Person: Campbell-Staton, Shane C.
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Campbell-Staton
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Shane C.
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Campbell-Staton, Shane C.
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Publication Phylogeographic History and Temperature-Mediated Evolution of the Green Anole, Anolis Carolinensis(2015-05-18) Campbell-Staton, Shane C.; Losos, Jonathan B.; Edwards, Scott V.; Hoekstra, Hopi E.; Girguis, Peter R.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. In 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. As 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.Publication Next-generation sequencing and the expanding domain of phylogeography(2015) Edwards, Scott; Shultz, Allison; Campbell-Staton, Shane C.Phylogeography is experiencing a revolution brought on by next generation sequencing methods. A historical survey of the phylogeographic literature suggests that phylogeography typically incorporates new questions, expanding on its classical domain, when new technologies offer novel or increased numbers of molecular markers. A variety of methods for subsampling genomic variation, including Restriction site associated DNA sequencing (Rad-seq) and other next generation approaches, are proving exceptionally useful in helping define major phylogeographic lineages within species as well as details of historical demography. Next generation methods are also blurring the edges of phylogeography and related fields such as association mapping of loci under selection, and the emerging paradigm is one of simultaneously inferring both population history across geography and genomic targets of selection. However, recent examples, including some from our lab on Anolis lizards and songbirds, suggest that genome subsampling methods, while extremely powerful for the classical goals of phylogeography, may fail to allow phylogeography to fully achieve the goals of this new, expanded domain. Specifically, if genome-wide linkage disequilibrium is low, as is the case in many species with large population sizes, most genome subsampling methods will not sample densely enough to detect selected variants, or variants closely linked to them. We suggest that whole-genome resequencing methods will be essential for allowing phylogeographers to robustly identify loci involved in phenotypic divergence and speciation, while at the same time allowing free choice of molecular markers and further resolution of the demographic history of species.Publication Out of Florida: mtDNA reveals patterns of migration and Pleistocene range expansion of the Green Anole lizard (Anolis carolinensis)(Blackwell Publishing Ltd, 2012) Campbell-Staton, Shane C.; Goodman, Rachel M; Backstrom, Hans Niclas; Edwards, Scott; Losos, Jonathan; Kolbe, Jason JAnolis carolinensis is an emerging model species and the sole member of its genus native to the United States. Considerable morphological and physiological variation has been described in the species, and the recent sequencing of its genome makes it an attractive system for studies of genome variation. To inform future studies of molecular and phenotypic variation within A. carolinensis, a rigorous account of intraspecific population structure and relatedness is needed. Here, we present the most extensive phylogeographic study of this species to date. Phylogenetic analyses of mitochondrial DNA sequence data support the previous hypothesis of a western Cuban origin of the species. We found five well-supported, geographically distinct mitochondrial haplotype clades throughout the southeastern United States. Most Florida populations fall into one of three divergent clades, whereas the vast majority of populations outside Florida belong to a single, shallowly diverged clade. Genetic boundaries do not correspond to major rivers, but may reflect effects of Pleistocene glaciation events and the Appalachian Mountains on migration and expansion of the species. Phylogeographic signal should be examined using nuclear loci to complement these findings.