested t h a t male t i l e f i s h compete f o r t e r r i t o r i e s t o monopolize mates. The ext e n t t o which males defend t e r r i t o r i e s t o monopolize females was examined by removing i n d i v i d u a l males (N=29). I f males compete f o r areas occupied by females, then removal of one harem-owner should e l i c i t attempts by one or more adjacent males t o c o n t r o l the vacant t e r r i t o r y , and t o monopolize spawnings wi t h the mates of the removed male. A l s o , d i f f e r e n t responses t o male removals were expected from unmated males and those w i t h harems. Unmated males should abandon t h e i r l o c a t i o n s and occupy the removed m a l e 1 s t e r r i t o r y because they stand t o l o s e o n l y t h e i r c u r r e n t burrows and f e e d i n g areas. By r e l o c a t i n g , these males may g a i n mating o p p o r t u n i t i e s as w e l l as new burrows and f e e d i n g areas. In c o n t r a s t , mated males were expected t o expand r a t h e r than r e l o c a t e t h e i r c u r r e n t t e r r i t o r i e s because the l a t t e r would i n v o l v e l o s i n g mates. The mating s t a t u s ( i . e . , unmated, or mated, and most cases the number of mates) of adjacent males was determined by 84 spawning o b s e r v a t i o n s b e f o r e and a f t e r 2 5 male removal t e s t s . In s i x male removals, r a t e s o f i n t r a - and i n t e r s e x u a l a g g r e s s i o n by a d j a c e n t males t h a t s h i f t e d l o c a t i o n s were reco r d e d f o r two days b e f o r e and a f t e r removals. To examine the extent t h a t t i l e f i s h males defend females independently o f the re s o u r c e s w i t h i n female t e r r i t o r i e s , a l l females were removed from 13 harems (harem removals). I f males defend females independently from r e s o u r c e s , they might abandon t h e i r c u r r e n t t e r r i t o r i e s and move toward o t h e r females when t h e i r mates are removed. Even though i n t r a s e x u a l c o m p e t i t i o n p r o b a b l y r e s t r i c t s male m o b i l i t y , the occurrence o f e x t r a -t e r r i t o r i a l f o r a y s by males (Chapter 5) suggested t h a t some movement w i t h i n c o l o n i e s may be p o s s i b l e by males. A l t e r n a t i v e l y , i f males defend one or more r e s o u r c e s important t o females, they would not be expected t o abandon t e r r i t o r i e s when t h e i r mates are removed. RESULTS F a c t o r s I n f l u e n c i n g the D i s t r i b u t i o n of Females A. I n f l u e n c e o f I n t r a s e x u a l Competition T h i r t y - t w o o f 38 (p<0.01, Binomial t e s t ) female removals r e s u l t e d i n r a p i d s p a t i a l changes by one adjacent female (Figure 12). C o n t r o l females never changed t h e i r t e r r i t o r i e s . Two types o f changes f o l l o w e d removals. In 25 female removal t e s t s , an a d j a c e n t female abandoned her burrow and occupied the removed female's burrow and t e r r i t o r y w i t h i n 2 days. In seven t e s t s , an adja c e n t female expanded her e x i s t i n g t e r r i t o r y t o i n c l u d e the 85 00 CO CD o CD _Q 4 0 3 0 2 0 1 0 0 ^ Changed or expanded territories Changed territories and males Non— Pre-removal Female removal T r e a t m e n t F i g u r e 12. Frequency of t e s t s t h a t one female changed t e r r i t o r i e s and male mates without female removals (non-removal c o n t r o l ) , b e f o r e a female was removed (pre-removal c o n t r o l , or f o l l o w i n g female removals. 86 area used by the removed occupant, but d i d not change her burrow. In s i x t e s t s , no females r e l o c a t e d o r expanded t h e i r t e r r i t o r i e s i n t o the vacant space. B. The I n f l u e n c e o f Males on the D i s t r i b u t i o n o f Females A female r e l o c a t e d i n t o the t e r r i t o r y o f another male i n 15 of 38 (p<0.01) female removal t e s t s , whereas female c o n t r o l s d i d not move (Fi g u r e 12). By c o n t r a s t , none of the 54 females changed the l o c a t i o n o f t h e i r burrows a f t e r removal o f t h e i r c u r r e n t mates. W i t h i n two days an adjacent male occupied the removed male's t e r r i t o r y and began spawning w i t h r e s i d e n t females (see below). C. I n f l u e n c e o f Burrows No females moved i n response t o removal o f t h e i r burrows. W i t h i n 3-6 h of burrow removals, each female had excavated a temporary refuge t h a t was l i t t l e more than a h o l e dug out underneath a c o r a l rock l e s s than 5 m away from the o r i g i n a l s i t e . Rather than improving the temporary burrow or e x c a v a t i n g unused mounds, females re-excavated a cavern w i t h i n 0.5 m of the entrance o f the removed burrow. T e s t females then gathered c o r a l r o c k - r u b b l e from throughout t h e i r t e r r i t o r i e s and c o n s t r u c t e d a new r o o f and entrance over the next two t o f o u r days. The r e c o n s t r u c t e d burrow was then occupied, and the temporary r e f u g e abandoned. These r e s u l t s i n d i c a t e a s t r o n g p r e f e r e n c e f o r the home burrowing s i t e over o t h e r p o t e n t i a l s i t e s . 87 D. D i s t r i b u t i o n and Abundance of Food The i n v e r t e b r a t e s i n sediment samples were the same as those found i n t i l e f i s h guts. Samples c o n t a i n e d an average of 1.91 g of i n v e r t e b r a t e biomass (N=103, SE=0.14), and a minimum of 0.5 g was found i n 91.3% of samples. W i t h i n c o l o n y v a r i a n c e t o mean r a t i o s ranged from 0.11 t o 1.31 (Table 5). None of these were s t a t i s t i c a l l y g r e a t e r than 1.0, i n d i c a t i n g t h a t p o t e n t i a l prey were not h i g h l y c o n c e n t r a t e d w i t h i n a few areas o f these c o l o n i e s . F o r a g i n g b i t e s were s p a t i a l l y clumped (p<0.05) w i t h i n the t e r r i t o r i e s of o n l y 2 of 54 females, which i s not d i f f e r e n t from t h a t expected by chance. D i s t r i b u t i o n of Males A. I n f l u e n c e of I n t r a s e x u a l Competition and Females Removal of one male r e s u l t e d i n r a p i d s p a t i a l changes by one or more adj a c e n t males i n a l l 29 t e s t s ( F i g u r e 13). In c o n t r a s t , o n l y one c o n t r o l male r e l o c a t e d h i s t e r r i t o r y spontaneously. W i t h i n 1-3 h of male removals, one or more ad j a c e n t males began t o i n t r u d e f r e q u e n t l y onto the t e r r i t o r y of the removed f i s h . W i t h i n two days, one of these males had s h i f t e d h i s o r i g i n a l t e r r i t o r y t o occupy p a r t or a l l of the removed male's former t e r r i t o r y . During t h i s p e r i o d , the frequency of a g g r e s s i v e i n t e r a c t i o n s between the males t h a t moved and o t h e r adjacent males t h a t d i d not move was much more fr e q u e n t than b e f o r e the m a n i p u l a t i o n ( F i g u r e 14). In 21 t e s t s , the male t h a t changed h i s t e r r i t o r y abandoned h i s c u r r e n t burrow and t e r r i t o r y and moved i n t o t h a t f o r m e r l y occupied by the removed male. A male expanded h i s e x i s t i n g t e r r i t o r y t o i n c l u d e 88 T a b l e 5. Mean prey biomass/sediment sample c o l l e c t e d from f i v e sand t i l e f i s h c o l o n i e s . Colony S i t e Reef Slope Channel C D E G Number of samples 47 10 10 21 15 X 1.82 3 . 06 2 . 08 1.50 1.96 S 2 2 . 39 3.82 0.22 1. 00 0.79 s 2 /x 1.31 1.25 0.11 0.67 0.40 t 1.49 0. 53 1.89 1. 04 1.59 p NS NS NS NS NS p i s the p r o b a b i l i t y t h a t t - c a l c u l a t e d i s s t a t i s t i c a l l y g r e a t e r than 1.0. 89 3 0 Non— P r e - Male removal removal T r e a t m e n t F i g u r e 13. Frequency of t e s t s t h a t males changed t e r r i t o r i e s w ithout male removals (non-removal c o n t r o l s ) , b e f o r e a male was removed (pre-removal c o n t r o l ) , or f o l l o w i n g male removals. 90 CO c o CJ o CD -+-> c 6 . 0 5 . 0 4 . 0 3 . 0 2 . 0 1 . 0 0 . 0 I I Pre—removal v//\ Post—removal 6 . 0 5 . 0 4 . 0 3 . 0 2 . 0 1 . 0 0 . 0 _CD D E CD CO c o o D 0 c I n t ra sexua l In ter sexua l F i g u r e 14. Rates (X ± SEM) of i n t r a - and i n t e r s e x u a l a g g r e s s i o n i n males t h a t changed l o c a t i o n s b e f o r e and a f t e r removal of one male. I n t r a s e x u a l r a t e s are bouts/h, i n t e r s e x u a l r a t e s are bouts/female/h. 91 most of the space f o r m e r l y occupied by the removed male, without abandonment o f h i s o r i g i n a l burrow and t e r r i t o r y i n seven t e s t s . i In one i n s t a n c e of expansion, the t e r r i t o r y o f the removed male was d i v i d e d by two adjacent males, n e i t h e r of which occupied the removed male's burrow. The responses of unmated males d i f f e r e d (p<0.01) from those o f mated males (F i g u r e 15). In a l l 11 t e s t s where an unmated male changed h i s t e r r i t o r y , the unmated male abandoned h i s burrow and t e r r i t o r y and r e l o c a t e d t o t h a t o f the removed male. By c o n t r a s t , when a mated male changed h i s t e r r i t o r y , i n n i n e of 14 t e s t s these males expanded t h e i r t e r r i t o r i e s but a l s o r e t a i n e d t h e i r o r i g i n a l t e r r i t o r y and burrow. Of the f i v e mated males t h a t r e l o c a t e d , i n t h r e e i n s t a n c e s the move i n c r e a s e d the harem s i z e o f the male t h a t moved. In one case, the number of mates remained the same. The o r i g i n a l harem s i z e o f the ot h e r male was not known. Males t h a t moved i n t o new t e r r i t o r i e s chased and a t t a c k e d the former mates of removed males. These i n t e r a c t i o n s o c c u r r e d much more f r e q u e n t l y (t=6.55, p<0.01) than those between removed males and these same females, p r i o r t o removals ( F i g u r e 14). Reproductive a c t i v i t y was u s u a l l y d i s r u p t e d d u r i n g the f i r s t spawning p e r i o d a f t e r removals by a g g r e s s i o n among males, and of males w i t h females. However, spawning resumed w i t h i n two days i n a l l o f these t e s t s . I n v a r i a b l y , females began spawning wi t h the male t h a t had expanded or moved, h i s t e r r i t o r y t o encompass t h e i r t e r r i t o r i e s . 92 00 00 CD O CD 1 5 r 10 0 i i expanded v//\ relocated o Mated U n m a t e d Male mating status F i g u r e 15. E f f e c t s of male mating s t a t u s on responses t o male removals. Hatched bars are t e s t s where ad j a c e n t males abandoned t h e i r c u r r e n t burrows and r e l o c a t e d t h e i r t e r r i t o r i e s t o monopolize new mates. Open bars are t e s t s where males expanded t h e i r e x i s t i n g t e r r i t o r i e s . 93 B. E f f e c t s of Removing Harems In s i x harem removals, a t l e a s t one s m a l l e r i n d i v i d u a l (presumably a female or j u v e n i l e ) moved i n t o a burrow and space f o r m e r l y o c cupied by removed females w i t h i n two days. In seven t e s t s no f i s h had r e c r u i t e d onto the vacant t e r r i t o r i e s 2-8 weeks a f t e r removal of the females. Males d i d not change t h e i r l o c a t i o n s i n any of the 13 t e s t s . DISCUSSION B e n e f i t s and Costs of Harem Formation t o Males One b e n e f i c i a l consequence of g r o u p - l i v i n g t o some t i l e f i s h males i s t h a t they are a b l e t o monopolize m u l t i p l e mates. R e s u l t s of male removals c o n f i r m t h a t male c o m p e t i t i o n f o r t e r r i t o r i e s i s r e l a t e d t o mate a c q u i s i t i o n . The presence of unmated males o u t s i d e of areas occupied by females i n d i c a t e s t h a t c o m p e t i t i o n excludes some males from access t o females. As expected, unmated males i n c r e a s e d t h e i r mating success by abandoning burrows and moving t o t e r r i t o r i e s c o n t a i n i n g females when these became a v a i l a b l e . Mated males, i n c o n t r a s t , more o f t e n expanded t e r r i t o r i e s t o i n c l u d e new females. I t i s noteworthy t h a t i n the few t e s t s i n which mated males abandoned t e r r i t o r i e s , t hese f i s h had o n l y one mate and they u s u a l l y i n c r e a s e d the s i z e s of t h e i r harems by moving. A r o l e of male a g g r e s s i o n i n e s t a b l i s h i n g mating r e l a t i o n s h i p s w i t h new females i s i n d i c a t e d by the marked i n c r e a s e of male i n t e r a c t i o n s w i t h the females r e s i d i n g i n r e c e n t l y annexed areas. Perhaps d u r i n g e x t r a - t e r r i t o r i a l f o r a y s (Chapter 5) males assess the number and 94 l o c a t i o n o f p o t e n t i a l mates and competitor males i n adj a c e n t harems. The p o t e n t i a l f o r i n c r e a s i n g mating success, i n r e l a t i o n t o the time and energy r e q u i r e d t o d r i v e o f f male com p e t i t o r s , may i n f l u e n c e whether or not males expand or r e l o c a t e when v a c a n c i e s r e s u l t from n a t u r a l p r e d a t i o n events. Harem ownership almost c e r t a i n l y c a r r i e s c o s t s . Continued defense o f t e r r i t o r i e s when a l l females had been removed and no replacements had r e c r u i t e d suggests t h a t males a c q u i r e mates by defe n d i n g female t e r r i t o r i e s as w e l l as females. The c o s t s o f harem ownership, t h e r e f o r e , are probably s i m i l a r t o those of t e r r i t o r y defense. E n e r g e t i c and temporal c o s t s , and p r e d a t i o n r i s k a s s o c i a t e d w i t h p a t r o l l i n g t e r r i t o r i e s may i n c r e a s e w i t h the s i z e o f defended areas (Hixon, 1980; 1987; Schoener, 1983). Because each female occupies a non-overlapping space, male t e r r i t o r y area i n c r e a s e s w i t h the s i z e o f t i l e f i s h harems (Chapter 5 ) . I n c r e a s i n g c o s t s t o males of defending space t o accommodate a d d i t i o n a l females, t h e r e f o r e , may be one f a c t o r t h a t l i m i t s harem s i z e i n M. p l u m i e r i . D i s t r i b u t i o n o f Females The f a i l u r e of females t o r e l o c a t e when t h e i r mates were removed suggests t h a t females do not choose a l o c a t i o n s o l e l y on the b a s i s o f p r o x i m i t y t o males. A l s o , even though females are sub o r d i n a t e t o males (Chapter 5), males do not prevent movement by females when v a c a n c i e s occur. I f i t were f e a s i b l e f o r males t o r e s t r i c t the l o c a t i o n o f mates through a g g r e s s i o n , males should not t o l e r a t e departures from t h e i r harems. S i n g l e female removal t e s t s i n d i c a t e t h a t female t i l e f i s h 95 compete f o r space, and t h a t c o m p e t i t i o n l i m i t s female movement w i t h i n c o l o n i e s . That c o m p e t i t i o n f o r c e s some f i s h t o occupy l e s s - p r e f e r r e d areas i s suggested by the r a p i d i t y w i t h which females r e l o c a t e d . T e r r i t o r y expansion shows t h a t c o m p e t i t i o n r e s t r i c t s the s i z e of areas defended by some females. Whether females r e l o c a t e d , expanded, or d i d not change t h e i r t e r r i t o r i e s was not r e l a t e d t o t h e i r a b s o l u t e o r r e l a t i v e body s i z e , o r t o the s i z e o f t h e i r t e r r i t o r i e s p r i o r t o removals. Perhaps q u a l i t a t i v e a s p e c t s of the re s o u r c e s o r males on vacant t e r r i t o r i e s i n f l u e