Data from: Testing the geographic 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 range, the expected pattern of northward expansion. Finally, the three largest mtDNA clades exhibited varying demographic patterns, with only one consistent with recent expansion. Despite substantial mtDNA cladogenesis, the predicted signature of northern range expansion was still detectable in T. gracilis. Our results bolster the notion that Post-Pleistocene range expansion was a dominant force shaping the genetic diversity of vertebrates in central North America.空间扩张与种群扩张可改变遗传变异模式，并带来可预测的时空效应。二维分布范围扩张应会使得遗传变异与扩张的地理轴呈现相关性。值得注意的是，广布物种种群的分布范围可能会异步经历扩张与收缩事件。我们以栖息于陆地扩散障碍极少的北美大平原的扁头蛇（Tantilla gracilis）为研究对象，探究其分布范围扩张带来的遗传效应。我们对扁头蛇整个分布范围内的线粒体DNA（mitochondrial DNA, mtDNA）与核DNA进行测序，推断其系统发育关系并构建单倍型网络。我们观测到多个地理限定的线粒体DNA进化枝，这些进化枝的空间分布范围差异显著，但核DNA在整个分布范围内的变异程度极低。线粒体序列变异在其地理分布范围内与纬度呈负相关，这符合北向扩张的预期模式。最后，三个最大的线粒体DNA进化枝表现出各异的种群动态模式，仅其中一个符合近期扩张的特征。尽管线粒体DNA存在显著的枝系发生分化，扁头蛇的北向分布范围扩张特征仍可被检测到。本研究结果进一步佐证了“更新世后分布范围扩张是塑造北美中部脊椎动物遗传多样性的主导力量”这一学术观点。