CHARACTERIZING POPULATION GENETIC STRUCTURE AND INFERRING THE INFLUENCE OF LANDSCAPE FEATURES ON GENE FLOW IN A TEMPERATE SNAKE SPECIES
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Patterns of genetic diversity in natural systems are influenced by landscape heterogeneity over spatial and temporal scales. Certain natural or anthropogenic landscape features may facilitate or impede organism dispersal and subsequent gene flow. Characterizing the geographical distribution of genetic diversity and identifying the factors contributing to population genetic structure is imperative for maintaining functional connectivity between isolated populations across a fragmented landscape. In this study, I combined genetic data and high-resolution land cover information to investigate patterns of population genetic structure in the threatened eastern hog-nosed snake (Heterodon platirhinos) at its northern range limit in Ontario, Canada. First, using putatively neutral microsatellite markers, I found evidence of genetic differentiation between two geographically disjunct regional populations: in the Carolinian region of southwestern Ontario, and along the eastern shoreline of Georgian Bay. Spatial and non-spatial Bayesian clustering algorithms also detected population genetic structure within each regional population. I found evidence of weak structure within Georgian Bay, roughly corresponding to regions north and south of Parry Sound. A genetic cluster at Wasaga Beach, located at the southern terminus of Georgian Bay, was highly differentiated from other populations, despite its geographic proximity to Georgian Bay. Excess homozygosity and reduced allelic diversity in Wasaga Beach compared to other sampled populations imply a population bottleneck event. Secondly, I inferred the role of landscape features on eastern hog-nosed snake dispersal and subsequent gene flow in the Georgian Bay regional population. Using techniques derived from electrical circuit theory, I estimated pairwise resistance distances between individuals by assigning costs to landscape features that are predicted to impede hog-nosed snake movement: open water, wetland, settlement and agriculture, and roads. Landscape features did not influence genetic structure within Wasaga Beach. However, I found weak evidence for an effect of landscape features, particularly open water and roads, on gene flow in eastern Georgian Bay. This study is the first to examine potential factors driving population genetic structure of eastern hog-nosed snakes and provides an empirical foundation for future tests of demographic models and spatially explicit simulations of gene flow.