Convergence and Divergence from Populations to Species: Phenotypic Evolution of Caribbean Anolis Lizards by Michael Lihan Yuan
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Convergence and Divergence from Populations to Species: Phenotypic Evolution of Caribbean Anolis Lizards By Michael Lihan Yuan A dissertation submitted in partial satisfaction of the requirements for the degree of Doctor of Philosophy in Environmental Science, Policy, and Management in the Graduate Division of the University of California, Berkeley Committee: Professor Ian J. Wang, Chair Professor Marvalee H. Wake Professor Erica Bree Rosenblum Spring 2021 Abstract Convergence and Divergence from Populations to Species: Phenotypic Evolution of Caribbean Anolis Lizards by Michael Lihan Yuan Doctor of Philosophy in Environmental Science, Policy, and Management University of California, Berkeley Professor Ian J. Wang, Chair This dissertation is primarily focused on understanding the generation and maintenance of phenotypic diversity through ecological selection. Natural selection acts on the phenotype because the phenotype lies at the interface between an organisms genotype and its environment. Thus, the study of phenotypic diversity is central to our understanding of evolution. I have primary addressed questions of phenotypic evolution using the radiations of Caribbean Anolis lizards. Chapter I of my dissertation examines if claw and toepad morphology formed an integrated phenotype correlated with microhabitat partitioning in Greater Antillean anoles. The Greater Antilles forms an exceptional system to study convergent evolution due to the repeated evolution of structural microhabitat specialist ‘ecomorphs’. As locomotor traits associated with clinging performance, claw and toepad traits are likely highly relevant to partitioning of vertical arboreal habitat. I found that correlative selection did drive the evolution of claw and toepads as an integrated phenotype to optimize performance on specific microhabitats. Additionally, rates of evolution were coupled between claws and toepads across most species, except twig specialists which experienced a dramatic reduction in claw structure. Thus, this study provides a convincing case study for correlative selection facilitating ecological divergence between species. Chapter II studies claw and toepad integration in the context of the species depauperate Lesser Antillean anole fauna. These anoles represent broad habitat generalists with only one or two species per island. Broadly, claw and toepad morphology correlated with overall island habitat availability on one species islands, but not two species islands. Here, I found that Anolis bimaculatus series anoles closely-related to the Greater Antillean adaptive radiations followed predictable patterns of divergence on two species islands in that they partitioned vertical habitat space and showed associated phenotypic integration between claws and toepads. However, the distantly-related A. roquet series anoles did not show predictable patterns of divergence on two species islands and a decoupling of claw and toepad traits. These results suggest that phylogenetic history may influence the capacity for adaptive divergence. 1 Chapter III tests for parallel intraspecific patterns of divergence across environmental gradients in nine species of A. bimaculatus series anoles inhabiting the northern Lesser Antilles. Species within the A. bimaculatus series are broadly generalist and occur widely throughout their native islands. Thus, each encounters a wide range of environmental variation ranging from xeric coastal scrub to montane rainforests. I found that patterns of morphological divergence across these environmental gradients were idiosyncratic. It is possible that due to many-to-one mapping of form to function, adaptation to environmental gradients can be achieved through different ecologically-relevant traits. However, strong patterns of convergence did emerge for some traits, notably dorsal coloration. Chapter IV examines the phenomenon of species richness-genetic diversity in the context of island biogeography and extends this framework to include phenotype diversity. Specifically, I examined the relative roles of island size, distance from mainland, environmental variance, and topographic complexity across the Lesser Antilles. I partitioned biogeographical effects across species, phenotypic, and genetic diversity using both native and introduced herpetofauna. I found that island size correlates with both species richness and genetic diversity in all contexts. Secondary island characteristic effects on species and genetic diversity differed between groups likely due to differences in their natural history. Phenotypic diversity was not correlated with tested island variables in all cases suggesting that macroecological forces which shape species and genetic diversity are decoupled from phenotypic diversity. 