Phylogeographic History and Temperature-Mediated Evolution of the Green Anole, Anolis Carolinensis

Temperature plays an important role in shaping the form and function of every species. Ectothermic organisms are particularly sensitive to fluctuations in their thermal environment. Their inability to produce appreciable amounts of heat through physiological mechanisms makes them particularly vulnerable to thermal shifts, and ideal for the study of temperature-mediated evolution. The central goal of this dissertation is to understand how temperature shapes the evolutionary history of terrestrial ectotherms during the colonization of novel environments. Towards this aim, I focus on a single species of lizard, the North American green anole, Anolis carolinensis. \nIn the first chapter of my dissertation I trace the phylogeographic history of A. carolinensis in order to identify the geographic distribution of major genetic lineages within the species and its Cuban relatives, date times of divergence between these lineages, and identify geographic barriers to dispersal. In the second chapter, I use an integrated approach to identify aspects of the environment that may have influenced evolutionary adaptation within the species. I combine geo-referenced climate data, environmental niche modeling, thermal physiology, common garden experiments and genomic techniques to understand phenotypic and genomic response of this historically subtropical Cuban lizard to the more temperate regions of the American Southeast. Finally, in the third chapter I use experimental temperature manipulations and physiological testing to explore the roles of phenotypic plasticity and local adaptation in shaping latitudinal variation in thermal tolerance and identify potential systemic mechanisms involved. \nAs a result, I have identified a Miocene origin of the initial over-water dispersal event leading to the establishment of the green anole in peninsular Florida, followed by a rapid Pleistocene range expansion of the species northward into higher latitudes. Range expansion on the mainland has led to thermal niche expansion, mediated by a combination of local adaptation of cold tolerance and genetic isolation by environment between populations from different thermal habitats. Phenotypic plasticity and canalized differentiation both shape variation in cold tolerance across latitude and energy conservation via metabolic suppression under acute and chronic cold onset may help to extend the limits of cold tolerance in this species at its northernmost latitudes.