A spatial genomic approach identifies time lags and historic barriers to gene flow in a rapidly fragmenting Appalachian landscape

Abstract

The resolution offered by genomic data sets coupled with recently developed spatially 12 informed analyses are allowing researchers to quantify population structure at increasingly fine 13 temporal and spatial scales. However, uncertainties regarding data set size and quality thresholds 14 and the time scale at which barriers to gene flow become detectable have limited both empirical 15 research and conservation measures. Here, we used restriction site associated DNA sequencing 16 to generate a large SNP data set for the copperhead snake (Agkistrodon contortrix) and address 17 the population genomic impacts of recent and widespread landscape modification across an 18 approximately 1000 km 2 region of eastern Kentucky. Nonspatial population-based assignment 19 and clustering methods supported little to no population structure. However, using individual-20 based spatial autocorrelation approaches we found evidence for genetic structuring which closely 21 follows the path of a historic highway which experienced high traffic volumes from ca. 1920 to 22 1970. We found no similar spatial genomic signatures associated with more recently constructed 23 31