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Variation in Female Mating Preferences in Swordtail Fishes: the Importance of Social Variation in Female Mating Preferences in Swordtail Fishes: the Importance of Social Experience, Male Aggression and Genetic Variation A dissertation presented to the faculty of the College of Arts and Sciences of Ohio University In partial fulfillment of the requirements for the degree Doctor of Philosophy Donelle M. Robinson August 2011 © 2011 Donelle M. Robinson. All Rights Reserve 2 This dissertation titled Variation in Female Mating Preferences in Swordtail Fishes: the Importance of Social Experience, Male Aggression and Genetic Variation by DONELLE M. ROBINSON has been approved for the Department of Biological Sciences and the College of Arts and Sciences by Molly R. Morris Professor of Biological Sciences Howard Dewald Interim Dean, College of Arts and Sciences 3 ABSTRACT ROBINSON, DONELLE M., Ph.D., August 2011, (Select Program Name from list:) Variation in Female Mating Preferences in Swordtail Fishes: the Importance of Social Experience, Male Aggression and Genetic Variation Director of Dissertation: Molly R. Morris Identifying the different factors that influence female preference is essential to our understanding of the evolution of female preferences. Plastic mate preferences can be favored by natural selection in varying environments, including social environments. In this dissertation, I addressed the following questions in Xiphophorus birchmanni, X. cortezi and X. malinche: 1) What factors affect variation in female preference for vertical bars; 2) Does experience with different male phenotypes affect female preferences for vertical bars; 3) Does female preference contribute to the evolution of the exaggerated dorsal fin; 4) Did the exaggerated dorsal fin evolve to enhance courtship displays; 5) What are the phylogenetic relationships within and across these species? Female preferences for vertical bars in X. cortezi varied with female bar state, female size, and population in wild-caught females. By further examining differences using lab-reared fish, I found that preferences varied by social experience with barred and barless males, and this relationship varied across populations. These results indicated a combination of both genetic (population, bar state) and environmental (female size) on female preferences. I also found that barless males were more aggressive toward females, 4 and suggest that these behavioral differences could explain how experience influences female preferences. Xiphophorus birchmanni females preferred dorsal fins that were larger than expected given the male’s size, and during male–female interactions, males raised their dorsal fins as part of their courtship display directed towards females. I suggest that female preference selected for enlarged dorsal fins in male X. birchmanni, and that female preferences are potentially disruptive for dorsal fin size. I also found that raising the dorsal fin is a signal directed at females in several species of Xiphophorus. However, sexual dimorphism in dorsal fin size evolved prior to increased use of the dorsal fin during courtship. It is possible that either female preferences or male competition led to initial exaggeration of the dorsal fin. In the three species phylogeography, haplotypes of X. malinche and X. cortezi were paraphyletic with respect to each other, while X. birchmanni haplotypes formed a monophyletic group. However, microsatellite analyses uncovered three genetic groups corresponding to the three species. Populations of X. malinche and X. cortezi clustered within their respective species, suggesting that these are separate species. Approved: _____________________________________________________________ Molly R. Morris Professor of Biological Sciences 5 ACKNOWLEDGMENTS I would like to thank my advisor, Molly Morris, for her support and guidance throughout my dissertation. Her support has contributed to the success of this research and increased the quantity of research that I could produce during the past five years. I thank members of the Morris lab past and present: Lisa Bono, Peter Braun, Jason Brewer, Andre Fernandez, Susan Lyons and Scarlett Tudor for their support and friendship. I thank my committee members Harvey Ballard, Oscar Rios-Cardenas and Matthew White for their comments on this dissertation. I thank Natalie Dubois for teaching me PCR reactions and David Cannatella for letting me work with his lab while I learned molecular techniques. I thank Kevin de Quieroz and Carla Gutierrez Rodriguez for their comments and suggestions for Chapter 5. There are several students who also helped with parts of this research: Elise Baron, Julie Bauerschmidt, Theresa Beham, Shawn Conaster, Dan Glaser, Sarah Klim, Katy Kovar, Andrew Morris, Britanny Tarselli. For assistance collecting fish, I thank the Morris lab, Jeff Baker, Angela Horner and Charles Nevill. I thank my advisors from Texas State University, Caitlin Gabor and Andrea Aspbury, for training me well as a graduate student so that I easily transitioned to doctoral student. I also thank Floyd Weckerly at Texas State University for making statistics approachable. There were several funding sources for my dissertation that I thank. Parts of this dissertation were funded by grants from the Animal Behavior Society and the Graduate Student Senate to D.M. Robinson, as well as a National Science Foundation grant to 6 M.R. Morris and O. Rios-Cardenas. During my research, I was also support by fellowships from the Ohio Center for Ecology and Evolutionary Studies, research assistantships in the Morris lab, and teaching assistantships in the Department of Biological Sciences. Travel to scientific conferences to present the first four chapters of this dissertation was provided by the Department of Biological Sciences, Graduate Student Senate, and the Animal Behavior Society. I also thank Christiane Meyer for providing Xiphophorus helleri for Chapter 4. Finally, I thank my friends and family for their constant support during these past five years. I especially thank my husband, Charles Nevill, for listening to me constantly discuss my research and for assisting with parts of my dissertation, including building the transparency machine for Chapter 3 and writing applets that helped analyses for Chapter 5. I thank my parents for raising me so that I believed I could pursue anything. I also thank my purr-fection support team, Cookie and Mac, who ensured that I was never lonely when I worked late. 7 TABLE OF CONTENTS Page Abstract............................................................................................................................... 3 Acknowledgments............................................................................................................... 5 List of Tables .................................................................................................................... 12 List of Figures................................................................................................................... 13 General Introduction......................................................................................................... 15 Study System and Research Directions ........................................................................ 19 References..................................................................................................................... 24 Chapter 1: Unraveling the Complexities of Variation in Female Mate Preference for Vertical Bars in the Swordtail, Xiphophorus cortezi ........................................................ 31 Abstract......................................................................................................................... 31 Introduction................................................................................................................... 32 Methods ........................................................................................................................ 35 Statistical Analyses ................................................................................................... 38 Results........................................................................................................................... 40 Discussion..................................................................................................................... 42 Acknowledgements....................................................................................................... 50 References..................................................................................................................... 50 Chapter 2: Female Preference Plasticity in Xiphophorus cortezi ..................................... 60 Abstract......................................................................................................................... 60 Introduction................................................................................................................... 61 8 Methods ........................................................................................................................ 66 Experiment 1-Manipulating Female Social Environment ........................................ 67 Fish Collection and Maintenance.......................................................................... 67 Experience Treatments.......................................................................................... 68 Female Growth...................................................................................................... 70 Female Preference Tests ......................................................................................
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