2 For my family and friends who got me through this. i TABLE OF CONTENTS Acknowledgements iii Preface iv Chapter I Abstract 1 Introduction 2 Methods 4 Results 7 Discussion 9 Conclusion 12 Figures and Tables 14 Chapter II Abstract 23 Introduction 24 Methods 26 Results 29 Discussion 30 Conclusion 33 Figures 35 Chapter III Abstract 41 Introduction 42 Methods 44 Results 46 Discussion 48 Conclusion 50 Figures and Tables 51 Chapter IV Abstract 58 Introduction 59 Methods 60 Results 62 Discussion 63 Conclusion 65 Figures and Tables 67 References 74 Appendix I 88 Appendix II 90 Appendix III 92 Appendix IV 96 ii ACKNOWLEDGEMENTS I am grateful to numerous individuals and institutions for facilitating the work presented in the following pages. I wish to thank my mentors and committee members Ian Wang, Marvalee Wake, Bree Rosenblum, Rayna Bell, and Kevin de Queiroz for their guidance. Members of both the Wang and Bell labs provided invaluable feedback throughout my dissertation progress. This research would not have been possible without access to natural history collections from the Museum of Vertebrate zoology (University of California, Berkeley, California), the California Academy of Sciences (San Francisco, California), the Museum of Comparative Zoology (Harvard University, Cambridge, Massachusetts), and the National Museum of Natural History (Smithsonian Institution, Washington, District of Columbia). I am particularly grateful to the curators and staff of these institutions for aiding in loan of materials and allowing use of their facilities including, but not limited to, Addison Wynn, Robert Wilson, Esther Langan, Kenneth Tighe, Jose Rosado, Lauren Scheinberg, Erica Ely, and Carol Spencer. For being a wonderful collaborator and friend, I thank Jeffrey Frederick. For helping me survive graduate school in numerous ways, I thank Natalie Graham. Catherine Jung was an invaluable undergraduate mentee who helped with many aspects of data collection. For help in the field, I thank Calvin Fenton, Sharon Veira, Livius Bozga, Melanie Meijer zu Schlochtern, the St. Kitts Department of Forestry Rangers, and the STENAPA staff and interns. For donating field supplies, I thank Dr. Pompei Bulfa and Candita Chapman at Ross University School of Veterinary Medicine and Heldder Renjifo at American University of the Caribbean School of Medicine. Work on St. Kitts and Nevis was conducted with permission from the Department of Environment under an access and benefit-sharing agreement with the Ministry of Agriculture, Marine Resources, Cooperatives, Environment and Human Settlement. I collected samples on Sint Eustatius under permits from the Sint Eustatius National Parks Foundation, on Sint Maarten under permits from the Nature Foundation Sint Maarten, on Montserrat under permits from the Department of Environment, and on Dominica under permits from the Department of Forestry. For permits, I thank Clarisse Buma, Melanie Meijer zu Schlochtern, Ernestine Corbett, Stephen Durand, Eavin Parry, and Dr. Tracey Challenger. For help in the lab, I am thankful to Guin Wogan and Lydia Smith. Sequencing facilities were provided by the Museum of Vertebrate Zoology’s Evolutionary Genetics Laboratory. Peter Ruzevich of the Steinhart Aquarium at the California Academy of Sciences provided x-ray facilities. Funding for the work presented in this dissertation was provided by the Museum of Vertebrate Zoology, Sigma Xi, the Lewis and Clark Fund for Exploration and Field Research from the American Philosophical Society, a Student Research Award from the American Society of Naturalists, and a Rosemary Grant Award from the Society for the Study of Evolution. I was supported by a Smithsonian Institution Graduate Fellowship, a Smithsonian Institution Predoctoral Fellowship, a Philomathia Fellowship in the Environmental Sciences from UC Berkeley, and a Junea W. Kelly Graduate Fellowship from the Museum of Vertebrate Zoology. Additional funding support was provided by the Department of Environmental Science, Policy, and Management at UC Berkeley. Finally, I thank the anoles because without them this dissertation would not exist. iii PREFACE Phenotypic variation represents a fundamental axis of biological diversity. It is the phenotype upon which natural selection directly acts and, thus, the phenotype which lies at the interface between an organism’s genetics and its environment. In short, without heritable phenotypic variation natural selection would not occur. Therefore, understanding the generation and maintenance of phenotypic diversity is central to the pursuit of evolutionary biology. It is from this perspective that I approach the work presented in this dissertation. Convergent evolution, including its subcase parallel evolution, provides an exceptional opportunity to study environment-phenotype