SEXUAL SELECTION AND FEMALE ORNAMENTATION IN A ROLE- REVERSED DANCE FLY By Jill Wheeler A thesis submitted in conformity with the requirements for the degree of MSc Graduate Department of Ecology and Evolutionary Biology University of Toronto © Copyright by Jill Wheeler (2008) Library and Bibliotheque et 1*1 Archives Canada Archives Canada Published Heritage Direction du Branch Patrimoine de I'edition 395 Wellington Street 395, rue Wellington Ottawa ON K1A0N4 Ottawa ON K1A0N4 Canada Canada Your file Votre reference ISBN: 978-0-494-45023-9 Our file Notre reference ISBN: 978-0-494-45023-9 NOTICE: AVIS: The author has granted a non­ L'auteur a accorde une licence non exclusive exclusive license allowing Library permettant a la Bibliotheque et Archives and Archives Canada to reproduce, Canada de reproduire, publier, archiver, publish, archive, preserve, conserve, sauvegarder, conserver, transmettre au public communicate to the public by par telecommunication ou par Plntemet, prefer, telecommunication or on the Internet, distribuer et vendre des theses partout dans loan, distribute and sell theses le monde, a des fins commerciales ou autres, worldwide, for commercial or non­ sur support microforme, papier, electronique commercial purposes, in microform, et/ou autres formats. paper, electronic and/or any other formats. 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Canada Sexual selection and female ornamentation in a role-reversed dance fly Jill Wheeler (MSc, 2008) Department of Ecology and Evolutionary Biology University of Toronto © Copyright by Jill Wheeler (2008) THESIS ABSTRACT Elaborate morphological traits (ornaments) can evolve if they increase the reproductive success of the bearer during competition for mates. However, such ornaments are very rare in females, potentially due to trade-offs between fecundity and ornaments. I examined sexual selection on female ornamentation in the dance fly Rhamphomyia longicauda. Female R. longicauda have two female-specific ornaments— inflatable abdominal sacs and pinnate leg scales. Using models of real females, I found that males prefer females with large ornaments, irrespective of the swarm sex-ratio. A selection analysis revealed stabilizing selection for the scale ornament only. However, only inflated abdomen area had a significant positive relationship with fecundity. Future studies should investigate the influence of viability selection and intrasexual competition on female ornamentation of this species. ii ACKNOWLEDGEMENTS The entire process of completing my Masters has been one of an exceptionally challenging but rewarding experience for me. I may have never started it—let alone completed it—without the support of many people. First, I would like to thank my advisor Darryl Gwynne for his guidance and support throughout this project. Darryl struck the ideal balance of offering help when I needed it, but also letting me figure things out for myself. His enthusiasm for the study system was a constant source of inspiration. I am amazed by his ability to see things from various perspectives and brainstorm alternate hypotheses, and it has pushed me to see the bigger picture. I am also very grateful to him and his family for putting me up. Not many graduate students live in their advisor's basement during their field work, but Darryl and his family — especially Sarah—made me feel very comfortable. I am also tremendously appreciative of my lab members: Laura, Edy, Murray and especially Kevin. Kevin always knew the answer to every question I asked him, and is one of the most selfless and helpful people I have ever met. The grueling hours at the microscope were made much easier by being surrounded by such caring and fun people. I'd also like to thank the community of graduate students at UTM and EEB, who were always willing to share their expertise. I probably would have never pursued graduate work if I hadn't had such a positive experience in my early academic career. I thank my first advisor Locke Rowe for hiring me to work in his lab in my second year of undergrad, and for his continued support. I was very fortunate to work with Russell Bonduriansky while in Locke's lab, and I thank him for all that he taught me. I also want to bestow a huge thank you to my 'academic mom' Helen Rodd who has always welcomed me into her office to talk about school, life, etc. in My thesis was made possible by the expertise contributed by the following individuals. Luc Bussiere has been remarkably generous in sharing his dance fly and statistics knowledge. I am