n c e whether or not adj a c e n t females change t e r r i t o r i e s f o l l o w i n g removals. F u r t h e r e x p e r i m e n t a t i o n i s r e q u i r e d t o e v a l u a t e the r e l a t i v e importance of such f a c t o r s . The r a p i d r e c o n s t r u c t i o n o f removed burrows s t r o n g l y suggests t h a t refuges a t f a m i l i a r s i t e s are v a l u a b l e r e s o u r c e s t o females. C l i f t o n and Hunter (1972) a l s o found t h a t , not onl y d i d t i l e f i s h r e b u i l d p a r t i a l l y disassembled burrows, but t h a t f i s h i n c o r p o r a t e d many of the same c o r a l fragments d u r i n g r e c o n s t r u c t i o n . I n d i v i d u a l s o f both sexes i n v e s t c o n s i d e r a b l e time and energy m a i n t a i n i n g home burrows (Chapter 3) which serve as the primary refuges from p r e d a t o r y a t t a c k s (Chapter 4 ) . T h e r e f o r e , the c o s t o f not having immediate access t o home refu g e s when a t t a c k e d i s probably h i g h . E x c l u s i v e use and maintenance of one s i t e should ensure t h a t i t be unoccupied and i n s u i t a b l e c o n d i t i o n when needed. Under such c o n d i t i o n s , defense and maintenance of one burrow i s probably advantageous, even when unoccupied burrows are not l i m i t i n g . Defense of e x c l u s i v e f e e d i n g t e r r i t o r i e s i s f e a s i b l e when; 1) food i s moderately d i s p e r s e d r a t h e r than h i g h l y c o n c e n t r a t e d , 96 and 2) food i s renewed r a p i d l y enough t h a t f o r a g i n g does not q u i c k l y d e p l e t e the supply (Horn, 1968; Jarman, 1974; H o l l d o b l e r and Lumsden, 1980; Davies and Houston, 1984). S e l e c t i o n may f a v o r defense o f e x c l u s i v e f e e d i n g t e r r i t o r i e s p a r t i c u l a r l y when i n d i v i d u a l s are r e s t r i c t e d t o home s i t e s (Waser and Wiley, 1979; Carpenter 1987; Hart 1987) such as burrows. Feeding experiments demonstrate t h a t food i n t a k e l i m i t s investment i n both r e p r o d u c t i o n and growth i n t i l e f i s h females. Female t e r r i t o r i a l i t y would ensure access t o a food supply without r i s k i n g f o r a g i n g t r i p s d i s t a n t from home r e f u g e s . F a m i l i a r i t y w i t h a p a r t i c u l a r area may a l s o enhance e f f i c i e n t prey d e t e c t i o n w h i l e s t i l l p e r m i t t i n g a h i g h l e v e l o f v i g i l a n c e f o r p o t e n t i a l p r e d a t o r s . Sampling i n d i c a t e d a random or even d i s t r i b u t i o n of prey organisms. A l s o , t i l e f i s h prey are probably renewed w i t h i n l o c a l areas by r e c r u i t m e n t o f p l a n k t o n i c i n v e r t e b r a t e l a r v a e . Dependence on home burrows, food l i m i t a t i o n o f r e p r o d u c t i o n and growth, and a randomly d i s t r i b u t e d but renewable food resource t o g e t h e r are c o n d i t i o n s under which s e l e c t i o n l i k e l y f a v o r s defense o f f e e d i n g t e r r i t o r i e s by t i l e f i s h females. Costs and B e n e f i t s of Harem-Formation t o Females Because t i l e f i s h are c o l o n i a l , m o n o p o l i z a t i o n o f harems might be f e a s i b l e f o r males even i f t h e r e i s no net advantage of t h i s mating system t o females. Costs of i n t r a s e x u a l c o m p e t i t i o n among female t i l e f i s h , however, are not so h i g h as t o prevent o c c u p a t i o n o f adj a c e n t t e r r i t o r i e s such t h a t some males are a b l e t o defend harems. S e v e r a l f a c t o r s may moderate the i n t e n s i t y o f a g g r e s s i o n among t i l e f i s h females. Prolonged i n t r u s i o n s i n t o 97 a d j a c e n t t e r r i t o r i e s might be s e l e c t e d a g a i n s t because the r i s k o f p r e d a t i o n i n c r e a s e s away from home burrows, and a g g r e s s i o n p r o b a b l y c a r r i e s o t h e r c o s t s such as time and energy ex p e n d i t u r e s and r i s k o f i n j u r y . The nature o f female t e r r i t o r i a l d i s p u t e s (Chapter 5) supports t h i s i n t e r p r e t a t i o n . Although n e i g h b o r i n g females i n t e r a c t f r e q u e n t l y , d i s p u t e s u s u a l l y take p l a c e along a d j o i n i n g t e r r i t o r y borders and prolonged e x c u r s i o n s by females i n t o a d j a c e n t t e r r i t o r i e s are avoided. A l s o , t i l e f i s h males o f t e n a t t a c k female mates when they f i g h t one another, t e r m i n a t i n g these d i s p u t e s (Chapter 5). Such male i n t e r v e n t i o n i n t o female d i s p u t e s may prevent female a g g r e s s i o n from e s c a l a t i n g t o such h i g h l e v e l s t h a t c o m p e t i t i o n c o s t s exceed p o t e n t i a l a n t i - p r e d a t o r advantages d e r i v e d by females from s e t t l i n g near t o c o n s p e c i f i c s . I t has been suggested f o r protogynous f i s h e s t h a t females may a l s o remain i n harems t o improve t h e i r f u t u r e r e p r o d u c t i v e p o t e n t i a l . By remaining w i t h i n harems and growing l a r g e , females may enhance t h e i r s o c i a l rank w i t h i n mating groups, thereby promoting t h e i r chances of changing sex should the dominant male d i e (Robertson and Hoffman, 1977). Observations on t i l e f i s h are not c o n s i s t e n t w i t h t h i s h y p o t h e s i s . F i r s t , t h e r e i s no i n d i c a t i o n t h a t female t i l e f i s h e x h i b i t s o c i a l h i e r a r c h i e s l i k e those o f some harem s p e c i e s (e.g., Robertson and Hoffman, 1977; Hoffman, 1985). More i m p o r t a n t l y , female t i l e f i s h d i d not change sex when harem-owners were removed. Harem formation may be a s u c c e s s f u l r e p r o d u c t i v e t a c t i c f o r females, however, when m a i n t a i n i n g c l o s e p r o x i m i t y t o home 98 burrows i s r e q u i r e d f o r p r e d a t o r avoidance. M o r t a l i t y of p l a n k t o n i c embryos, l i k e those of t i l e f i s h , i s h i g h and u n p r e d i c t a b l e (Barlow, 1981; V i c t o r , 1983; Doherty, e t a l . 1985). T h e r e f o r e , s e l e c t i o n p robably f a v o r s t i l e f i s h females t h a t spawn r e g u l a r l y and f r e q u e n t l y such t h a t m o r t a l i t y r i s k s a re spread over numerous batches of o f f s p r i n g (Strathman 1974; L e v i n t o n 1982). Because females each defend a r e f u g e and t e r r i t o r y t h a t c o n t a i n s both food r e s o u r c e s and a mating s i t e (Chapter 5), they should o n l y f u r t h e r r e q u i r e access t o a male t o spawn dependably. Swimming throughout c o l o n i e s t o s e l e c t from a v a i l a b l e males would probably i n c r e a s e both p r e d a t i o n r i s k and a g g r e s s i o n from female neighbors, d i m i n i s h i n g p o t e n t i a l advantages gained by choosing " s u p e r i o r " males. Moreover, because males l o c a t e t h e i r t e r r i t o r i e s where females r e s i d e , r e l i a b l e spawning o p p o r t u n i t i e s near t o burrows are assured f o r females. The a b i l i t y of males t o exclude competitors should be a r e l i a b l e i n d i c a t o r t o females of male q u a l i t y . A l s o , s h a r i n g a male should not be c o s t l y t o females, p r o v i d e d t h a t male f e c u n d i t y i s s u f f i c i e n t t o perform " f e r t i l e " spawnings w i t h a l l harem members. Under these c o n d i t i o n s , s e l e c t i o n p robably f a v o r s females t h a t spawn with whichever male occ u p i e s a t e r r i t o r y t h a t surrounds t h e i r home burrow and f e e d i n g space, r e g a r d l e s s of whether or not t h a t male a l s o spawns w i t h o t h e r females. 99 CHAPTER SUMMARY 1. Females each defend a home burrow and surrounding feeding space. 2. Intrasexual competition r e s t r i c t s the location and amount of space occupied by some females. Males did not r e s t r i c t the location of females, and males did not abandon t h e i r t e r r i t o r i e s when t h e i r mates were removed. 3. Females spawn with whichever male occupies t h e i r feeding area, rather than locating t e r r i t o r i e s to be near to males. 4. Net costs of intrasexual competition to females are not so great as to prevent t h e i r j o i n i n g colonies, and settlement near conspecifics may promote dependable spawning opportunities for females near to t h e i r burrows. 5. Male t i l e f i s h compete for t e r r i t o r i e s to acquire mates, and colony formation promotes monopolization of more than one mate by some males. 100 CHAPTER 7 HABITAT DIFFERENCES IN POPULATION DENSITY AND REPRODUCTIVE EFFORT INTRODUCTION The a d a p t i v e s i g n i f i c a n c e of the d i s t r i b u t i o n and behavior of i n d i v i d u a l s of the same s p e c i e s i n d i f f e r e n t h a b i t a t s i s p o o r l y s t u d i e d , e s p e c i a l l y i n t r o p i c a l marine f i s h e s . Two models have been proposed t o examine the i n f l u e n c e o f reso u r c e s and c o s t s o f t e r r i t o r y defense on the s e l e c t i o n o f h a b i t a t s by i n d i v i d u a l s i n s p e c i e s w i t h seasonal b r e e d i n g h a b i t s ( F r e t w e l l and Lucas, 1969; F r e t w e l l , 1972). The i d e a l f r e e model p r e d i c t s t h a t h a b i t a t s w i t h h i g h q u a l i t y r e s o u r c e s a t t r a c t more i n d i v i d u a l s than poorer h a b i t a t s . S e l e c t i o n w i l l f a v o r i n d i v i d u a l s t h a t s e t t l e i n areas w i t h the bes t r e s o u r c e s , so lo n g as the c o s t s of defense do not completely o f f s e t the advantages gained. When the c o s t s o f defense exceed the b e n e f i t s o f access t o h i g h q u a l i t y r e s o u r c e s , s e l e c t i o n w i l l f a v o r s e t t l e m e n t o f poorer h a b i t a t s . Because h a b i t a t s w i t h poorer r e s o u r c e s a l s o a t t r a c t fewer competitors, the r e p r o d u c t i v e success o f i n d i v i d u a l s t h a t s e t t l e these areas i s expected t o equal t h a t of i n d i v i d u a l s i n h i g h - q u a l i t y h a b i t a t s ( F r e t w e l l and Lucas, 1969; F r e t w e l l , 1972). The i d e a l dominance model proposes t h a t the t e r r i t o r i a l b e h a v i o r o f dominant i n d i v i d u a l s l i m i t s the number of competitors t h a t are a b l e t o breed i n h i g h - q u a l i t y h a b i t a t s . Reproductive success i s expected t o be c o r r e l a t e d p o s i t i v e l y 101 w i t h p o p u l a t i o n d e n s i t y under the i d e a l dominance model, because the c o s t s o f c o m p e t i t i o n do not i n c r e a s e as r a p i d l y as the b e n e f i t s o f br e e d i n g i n the b e s t h a b i t a t s ( F r e t w e l l and Lucas, 1969; F r e t w e l l , 1972). E i t h e r o f these models might e x p l a i n the marked d i f f e r e n c e i n t i l e f i s h d e n s i t y i n r e e f s l o p e and channel h a b i t a t s a t Gl o v e r ' s Reef. However, both the i d e a l f r e e and i d e a l dominance models assume t h a t i n d i v i d u a l s move between d i f f e r e n t h a b i t a t s t o s e l e c t b r e e d i n g t e r r i t o r i e s . T h i s assumption may not be v a l i d f o r many marine f i s h e s , such as M. p l u m i e r i , i n which a d u l t s t h a t breed throughout the year appear t o remain near where they s e t t l e d from the plan k t o n as l a r v a e (see s i m i l a r l y Warner and Hoffman 1980a; 1980b; Warner, 1984; Shapiro, 1987b). I f a d u l t s are sedentary, then the d i s t r i b u t i o n and abundance of f i s h may be an emergent consequence of l a r v a l s e t t l e m e n t p r o c e s s e s ( V i c t o r , 1984; Shapiro, 1987a) r a t h e r than an adapted consequence of h a b i t a t s e l e c t i o n . The r e p r o d u c t i v e success o f i n d i v i d u a l s i n d i f f e r e n t l o c a l h a b i t a t s may a l s o be i n f l u e n c e d by f a c t o r s o t h e r than the q u a l i t y o f r e s o u r c e s and co m p e t i t i o n c o s t s , p a r t i c u l a r l y i f a d u l t s are sedentary. For example, l i f e t i m e r e p r o d u c t i v e success depends on the p r o b a b i l i t y o f s u r v i v a l so t h a t f u t u r e r e p r o d u c t i v e p o t e n t i a l can be r e a l i z e d (Cody, 1966; W i l l i a m s 1966; Stearns, 1976; Resnick and Bryga, 1987). The i n t e n s i t y and type o f p r e d a t i o n r i s k , t h e r e f o r e , may have an important i n f l u e n c e on how i n d i v i d u a l s i n d i f f e r e n t h a b i t a t s a c h ieve r e p r o d u c t i v e success. P a r t i c u l a r l y when a d u l t s do not choose h a b i t a t s , s e l e c t i o n may f a v o r f l e x i b i l i t y i n b e h a v i o r a l and 102 l i f e - h i s t o r y t a c t i c s t o maximize r e p r o d u c t i v e success under the types of p r e d a t i o n t h r e a t t h a t e x i s t i n l o c a l areas (Resnick and Bryga, 1987) . For example i n t i l e f i s h , h i g h investment i n p r e s e n t r e p r o d u c t i o n may be advantageous when pr e d a t o r y a t t a c k s are u n p r e d i c t a b l e and the t h r e a t of a d u l t m o r t a l i t y i s h i g h , as i s j suggested f o r channel f i s h (Chapter 4). Under these c o n d i t i o n s , h i g h l e v e l s of p r e s e n t r e p r o d u c t i o n may be s e l e c t e d because the p r o b a b i l i t y of r e a l i z i n g f u t u r e b r e e d i n g o p p o r t u n i t i e s are d i m i n i s h e d and u n c e r t a i n . I n d i v i d u a l s may opt f o r lower l e v e l s of p r e s e n t r e p r o d u c t i o n i n r e e f s l o p e s , where a t t a c k s from s t a l k i n g - t y p e p r e d a t o r s might be more p r e d i c t a b l e (Chapter 4). Lower r a t e s of spawning may be advantageous under these c o n d i t i o n s , p a r t i c u l a r l y i f b r e e d i n g a c t s or the a c q u i s i t i o n of the r e s o u r c e s necessary t o reproduce i n c r e a s e v u l n e r a b i l i t y t o a t t a c k s by s t a l k i n g p r e d a t o r s . The o b j e c t i v e of t h i s chapter i s t o compare the r e p r o d u c t i v e b e h a v i o r and l i f e - h i s t o r y t r a i t s of r e e f s l o p e and channel t i l e f i s h t o examine the extent t o which: 1) the i d e a l f r e e or i d e a l dominance h a b i t a t s e l e c t i o n models may e x p l a i n the d i s t r i b u t i o n of M. p l u m i e r i . 