Using a comparative approach to investigate the relationship between landscape and genetic connectivity among woodland salamander populations

Abstract

For many amphibian species, reduced landscape connectivity results in reduced genetic connectivity among populations. However, large effective population sizes (Ne) slow the rate of genetic drift, causing subdivided populations to remain genetically similar despite little gene flow among them. Therefore, it is important to address the combined effects of Ne and matrix permeability to quantify the relative importance of gene flow and genetic drift on isolated amphibian populations. We applied a landscape genetic approach to investigate how patterns of gene flow (m), Ne (inferred via θ) and genetic differentiation differ among Eastern Red-backed Salamander (Plethodon cinereus) populations in a fragmented landscape (n = 4) compared to a continuous forest (n = 4). We assayed a panel of 10 microsatellite markers for population genetic analyses. Additionally, we constructed and validated a distribution model to generate resistance surfaces for examining the relationship between landscape connectivity, m, θ, and genetic differentiation (FST) using maximum-likelihood population-effects models (MLPE). Populations in continuous habitat were undifferentiated, whereas fragmented populations exhibited genetic structure driven by a single population. Results of the MLPE models in the fragmented landscape revealed spatial variation in θ as the best predictor of pairwise FST, followed by estimates of m, suggesting migration-drift interactions have a stronger influence on genetic differentiation than matrix permeability. Moreover, model coefficients for landscape resistance were comparable between landscapes. Overall, our results provide insight as to how the interaction of gene flow and genetic drift shapes population structure for a dispersal-limited species within a predominately anthropogenic landscape.