grateful to David Funk for sending me the templates he used for his dance fly models. Janice Ting offered valuable assistance in constructing the models. I thank John Hunt for his help with the selection analyses. Thank you to Vicki Simkovic for her assistance in the field. Finally, I want to acknowledge the tremendous support of my family and friends. I thank my family— Mum, Jenn, Fam, Dad and Erick~for their love, patience and understanding. I am incredibly fortunate to have the friends I do- especially Michelle, Matthew, Heath, Christine and Lorissa—who never fail to check in on me, listen to my rants or take me out when I need stress relief. I also want to thank my 'bosses'—Petra and Myriam—for their patience and support. IV CONTENTS CHAPTER 1 GENERAL INTRODUCTION 1.1 AN OVERVIEW OF SEXUAL SELECTION 1.1.1 THE THEORY OF SEXUAL SELECTION 1.1.2 THE DIRECTION OF SEXUAL SELECTION 1.1.3 FEMALE ORNAMENTATION 1.2 THE STUDY SPECIES 1.2.1 FEMALE ORNAMENTATION IN THE EMPIDIDAE 1.2.2 THE LONG-TAILED DANCE FLY RHAMPHOMYIA LONGICAUDA 1.3 OUTLINE OF THESIS CHAPTER 2 MALE MATE CHOICE FOR FEMALE ORNAMENTS OF THE DANCE FLY RHAMPHOMYIA LONGICAUDA 2.1 ABSTRACT 2.2 INTRODUCTION 2.3 METHODS 2.4 RESULTS 2.5 DISCUSSION 2.6 FIGURES 2.7 TABLES CHAPTER 3 SEXUAL SELECTION FOR FEMALE ORNAMENTS AND THEIR RELATIONSHIP TO FECUNDITY IN THE DANCE FLY RHAMPHOMYIA LONGICAUDA 3.1 ABSTRACT 3.2 INTRODUCTION 3.3 METHODS 3.4 RESULTS 3.5 DISCUSSION 3.6 FIGURES 3.7 TABLES CHAPTER 4 CONCLUSIONS LITERATURE CITED VI 1 Chapter 1: General Introduction 1. GENERAL INTRODUCTION 1.1 An overview of sexual selection 1.1.1. Theory of sexual selection Darwin (1871) was inspired by showy morphological traits to formulate his theory of sexual selection; he posited that traits such as ornaments and weapons arise within a species through differential reproductive success. This difference in reproductive success can occur if one sex invests more resources in reproduction, and thus will be the limiting sex (Trivers, 1972). The limiting sex consequently will require more time between matings and will therefore have a lower potential reproductive rate (PRR: Clutton-Brock & Vincent, 1991; Clutton-Brock & Parker, 1992). These conditions lead to the limiting sex being less abundant, and the operational sex ratio (OSR) will be biased towards the non-limiting sex (Emlen & Oring, 1977). Sexual selection will act more strongly upon the non-limiting sex. Sexual selection can act through two mechanisms: mate choice and intra- sexual competition. Mate choice occurs when the limiting sex bases its mating decisions on the expression of certain traits of the non-limiting sex. Why these traits 2 are the target of mate choice—and how mating preferences are maintained—has been the focus of extensive research in the field of sexual selection (Bateson, 1983; Andersson, 1994). Exercising mate choice is thought to offer the choosy sex either direct benefits (e.g., nutrition in a nuptial gift (Gwynne, 1984) or a high quality territory (Bensch & Hasselquist, 1992)) or indirect benefits (e.g. enhanced offspring viability and/or attractiveness). Intra-sexual competition occurs when there is competition within the non-limiting sex over access to mates, or access to resources that may increase reproductive success. Within this context, the sexually-selected traits of the non-limiting sex enhance its competitive ability. 1.1.2. The direction of sexual selection Typically, sexual selection acts more strongly on males than females, but sexual selection can act on females (e.g. Gwynne & Simmons, 1990). Since eggs are more costly to produce than sperm, females are typically the limiting sex. However, females can become the target of sexual selection if males incur high breeding costs (Kokko & Monaghan, 2001; Kokko & Johnstone, 2002) and/or if there is high variation in female quality (Parker, 1983; Owens & Thompson, 1994; Johnstone et ah, 1996; Kvarnemo & Simmons, 1999). Males can incur breeding costs by producing or obtaining nuptial gifts (Gwynne, 1981,1984; Davies & Dadour, 1989), performing long courtship or copulatory behaviours (Saeki et al., 2005), or by the increased mortality risk of engaging in these activities (Jiggins et ah, 2000). Female quality can vary with respect to fecundity (Kvarnemo & Simmons, 1999) or stage of egg 3 development (Funk & Tallamy, 2000). If there is high sperm competition, females may vary with respect to the likelihood of using males' sperm for egg fertilization: males may reject recently mated females if there is first-male sperm precedence (e.g.