2) the d i s t r i b u t i p n of a d u l t s a r i s e s from f a c t o r s t h a t i n f l u e n c e l a r v a l s e t t l e m e n t , and 3) investment i n p r e s e n t r e p r o d u c t i o n and growth i s f l e x i b l e and i s c o r r e l a t e d w i t h apparent h a b i t a t d i f f e r e n c e s i n s u r v i v a l . F i r s t , I assess the q u a l i t y of r e e f s l o p e and channel h a b i t a t s by comparing: 1) d a i l y b atch f e c u n d i t y and frequency of spawning, 2) body s i z e and growth r a t e s , and 3) the a v a i l a b i l i t y 103 of r e s o u r c e s t h a t probably l i m i t r e p r o d u c t i o n i n each sex. Reproduction i n females i s most u s u a l l y l i m i t e d by the energy t h a t can be i n v e s t e d i n p r o d u c t i o n of o f f s p r i n g (e.g. Bateman, 1948; W i l l i a m s , 1966; T r i v e r s , 1972; B o r g i a , 1979; Hoffman, 1983) . When embryos and l a r v a e are p l a n k t o n i c , maternal investment i s r e s t r i c t e d t o the n u t r i e n t s a l l o c a t e d t o egg p r o d u c t i o n . T h e r e f o r e , food may p l a y an important r o l e i n the r e p r o d u c t i v e output of t i l e f i s h females. The importance of food i n t a k e i n female egg p r o d u c t i o n and growth i s examined by supplementing the d i e t of females and comparing egg p r o d u c t i o n , spawning r a t e , and growth i n f e d and non-fed females. I a l s o assess the a v a i l a b i l i t y of food i n r e e f s l o p e and channel h a b i t a t s by comparing the biomass of p o t e n t i a l prey i n sediment samples (Chapter 6). Male mating success i s u s u a l l y l i m i t e d by access t o females when p a t e r n a l care i s absent (Bateman, 1948; W i l l i a m s , 1966; T r i v e r s , 1972; Hoffman, 1983). In s p e c i e s w i t h harems, male r e p r o d u c t i v e success i s l a r g e l y dependent on harem s i z e . The d i s t a n c e s e p a r a t i n g n e i g h b o r i n g females may be one f a c t o r t h a t i n f l u e n c e s the number of mates t h a t males are a b l e t o monopolize, because female t e r r i t o r i e s do not o v e r l a p . However, because males a l s o must exclude competitors t o monopolize spawnings, the i n t e n s i t y of p r e s s u r e from i n t r u d e r s may a l s o i n f l u e n c e harem s i z e . Pressure from i n t r u d i n g males i s probably c o r r e l a t e d w i t h the number of competitors r e l a t i v e t o the number of p o t e n t i a l female mates w i t h i n each colony. To assess the p o t e n t i a l f o r males t o monopolize mates i n r e e f s l o p e and channel h a b i t a t s , I compare both the s p a c i n g of females and the 104 o v e r a l l sex r a t i o w i t h i n each colony. To examine the p r e d i c t i o n s o f the i d e a l f r e e and i d e a l dominance models, I combine estimates o f the average d a i l y mating success of females and males wi t h r e l a t i v e measurements of s u r v i v a l (Chapter 4) t o d e r i v e e s t i m a t e s of net r e p r o d u c t i v e r a t e ( a f t e r Warner, 1984b) i n each h a b i t a t . L a s t l y , i f investment p a t t e r n s i n p r e s e n t egg p r o d u c t i o n and growth are i n f l u e n c e d by h a b i t a t - s p e c i f i c p r o b a b i l i t i e s o f s u r v i v a l t o f u t u r e b r e e d i n g p e r i o d s , then channel and r e e f s l o p e f i s h may have d i f f e r e n t responses when the a v a i l a b i l i t y o f a c r i t i c a l r e s o u r c e i s i n c r e a s e d . To t e s t t h i s p o s s i b i l i t y , I compare the e f f e c t s o f d i e t supplementation on frequency o f spawning, r a t e s o f growth, and i n d i c e s o f f e c u n d i t y i n r e e f s l o p e and channel females. METHODS Frequency o f C o u r t s h i p and Spawning Reproductive behavior i n t i l e f i s h i s r e s t r i c t e d t o 1630-1830 each day. Furthermore, females e x h i b i t almost e x c l u s i v e f i d e l i t y t o one mate (Chapter 5 ) . Th e r e f o r e , the frequency o f spawning by a l l f i s h i n a harem c o u l d be monitored by f o l l o w i n g i n d i v i d u a l males. Reproductive a c t i v i t i e s were recorded on a t l e a s t f i v e days f o r channel (N=54 females, N=17 males) and r e e f s l o p e (N=44 females, N=22 males) f i s h , from approximately 1630 h u n t i l f i s h e ntered t h e i r burrows f o r the n i g h t . 105 Body S i z e and Growth Rates S i z e - f r e q u e n c y d i s t r i b u t i o n s o f males (N=27 r e e f s l o p e , N=34 channel) and females (N=63 r e e f s l o p e , N=89 channel) were compiled t o compare the s i z e o f f i s h i n the two h a b i t a t s . Only males t h a t were observed t o spawn, and females t h a t were observed t o spawn or had o v u l a t e d ova were i n c l u d e d i n comparisons. I t was p o s s i b l e t o measure 95% o f the f i s h i n r e e f s l o p e c o l o n i e s and 80% of the f i s h w i t h i n the channel study area. T h e r e f o r e , my samples i n c l u d e most of the p o p u l a t i o n s of r e p r o d u c t i v e l y a c t i v e a d u l t s i n these areas. Growth r a t e s o f females (N=13 r e e f s l o p e , N=13 channel), males (N=7 r e e f s l o p e , N=6 channel), and j u v e n i l e s (N=3) were c a l c u l a t e d as the change i n SL measured between the date of ta g g i n g and date o f re c a p t u r e , d i v i d e d by the t o t a l number of days d e t e r m i n i n g t h a t p e r i o d (40-60 days). Standard l e n g t h was measured t o the ne a r e s t mm as the d i s t a n c e from the t i p o f the lower jaw t o the edge of the most p o s t e r i o r s c a l e i n the crease a t the caudal peduncle caused by bending the f i s h ' s t a i l . The purpose o f growth measurements i s o n l y t o compare r e l a t i v e r a t e s i n the two h a b i t a t s . Sample s i z e was sm a l l and the time p e r i o d between t a g g i n g and r e c a p t u r e was s h o r t . A l s o , t a g g i n g causes t i s s u e damage, the r e p a i r o f which may d i m i n i s h growth. T h e r e f o r e , the measured r a t e s may underestimate the n a t u r a l growth r a t e s o f M. p l u m i e r i . Male Harem S i z e To examine the r e l a t i o n s h i p between female s p a c i n g and male harem s i z e , I measured the d i s t a n c e between each 106 female's burrow and the burrow of her n e a r e s t female neighbor ( i n t e r - f e m a l e d i s t a n c e ) . Harem s i z e was then examined i n r e l a t i o n t o the mean i n t e r - f e m a l e d i s t a n c e i n harems w i t h more than one female. In harems wi t h o n l y one female, the i n t e r -female d i s t a n c e was measured between female burrows and the next n e a r e s t female i n a n e i g h b o r i n g harem. I a l s o examined the d i s t a n c e between male and female burrows (male-female d i s t a n c e ) i n r e e f s l o p e and channel harems. The d i s t a n c e between each male's burrow and the burrows of the s i x c l o s e s t females was measured i n seven r e e f s l o p e c o l o n i e s (N=17 males) and f o r 23 males w i t h i n the channel study area d u r i n g 1984, 1985, and 1986. Females were ranked a c c o r d i n g t o p r o x i m i t y t o males. The mean male-female d i s t a n c e f o r each r a n k i n g ( i . e . , n e a r e s t females, second n e a r e s t ... s i x t h nearest) was then compared f o r r e e f s l o p e and channel h a b i t a t s . To examine the r e l a t i o n s h i p between mean harem s i z e and the sex r a t i o w i t h i n l o c a l p o p u l a t i o n s , I determined the number of females mating w i t h the males i n the channel study area d u r i n g 1983-1986 and i n seven r e e f s l o p e c o l o n i e s . I a l s o estimated gonosomatic i n d i c e s of males (GSI) t o determine i f t h e r e was a r e l a t i o n s h i p w i t h harem s i z e , or i f GSI of s i m i l a r l y s i z e d r e e f s l o p e (N=15) and channel males (N=ll) d i f f e r s . Male gonosomatic index was c a l c u l a t e d as f o l l o w s : GSI = ( t e s t i s m a s s / t o t a l body mass) X 100. T e s t e s were d i s s e c t e d from males captured b e f o r e spawning, p r e s e r v e d i n bouin's f i x a t i v e , b l o t t e d dry and weighed t o the n e a r e s t 0.001 g on a m e t t l e r balance. Body weights of these f i s h are not a v a i l a b l e due t o the m a l f u n c t i o n of my balance. 107 T h e r e f o r e , t o t a l male body mass was estimated by a l e a s t squares r e g r e s s i o n of body mass on l e n g t h i n males t h a t were weighed and measured p r e v i o u s l y , d e s c r i b e d by the equation: t o t a l body mass = -420.1 + 2.21 standard l e n g t h (r=0.94, p<0.001, N=30). Est i m a t e s of Food Abundance and Female F o r a g i n g Observations of f e e d i n g and examination of stomach contents r e v e a l e d t h a t t i l e f i s h feed p r i m a r i l y on b e n t h i c c r u s t a c e a n s , mollusks and a n n e l i d s (Chapter 5). I compared the percentage of stomachs i n r e e f s l o p e (N=12) and channel (N=13) females c o n t a i n i n g remains of each prey type t o examine whether females i n the two h a b i t a t s i n g e s t e d s i m i l a r prey. The abundance of p o t e n t i a l prey i n r e e f s l o p e and channel h a b i t a t s was estimated by measuring the t o t a l biomass of each type of i n v e r t e b r a t e and the s i z e of a random sub-sample of these organisms i n s u r f a c e sediment samples (Chapter 6). To examine f o r a g i n g e f f o r t i n channel and r e e f s l o p e females, I recorded the number of f o r a g i n g b i t e s per u n i t time and the d i s t a n c e over which females swam d u r i n g s p a t i a l t r a c e s . D i s t a n c e t r a v e l l e d was measured by t r a c i n g maps of swimming paths w i t h a d i g i t i z i n g t a b l e t . The t o t a l d i s t a n c e t r a v e l l e d d u r i n g r e p l i c a t e t r a c e s was d i v i d e d by the t o t a l minutes of o b s e r v a t i o n t o y i e l d a r a t e of movement. Female Investment i n Present Reproduction I examined female investment i n p r e s e n t r e p r o d u c t i o n by c a l c u l a t i n g gonosomatic index (GSI) as f o l l o w s : GSI = (ovary m a s s / t o t a l body mass) X 100. 108 GSI i s o n l y a v a l i d measure wit h which t o compare r e p r o d u c t i v e investment i n females from d i f f e r e n t h a b i t a t s i f the a l l o m e t r i c r e l a t i o n s h i p between ovary mass and body mass i s c o n t r o l l e d by comparing f i s h of s i m i l a r s i z e (DeVlaming e t a l . , 1982; E r i c k s o n e t a l . , 1985). To c o n t r o l f o r e f f e c t s of body mass, females were chosen f o r comparison so t h a t the mean s i z e of r e e f s l o p e (X=23.4 cm SL, SE=0.7) and channel females (X=22.0 cm, SE=0.5) was not s t a t i s t i c a l l y d i f f e r e n t . Between group comparisons of GSI a l s o r e q u i r e t h a t females are i n l i k e stages of gonad development (DeVlaming e t a l . 1982). To s a t i s f y t h i s requirement, GSI was estimated o n l y i n females whose o v a r i e s c o n t a i n e d eggs t h a t had been r e l e a s e d i n t o the o v a r i a n lumen ( o v u l a t i o n ) and had absorbed water d u r i n g the f i n a l stage of development ( h y d r a t i o n ) . Because r e p r o d u c t i o n i n t i l e f i s h i s r e s t r i c t e d t o the 2 h p e r i o d p r i o r t o sunset (Chapter 5), r i p e females c o u l d be captured b e f o r e spawning by c a g i n g them a t the b e g i n n i n g of the r e p r o d u c t i v e p e r i o d . Captured females were maintained a l i v e i n 15 1 c o n t a i n e r s f o r a t l e a s t 1 h t o ensure t h a t eggs were f u l l y h ydrated. F i s h were then p i t h e d , and the o v a r i e s e x t r a c t e d . O v a r i e s p l u s a l l running hydrated eggs were p r e s e r v e d w h i l e f r e s h i n 10% seawater f o r m a l i n and l a t e r b l o t t e d dry and weighed (2 r e p l i c a t e s / s p e c i m e n ) t o the n e a r e s t 0.01 g. E s t i m a t e s of female body mass f o r GSI c a l c u l a t i o n s were d e r i v e d from a r e g r e s s i o n of body mass on standard l e n g t h d e s c r i b e d by the e q u a t i o n : t o t a l female body mass = -199.2 + 1.36 s t a n d a r d l e n g t h (r=0.97, N=82, p<0.001). 109 E s t i m a t e s of Female D a i l y Batch F e c u n d i t y The a b i l i t y t o c o l l e c t females s h o r t l y b e f o r e spawning made i t p o s s i b l e t o estimate the number of hydrated eggs p r e s e n t i n o v a r i e s a t the b e g i n n i n g of the d a i l y r e p r o d u c t i v e p e r i o d (average batch f e c u n d i t y ) . Hydrated ova were washed out of p r e s e r v e d o v a r i e s t h a t were d i s s e c t e d under m a g n i f i c a t i o n . Ovulated eggs i n the o v a r i a n lumen were e a s i l y d i s t i n g u i s h e d as they were unattached t o o v a r i a n t i s s u e , t r a n s l u c e n t , and much l a r g e r than opaque non-hydrated eggs. The t o t a l number of o v u l a t e d eggs c o l l e c t e d from each specimen were then b l o t t e d dry and weighed. F i f t y p r e s e r v e d eggs t h a t had undergone h y d r a t i o n were chosen a t random from each specimen and the g r e a t e s t diameter was measured under m a g n i f i c a t i o n . Eggs from i n d i v i d u a l s v a r i e d l i t t l e i n s i z e . T h e r e f o r e , I counted the number of eggs i n subsamples from each specimen. Subsamples were then weighed t o determine the r e l a t i o n s h i p between egg mass and egg number. T o t a l egg mass from each specimen c o u l d then be c o n v e r t e d t o an estimate of d a i l y batch f e c u n d i t y . Female t i l e f i s h sometimes spawned more than once d u r i n g a s i n g l e r e p r o d u c t i v e p e r i o d , p a r t i c u l a r l y i n the channel (see below). To compare the number of hydrated ova p r e s e n t i n o v a r i e s b e f o r e second spawnings wi t h the number p r e s e n t b e f o r e f i r s t spawnings, I c o l l e c t e d o v a r i e s from a s m a l l sample (N=6 channel, 1 r e e f s l o p e female) of females b e f o r e they spawned a second time. Females t h a t had been observed t o spawn once were watched c o n t i n u o u s l y u n t i l they performed an a r c d i s p l a y and p a i r e d t o g e t h e r a second time w i t h t h e i r mate. Before these 110 females spawned again, they were speared through the head so as not t o damage the o v a r i e s . The number of eggs r e l e a s e d d u r i n g t h i r d d a i l y spawnings was not estimated because these a c t s were r a r e (see r e s u l t s ) and u n p r e d i c t a b l e . E s t i m a t e s of Net Y e a r l y Mating Success To perform an unequivocal t e s t of the p r e d i c t i o n s of the i d e a l f r e e and i d e a l dominance h a b i t a t s e l e c t i o n models, i t i s necessary t o compare the l i f e t i m e r e p r o d u c t i v e success of f i s h i n r e e f s l o p e and channel h a b i t a t s . Measurement of r e p r o d u c t i v e success i n t i l e f i s h r e q u i r e s i n f o r m a t i o n on the number of p l a n k t o n i c o f f s p r i n g t h a t s u r v i v e t o reproduce. I d i d not measured s u r v i v a l of p l a n k t o n i c t i l e f i s h l a r v a e . Rather, I measure spawning frequency and number of mates i n males, and spawning frequency and egg p r o d u c t i o n i n females t o estimate d a i l y mating success. For purposes of comparing the r e l a t i v e mating success of r e e f s l o p e and channel f i s h , I assume equal s u r v i v o r s h i p of the l a r v a e spawned i n the two h a b i t a t s . E s t i m a t e s of l i f e t i m e r e p r o d u c t i v e success a l s o r e q u i r e i n f o r m a t i o n on r e p r o d u c t i v e l i f e s p a n . Attempts a t aging t i l e f i s h by counts of o t o l i t h r i n g s proved i n c o n c l u s i v e . A l s o , sample s i z e s of growth measurements are too s m a l l t o r e l i a b l y b a c k - c a l c u l a t e age from body s i z e measurements. T h e r e f o r e , I l i m i t comparison of r e p r o d u c t i v e success i n r e e f s l o p e and channel f i s h t o estimates of net mating success (see below) of females and males over an a r b i t r a r i l y chosen one-year p e r i o d . Net mating success i s the expected mating success over a g i v e n time p e r i o d d i s c o u n t e d by the p r o b a b i l i t y of m o r t a l i t y 111 d u r i n g t h a t p e r i o d (Warner, 1984b). My e s t i m a t e s of net mating success are based on e m p i r i c a l l y determined mean v a l u e s f o r s e v e r a l parameters, and are t h e r e f o r e s u b j e c t t o problems of compounded e r r o r s . S e v e r a l assumptions ( s t a t e d below) r e g a r d i n g parameters f o r which data are u n a v a i l a b l e are a l s o r e q u i r e d . Comparison of estimated y e a r l y net mating success of r e e f s l o p e and channel f i s h , t h e r e f o r e , i s an e q u i v o c a l t e s t of the two h a b i t a t s e l e c t i o n models. My e s t i m a t e s of average male mating success i n r e e f s l o p e and channel h a b i t a t s r e q u i r e two assumptions. F i r s t , I assume t h a t the average percentage of eggs t h a t i s f e r t i l i z e d i s the same f o r males spawning i n the two h a b i t a t s . S i m i l a r GSI's i n r e e f s l o p e and channel males supports t h i s assumption, because t e s t e s of s i m i l a r s i z e probably produce s i m i l a r q u a n t i t i e s of spermatozoa. Second, I assume t h a t the average number of eggs released/spawn by r e e f s l o p e and channel females i s s i m i l a r . In support of t h i s assumption, n e i t h e r e stimates of the number of o v u l a t e d eggs i n o v a r i e s b e f o r e spawning, nor female GSI's were s t a t i s t i c a l l y d i f f e r e n t i n s i m i l a r l y s i z e d non f e d r e e f s l o p e and channel females (see below). I f these assumptions are c o r r e c t , then the average d a i l y frequency of mating w i t h females t h a t have not a l r e a d y spawned es t i m a t e s the average d a i l y mating success of males. Average mating success f o r males i n r e e f s l o p e and channel h a b i t a t s was c a l c u l a t e d as: average d a i l y — average # of ^ X % of days t h a t male mating success female mates females spawned The average number of eggs spawned per day e s t i m a t e s the d a i l y mating success of females, assuming equal f e r t i l i z a t i o n 112 r a t e s and equal o f f s p r i n g s u r v i v o r s h i p i n the two h a b i t a t s . I a l s o assumed t h a t females hydrate a s i n g l e b atch of eggs and then r e l e a s e them d u r i n g one or more spawnings r a t h e r than h y d r a t i n g a separate batch b e f o r e second and t h i r d spawnings. The s m a l l number of hydrated eggs p r e s e n t i n specimens captured immediately b e f o r e second spawnings (see below) suggests t h a t t h i s assumption i s j u s t i f i e d . I f females o v u l a t e a s i n g l e batch, then the number of o v u l a t e d eggs i n o v a r i e s p r i o r t o spawning should estimate d a i l y batch f e c u n d i t y . The average number of eggs spawned per day by females i n each h a b i t a t was estimated as: Average # — X % of days t h a t ^ X number of o v u l a t e d o f eggs/day females spawned eggs i n o v a r i e s Frequencies of disappearance (Chapter 4) were used t o d e r i v e e s t i m a t e s of the per c a p i t a d a i l y death r a t e ( a f t e r Warner, 1984b) i n each h a b i t a t as: d a i l y p e r c a p i t a — % of tagged f i s h y t o t a l number of death r a t e disappearing/day * f i s h tagged Assuming t h a t the v a r i a b l e s i n the above equations remain c o n s t a n t over one year, then net y e a r l y mating success over a year i s c a l c u l a t e d as: Net y e a r l y — expected mating success y p r o b a b i l i t y of mating success d u r i n g 1 year * s u r v i v i n g 1 year. Food Supplementation Experiments Supplemental f e e d i n g was accomplished by l u r i n g s p e c i f i c f i s h t o chopped p i e c e s (2-4 mm ) of conch (Strombus), and i n t e r t i d a l top s h e l l s ( C i t t a r i u m ) p l a c e d a t the entrances of t h e i r burrows. Mo l l u s k s are a n a t u r a l food item of t i l e f i s h (Chapter 5). F i s h were q u i c k l y a t t r a c t e d and ate u n t i l t h e i r abdomens were d i s t e n d e d . Non-fed females t h a t l i v e d w i t h i n the same or a d j a c e n t harems served as c o n t r o l s (N=23 channel and 2 3 r e e f s l o p e ) . C o n t r o l females as w e l l as males were prevented from e a t i n g by e n c l o s i n g them i n s i d e t h e i r burrows w i t h a cage. When experimental f i s h were s a t i a t e d , any uneaten food and cages were removed. Feedings were completed w i t h i n 3 0 min, t h e r e f o r e , the a c t i v i t i e s o f c o n t r o l f i s h were d i s r u p t e d f o r o n l y a s h o r t time. Females (N=16 channel, 16 r e e f slope) were f e d each day between 1000 and 1200 h f o r 20-23 days up u n t i l and i n c l u d i n g the day o f c o l l e c t i o n . C o n t r o l females were c o l l e c t e d s i m u l t a n e o u s l y w i t h experimental f i s h . C o n t r o l and experimental females were s e l e c t e d so t h a t the i n i t i a l s i z e of r e e f s l o p e (non-fed X SL=23.4 cm, SE=0.7; f e d X SL=23.1 cm, SE=0.7) and channel (non-fed S L X=22.0 cm, SE=0.5; f e d X SL=22.7 cm, SE=0.7) s u b j e c t s were not s t a t i s t i c a l l y d i f f e r e n t w i t h i n and between h a b i t a t s or treatments. T h e r e f o r e , comparisons of GSI's and batch f e c u n d i t i e s of females from d i f f e r e n t h a b i t a t s and treatments are not confounded by d i f f e r e n c e s i n body s i z e (see above). C o l l e c t i o n of f i s h and measurement of GSI and growth were done as d e s c r i b e d above. Two-way a n a l y s i s of v a r i a n c e was performed t o determine i f f e d females grew f a s t e r , had h i g h e r GSI's, or produced more eggs than c o n t r o l s , and i f responses d i f f e r e d i n r e e f s l o p e and channel females. Means were were compared u s i n g Tukey's A t e s t . O b s e r vations on spawning were a l s o conducted t o examine the e f f e c t s o f food supplementation on spawning frequency. Spawning 114 o b s e r v a t i o n s were conducted on females ( r e e f s l o p e N=7, channel N=10) on days 5, 6, and 7 of female food supplementation. Beginning on the e i g h t h day of female f e e d i n g , males (N=7 r e e f s l o p e , N=12 channel) i n these harems were a l s o f e d . Spawning o b s e r v a t i o n s were conducted again when females had been f e d f o r 10-12 days and males had been f e d f o r 5-7 days. RESULTS H a b i t a t Comparisons of Body S i z e and Growth Rates The average s i z e of females i n the channel was s m a l l e r (t=14.49, p<0.01) than i n r e e f s l o p e h a b i t a t s , and the s m a l l e s t r e p r o d u c t i v e l y a c t i v e females were a l s o observed i n the channel ( F i g u r e 16a). Males were a l s o s m a l l e r (t=13.85, p<0.01) i n the channel ( F i g u r e 16b). Mean growth r a t e s of non-fed f i s h of both sexes were low. S i x of t h i r t e e n r e e f s l o p e females, and f i v e of t h i r t e e n channel females d i d not e x h i b i t d e t e c t a b l e changes i n SL between t a g g i n g and r e c a p t u r e . Three of seven and two of s i x males d i d not grow i n r e e f s l o p e and channel h a b i t a t s r e s p e c t i v e l y . Mean growth r a t e s of non-fed r e e f s l o p e and channel f i s h of both sexes were not s t a t i s t i c a l l y d i f f e r e n t , but were about 1.6 times h i g h e r i n channel females and 1.9 times h i g h e r i n channel males (F i g u r e 17). Male Spawning Frequency Channel males spawned more than twice as f r e q u e n t l y (t=5.43, p<0.01) as r e e f s l o p e males ( F i g u r e 18), p r i m a r i l y because harems were l a r g e r (t=3.50, p<0.01) i n the channel (Table 6). However, channel males a l s o spawned more than twice 115 0 1 I I I I I I I I I I I I I I i I £ 16 18 20 22 24 26 28 30 32 CD (J CD CL I , i i i i i i i , i I . I . I 26 28 30 32 34 36 38 40 42 s i z e c l a s s ( c m ) F i g u r e 16. A. S i z e d i s t r i b u t i o n o f r e e f s l o p e (N=63) and channel females (N=89). B. S i z e d i s t r i b u t i o n of r e e f s l o p e (N=27) and channel males (N=34). Data are the percentage of the t o t a l sample i n 1.0 cm s i z e c l a s s e s . 116 (VI 'o x >> D CD o o 10.0 8.0 6.0 4.0 2.0 0.0 I I reef s lope v//\ channe l V. A f e m a l e s m a l e s F i g u r e 17. Growth r a t e s (X ± SEM) of non-fed r e e f s l o p e and channel females and males. 117 o 00 c c o 00 5 4 3 2 0 I I reef slope Y //\ channel -i 5 s pawn i ng s d i sp l ay s 4 3 2 0 00 T 3 F i g u r e 18. Spawning and d i s p l a y r a t e s (X ± SEM) i n r e e f s l o p e (N=22) and channel (N=17) males. 118 T a b l e 6. D a i l y mating success (X ± SEM) i n r e e f s l o p e and channel males. Mean Percentage of Harem days t h a t Average male d a i l y s i z e females spawned mating success Reef s l o p e 1.8 (0.2) 59.8 (4.6) 1.08 (0.09) (N=22) Channel 2.8 (0.2) 86.5 (2.3) 2.42 (0.01) (N=17) d a i l y male mating success i s the product of the number of female mates and the average percentage of days t h a t males spawned w i t h females t h a t had not a l r e a d y spawned t h a t day. 119 as f r e q u e n t l y (t=10.07, p<0.01) wit h each female, and performed advertisement d i s p l a y s a t more than f i v e times the r a t e (t=6.31, p<0.01) of r e e f s l o p e males (F i g u r e 18). GSI's of r e e f s l o p e (X=0.0022, SE=0.0003, N=15) and channel (X=0.0028, SE=0.0004, N=ll) males were s i m i l a r and t h e r e was no c o r r e l a t i o n between male GSI and harem s i z e (r=0.19). C o r r e l a t i o n s With Male Harem S i z e There was a weak c o r r e l a t i o n (r=-0.36, p<0.05) between harem s i z e and i n t e r - f e m a l e d i s t a n c e ( F i g u r e 19). However, i n t e r -female d i s t a n c e i n the channel (X=11.3 m, SE=1.1, N=44) and r e e f s l o p e c o l o n i e s (X=10.1 m, SE=0.6, N=46) was not s t a t i s t i c a l l y d i f f e r e n t (t=0.24) even though harems were l a r g e r i n the channel. D i s t a n c e from male burrows t o the second, t h i r d , f o u r t h , and f i f t h c l o s e s t females were not s t a t i s t i c a l l y d i f f e r e n t i n r e e f s l o p e and channel h a b i t a t s ( F i g u r e 20). D i s t a n c e t o c l o s e s t females was g r e a t e r (t=2.99, p<0.01) f o r channel males, whereas d i s t a n c e t o the s i x t h n e a r e s t females was g r e a t e r (t=3.61, p<0.01) i n r e e f s l o p e males. The s l o p e s of the r e g r e s s i o n l i n e s r e l a t i n g male-female inter-burrow d i s t a n c e t o female p r o x i m i t y rank ( F i g u r e 20) were not d i f f e r e n t (t=0.39) i n the two h a b i t a t s . The r a t i o of females t o males i n the channel study area (X=2.4, SE=0.1, N=4) was twice t h a t (t=6.19, p<0.01) observed i n r e e f s l o p e c o l o n i e s (X number of females/male=l.2, SE=0.2, N=7). There 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 (r=0.96, p<0.001) between the mean harem s i z e i n each colony and the o v e r a l l r a t i o of females t o males on each s i t e ( F i g u r e 21). A l s o , f i f t e e n 120 6 CD N CO E 3 CD D X • • • • • • • 0 I I I I 10 J I I L 15 J I I L 20 25 30 n ter—female d i s t ance (m) F i g u r e 19. Harem s i z e (number of females) graphed as a f u n c t i o n of the d i s t a n c e between each female and her ne a r e s t female neighbor. Data are mean i n t e r - f e m a l e d i s t a n c e s f o r each harem (channel, N=19; r e e f s l o p e , N=23). L i n e i s l e a s t squares r e g r e s s i o n f o r a l l harems pooled (N=42) d e s c r i b e d by the equ a t i o n : harem s i z e = 3.35 x -0.08 i n t e r - f e m a l e d i s t a n c e . 121 CD O c D 00 _CD O CD T _CD D 40 35 30 25 20 15 10 5 0 o channel • reef slope 4 Female proximity rank F i g u r e 20. Di s t a n c e between males (N=23 channel, N=17 r e e f slope) and the s i x c l o s e s t females graphed as a f u n c t i o n o f female p r o x i m i t y rank (nearest t o f a r t h e s t ) . Data are mean male-female d i s t a n c e s f o r each p r o x i m i t y rank and 95% conf i d e n c e i n t e r v a l s . L i n e s are l e a s t squares r e g r e s s i o n s f o r each h a b i t a t d e s c r i b e d by the equations: s o l i d l i n e = r e e f s l o p e , male-female d i s t a n c e = 1.97 + 3.80 female p r o x i m i t y rank; dashed l i n e = channel, male-female d i s t a n c e = -1.38 +5.69 female p r o x i m i t y rank. 122 CD N 00 CD o c D CD 3 0 0.5 1.0 1.5 2.0 2.5 3.0 ntra —colony sex rat io f e m a l e s / m a l e s F i g u r e 21. Mean harem s i z e i n r e e f s l o p e c o l o n i e s (N=7) and the channel (N=4 years) graphed as f u n c t i o n o f the r a t i o o f females t o males. L i n e i s l e a s t squares r e g r e s s i o n d e s c r i b e d by the equation: mean harem s i z e = 0.3 3 + 1.19 female t o male r a t i o . 123 unmated males were observed i n r e e f s l o p e c o l o n i e s , where average harem s i z e was s m a l l , whereas on l y t h r e e unmated males were observed i n the channel. I monitored the l o c a t i o n s of 15 unmated males (3 channel, 12 r e e f slope) t o determine whether or not they moved t o o t h e r h a b i t a t s . A l l of these males remained on t e r r i t o r i e s without r e s i d e n t females f o r a t l e a s t two months. F o l l o w i n g male removals, e l e v e n unmated males r e l o c a t e d t o a d j a c e n t t e r r i t o r i e s w i t h r e s i d e n t females w i t h i n these same c o l o n i e s (Chapter 6), w h i l e the o t h e r s occupied the same l o c a t i o n s u n t i l they were c o l l e c t e d or u n t i l the end o f o b s e r v a t i o n s 2-4.5 months). One male t h a t remained unmated from A p r i l 1985 t o the end of o b s e r v a t i o n s i n August, 1985, occupied an a d j a c e n t t e r r i t o r y and had two mates i n A p r i l 1986. Female Spawning Frequency Mean d a i l y spawning frequency of channel females (X=1.12, SE=0.06) was h i g h e r (t=4.73, p<0.01) than t h a t of r e e f s l o p e females (X=0.67, SE=0.06). Reef s l o p e females f a i l e d t o spawn on a h i g h e r percentage of days (t=7.39, p<0.01) than channel females ( F i g u r e 22). Females i n the two h a b i t a t s spawned once a day on a s i m i l a r percentage of days, but channel females spawned tw i c e a day more f r e q u e n t l y (p<0.01, t=4.98). A l s o , channel females spawned t h r e e times on 4.8 percent of days, w h i l e r e e f s l o p e females were not observed t o spawn t h r e e times i n a day. Female Fo r a g i n g Behavior and Abundance of P o t e n t i a l Prey The f o r a g i n g b ehavior of channel and r e e f s l o p e females d i f f e r e d markedly. Channel females swam n e a r l y 2 m f a r t h e r per 124 60 ] r e e f s l o p e 0 1 2 3 female spawn ings /day F i g u r e 22. D a i l y spawning frequency i n channel and r e e f s l o p e females. 