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Divergent Mating Behavior and the Evolution of Reproductive Isolation

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Divergent Mating Behavior and the Evolution of Reproductive Isolation Title Page Divergent Mating Behavior and the Evolution of Reproductive Isolation by Yu-San Yang B.S. in Life Sciences, National Taiwan University, 2013 Submitted to the Graduate Faculty of the Dietrich School of Arts and Sciences in partial fulfillment of the requirements for the degree of Doctor of Philosophy University of Pittsburgh 2020 Committee Page UNIVERSITY OF PITTSBURGH DIETRICH SCHOOL OF ARTS AND SCIENCES This dissertation was presented by Yu-San Yang It was defended on April 29, 2020 and approved by Dr. Walter P. Carson, Associate Professor, University of Pittsburgh, Department of Biological Sciences Dr. Mark Rebeiz, Associate Professor, University of Pittsburgh, Department of Biological Sciences Dr. Martin Turcotte, Assistant Professor, University of Pittsburgh, Department of Biological Sciences Dr. Maria R. Servedio, Assistant Professor, University of North Carolina at Chapel Hill, Department of Biology Dissertation Advisor: Dr. Corinne L. Richards-Zawacki, Associate Professor, University of Pittsburgh, Department of Biological Sciences ii Copyright © by Yu-San Yang 2020 iii Abstract Divergent Mating Behaviors and the Evolution of Reproductive Isolation Yu-San Yang, Ph.D. University of Pittsburgh, 2020 Sexual selection can cause rapid co-divergence of mating traits and mate preferences, generate reproductive barriers among individuals bearing divergent mating traits, and potentially lead to speciation. In my dissertation, I focused on two emerging topics that challenge this traditional speciation-by-mate-choice paradigm. First, sexual selection encompasses both mate preferences and intrasexual competition, yet speciation research disproportionally focused on the role of the former. Second, sexual behaviors are usually assumed to be genetically inherited, but they may often be shaped by learning instead, which can generate very different evolutionary trajectories for traits and preferences. Using studies of the highly polymorphic strawberry poison frogs (Oophaga pumilio), I demonstrated how incorporating (i) male-male competition and (ii) behavioral learning can enhance our understanding of the potential for speciation to be driven by sexual selection. I first characterized behavioral patterns across a natural contact zone between color morphs and showed that coloration (the divergent mating trait) mediates both female choice and male-male competition. Females often prefer males of their own (local) color over a novel color, and males, when defending territories, are more aggressive against their own color morph. I then tested how these color-mediated female preferences and male aggression biases interact to determine mating patterns. I conducted a controlled breeding experiment in which male-male competition and female mate choice act either in same or in opposing directions. In this study, females reproduced more often with the territorial male over the non-territorial male, regardless of the males’ coloration. This challenges the common assumption that knowledge of female preferences for male mating traits is sufficient to predict mating patterns. Finally, I discovered that iv learning from mothers during the tadpole stage shapes both female mate preferences and male aggression biases in O. pumilio. Based on this finding, I built a population genetic model and used it to demonstrate a simple and elegant mechanism by which sexual selection alone has the potential to initiate speciation. My research highlights the importance of considering interactions between mate choice, intrasexual competition, and behavioral learning, for studies of mating trait evolution and sexual selection’s role in speciation. v Table of Contents Preface .......................................................................................................................................... xii 1.0 Chapter 1: Introduction ......................................................................................................... 1 2.0 Chapter 2: Poison Frog Color Morphs Express Assortative Mate Preferences in Allopatry but not Sympatry ........................................................................................................ 5 2.1 Chapter Summary .......................................................................................................... 5 2.2 Introduction .................................................................................................................... 6 2.3 Methods ........................................................................................................................... 9 2.3.1 Study Species ........................................................................................................9 2.3.2 Study Animals ....................................................................................................10 2.3.3 Experiment Design and Protocol ......................................................................11 2.3.4 Statistical Analyses .............................................................................................14 2.4 Results ............................................................................................................................ 15 2.5 Discussion ...................................................................................................................... 19 2.6 Acknowledgements ....................................................................................................... 24 3.0 Chapter 3: Poison Frog Color Morphs Express Assortative Aggression Biases in Allopatry but not Sympatry ...................................................................................................... 25 3.1 Chapter Summary ........................................................................................................ 25 3.2 Introduction .................................................................................................................. 26 3.3 Methods ......................................................................................................................... 29 3.3.1 Study Species ......................................................................................................29 3.3.2 Study Populations ..............................................................................................30 vi 3.3.3 Experimental Design and Protocol ...................................................................31 3.3.4 Male Agonistic Behaviors ..................................................................................33 3.3.5 Color Quantification ..........................................................................................35 3.3.6 Statistical Analyses .............................................................................................35 3.4 Results ............................................................................................................................ 37 3.4.1 Does Male Aggression Pattern Vary with Population Morph Frequency? ..37 3.4.2 Do Males Bias Aggression toward Intruders of Their Own Color in the Polymorphic Populations? .........................................................................................41 3.5 Discussion ...................................................................................................................... 43 3.6 Acknowledgements ....................................................................................................... 47 4.0 Chapter 4: Male-male Territorial Contest Limits the Expression of Assortative Mate Preferences in a Polymorphic Poison Frog ............................................................................... 49 4.1 Chapter Summary ........................................................................................................ 49 4.2 Introduction .................................................................................................................. 50 4.3 Methods ......................................................................................................................... 54 4.3.1 Study Species ......................................................................................................54 4.3.2 Experiment Design .............................................................................................55 4.3.3 Animals ...............................................................................................................55 4.3.4 Determining Male Territoriality .......................................................................57 4.3.5 Mating Trials ......................................................................................................57 4.3.6 Statistical Analyses .............................................................................................59 4.4 Results ............................................................................................................................ 60 4.4.1 Analysis of Mating Patterns ..............................................................................61 vii 4.4.2 Reproductive Timing .........................................................................................62 4.5 Discussion ...................................................................................................................... 63 4.6 Acknowledgements ....................................................................................................... 67 5.0 Chapter 5: Imprinting Sets the Stage for Speciation ......................................................... 68
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