Reproductive behaviour in the male poeciliid fish Brachyrhaphis episcopi Helen R. Simcox Submitted for the Degree of Doctor of Philosophy University of Edinburgh 2006 Abstract Abstract Ecology has a major impact on the evolution of reproductive traits. The extent of ecological selection on adaptive traits such as reproductive behaviour has been powerfully demonstrated using cross-species comparisons. Such comparisons typically assume that behaviour is invariant within a species but there is increasing evidence that within a species, reproductive behaviours show substantial geographical and temporal variation. I have examined variation in the reproductive behaviour of the Panamanian bishop Brachyrhaphis episcopi, a tropical poeciliid fish. Firstly, I explored male mate choice, which is an understudied but rapidly growing area of research. I found that even in this promiscuous species, males were choosy about the females that they mated with. Males showed mating preferences for unfamiliar females and for larger females, preferences that could increase the number of offspring sired. Male mate choice showed some degree of plasticity both seasonally and on a much shorter time-scale, which may reflect fluctuations in the costs and benefits of being choosy. Secondly, I examined between and within population variation in reproductive behaviour to find out whether ecological factors driving variation in closely-related species could be more generally applied. Field observations revealed that, despite large inter-population variation in predation pressure, there was little inter-population variation in male reproductive activity or behavioural repertoire. Instead, male reproductive behaviour showed significant variation within populations, which may be linked to local operational sex ratio. Reproductive success in this species is likely to be linked to male-male competition rather than female choice. Thirdly, I examined variation in individual reproductive investment by males. I looked at both reproductive tactics and other traits associated with mating success, such as testes mass. I found relationships between male size and mating behaviour, but no size-based differences in relative testes investment. Contents Contents Contents List of figures and tables v Declaration vi Acknowledgements vii 1. Introduction 1 1.1 Variation in reproductive behaviour 1 1.2 Environmental effects 2 1.2.1 General environmental effects 2 1.2.2 Operational sex ratio 4 1.2.3 Predation pressure 6 1.2.4 Habitat quality 10 1.3 Phenotypic effects 13 1.4 Social effects 15 1.5 Interactions among factors 16 1.6 Non-adaptive explanations for variation 17 1.7 Summary 19 1.8 Ecology and biology of Brachyrhaphis episcopi 19 1.9 Aims 23 2. Context-dependent male mating preferences for unfamiliar females 24 2.1 Abstract 24 2.2 Introduction 25 2.3 Methods 27 2.3.1 Study System 27 2.3.2 Laboratory Experiment (June-August 2003) 28 2.3.3 Field Experiment (January-April 2004) 31 2.3.4 Data Analyses 33 2.4 Results 34 2.4.1 Laboratory Experiment 34 2.4.2 Field Experiment 36 2.5 Discussion 39 2.6 Acknowledgements 44 11 Contents Seasonal variation in male mate choice 45 3.1 Abstract 45 3.2 Introduction 46 3.3 Methods 48 3.3.1 Re-examination of Turner's (1938) data 48 3.3.2 Experimental test 49 3.3.3 Statistical analyses 51 3.4 Results 52 3.4.1 Re-examination of Turner's (1938) data 52 3.4.2 Experimental test 54 3.5 Discussion 57 3.5.1 Seasonal variation in male mate choice 57 3.5.2 Predator density 60 3.5.3 Familiarity 60 3.5.4 Female mate choice 61 3.5.5 Summary 62 3.6 Acknowledgements M. In situ observations of mating behaviours: effects of predator density and operational sex ratio 64 4.1 Abstract 64 4.2 Introduction 65 4.3 Methods 68 4.3.1 Experimental design 68 4.3.2 Statistical methods 71 4.4 Results 73 4.4.1 Fish communities 73 4.4.2 Reproductive behaviours 74 4.4.3 Aggression 76 4.4.4 Foraging 78 4.4.5 Relationships amongst behaviours 78 4.5 Discussion 4.6 Acknowledgements 16, The effects of male size and competitor size on male reproductive behaviour 85 5.1 Abstract . 85 • 5.2 Introduction 86 5.3 Methods 89 5.3.1 Experimental design 89 5.3.2 Statistical analyses 90 5.4 Results 92 5.5 Discussion 98 ff Contents 5.6 Acknowledgements 102 6. Individual variation in traits associated with male mating success 103 6.1 Abstract 103 6.2 Introduction 103 6.3 Methods 107 6.3.1 Data collection 107 6.3.2 Statistical methods 109 6.4 Results 110 6.4.1 Male body size 110 6.4.2 Testes investment 111 6.4.3 Gonopodiuin investment 113 6.4.4 Male ,nelanic markings and body conditions 114 6.5 Discussion 116 6.5.1 Male body size 117 6.5.2 Testes investment 117 6.5.3 Gonopodium length 119 6.5.4 Male melanic markings and body condition . 