125 min (t=4.91, p<0.01) and average b i t e r a t e of channel females was 1.7 times h i g h e r (t=4.00, p<0.01) than t h a t o f r e e f s l o p e females ( F i g u r e 23). The p r o p o r t i o n of female stomachs c o n t a i n i n g remains of mollusks, p o l y c h a e t e s and cru s t a c e a n s were not d i f f e r e n t (X^=1.77, df=2) i n r e e f s l o p e and channel specimens ( F i g u r e 24). The t o t a l biomass of i n v e r t e b r a t e s of the type and s i z e found i n female stomachs were not d i f f e r e n t i n samples of s u r f a c e sediments c o l l e c t e d i n r e e f s l o p e and channel h a b i t a t s ( F i g u r e 25). The mass of mollusks/sample was h i g h e r (t=3.62, p<0.01) i n channel h a b i t a t s , w h i l e t h a t o f a n n e l i d s was s i m i l a r i n r e e f s l o p e and channel samples. The mass of crustaceans/sample was somewhat h i g h e r i n r e e f s l o p e h a b i t a t s , but the d i f f e r e n c e was not s t a t i s t i c a l l y s i g n i f i c a n t ( F i g u r e 26). Crustaceans were l a r g e r (t=4.03, p<0.01) i n the channel, but the s i z e o f mollusks and pol y c h a e t e s were not d i f f e r e n t i n the two h a b i t a t s ( F i g u r e 26). D a i l y Female Batch F e c u n d i t y The number of o v u l a t e d eggs i n o v a r i e s of females c o l l e c t e d p r i o r t o spawning v a r i e d markedly among females i n both h a b i t a t s (Table 7 ) . The number of hydrated eggs w i t h i n both non-fed and f e d treatments were not s t a t i s t i c a l l y d i f f e r e n t i n both r e e f s l o p e and channel females. D a i l y batch f e c u n d i t y was not c o r r e l a t e d with body mass i n e i t h e r c o n t r o l (r=0.07) or fed (r=0.34) females, but ovary mass was c o r r e l a t e d w i t h body mass i n both c o n t r o l (r=0.43, p<0.01) and f e d (r=0.53, p<0.01) females. F i v e and e i g h t non-fed r e e f s l o p e and channel females r e s p e c t i v e l y had fewer than 200 hydrated eggs, w h i l e the others 126 A. B GO CD CD 0.5 0.4 7= 0.3 0.2 0.1 0.0 RS CH c CD CD > O o CD O 8 0 RS CH F i g u r e 23. Comparison of f o r a g i n g behavior (X ± SEM) i n r e e f s l o p e (N=29) and channel (N=25) females. Panel A shows b i t e r a t e , p a n e l B shows mean r a t e of movement. 127 CO CJ D E o CO o CD o c CD o CD 100 80 60 40 20 0 i i reef slope Y//\ channel polychaetes mollusks crustaceans F i g u r e 24. Percentage of r e e f s l o p e (N=12) and channel (N=13) female stomachs c o n t a i n i n g remains of p o l y c h a e t e s , mollusks, and cr u s t a c e a n s . 128 3 r _CD CL O 00 CJ> 2 oo 00 D CD O _Q CD -t—* <^  CD > C 1 -0 i i r e e f s l o p e Y//\ c h a n n e l zl polychaetes mollusks crustaceans total F i g u r e 25. Mass (X ± SEM) of i n v e r t e b r a t e s per sample from channel and r e e f s l o p e h a b i t a t s . 129 (VI I o x CD CO CO o CD CD Q_ 5.0 4.0 3.0 2.0 1.0 0.0 I I reef s lope Y//\ channe l 1 -5-1 21 / / / 'A polychaetes mollusks crustaceans F i g u r e 26. I n d i v i d u a l mass (X ± SEM) of p o l y c h a t e s (N=100), mollusks (N=3 0), and crustaceans (N=3 0) i n samples from r e e f s l o p e and channel h a b i t a t s . 130 T a b l e 7. Number of eggs (X ± SEM) spawned per day i n r e e f s l o p e and channel females of s i m i l a r s i z e . i Percentage SL Ovulated eggs of days when Eggs (cm) i n o v a r i e s females spawned spawned/day Reef s l o p e 23.4 (0.7) 4,001 (1,471) 0.58 2,321 (853) (N=23) Channel 22.0 (0.5) 2,694 (643) 0.75 2,021 (482) (N=23) x c a l c u l a t e d as the number of days when females spawned, d i v i d e d by the t o t a l number of female o b s e r v a t i o n days. 131 had between 250 and 24,000 eggs. In f e d females, a l l but one r e e f s l o p e specimen and a l l channel specimens had more than 500 hydrated eggs. Second d a i l y spawning ascents were n o t i c e a b l y s h o r t e r than those of f i r s t spawnings, s u g g e s t i n g t h a t they may i n v o l v e r e l e a s e of fewer eggs. C o n s i s t e n t w i t h t h i s o b s e r v a t i o n , the number of hydrated eggs c o l l e c t e d from females p r i o r t o second spawnings (X=75 eggs, SE=43, N=7) was o n l y 2.2% of the average number c o l l e c t e d p r i o r t o f i r s t spawnings (Table 7 ) . T h i r d spawning ascents were even s h o r t e r and lower than second d a i l y spawnings, s u g g e s t i n g t h a t t h i r d spawnings pr o b a b l y a l s o i n v o l v e the r e l e a s e of few eggs. Net Mating Success of Females and Males Es t i m a t e s of average mating success of channel males were more than twice t h a t of r e e f s l o p e males, because channel males had l a r g e r harems and channel females spawned on a h i g h e r percentage of days (Table 6). Even when d i s c o u n t e d by the h i g h e r per c a p i t a m o r t a l i t y r a t e i n the channel, the expected net mating success f o r channel males over one year i s two times t h a t of r e e f s l o p e males (Table 8). In females, the standard e r r o r s around the mean d a i l y batch f e c u n d i t i e s of s i m i l a r l y - s i z e d channel and r e e f s l o p e females are extremely l a r g e and o v e r l a p c o n s i d e r a b l y (Table 7 ) . As a consequence, the estimates of the average number of eggs spawned/day are not s t a t i s t i c a l l y d i f f e r e n t i n the two h a b i t a t s , even though channel females spawned on a h i g h e r percentage of days. When d i s c o u n t e d by m o r t a l i t y , the expected 132 Table 8. Estimated net mating success in reef slope and channel males. Daily mating success Habitat ( X spawns±SE) Expected 1-yr. mating Per capita success daily death (# spawns) rat e 1 Expected per capita probability Net 1 yr. of mortality mating during 1 yr. success 2 Reef Slope 1.08 (0.9) 394 4.6 X 10"6 0.002 393 Channel 2.42 (0.1) 883 4.3 X 10~5 0.016 869 1 calculated as the percentage of tagged fish disappearing/day/total number of fish tagged in each habitat. 2 net 1 year mating success = (# of spawns expected during 1 year) x (1.0 - probability of mortality during 1 year) number o f eggs spawned d u r i n g one year by r e e f s l o p e females i s o n l y s l i g h t l y h i g h e r (1.16 times) than t h a t of channel females (Table 9 ) . The magnitude of t h i s d i f f e r e n c e i s w e l l w i t h i n the range of the standard e r r o r s of e s t i m a t e s of average d a i l y batch f e c u n d i t y . E f f e c t s of Food Supplementation N e i t h e r f e e d i n g females alone or f e e d i n g females and males i n c r e a s e d spawning r a t e s . In both h a b i t a t s , the three-day spawning frequency of f e d females was s i m i l a r t o t h e i r r a t e s b e f o r e f e e d i n g , and t o t h a t of non-fed c o n t r o l females. S i m i l a r l y , t h e r e was no i n c r e a s e i n the t o t a l frequency of male spawnings/day, d a i l y spawnings/female, or the frequency of advertisement d i s p l a y s when both males and females were f e d . Growth r a t e s of food-supplemented females were markedly h i g h e r (F=10.19, p<0.01) than those of c o n t r o l s i n both h a b i t a t s ( F i g u r e 27). The i n t e r a c t i o n between h a b i t a t and growth r a t e was not s t a t i s t i c a l l y s i g n i f i c a n t (F=2.41, p>0.05). However, the mean growth r a t e of f e d r e e f s l o p e females was more than f o u r times t h a t of c o n t r o l s (p<0.05, Tukey's A t e s t ) compared w i t h o n l y a 1.9 f o l d d i f f e r e n c e i n the channel ( F i g u r e 27). Gonosomatic i n d i c e s of f e d females were h i g h e r (F=11.67, p<0.01) than non-fed females i n both h a b i t a t s ( F i g u r e 28). The i n t e r a c t i o n between h a b i t a t and e f f e c t s of f e e d i n g on GSI was not s t a t i s t i c a l l y s i g n i f i c a n t (F=0.42). The gonosomatic index of f e d females i n the channel, however, was h i g h e r (p<0.05, Tukey's A t e s t ) than t h a t of c o n t r o l females. By c o n t r a s t , GSI of food-supplemented r e e f s l o p e females was not s t a t i s t i c a l l y h i g h e r 134 Table 9. Estimated net mating success (number of eggs) i n s i m i l a r l y sized reef slope and channel females. Expected # of eggs Expected per c a p i t a released/ # of eggs per capita p r o b a b i l i t y Net 1 yr. day 1 released d a i l y death of m o r t a l i t y mating Habitat (X±SE) /1-year rate during 1 yr. success 2 Reef slope 2,321(853) 847,165 4.6xl0~ 6 .002 845,471 Channel 2,021(482) 737,665 4.3xl0 - 5 .016 725,862 1 based on estimates of the number of hydrated eggs i n ovaries of females c o l l e c t e d p r i o r to spawning. 2 net 1-year mating success = (expected # of eggs released/year) x (1.0 - p r o b a b i l i t y of mortality during 1 year), assumes 100% f e r t i l i z a t i o n and o f f s p r i n g s u r v i v a l (see t e x t ) . CN I O x >> D CD \—> O o 16.0 14.0 12.0 10.0 8.0 6.0 4.0 2.0 0.0 v reef s lope channel F i g u r e 27. Growth r a t e s (X ± SEM) of non-fed and f e d r e e f s l o p e and channel females. 136 o o x o _Q D > O 3 . 0 2 . 5 2 . 0 1 .5 1 .0 0 . 5 0 . 0 7 reef s lope channe l F i g u r e 28. Gonosomatic i n d i c e s (X ± SEM) of non-fed and f e d r e e f s l o p e and channel females. 137 than t h a t of c o n t r o l s ( F i g u r e 28). O v a r i e s of a l l f e d females c o n t a i n e d more than 500 hydrated ova, and the number of eggs was h i g h e r (F=12.45, p<0.01) than t h a t of non-fed females i n both h a b i t a t s ( F i g u r e 29). The mean number of hydrated eggs i n f e d females were 1.7 and 1.9 times h i g h e r than those of non-fed females i n r e e f s l o p e and channel h a b i t a t s r e s p e c t i v e l y , however, these d i f f e r e n c e s are not s t a t i s t i c a l l y s i g n i f i c a n t . DISCUSSION Male Harem S i z e Channel males had l a r g e r harems and spawned more f r e q u e n t l y w i t h each female than r e e f s l o p e males (Table 6). Harem s i z e was r e l a t e d t o female s p a c i n g as w e l l as t o the w i t h i n - c o l o n y r a t i o of females t o males. I n t e r - f e m a l e d i s t a n c e , however, accounted f o r o n l y a s m a l l p r o p o r t i o n of the v a r i a n c e i n harem s i z e (r 2=0.13), and n e i t h e r i n t e r - f e m a l e d i s t a n c e nor male-female d i s t a n c e were s h o r t e r i n the channel where harems were l a r g e r . By c o n t r a s t , the r a t i o of females t o males accounted f o r a l a r g e p r o p o r t i o n (r 2=0.90) of the v a r i a t i o n i n harem s i z e , and female t o male r a t i o s were l a r g e r i n the channel. These r e s u l t s are more c o n s i s t e n t with the h y p o t h e s i s t h a t male harem s i z e i s l i m i t e d by the r a t i o of competitors t o p o t e n t i a l mates than by the d i s t a n c e s e p a r a t i n g females. U n l i k e some oth e r polygynous v e r t e b r a t e s , h i g h mating success i n t i l e f i s h males does not appear t o be r e l a t e d t o l a r g e body s i z e . Unmated males were sometimes l a r g e r than mated males w i t h i n t h e i r c o l o n i e s , and the l a r g e s t males o f t e n d i d not have 138 10.0 I I n o n - f e d EZZ fed reef s lope channe l F i g u r e 29. E s t i m a t e s (X ± SEM) of the number of hydrated eggs i n o v a r i e s of non-fed and f e d r e e f s l o p e and channel females c o l l e c t e d p r i o r t o spawning. the l a r g e s t harems. The r e s u l t s of male removals suggest t h a t harem s i z e may be i n f l u e n c e d more by p r e d a t i o n and r e c r u i t m e n t events than by e f f e c t s of s i z e on s o c i a l s t a t u s . In a l l male removals, replacement males were the occupants of n e i g h b o r i n g t e r r i t o r i e s even though l a r g e r males were o f t e n p r e s e n t elsewhere w i t h i n these c o l o n i e s . Perhaps p r i o r r e s i d e n c y on a n e i g h b o r i n g t e r r i t o r y i n f l u e n c e s which males can move i n t o vacant a r e a s . P r e d a t i o n on females may a l s o i n f l u e n c e the number of mates t h a t males monopolize. T h e r e f o r e , the s i z e of a p a r t i c u l a r male's harem a t any p o i n t i n time may r e f l e c t the h i s t o r y of p r e d a t i o n events and r e c r u i t m e n t i n t h a t l o c a l area. Spawning Frequency and F e c u n d i t y of Females Female t i l e f i s h sometimes spawned more than once per day, e s p e c i a l l y i n the channel. M u l t i p l e d a i l y spawning appears t o be unusual among marine f i s h e s t h a t broadcast p l a n k t o n i c gametes, but has been suggested f o r M. p l u m i e r i ( C o l i n and C l a v i j o , i n p r e s s ) , and documented i n a t l e a s t two l a b r i d s (011a e t a l . , 1981; Hoffman, 1983). The presence of v e r y few eggs i n the o v a r i e s of t i l e f i s h females t h a t had p a i r e d w i t h t h e i r mates a second time suggests t h a t females r e l e a s e most of t h e i r d a i l y egg batch d u r i n g f i r s t spawnings. I n f o r m a t i o n on the temporal c y c l e of oocyte maturation i n r e l a t i o n t o spawning frequency and p e r i o d i c i t y i s a p p a r e n t l y s c a r c e i n t r o p i c a l marine f i s h e s t h a t can spawn more than once each day. Although i t i s p o s s i b l e t h a t s e p a r a t e batches of eggs are o v u l a t e d p r i o r t o each m u l t i p l e d a i l y spawning, i t seems more l i k e l y t h a t o v u l a t i o n occurs once per day. Very few 140 eggs were found i n o v a r i e s p r i o r t o second spawnings. A l s o , second spawnings o c c u r r e d as soon as 6 min a f t e r f i r s t spawnings. These data suggest t h a t second and t h i r d spawnings pro b a b l y r e l e a s e r e s i d u a l eggs from a s i n g l e batch t h a t i s o v u l a t e d b e f o r e f i r s t spawnings. The o b s e r v a t i o n t h a t females do not spawn every day r a i s e s the q u e s t i o n of whether eggs are sometimes o v u l a t e d and r e t a i n e d u n t i l f u t u r e r e p r o d u c t i v e p e r i o d s r a t h e r than b e i n g r e l e a s e d d u r i n g t h a t same day. Twenty-eight pe r c e n t of non-fed females c o l l e c t e d b e f o r e spawning had fewer than 200 hydrated eggs. I f o v u l a t e d eggs t h a t have undergone h y d r a t i o n may be s t o r e d u n t i l f u t u r e r e p r o d u c t i v e p e r i o d s , then i t i s p o s s i b l e t h a t these females were not ready t o spawn when they were c o l l e c t e d . I d i d not determine e m p i r i c a l l y i f hydrated ova are s t o r e d , and whether they remain v i a b l e u n t i l f u t u r e r e p r o d u c t i v e p e r i o d s . I f r i p e ova can be s t o r e d , then females may accumulate eggs over more than one day p r i o r t o spawning. The o p t i o n t o s t o r e r i p e eggs c o u l d be advantageous i n the event t h a t environmental c o n d i t i o n s f o r spawning become adverse on a p a r t i c u l a r day. For example, females sometimes d i d not spawn f o l l o w i n g barracuda a t t a c k s d i r e c t e d a t them or t h e i r mates, or when males were i n v o l v e d i n heightened a g g r e s s i o n f o l l o w i n g male removals (Chapter 6 ) . Under the h y p o t h e s i s t h a t eggs may be s t o r e d , the number of eggs r e l e a s e d on a g i v e n day c o u l d v a r y w i t h the number of days s i n c e eggs were l a s t spawned. Such f a c t o r s may have c o n t r i b u t e d t o both the l a r g e v a r i a b i l i t y i n e s t i m a t e s of d a i l y b a tch f e c u n d i t y , and the absence of a c o r r e l a t i o n between the 141 number of hydrated ova and body mass, even though ovary mass i s c o r r e l a t e d w i t h body mass. A l s o , although the d i f f e r e n c e was not s t a t i s t i c a l l y s i g n i f i c a n t , the o v a r i e s of non-fed r e e f s l o p e females tended t o c o n t a i n more o v u l a t e d eggs than o v a r i e s of channel females of s i m i l a r s i z e ( F i g u r e 29). T h i s t r e n d might a l s o be e x p l a i n e d by egg s t o r a g e . There i s a h i g h e r p r o b a b i l i t y of c a p t u r i n g a r e e f s l o p e female t h a t had s t o r e d eggs f o r more than one day, because females