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ABSTRACT OF DISSERTATION

J. Chadwick Johnson

The Graduate School University of Kentucky 2003

PRE-COPULATORY SEXUAL CANNIBALISM IN FISHING SPIDERS: THE ECOLOGY OF AN EXTREME SEXUAL CONFLICT

________________________________________ ABSTRACT OF DISSERTATION ________________________________________ A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the College of Arts and Sciences at the University of Kentucky By J. Chadwick Johnson Lexington, Kentucky Director: Dr. Andrew Sih, Professor of Biological Sciences Lexington, Kentucky 2003 Copyright © J. Chadwick Johnson 2003

ABSTRACT OF DISSERTATION

PRE-COPULATORY SEXUAL CANNIBALISM IN FISHING SPIDERS: THE ECOLOGY OF AN EXTREME SEXUAL CONFLICT Pre-copulatory sexual cannibalism (pre-SC), or predation of a potential mate before sperm transfer, provides an ideal model system for behavioral ecology’s current focus on intersexual conflict. Studying the North American fishing spider (Dolomedes triton), I tested three female-benefit hypotheses for pre-SC: indirect benefits, direct benefits, and aggressive spillover. First, pre-SC may reflect a mating bias providing females with ‘good-genes’ benefits. By manipulating each female’s options with regard to the most cited phenotypic advantage in male spiders, body size, I show that while females exhibit no bias in their attack tendency on males of different body sizes, large males mate significantly more often than small males. Second, pre-SC may be explained by direct benefits if females use it as an adaptive foraging/mating trade-off. My work provides mixed support for this idea: (i) females vary attacks according to the availability of mates, (ii) females do not vary attacks according to the availability of food, and (iii) females derive discrete fecundity benefits from consuming a male. Finally, I tested the aggressive-spillover hypothesis, which posits that pre-SC is a by-product of selection for high levels of aggression towards prey in traditional foraging contexts. Path analysis indicated intraindividual, positive correlations between aggression in foraging contexts and the mating context, thus supporting the hypothesis. I conclude by stressing that pre-SC in a given species may rarely be explained by one hypothesis, and that studies accounting for multiple benefits that fluctuate as behavioral-ecological contexts shift should give a more realistic glimpse of behavioral ecology and evolution.

KEYWORDS:

Sexual cannibalism, Sexual conflict, Mating systems, Behavioral syndromes, Fishing spiders

James Chadwick Johnson 7-15-03

PRE-COPULATORY SEXUAL CANNIBALISM IN FISHING SPIDERS: THE ECOLOGY OF AN EXTREME SEXUAL CONFLICT

By J. Chadwick Johnson

Andrew Sih Peter Mirabito 7-15-03

RULES FOR THE USE OF DISSERTATIONS Unpublished dissertations submitted for the Doctor’s degree and deposited in the University of Kentucky Library are as a rule open for inspection, but are to be used only with due regard to the rights of the authors. Bibliographical references may be noted, but quotations of summaries of parts may be published only with the permission of the author, and with the usual scholarly acknowledgements. Extensive copying or publication of the dissertation in whole or in part also requires the consent of the Dean of the Graduate School of the University of Kentucky.

DISSERTATION

J. Chadwick Johnson

The Graduate School University of Kentucky 2003

PRE-COPULATORY SEXUAL CANNIBALISM IN FISHING SPIDERS: THE ECOLOGY OF AN EXTREME SEXUAL CONFLICT

_______________________________________ DISSERTATION ________________________________________ A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the College of Arts and Sciences at the University of Kentucky By J. Chadwick Johnson Lexington, Kentucky Director: Dr. Andrew Sih, Professor of Biological Sciences Lexington, Kentucky 2003 Copyright © J. Chadwick Johnson 2003

This work is dedicated to my beautiful soon-to-be wife Gina Hupton, my remarkable powerhouse of a mother Sandra Deer, Jim Johnson, the man I have tried to emulate, Jennifer Deer, the best friend a brother could hope for, Penny, who never wavers in her love and enthusiasm, and all of my friends and loved ones.

