Shallow phylogeographic structure in the declining Mexican Lance-headed Rattlesnake, Crotalus polystictus (Serpentes: Viperidae).

Shallow phylogeographic structure in the declining Mexican Lance-headed Rattlesnake, Crotalus polystictus (Serpentes: Viperidae). We investigated matrilineal relationships among populations of the Mexican lance‑headed rattlesnake (Crotalus polystictus), a pitviper inhabiting high‑elevation valleys of the densely populated southern Mexican Plateau. A fragment of the mitochondrial ATPase 8 and 6 genes (589 base pairs) revealed comparatively low levels of genetic diversity, with few nucleotide polymorphisms across the portion of the geographic distribution sampled. The shallow intraspecific sequence divergence (1.0%) in C. polystictus ATPase 8 and 6 genes contrasts with deep divergences (~1.0-14.1%) observed within other montane rattlesnake lineages from the Mexican highlands, and is more typical of intraspecific variation observed in lowland rattlesnake species with similar distributional extents (e.g., C. tigris). We posit that the low genetic diversity in C. polystictus relative to that of other highland rattlesnakes may reflect ecological differences resulting in a different evolutionary response to Pleistocene climatic events. Our finding of apparently low genetic diversity in C. polystictus highlights the importance of conservation initiatives to protect high elevation grasslands in central Mexico.