spawned l e s s f r e q u e n t l y i n t h i s h a b i t a t ( F i g u r e 22). Because s e v e r a l f a c t o r s may i n f l u e n c e the number of eggs t h a t are o v u l a t e d on a g i v e n day, I conclude t h a t gonosomatic index i s the more r e l i a b l e estimate of the energy i n v e s t e d by females i n p r e s e n t r e p r o d u c t i o n . I n f l u e n c e of Food Intake on Female Reproduction and Growth Feeding d i d not i n c r e a s e the frequency of female spawning, but f e d females i n both h a b i t a t s had h i g h e r GSI's, growth r a t e , and d a i l y f e c u n d i t i e s , than non-fed females. Increased GSI and d a i l y f e c u n d i t i e s of f e d f i s h c l e a r l y suggests t h a t p r e s e n t egg p r o d u c t i o n of females i s l i m i t e d by food i n t a k e . Increased growth r a t e s of f e d females i n d i c a t e s t h a t growth, and t h e r e f o r e , f u t u r e c a p a c i t y t o produce eggs, i s a l s o l i m i t e d by energy i n t a k e . Responses t o f e e d i n g l e n d f u r t h e r support t o my i n t e r p r e t a t i o n of removal t e s t s t h a t the f u n c t i o n of female t e r r i t o r i a l i t y i s defense of a food supply surrounding home burrows (Chapter 6). In s p e c i e s where males compete f o r mates, sex u a l s e l e c t i o n t h e o r y p r e d i c t s t h a t female r e p r o d u c t i v e success i s l i m i t e d by r e s o u r c e s t h a t can be devoted t o p r o d u c t i o n of o f f s p r i n g r a t h e r than by access t o males (Bateman, 142 1948; W i l l i a m s , 1966; T r i v e r s , 1972; Bo r g i a , 1979; Alexander and Bo r g i a , 1979). My r e s u l t s are c o n s i s t e n t w i t h t h i s p r e d i c t i o n . I n f l u e n c e o f H a b i t a t S e l e c t i o n and L a r v a l Settlement on the D i s t r i b u t i o n o f A d u l t s E s t i m a t e s o f net y e a r l y mating success a re s i m i l a r i n r e e f s l o p e and channel females (Table 8 ) . T h i s r e s u l t i s c o n s i s t e n t w i t h p r e d i c t i o n s o f the i d e a l f r e e model, assuming t h a t estimated parameters used i n t h i s c a l c u l a t i o n are cons t a n t over the r e p r o d u c t i v e l i f e s p a n o f females. I f t h i s assumption i s v a l i d , then d e n s i t y may be h i g h i n the channel because females s e t t l e i n t h i s area p r e f e r e n t i a l l y u n t i l i n c r e a s i n g c o s t s o f co m p e t i t i o n make i t more p r o f i t a b l e t o move t o r e e f s l o p e s . Other o b s e r v a t i o n s on females are a l s o c o n s i s t e n t w i t h p r e d i c t i o n s o f the i d e a l f r e e model. A l l s i x of the harem removals where no r e c r u i t m e n t o c c u r r e d were i n r e e f s l o p e c o l o n i e s . In c o n t r a s t , r a p i d r e c r u i t m e n t f o l l o w e d a l l seven channel harem removals (Chapter 6), s u p p o r t i n g the n o t i o n t h a t females s e t t l e p r e f e r e n t i a l l y i n the channel. On the o t h e r hand, the food r e s o u r c e s t h a t l i m i t female r e p r o d u c t i o n were not more abundant i n the channel as would be expected under the i d e a l f r e e model. In c o n t r a s t , the h i g h net mating success o f channel males r e l a t i v e t o r e e f s l o p e males i s c o n s i s t e n t w i t h p r e d i c t i o n s o f the i d e a l dominance model. I f the i d e a l dominance model a p p l i e s t o M. p l u m i e r i males, then s u p e r i o r competitors are a b l e t o a c q u i r e t e r r i t o r i e s i n the channel where p o t e n t i a l mates are 143 most abundant, and i n f e r i o r competitors are f o r c e d onto r e e f s l o p e s w i t h fewer p o t e n t i a l mates. Unmated males t h a t were more common i n r e e f s l o p e s , might be f i s h t h a t c o u l d not o b t a i n t e r r i t o r i e s i n the channel and were d i s p l a c e d i n t o r e e f s l o p e h a b i t a t s . Both of these h a b i t a t s e l e c t i o n models are p r e d i c a t e d on the assumption t h a t a d u l t s are a b l e t o move f r e e l y between h a b i t a t s t o a ssess re s o u r c e s and competitor d e n s i t y p r i o r t o c hoosing a t e r r i t o r y ( F r e t w e l l and Lucas, 1969; F r e t w e l l , 1972). I found no evidence t h a t s e t t l e d t i l e f i s h move among r e e f s l o p e c o l o n i e s or between the r e e f s l o p e and the channel, although I cannot be c e r t a i n t h a t a d u l t s do not a c t i v e l y choose from among a v a i l a b l e h a b i t a t s . Such movements seem u n l i k e l y because t i l e f i s h remain near home burrows t o a v o i d p r e d a t o r s (Chapters 3 and 4). Movement between c o l o n i e s would r e q u i r e swimming acr o s s l a r g e u n f a m i l i a r sand f l a t s where t h e r e are no burrows t o serve as r e f u g e s from p r e d a t o r a t t a c k s . R e l o c a t i o n of t e r r i t o r i e s was not observed u n l e s s one or more neighbors were removed. Even then replacements moved from adjacent t e r r i t o r i e s r a t h e r than from o t h e r c o l o n i e s (Chapter 6). Although unoccupied space was a v a i l a b l e , new a d u l t s d i d not r e c r u i t i n t o study c o l o n i e s as might be expected i f movements by a d u l t s were common. A l s o , unmated males i n c o l o n i e s where o n l y a few females were pr e s e n t r e l a t i v e t o the number of males, probably had the most t o g a i n from moving t o o t h e r h a b i t a t s . Nonetheless, these males d i d not move from t e r r i t o r i e s without females f o r the d u r a t i o n of o b s e r v a t i o n s , p e r i o d s of up t o 4.5 months. The apparent absence 144 of movement between c o l o n i e s , t h e r e f o r e , suggests t h a t a d u l t t i l e f i s h do not a c t i v e l y assess t e r r i t o r i e s i n more than one h a b i t a t as assumed by the i d e a l f r e e and i d e a l dominance models. Obs e r v a t i o n s on the d i s t r i b u t i o n o f l a r v a e i n t i l e f i s h and ot h e r s p e c i e s , and c u r r e n t p a t t e r n s a t G l o v e r ' s Reef are c o n s i s t e n t w i t h an a l t e r n a t e h y p o t h e s i s t h a t the d i s t r i b u t i o n and abundance of sedentary a d u l t s i s a consequence of p l a n k t o n i c l a r v a l s e t t l e m e n t . Much of the oce a n i c water t h a t flows onto G l o v e r ' s Reef e n t e r s through passages l i k e the channel between Long and Northeast Cays (Stoddart, 1962). T h e r e f o r e , l a r g e numbers of t i l e f i s h l a r v a e may encounter the channel b e f o r e they reach r e e f s l o p e s i t e s i n s i d e the lagoon. Shapiro (1987) has pre s e n t e d evidence f o r A n t h i a s squamipinnis t h a t p l a n k t o n i c l a r v a e s e t t l e on the f i r s t s u i t a b l e s u b s t r a t e s t h a t are encountered, even though these l o c a t i o n s do not appear t o be the be s t a v a i l a b l e s i t e s . Opting f o r e a r l y s e t t l e m e n t may be the be s t s t r a t e g y f o r l a r v a e because f a c t o r s t h a t a f f e c t s u r v i v a l i n the p l a n k t o n are h i g h l y s t o c h a s t i c (Barlow, 198.1; V i c t o r , 1983; Doherty e t a l . , 1985), and t h e r e i s no guarantee t h a t a b e t t e r s i t e w i l l be encountered i f set t l e m e n t i s postponed. E a r l y s e t t l e m e n t i n the f i r s t h a b i t a t encountered, t h e r e f o r e , may e x p l a i n the l a r g e dense c o n c e n t r a t i o n o f t i l e f i s h i n the channel. In support o f t h i s h y p o t h e s i s , j u v e n i l e s were 15 times more common i n the channel than i n r e e f s l o p e c o l o n i e s (Chapter 4 ) . A l s o , replacement by s m a l l females or j u v e n i l e s o c c u r r e d much more r e a d i l y i n the channel f o l l o w i n g f i s h removals. L a s t l y , examination of another east-west passage through the n o r t h e r n 145 p a r t o f the a t o l l a l s o r e v e a l e d the presence o f a l a r g e t i l e f i s h c o l o n y . A l l o f these o b s e r v a t i o n s support the h y p o t h e s i s t h a t , even though h i g h p r e d a t i o n r i s k may make i t more dangerous than r e e f s l o p e s , many r e c r u i t s s e t t l e i n the channel as a consequence of p r e v a i l i n g water c i r c u l a t i o n . Food a v a i l a b i l i t y and Female Spawning Frequency Feeding d i d not i n c r e a s e spawning frequency. T h i s suggests t h a t a h i g h e r r a t e o f food i n t a k e probably does not e x p l a i n why channel females spawn more f r e q u e n t l y than r e e f s l o p e females. On the c o n t r a r y , h i g h e r b i t e and swimming r a t e s suggest t h a t i t may be necessary f o r channel females t o expend more e f f o r t f o r a g i n g , p o s s i b l y because food r e s o u r c e s are i n f e r i o r i n t h i s h a b i t a t . E s t i m a t e s o f food a v a i l a b i l i t y , however, do not support the l a t t e r h y p o t h e s i s e i t h e r . Stomach co n t e n t s r e v e a l e d t h a t females i n the two h a b i t a t s i n g e s t s i m i l a r prey. The onl y evidence t h a t prey are more s c a r c e i n the channel i s the lower biomass of mollusks. O v e r a l l , the esti m a t e s o f prey abundance are s i m i l a r i n the two h a b i t a t s , and cru s t a c e a n s o f the s i z e range t h a t t i l e f i s h eat, were even l a r g e r i n the channel. F i n a l l y , e s t i m a t e s o f d a i l y batch f e c u n d i t y , GSI, and growth r a t e s of non-fed females i n the two h a b i t a t s were not s t a t i s t i c a l l y d i f f e r e n t , s u g g e s t i n g t h a t r e e f s l o p e and channel females p r o b a b l y have access t o s i m i l a r amounts of food. Together these r e s u l t s suggest t h a t the abundance or q u a l i t y of food r e s o u r c e s alone does not e x p l a i n the s t r i k i n g d i f f e r e n c e s i n r a t e s o f spawning and f o r a g i n g by females i n the two h a b i t a t s . 146 The R e l a t i o n s h i p Between Female Reproductive E f f o r t and  the Behavior of P r edators Disappearance r a t e s of tagged f i s h suggest t h a t r i s k of p r e d a t i o n i s h i g h e r i n the channel. Where p r e d a t i o n r i s k i s h i g h , females might be expected t o spawn l e s s f r e q u e n t l y and forage c l o s e r t o t h e i r burrows t o minimize v u l n e r a b i l i t y . Conversely, r e e f s l o p e females might be expected t o forage f a r t h e r from t h e i r burrows and perhaps spawn more f r e q u e n t l y because p r e d a t i o n r i s k i s lower. I observed the o p p o s i t e p a t t e r n . One p o s s i b l e e x p l a n a t i o n of t h i s paradox i s t h a t the d i f f e r e n t b e h a v i o r p a t t e r n s of r e e f s l o p e and channel females are r e l a t e d t o d i f f e r e n c e s i n the h u nting t a c t i c s used by barracuda i n the two h a b i t a t s . In r e e f s l o p e h a b i t a t s , spawning f r e q u e n t l y and f o r a g i n g d i s t a n t from burrows might g r e a t l y i n c r e a s e v u l n e r a b i l i t y t o a t t a c k , because barracuda l u r k on these s i t e s and s t a l k t i l e f i s h . By remaining c l o s e r t o burrows and o p t i n g f o r a lower r a t e of spawning and f o r a g i n g , r e e f s l o p e females are a p p a r e n t l y a b l e t o counter the e f f e c t i v e n e s s of l u r k i n g p r e d a t o r s . By c o n t r a s t , channel females appear t o s u f f e r h i g h e r p r e d a t i o n r i s k , y e t they e x h i b i t behavior t h a t makes them v u l n e r a b l e t o a t t a c k . I t i s not c l e a r why such b e h a v i o r i s maintained. One p o s s i b i l i t y i s t h a t channel females do not r e a d i l y d e t e c t the p r e d a t o r s t h a t swim above them, and behave as i f r i s k of a t t a c k were low. Channel females might a l s o h a b i t u a t e t o the d a i l y m i g r a t i o n by l a r g e p i s c i v o r e s through the 147 channel, and simply do not r e a c t as r e a d i l y as r e e f s l o p e females. Another p o s s i b i l i t y , however, i s t h a t channel females are making the b e s t of a bad s i t u a t i o n by spawning f r e q u e n t l y i n a h i g h r i s k h a b i t a t . When the r i s k t o i n d i v i d u a l s of a t t a c k i s h i g h and u n p r e d i c t a b l e , bet-hedging t h e o r y p r e d i c t s , t h a t i n d i v i d u a l s should maximize p r e s e n t r e p r o d u c t i v e e f f o r t s . The b e h a v i o r of channel females i s c o n s i s t e n t w i t h t h i s p r e d i c t i o n . F o r a g i n g a t a h i g h r a t e , d i s t a n t from burrows suggests i n c r e a s e d e f f o r t s t o o b t a i n the food r e s o u r c e s t h a t l i m i t egg p r o d u c t i o n even though f o r a g i n g may a l s o i n c r e a s e v u l n e r a b i l i t y t o a t t a c k and reduce v i g i l a n c e . The most s t r i k i n g i n d i c a t i o n t h a t channel females maximize p r e s e n t r e p r o d u c t i v e e f f o r t i s the frequent occurrence o f m u l t i p l e d a i l y spawnings. Second and t h i r d d a i l y spawnings were much more common i n channel females even though o n l y a s m a l l number of eggs was r e l e a s e d d u r i n g these matings. When p r e d a t o r a t t a c k s occur a t any time w i t h l i t t l e warning, the b e s t r e p r o d u c t i v e t a c t i c may be t o take the f u l l e s t advantage of p r e s e n t spawning o p p o r t u n i t i e s . The frequent occurrence of m u l t i p l e spawns, even though they c o n t r i b u t e r e l a t i v e l y few eggs, i s c o n s i s t e n t w i t h the h y p o t h e s i s t h a t channel females maximize immediate spawning o p p o r t u n i t i e s . By c o n t r a s t , r e e f s l o p e females had much lower r a t e s of spawning even though food a v a i l a b i l i t y and GSI were as h i g h as those o f channel females. A t t a c k s by l u r k i n g p r e d a t o r s may be more p r e d i c t a b l e , and thus a v o i d a b l e , than i n the channel. Under t h i s type of p r e d a t i o n t h r e a t , r e e f s l o p e f i s h might opt f o r a lower r a t e of spawning because the p r o b a b i l i t y of p r e d a t i o n 148 b e f o r e f u t u r e r e p r o d u c t i v e bouts i s lower. The d i f f e r e n t response by r e e f s l o p e and channel females t o i n c r e a s e d food i n t a k e i s the s t r o n g e s t evidence t o support the hy p o t h e s i s t h a t female r e p r o d u c t i v e t a c t i c s a re i n f l u e n c e d by the type o f p r e d a t i o n r i s k . N e i t h e r channel o r r e e f s l o p e females spawned more f r e q u e n t l y when f e d e x p e r i m e n t a l l y . However, t h e r e was an obvious t r e n d i n how females a l l o c a t e d a d d i t i o n a l energy t o somatic growth and t o o v a r i e s . Reef s l o p e females grew p r o p o r t i o n a t e l y more and thereby i n c r e a s e d t o a g r e a t e r degree t h e i r c a p a c i t y f o r f u t u r e egg p r o d u c t i o n . High growth r a t e s i n response t o i n c r e a s e d food i n t a k e might be expected when the r i s k o f p r e d a t i o n b e f o r e f u t u r e r e p r o d u c t i v e p e r i o d s i s low. By c o n t r a s t , channel females might be expected t o i n v e s t more energy i n egg p r o d u c t i o n when r e s o u r c e s a re abundant, because the r i s k of p r e d a t i o n b e f o r e f u t u r e r e p r o d u c t i v e bouts i s h i g h e r . In accordance w i t h t h i s e x p e c t a t i o n , f e d channel females had h i g h e r GSI's and a tendency t o produce more eggs, s u g g e s t i n g t h a t they a l l o c a t e more energy t o p r e s e n t r e p r o d u c t i o n than f e d r e e f s l o p e females. 