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The influence of history, geography, and environment on patterns of diversification in garter snakes (Thamnophis)
AuthorHallas, Joshua Mark
Ecology, Evolution and Conservation Biology
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A major goal of biology is to determine how and why diversity is generated and maintained–from subtle genetic variation between populations of the same species, to ecological differences between closely related species, to phenotypic divergence across deep phylogenetic lineages. Two key aspects in the evolution of biological diversity are space and time. When populations become physically isolated for long periods of time, evolutionary forces uniquely alter those populations and set them on distinct evolutionary trajectories. The spatial structure of genetic differentiation is greatly influenced by variation in evolutionary forces stemming from heterogeneous landscapes. Isolation among populations is largely mediated by physical features or ecological variation, which can fragment populations and allow for local adaptation to divergent ecologies. Because landscapes are dynamic and ever shifting, evolutionary forces such as gene flow, selection, and genetic drift continuously shape and reshape the spatial patterning of genetic variation and adaptive traits across a continuum of spatial and temporal scales. My dissertation research investigates these mechanisms by looking at patterns of phenotypic and genetic diversification at differing spatial and temporal scales in garter snakes–spanning entire clades of animals that have diversified across broad areas over long time periods, to fine-scale patterns of differentiation among populations of the same species. This largely focused on contemporary and historic biogeographic features and ecological influences on shaping genetic and phenotypic variation in garter snakes (Thamnophis). My first project investigates how biogeography and feeding ecology have shaped lineage diversification and morphological evolution across all of Thamnophis by reassessing phylogenetic relationships. My second project investigates how historical biogeography and environmental variation influence patterns of genetic diversity among and within three subspecies of T. elegans. My final project investigates how historical divergence and spatial genetic structure of populations underly geographic variation in an adaptive phenotype in T. atratus. For each of my projects, I used reduced representation double-digest restriction associated DNA sequencing (ddRADseq). This large-scale dataset was used to quantify spatial genetic variation, characterize population genetic structure, and estimate phylogenetic relationships of lineages of garter snakes.