121 6.5.5 Summary 122 6.6 Acknowledgements 122 Discussion 123 References 134 Appendix 1. Preliminary laboratory studies of male mating behaviour in Brachyrhaphis episcopi 153 A1.1 Aims 153 A1.2 Methods 153 A1.2.1 Experimental proceedure 153 A]. 2.2 Statistical analyses 154 A1.3 Results 155 A1.3.1 Relationships among mean behaviours of males from each tank 155 A]. 3.2 Fish sizes and effects offetnale-deprivation 156 A1.4 Summary 156 Appendix 2. Simcox, H., N. Colegrave, A. Heenan, C. Howard & V. A. Braithwaite. Context-dependent male mating preferences for unfamiliar females. (2005) Animal Behaviour 70: 1429-1437 .............................. 153 and tables List of figures and tables Table 1.1 Relative percentages of fish fauna found in each stream 20 Figure 1.1 Location of study area and study populations 21 Table 1.2 Descriptions of male mating behaviours in B. episcopi 22 Figure 1.2 Mature female and mature male B. episcopi 23 Figure 2.1 Positions of high and low predator density populations 28 Figure 2.2 Schematic diagram of experimental apparatus 30 Figure 2.3 Male mating preferences in the laboratory 35 Table 2.1 Correlations between male and female behaviours in the laboratory 36 Table 2.2 Correlations between male behaviours in the field 37 Figure 2.4 Male courtship preferences in the field 58 Table 3.1 Numbers of females released into each study pool 51 Figure 3.1 Monthly rainfall and residual variance in brood size 53 Figure 3.2 Monthly rainfall and residual mean brood size 53 Figure 3.3 Effects of season and female size on probability of male association 54 Figure 3.4 Effects of season and female size on probability of thrust attempts 55 Figure 3.5 Effects of season and female size on percentage male association time 56 Figure 3.6 Effects of season and female size on rate of thrust attempts 57 Table 4.1 Number and percentage of fish fauna observed in each population 70 Table 4.2 Definitions and notes on measured behaviours 71 Table 4.3 Numbers of pools where females received thrust attempts 74 Figure 4.1 Effects of OSR on proportion of male association time 75 Figure 4.2 Aggression given and received by females and males 76 Figure 4.3 Effects of OSR on male-male aggression 77 Figure 4.4 Effects of stream of origin and size on foraging frequency 78 Table 4.4 Correlations between behaviours for each sex 79 Figure 5.1 Effects of male role and focal male size on association time 94 Figure 5.2 Effects of male role and focal male size on thrust attempts 95 Figure 5.3 Effects of male role and focal male size on aggression to rival male 96 Figure 5.4 Effects of male role and rival male size on thrust attempts 97 Figure 5.5 Effects of male role and rival male size on aggression to rival male 98 Table 6.1 Number and percentage of fish fauna in Quebrada Juan Grande 108 Figure 6.1 Male showing measures of standard and gonopodium length 109 Figure 6.2 Distributions of male standard length and male mass 112 Table 6.2 Allometric relationships of testes mass and gonopodium length 113 Figure 6.3 Relationships between soma mass and testes mass 114 Figure 6.4 Relationships between whole mass and standard length 115 Figure 6.5 Relationships between melanic bar number and body condition factor 116 Figure 6.6 Relationship between melanic bar intensity and body condition factor 116 Table 6.3 Intensity of melanic bars in each population 117 Table Al Numbers.of males tested from each population 156 Table A2 Percentage of trials in which behaviours were observed 156 V Declaration Declaration The research reported in this thesis is work that I have devised, run, analysed and interpreted. However, I feel it is important to recognise that a number of people have helped to shape and direct my work, and collect data. In recognition of this, I have written chapters 2 to 6 using plural authorship and each is written as a stand-alone paper, so some repetition of information is inevitable. My co-authors are my supervisors, Dr. Victoria Braithwaite and Dr. Nick Colegrave, and Dr. Culum Brown, Chris Howard and Adel Heenan who have helped me collect data and work in the field. I am the first author for each of the papers, as detailed at the beginning of each chapter. Chapter 2 is published in Animal Behaviour (see Appendix 2) and the remaining chapters are written in paper format but have yet to be submitted.