149 CHAPTER SUMMARY 1. Average s i z e of both sexes was s m a l l e r i n the channel, w h i l e growth r a t e s i n the two h a b i t a t s were s i m i l a r . 2. Channel males had l a r g e r harems and spawned more than twice as f r e q u e n t l y as r e e f s l o p e males. Harem s i z e was c o r r e l a t e d more s t r o n g l y w i t h the w i t h i n - c o l o n y r a t i o of females t o males than the d i s t a n c e s e p a r a t i n g females. 3. Channel females forage a t h i g h e r r a t e s over l a r g e r areas, and spawn more f r e q u e n t l y than r e e f s l o p e females. 4. Abundance and s i z e of prey i n s u b s t r a t e samples from r e e f s l o p e c o l o n i e s and the channel were s i m i l a r . 5. D a i l y b atch f e c u n d i t y of non-fed females was h i g h l y v a r i a b l e and was not s t a t i s t i c a l l y d i f f e r e n t i n r e e f s l o p e and channel h a b i t a t s . 6. D i e t supplementation d i d not i n c r e a s e spawning frequency, but f e d females i n both h a b i t a t s grew f a s t e r , produced more eggs, and had h i g h e r GSI's than non-fed c o n t r o l s . 7. E s t i m a t e s of net y e a r l y mating success were s i m i l a r i n r e e f s l o p e and channel females, w h i l e net mating success of channel males was more than twice t h a t of r e e f s l o p e males. These e s t i m a t e s are c o n s i s t e n t w i t h p r e d i c t i o n s of the i d e a l f r e e model i n females and the i d e a l dominance model i n males. However, a c t i v e h a b i t a t s e l e c t i o n i n a d u l t t i l e f i s h appears u n l i k e l y because they a p p a r e n t l y do not move f r e e l y between 150 h a b i t a t s . 8. The d i s t r i b u t i o n of j u v e n i l e s i n r e l a t i o n t o p r e v a i l i n g c u r r e n t p a t t e r n s , i s c o n s i s t e n t w i t h the a l t e r n a t e h y p o t h e s i s t h a t the d i s t r i b u t i o n and abundance of a d u l t s i s a consequence of l a r v a l s e t t l e m e n t p r o c e s s e s . 9. D i f f e r e n t responses t o d i e t supplementation by r e e f s l o p e and channel females t h a t are c o r r e l a t e d w i t h d i f f e r e n c e s i n p r e d a t i o n , support the h y p o t h e s i s t h a t i n d i v i d u a l s may modify r e p r o d u c t i v e t a c t i c s i n accordance w i t h r i s k of p r e d a t i o n b e f o r e f u t u r e r e p r o d u c t i v e p e r i o d s . CHAPTER 8 GENERAL DISCUSSION The Role of Female T e r r i t o r i a l i t y i n Marine F i s h Harems In p e l a g i c a l l y - s p a w n i n g marine f i s h e s , the degree t o which polygynous males monopolize more than one of the same females may be r e l a t e d t o the s p a t i a l d i s t r i b u t i o n of females d u r i n g spawning p e r i o d s . When females depart t h e i r f e e d i n g ranges and migrate independently t o a l i m i t e d number of f a v o r a b l e spawning s i t e s , i t may not be f e a s i b l e f o r males t o m a i n t a i n c o n t a c t with and monopolize spawnings w i t h the same s e t of mates (Robertson and Hoffman, 1977; Robertson, 1981). In a d d i t i o n , p r e d i c t a b l e c o n g r e g a t i o n s of females t h a t are ready t o spawn would almost c e r t a i n l y a t t r a c t l a r g e numbers of male competitors, making i t more d i f f i c u l t f o r i n d i v i d u a l males t o monopolize d a i l y spawnings w i t h a harem. Consequently, the mating systems of s p e c i e s i n which females congregate i n c e r t a i n spawning s i t e s may resemble l e k s r a t h e r than harems. In l e k - l i k e s p e c i e s , c e r t a i n males e s t a b l i s h temporary t e r r i t o r i e s each day i n areas p r e f e r r e d by females f o r spawning (e.g., Moyer and Yogo, 1982; Warner, 1984b; 1987; Hoffman, 1985). T e r r i t o r i a l males may mate w i t h numerous females each day, but they do not m a i n t a i n s o c i a l c o n t a c t and monopolize d a i l y spawnings w i t h the same females over prolonged p e r i o d s . By c o n t r a s t , when females each spawn w i t h i n an a l l - p u r p o s e t e r r i t o r y , they do not migrate, and are not h i g h l y aggregated d u r i n g spawning p e r i o d s . In s p e c i e s i n which females are t e r r i t o r i a l , male m o n o p o l i z a t i o n of harems may be f e a s i b l e when 152 females are l o c a t e d s u f f i c i e n t l y c l o s e t o g e t h e r t h a t males are a b l e t o exclude competitors from more than one female t e r r i t o r y . Kuwamura (1984) has argued t h a t harems do not form i n s p e c i e s w i t h t e r r i t o r i a l females. Kuwamura (1984) suggests t h a t harems c o n s i s t i n g of t e r r i t o r i a l females are r a r e , and t h a t i n t e r s e x u a l c o m p e t i t i o n f o r food prevents formation of harems when females defend f e e d i n g t e r r i t o r i e s . The c l e a n e r wrasse, L. dimidatus, has been regarded as a good example of a s p e c i e s w i t h harems composed of adjacent t e r r i t o r i a l females (Robertson, 1972; Robertson and Hoffman, 1977), but Kuwamura (1984) concluded t h a t females i n t h i s s p e c i e s do not defend t r u e f e e d i n g t e r r i t o r i e s . Data on t i l e f i s h show c l e a r l y t h a t males may monopolize harems when females are t e r r i t o r i a l . Sand t i l e f i s h harems are composed of a d j a c e n t female t e r r i t o r i e s encompassed by the t e r r i t o r y of one male. Both sexes feed w i t h i n t e r r i t o r i e s t h a t o v e r l a p the t e r r i t o r i e s of t h e i r mates. T h e r e f o r e , i n t e r s e x u a l c o m p e t i t i o n f o r food does not prevent the f o r m a t i o n of harems i n M. p l u m i e r i . S o c i a l o r g a n i z a t i o n s s i m i l a r t o t h a t of M. p l u m i e r i have been d e s c r i b e d i n a number of p e l a g i c a l l y - s p a w n i n g marine f i s h e s . Females defend t e r r i t o r i e s t h a t are used f o r f e e d i n g i n a r e e f - d w e l l i n g a n g e l f i s h (Hourigan, 1986), two sand f l a t -d w e l l i n g r a z o r f i s h e s ( C l a r k e , 1983; V i c t o r , 1987; B a i r d , 1988), and a w e a v e r f i s h (Stroud, 1981). In each of these s p e c i e s , males monopolize spawnings wi t h a number of females by defending a l l - p u r p o s e t e r r i t o r i e s t h a t o v e r l a p those of females. These s t u d i e s i n d i c a t e c l e a r l y t h a t harems composed of a d j a c e n t 153 t e r r i t o r i a l females are not r a r e as suggested by Kuwamura (1984) . In t i l e f i s h , two aspects of s p a c i n g b e h a v i o r d i s t r i b u t e females i n a way t h a t may f a c i l i t a t e r a t h e r than prevent harem form a t i o n . Under the r i s k of p r e d a t i o n , s e l e c t i o n may f a v o r females t h a t s e t t l e near o t h e r t i l e f i s h ( i . e . , c o l o n y f o r m a t i o n ) . Females are o n l y moderately c o n c e n t r a t e d w i t h i n c o l o n i e s , however, because they defend non-overlapping . t e r r i t o r i e s . A moderate c o n c e n t r a t i o n of s i t e - r e s t r i c t e d females i s p r e c i s e l y the c o n d i t i o n under which some males might be expected t o monopolize more than one mate (Emlen and Oring, 1977) . Harems i n Pelacricallv-Spawnincr Marine F i s h e s : Female o r Resource  Defense? P e l a g i c a l l y - s p a w n i n g f i s h e s t h a t breed year-round p r e s e n t a p a r t i c u l a r l y d i f f i c u l t c h a l l e n g e f o r the q u e s t i o n of whether harems a r i s e through resource or female defense. In most ( i f not a l l ) of these s p e c i e s where spawning data on i n d i v i d u a l s has been c o l l e c t e d t o document harem-type mating systems, males a p p a r e n t l y defend permanent t e r r i t o r i e s t h a t c o n t a i n both females and t h e i r r e s o u r c e s . T h e r e f o r e , u n l i k e many harem-forming homeotherms, whether males defend r e s o u r c e s or a t t a c h themselves t o female groups cannot be d i s t i n g u i s h e d r e a d i l y by d i f f e r e n c e s i n the degree t o which males and females are r e s t r i c t e d t o , or d i s p e r s e from b r e e d i n g s i t e s (Greenwood, 1980; Armitage, 1986). 154 The c r i t i c a l q u e s t i o n i n pelagic-spawning f i s h e s i s : Why are females r e s t r i c t e d t o s i t e s such t h a t males are a b l e t o monopolize d a i l y spawnings wi t h more than one mate? So long as males are a b l e t o monopolize m u l t i p l e mates, a t l e a s t i n p a r t because females are r e s t r i c t e d t o areas where they consume food a l l o c a t e d t o d a i l y egg p r o d u c t i o n , the r e s o u r c e defense h y p o t h e s i s cannot be r e j e c t e d e n t i r e l y . Invoking female defense i n l i e u o f r e s o u r c e defense should be r e s e r v e d f o r s p e c i e s f o r which i t i s demonstrated t h a t : 1) males monopolize females t h a t are s i t e - r e s t r i c t e d e x c l u s i v e l y f o r reasons u n r e l a t e d t o a c q u i s i t i o n of food or o t h e r r e s o u r c e s necessary f o r r e p r o d u c t i o n , or 2) males c o n t r o l mobile females t h a t group t o g e t h e r f o r reasons u n r e l a t e d t o r e p r o d u c t i o n . R e s u l t s of t h i s study s t r o n g l y suggest t h a t t i l e f i s h males monopolize mates by defending t e r r i t o r i e s c o n t a i n i n g food r e s o u r c e s t h a t are important f o r egg p r o d u c t i o n . A l s o , t i l e f i s h males n e i t h e r c o n t r o l the movement and l o c a t i o n of t h e i r mates, nor abandon t e r r i t o r i e s when t h e i r mates are removed. These r e s u l t s support a r o l e of resource defense i n the e v o l u t i o n of t i l e f i s h harems. Females i n most ot h e r pelagic-spawning f i s h e s t h a t are known t o form t r u e harem mating u n i t s a l s o occupy f e e d i n g t e r r i t o r i e s o r f i x e d but undefended f e e d i n g ranges (Robertson & Hoffman, 1977; Moyer & Nakazono, 1978; Stroud, 1981; C l a r k , 1983; Hoffman, 1983; Kuwamura, 1984; Hourigan, 1986; V i c t o r , 1987; Petersen and F i s c h e r , 1987). T h e r e f o r e , e x c l u s i v e male spawning access t o m u l t i p l e females t h a t mate d a i l y may be f e a s i b l e o n l y when females are r e s t r i c t e d t o s i t e s 155 where they forage (Robertson, 1981). On the o t h e r hand, t i l e f i s h males c l e a r l y p o s i t i o n t h e i r t e r r i t o r i e s where females r e s i d e . I t i s probably o n l y f e a s i b l e f o r males t o defend more than one mate because females occupy a d j a c e n t t e r r i t o r i e s . Such group l i v i n g i n t i l e f i s h may, a t l e a s t i n p a r t , be s e l e c t e d because p r o x i m i t y t o c o n s p e c i f i c s reduces p r e d a t i o n r i s k (Chapter 4). S i m i l a r l y , r a z o r f i s h e s t h a t form harems l i k e those of M. p l u m i e r i . a l s o appear t o accrue a n t i - p r e d a t o r b e n e f i t s from l i v i n g i n groups ( C l a r k , 1983; V i c t o r , 1987). Harem formation i n s p e c i e s t h a t l i v e i n groups t o reduce p r e d a t i o n r i s k i s c o n s i s t e n t w i t h the female defense h y p o t h e s i s . I suggest t h a t a dichotomy between r e s o u r c e and female defense, may not apply w e l l t o harem-forming f i s h e s where females are s i t e - r e s t r i c t e d and p r o d u c t i o n of p l a n k t o n i c eggs i s i t e r a t e d year-round. Among the c l e a r e s t examples of r e s o u r c e defense are marsh-nesting b i r d s i n which males e s t a b l i s h t e r r i t o r i e s p r i o r t o the a r r i v a l of females i n n e s t i n g h a b i t a t s (Searcy & Yasukawa, 1983; Robinson, 1986). Such an obvious i n d i c a t i o n t h a t males c o n t r o l areas t o which females are a t t r a c t e d i s l a c k i n g i n f i s h e s where females and males m a i n t a i n b r e e d i n g r e l a t i o n s h i p s throughout the year, and spawning i s not l i m i t e d t o c e r t a i n l o c a t i o n s . D i r e c t female defense i s perhaps most c l e a r i n ungulates where males a c t i v e l y herd t o g e t h e r female mates ( G o s l i n g , 1986), or i n marmots where males dominate female k i n groups (Armitage, 1986). Although s o - c a l l e d "pure female defense" has been suggested f o r harem-forming f i s h e s 156 (Kuwamura, 1984; Hourigan, 1986; V i c t o r , 1987), t h i s c o n c l u s i o n seems unwarranted when males are a b l e t o monopolize mates p a r t l y because females are r e s t r i c t e d t o t e r r i t o r i e s or home ranges where they feed and spawn. I urge c a u t i o n i n c o n c l u d i n g t h a t e i t h e r mechanism alone e x p l a i n s the e v o l u t i o n of harems i n these f i s h e s without r i g o r o u s demonstration. In my view, c h a r a c t e r i z a t i o n of harems as female defense polygyny alone r e q u i r e s : 1) documentation of c o n s i s t e n t mating f i d e l i t y among females i n h i g h l y mobile aggregations and i n d i v i d u a l males t h a t defend these groups, or 2) demonstration t h a t males abandon t h e i r t e r r i t o r i e s when females are removed and move t o seek o t h e r mates. As f a r as I know, n e i t h e r of these s i t u a t i o n s has y e t been demonstrated i n pelagic-spawning f i s h e s w i t h harem-type mating systems. Burrowing and C o l o n i a l i t y i n Marine F i s h e s : P o s s i b l e Adaptations  t o L i f e i n Open Seabed H a b i t a t s C o l o n i a l i t y i s thought t o be r a r e i n f i s h e s compared wi t h b i r d s , rodents, and p i n n i p e d s . The n e s t i n g c o l o n i e s of male b l u e g i l l s u n f i s h e s are the b e s t known example of f i s h c o l o n i a l i t y (Dominey, 1981; Gross and MacMillan, 1981), although c o l o n i a l n e s t i n g has a l s o been d e s c r i b e d i n c i c h l i d s ( L o i s e l l e , 1977). B l u e g i l l s u n f i s h are c h a r a c t e r i z e d by h i g h l y s y n c h r o n i z e d n e s t i n g , e g g - l a y i n g , and nest-guarding, as i s a l s o seen i n some c o l o n i a l b i r d s (Wittenberger, 1981 and r e f e r e n c e s ) . Perhaps c o l o n i a l i t y i s more common but has not been r e c o g n i z e d w i d e l y among t r o p i c a l marine f i s h e s because few ( i f any) s p e c i e s l a y eggs i n n e s t i n g c o l o n i e s . N e v e r t h e l e s s , s e v e r a l of the same 157 s p e c i e s t h a t c o n s t r u c t burrows i n open seabed h a b i t a t s a l s o form groups t h a t f i t Wittenberger's (1981) d e f i n i t i o n of c o l o n i a l i t y . Two s p e c i e s of burrowing r a z o r f i s h e s , X. m a r t i n i c e n i s ( V i c t o r , 1987) , and X. p e n t a d a c t y l u s ( C l a r k , 1983) l i v e i n c o l o n i e s on sand f l a t s . F r i c k e and Kacher (1982) r e p o r t t h a t another t i l e f i s h , H o p l o l a t i l u s qeo. occurs i n d i s c r e t e c o l o n i e s w i t h i n which i n d i v i d u a l s or p a i r s occupy f i x e d mounded burrows. F i n a l l y , the burrowing garden e e l s , Taeniconqer h a s s i and G o r q a s i a s i l l n e r i , and the yellowheaded j a w f i s h a l s o c o n c e n t r a t e i n c o l o n i e s , even though a p p a r e n t l y s u i t a b l e unoccupied s u b s t r a t e i s abundant ( F r i c k e , 1970; C o l i n , 1973). The occurrence of burrowing and c o l o n i a l i t y i n marine f i s h e s from a t l e a s t f o u r f a m i l i e s suggests t h a t t h i s l i f e s t y l e i s a response t o s e l e c t i o n p r e s s u r e s t h a t are p e c u l i a r t o l i f e i n open seabeds, such as v u l n e r a b i l i t y t o p r e d a t o r s . S i m i l a r i t i e s between the the behavior of some rodents t h a t occupy open t e r r e s t r i a l h a b i t a t s and c o l o n i a l burrowing f i s h e s lends support t o t h i s h y p o t h e s i s . P r a i r i e dogs, marmots, and ground s q u i r r e l s , f o r example, d i g complex burrows t h a t p r o v i d e the primary s h e l t e r from p r e d a t i o n . Furthermore, these s p e c i e s l i v e i n dense c o l o n i e s (e.g., C a r l , 1971; Armitage and Downhower, 1974; Hoogland, 1979; 1980), sometimes c h a r a c t e r i z e d by harem s o c i a l and mating o r g a n i z a t i o n s (Downhower and Armitage, 1971; Wittenberger, 1979). C o l o n i a l rodents u s u a l l y share c e n t r a l l y - l o c a t e d communal burrows (Wittenberger, 1979), r a t h e r than each occupying separate refuges as i n burrowing f i s h e s . 