Evolutionary History Of A Specialized And Diverse Highland Snake Complex (crotalus Willardi)

The Ridgenosed rattlesnake (Crotalus willardi) is a highly unique group of small rattlesnakes consisting of 5 subspecies that inhabit the high elevation pine oak woodlands of the Sierra Madre Occidental and the Madrean Archipelago. They remain one of the most understudied groups of rattlesnakes with little understanding of the relationships between the subspecies. I utilize genomic level genetic data collected using ddRAD-seq methodology on 60 individuals encompassing all 5 subspecies and the majority of the range. Utilizing co-ancestry analysis, Admixture, and Phylogenetic analyses (both maximum likelihood and Bayesian approaches) we uncovered seven separate genetic groups. Of these, three consisted of a single described subspecies with the remaining two subspecies being paraphyletic. One integrade was uncovered by our analysis but Treemix modeling indicated that 98% of variation in the gene trees could be explained without geneflow. Admixture, however, should slight mixing in some groups which may be indicative of ancestral gene flow. The deepest divergences occur in the southernmost subspecies with some strange patterns occurring where sister lineages were not the closest to each other geographically. These results suggest that current taxonomy may not be adequate in explaining the variation in the complex. They also suggest that there has been little to no recent gene flow with the group first evolving in the south and moving north.