ACKNOWLEDGEMENTS First and foremost I would like to thank my advisor Andy Sih for his guidance, generosity, enthusiasm, endless energy, and good humor. Anyone that has encountered Andy at a conference knows what I mean. In addition, I would like to thank my Dissertation Committee-David Westneat, Phil Crowley, David Wise, Charles Fox, and my outside examiner, Chana Akins. Each has provided encouragement and constructive criticism that has improved the final product. Throughout my graduate work I have been very fortunate to be surrounded by mentors, colleagues and friends that have made this process stimulating, challenging and fun. I won’t attempt to name all of those individuals, but they have enriched my life greatly and I will always be in their debt. Finally, this work has been funded at different times by the following organizations: University of Kentucky Graduate School and Department of Biological Sciences, Animal Behavior Society, Sigma Xi, National Science Foundation. As always I thank my unwavering fanbase: Gina, Sandra, Jennifer, Jane, and Penny. This would have been impossible without your love and support.

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TABLE OF CONTENTS Acknowledgements……………………………………………………………............................iii List of Tables……………………………………………………………………………………..vi List of Figures……………………………………………………………………………………vii List of Files……………………………………………………………………………………...viii Chapter One:

Overview of the thesis Introduction…….…...……………………………………………..1 Review of hypotheses……………………………………..2 Conclusions………………………………………………………..7

Chapter Two:

Sexual cannibalism: the ecology of an extreme sexual conflict Summary……..…………………………………………………..13 Introduction………………………………………………………14 Adaptive hypotheses (male benefits)…………………….17 Adaptive hypotheses (female benefits)…………………..29 Non-adaptive hypotheses………………………………...43 Conclusion……………………………………………………….51

Chapter Three:

The role of male body size and sexual size dimorphism in mating interactions of the sexually cannibalistic fishing spider Dolomedes triton (Araneae: Pisauridae). Summary……..…………………………………………………..54 Introduction………………………………………………………55 Methods…………………………………………………………..58 Results……………………………………………………………60 Discussion………………………………………………………..62

Chapter Four:

Sexual cannibalism in fishing spiders (Dolomedes triton): an evaluation of two explanations for female aggression towards potential mates. Summary……..…………………………………………………..68 Introduction………………………………………………………69 Methods…………………………………………………………..73 Results……………………………………………………………75 Discussion………………………………………………………..78

Chapter Five:

Pre-copulatory sexual cannibalism in fishing spiders (Dolomedes triton): does male-female cohabitation influence female use of males as food versus sperm? Summary……..…………………………………………………..90 Introduction………………………………………………………91

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Methods…………………………………………………………..94 Results……………………………………………………………96 Discussion………………………………………………………..98 Chapter Six:

Pre-copulatory sexual cannibalism in fishing spiders (Dolomedes triton): a test of the aggressive-spillover hypothesis. Summary……..…………………………………………………103 Introduction……………………………………………………..104 Methods…………………………………………………………109 Results…………………………………………………………..112 Discussion………………………………………………………115

References………………………………………………………………………………………124 Vita……………………………………………………………………………………………...145

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LIST OF TABLES Table 1.1

The observed and expected frequency distributions of four distinct strategy sets (e.g. attack males of both size classes, attack one size class but not the other, or attack neither size class, n=33)……………………………………………………9

Table 1.2

Least square means ± standard error (n) for two adult diet regimes. Food contrasts indicate support for the idea that adult food benefits fecundity………………….10

Table 2.1

A comprehensive listing of the hypotheses for sexual cannibalism……………..52

Table 4.1

Least square means ± standard error (n) for four diet regimes. Food contrasts indicate support for both the adaptive foraging and aggressive-spillover hypotheses………………………………………………………………………..87

Table 4.2

Likelihood of a sexually cannibalistic attack given variables predicted to be important by the adaptive foraging model……………………………………….88

Table 4.3

The adaptive foraging tactic (# 3) is employed by females more often than can be explained by the expected frequency distribution given an estimated experimentwide 29% probability of attack…………………………………………………..89

Table 5.1

The effects of fixed adult size, adult hetero-specific foraging success and pre-SC kills on several measures of female reproductive success……………………...102

Table 6.1

Correlations among submergence behaviors in the anti-predator context (A-P) for juveniles, adults and adults with egg sacs, the foraging context for juveniles and adults and the mating context for adults……………………..119

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LIST OF FIGURES Figure 1.1 Regression of fixed adult body size on adult body mass (= body condition) demonstrating the substantial amount of size and mass variation that exists both within each sex and between the sexes (i.e. sexual size dimorphism)…………………………………..11 Figure 1.2 A test of the predictions of the aggressive spillover hypothesis. Note that I emphasize a new formulation of the spillover hypothesis with the statistically significant relationship between adult voracity/foraging success, adult mass with the egg sac and fecundity. All p-values are for 1-tailed t-tests. *=p