158 Both burrowing rodents and f i s h e s are hunted by l a r g e p r e d a t o r s ( i . e . , r a p t o r s f o r rodents, l a r g e p i s c i v o r e s f o r burrowing f i s h e s ) t h a t may a t t a c k suddenly, and from any d i r e c t i o n . Moreover, some of these rodents have e v o l v e d e l a b o r a t e s o c i a l s i g n a l s f o r p r e d a t o r avoidance (e.g., Waring, 1970; Sherman, 1977; Owings and V i r g i n i a , 1978; Hoogland, 1979). Among the burrowing f i s h e s , a t l e a s t t i l e f i s h , garden e e l s , and s t r a i g h t - t a i l e d r a z o r f i s h are known t o e x h i b i t contagious r e a c t i o n s t o alarm responses by neighbors ( F r i c k e , 1970; V i c t o r , 1987). The adoption o f p a r a l l e l b e h a v i o r p a t t e r n s by p h y l e t i c a l l y d i v e r s e s p e c i e s suggests a common s o l u t i o n t o problems imposed by s i m i l a r environmental c o n d i t i o n s (Alcock, 1984). I suggest t h a t adoption o f a burrowing and c o l o n i a l l i f e s t y l e among rodents and p h y l e t i c a l l y d i s t a n t marine f i s h e s i s a convergent e v o l u t i o n a r y s o l u t i o n t o the e x t r a o r d i n a r y p r e d a t i o n r i s k a s s o c i a t e d w i t h occupying open environments where s h e l t e r i s s c a r c e . The D i s t r i b u t i o n o f T r o p i c a l Marine F i s h e s : A d u l t H a b i t a t  S e l e c t i o n o r Consequence of L a r v a l Settlement? The i d e a l f r e e and i d e a l dominance h a b i t a t s e l e c t i o n models were proposed f o r d i s p e r s i v e s p e c i e s i n which i n d i v i d u a l s migrate i n t o b r e e d i n g h a b i t a t s each season where they e s t a b l i s h r e p r o d u c t i v e t e r r i t o r i e s ( F r e t w e l l and Lucas, 1969; F r e t w e l l , 1972). I n d i v i d u a l s i n such s p e c i e s are almost c e r t a i n l y a b l e t o move f r e e l y among a v a i l a b l e h a b i t a t s t o s e l e c t s i t e s , p a r t i c u l a r l y b e f o r e they have e s t a b l i s h e d t e r r i t o r i e s . In c o n t r a s t , t i l e f i s h a p p a r e n t l y h o l d t e r r i t o r i e s and 159 spawn year-round. (Chapter 5) . I found no evidence o f a d u l t m i g r a t i o n between channel and r e e f s l o p e h a b i t a t s o r among r e e f s l o p e c o l o n i e s (Chapter 7), although I cannot be c e r t a i n t h a t such movements never occur. There i s growing evidence t h a t some t r o p i c a l marine f i s h e s spend most of t h e i r l i v e s i n the h a b i t a t s where they s e t t l e d as l a r v a e , and t h a t immigration i n t o l o c a l p o p u l a t i o n s i s l i m i t e d t o r e c r u i t m e n t by p l a n k t o n i c l a r v a e . P o p u l a t i o n s o f T. b i f a s c i a t u m on patch r e e f s , f o r example, are b e l i e v e d t o be l i n k e d o n l y by mixing o f p l a n k t o n i c l a r v a e (Warner and Hoffman, 1980a; 1980b; V i c t o r , 1983; Warner, 1984b). A n t h i a s squamipinnis i s most abundant on deep r e e f s , even though the l a r g e r s i z e o f i n d i v i d u a l s on shallow r e e f s suggests t h a t , i f a d u l t s were mobile, i t would be advantageous t o migrate from deep t o shallow areas (Shapiro, 1987). A n g e l f i s h e s have been observed t o occupy the same areas f o r as lo n g as 3.5 ye a r s (Aldenhoven, 1986), and Moyer (1986) has observed i n d i v i d u a l s o f f i v e s p e c i e s i n the same l o c a t i o n s f o r from 5 t o 14 y e a r s . These o b s e r v a t i o n s suggest t h a t movement between d i f f e r e n t h a b i t a t s i s uncommon i n t r o p i c a l marine f i s h e s . Such s i t e - r e s t r i c t i o n i n t i l e f i s h would p r o h i b i t i n d i v i d u a l s from a s s e s s i n g t e r r i t o r i e s i n more than one h a b i t a t p a tch and then s e t t l i n g i n the b e s t a v a i l a b l e s i t e . As the a b i l i t y t o d i s p e r s e f r e e l y among h a b i t a t s i s a fundamental assumption of the i d e a l f r e e and i d e a l dominance models, these hypotheses are not l i k e l y t o apply t o t i l e f i s h o r ot h e r sedentary marine s p e c i e s w i t h p l a n k t o n i c l a r v a e . 160 I f a d u l t t i l e f i s h do not change h a b i t a t s once they have s e t t l e d , then c o l o n i e s would p e r s i s t i n the same l o c a t i o n s o n l y i f a t l e a s t some v i c t i m s o f p r e d a t i o n are r e p l a c e d by r e c r u i t m e n t of j u v e n i l e s . E x t i n c t i o n o f c o l o n i e s was not observed over f o u r study seasons, although the presence of burrows on unoccupied s i t e s i n d i c a t e s t h a t c o l o n i e s might sometimes become e x t i n c t . No new c o l o n i e s were d i s c o v e r e d where t i l e f i s h were absent d u r i n g p r e v i o u s y e a r s , and j u v e n i l e s were encountered e x c l u s i v e l y near a d u l t s r a t h e r than i n a l l j u v e n i l e groups. These o b s e r v a t i o n s suggest t h a t p r e f e r e n t i a l s e t t l e m e n t near a d u l t s by l a r v a e and/or j u v e n i l e s a l s o may occur i n M. p l u m i e r i . and t h a t t h i s p rocess perpetuates c o l o n i e s through time. L a r v a l a t t r a c t i o n t o a d u l t s has been demonstrated i n some s e s s i l e i n v e r t e b r a t e s (Levinton, 1982). R e l a t i v e L i f e t i m e Reproductive Success of Reef Slope and  Channel F i s h Although the dense colony of t i l e f i s h i n the channel may be l a r g e l y a consequence of l a r v a l t r a n s p o r t , s e t t l e m e n t i n such areas may a l s o be advantageous i f some i n d i v i d u a l s s u r v i v e long enough t o o b t a i n l a r g e harems and garner h i g h l i f e t i m e r e p r o d u c t i v e success d e s p i t e h i g h p r e d a t i o n r i s k . H i s t o l o g i c a l evidence suggests t h a t most i f not a l l male t i l e f i s h are sex-changed females (monandry, Chapter 5). I f t i l e f i s h are monandric, then the l i f e t i m e r e p r o d u c t i v e success o f f i s h t h a t change sex and o b t a i n harems i n c l u d e s t h e i r success as a female p l u s t h a t as a male. Estimated net y e a r l y mating success o f s i m i l a r l y s i z e d females was not s t a t i s t i c a l l y d i f f e r e n t i n the 161 two h a b i t a t s (Table 8). In marked c o n t r a s t , the net y e a r l y mating success of channel males was over twice t h a t o f r e e f s l o p e males (Table 9). T h e r e f o r e , i f one assumes t h a t o f f s p r i n g spawned i n the two h a b i t a t s s u r v i v e e q u a l l y w e l l , and t h a t the d u r a t i o n of the mating l i f e s p a n as females and males i s s i m i l a r i n the two h a b i t a t s , then channel f i s h w i l l o b t a i n h i g h e r l i f e t i m e r e p r o d u c t i v e success than r e e f s l o p e f i s h . A l s o , o p p o r t u n i t i e s f o r sex change and a c q u i r i n g harems may i n c r e a s e w i t h p o p u l a t i o n d e n s i t y (Aldenhoven, 1986; Warner, 1988). The s m a l l e r s i z e of channel males even though they grew a t s i m i l a r or h i g h e r r a t e s suggests t h a t sex change may occur e a r l i e r i n t h i s h a b i t a t . S e l e c t i o n may f a v o r s e t t l e m e n t i n the channel, t h e r e f o r e , because the l i f e t i m e mating success of f i s h t h a t s u r v i v e l o n g enough t o change sex and then a c q u i r e l a r g e harems i s h i g h e r than t h a t of sex-changed r e e f s l o p e f i s h t h a t o b t a i n fewer mates. Under t h i s h y p o t h e s i s , sex-changed r e e f s l o p e f i s h may be making the b e s t of a bad s i t u a t i o n . A l t e r n a t i v e l y , the l i f e t i m e mating success of r e e f s l o p e f i s h may equal or surpass t h a t of channel f i s h , i f r e e f s l o p e f i s h reproduce over a l o n g e r l i f e s p a n . I d i d not determine the age of t i l e f i s h . T h e r e f o r e , I cannot accept or r e j e c t the p o s s i b i l i t y t h a t the average l i f e s p a n of male r e e f s l o p e f i s h i s s u f f i c i e n t l y l o n g t o balance the short-term r e p r o d u c t i v e advantage of channel f i s h . The lower r a t e s of disappearance and the l a r g e r s i z e of r e e f s l o p e f i s h , however, are both c o n s i s t e n t w i t h t h i s h y p o t h e s i s . 162 H a b i t a t D i f f e r e n c e s i n P r e d a t i o n R i s k and Female Spawning Rates I t i s c o n c e i v a b l e t h a t females with h i g h and low spawning r a t e s are two g e n e t i c a l l y f i x e d b e h a v i o r p a t t e r n s , and t h a t h a b i t a t d i f f e r e n c e s r e s u l t because each genotype s e t t l e s p r e f e r e n t i a l l y i n t o a h a b i t a t where i t s r e p r o d u c t i v e b e h a v i o r i s b e s t s u i t e d . Such h a b i t a t s e l e c t i o n would have t o occur d u r i n g l a r v a l s e t t l e m e n t i f a d u l t s are sedentary. For t h i s h y p o t h e s i s t o be p l a u s i b l e , l a r v a e would need t o assess a t the time of s e t t l i n g the type of p r e d a t i o n t h r e a t experienced by a d u l t s . I cannot r e j e c t t h i s as a p o s s i b i l i t y . However, assessment of the i n t e n s i t y and type of p r e d a t i o n on a d u l t s p r i o r t o a c t u a l s e t t l e m e n t on the s i t e seems u n l i k e l y . I t seems much more l i k e l y t h a t females i n r e e f s l o p e and channel h a b i t a t s are not g e n e t i c a l l y d i s t i n c t p o p u l a t i o n s , because p e l a g i c l a r v a e o r i g i n a t i n g from d i f f e r e n t h a b i t a t s are mixed d u r i n g the p l a n k t o n i c d i s p e r s a l phase (Avise and Shapiro, 1987). I f r e e f s l o p e and channel f i s h are not g e n e t i c a l l y d i s t i n c t t ypes, then h a b i t a t d i f f e r e n c e s i n spawning r a t e s may be two c o n d i t i o n a l r e p r o d u c t i v e t a c t i c s , where the adoption of one or the o t h e r depends upon the type of h u n t i n g b e h a v i o r e x h i b i t e d by p r e d a t o r s i n the two h a b i t a t s . In r e e f s l o p e h a b i t a t s , spawning may i n c r e a s e v u l n e r a b i l i t y t o a g r e a t e r degree than i n the channel, because p r e d a t o r s l u r k on these s i t e s . By c o n t r a s t , because channel females are s u b j e c t t o h i g h u n p r e d i c t a b l e a t t a c k s from mobile p r e d a t o r s , f r e q u e n t spawning may not i n c r e a s e r i s k beyond t h a t of what i t would be i f females spawned l e s s f r e q u e n t l y . 163 Two o t h e r r e c e n t f i e l d s t u d i e s on f i s h e s have suggested t h a t r e p r o d u c t i v e t a c t i c s are c o n d i t i o n a l upon l o c a l environmental c o n d i t i o n s . Resnick and Bryga (1987) r e p o r t s h i f t s i n the r e p r o d u c t i v e t a c t i c s of guppies i n response t o an experimental m a n i p u l a t i o n s of p r e d a t i o n r i s k . U n l i k e t i l e f i s h , R esnick and Bryga's (1987) study i n v o l v e s i s o l a t e d s u b p o p u l a t i o n s , such t h a t s h i f t s i n r e p r o d u c t i v e t a c t i c s may i n v o l v e g e n e t i c changes. However, d i f f e r e n c e s i n r e p r o d u c t i v e i t a c t i c s i n response to conditions i n l o c a l habitats have alsoV i been shown i n a marine f i s h where p l a n k t o n i c l a r v a l d i s p e r s a l ensures g e n e t i c homogeneity among a d u l t s u b p o p u l a t i o n s . The amount o f time and energy t h a t male wrasses, Thallasoma  b i f a s c i a t u m , a l l o c a t e t o p r e s e n t r e p r o d u c t i v e e f f o r t v e r s u s growing t o l a r g e s i z e t o enhance f u t u r e c o m p e t i t i v e a b i l i t y i s c o n d i t i o n a l upon prese n t and f u t u r e p r o b a b i l i t i e s of a c q u i r i n g mates through i n t r a s e x u a l c o m p e t i t i o n (Warner, 1984b). S i m i l a r l y , t h e r e may be s e l e c t i o n f o r f l e x i b i l i t y i n the r e p r o d u c t i v e t a c t i c s of female t i l e f i s h i n response t o d i f f e r e n t I types of p r e d a t o r a c t i v i t y . For such s e l e c t i o n t o occur would r e q u i r e : 1) t h a t h a b i t a t v a r i a t i o n i n the type (of p r e d a t o r a c t i v i t y has been p r e v a l e n t d u r i n g the e v o l u t i o n a r y h i s t o r y of M. p l u m i e r i . and 2) s u f f i c i e n t g e n e t i c f l e x i b i l i t y t h a t i n d i v i d u a l s are capable of a d j u s t i n g t h e i r b e h a v i o r and i investments i n egg p r o d u c t i o n and growth a c c o r d i n g t o environmental cues of p r e d a t i o n r i s k . Such cues might i n c l u d e the type of a t t a c k s e x h i b i t e d by p r e d a t o r s , the frequency of p r e d a t o r s i g h t i n g s or u n s u c c e s s f u l a t t a c k s . Pronounced h a b i t a t v a r i a t i o n i n the type of p r e d a t o r a c t i v i t y t h a t M. p l u m i e r i i s 164 exposed t o i s l i k e l y , c o n s i d e r i n g the p o t e n t i a l f o r d i s p e r s a l i n t o a v a r i e t y of h a b i t a t s through the p l a n k t o n . D i f f e r e n t i a l responses t o food supplementation demonstrate the p o t e n t i a l f o r f l e x i b i l i t y i n r e p r o d u c t i v e t a c t i c s . I suggest, t h e r e f o r e , t h a t h a b i t a t d i f f e r e n c e s i n female spawning r a t e s may be a m a n i f e s t a t i o n of a f l e x i b l e r e p r o d u c t i v e s t r a t e g y i n which p r e s e n t r e p r o d u c t i v e e f f o r t depends upon the type of p r e d a t o r a c t i v i t y i n l o c a l h a b i t a t s . 165 References C i t e d Able, K.W., C.B. Grimes, R.A. Cooper, & J.R. Uzmann. 1982. 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