Testing the geographical dimensions of genetic diversity following range expansion in a North American snake

Spatial and demographic expansion can alter patterns of genetic variation and have predictable spatial and temporal consequences. Two-dimensional range expansion should result in genetic variation that is correlated with the geographical axis of expansion. Notably, populations across the range of a geographically widespread species may asynchronously experience expansion and contraction events. We tested for the genetic consequences of range expansion in the flat-headed snake, Tantilla gracilis, which inhabits the North American Great Plains, which has few barriers to terrestrial dispersal. We sequenced mitochondrial (mtDNA) and nuclear DNA from across the range of T. gracilis, inferred phylogenies, and constructed haplotype networks. We observed multiple geographically circumscribed mtDNA clades that varied greatly in their spatial extent, but little range-wide variation in nuclear DNA. Mitochondrial sequence variation was negatively associated with latitude across their geographic ran...