Exploring snake evolution through time and space

Abstract

Lineages diversify as they disperse through time and space, which provides ever increasing complexity to be considered in investigations at different taxonomic levels. Population genetic and phylogenetic signal sometimes correspond or are driven by spatial features or historic vicariant events, from which one might reasonably conclude that similarly distributed species might exhibit similar patterns. In chapter 1, I address shared and divergent population patterns in the first comparative population genetic study of the garter snake (Thamnophis) assemblage from the San Juan Archipelago, which has likely only been recolonized post-Pleistocene glacial retreat in the last 10,000 years. In chapter 2, I characterized the rangewide phylogeography of the widest ranging of these three species featured on the San Juan Archipelago, T. sirtalis, which is distributed throughout North America. To characterize the influence of long established and nascent geographic barriers that characterize the North American continent, I conduct ecological niche modeling on the inferred genetic lineages, and comment on the tempo and mode of a species that has rapidly spread across an entire continent. In Chapter 3, I expand the coalescent methodology to trans-continental evolutionary histories, where I reevaluate the evolutionary relationships of the cobras and closely related elapids (family Elapidae) from targeted sequence capture of UCEs and SNPs derived from ddRADseq data. I assess the stability of divergence times from prior mtDNA and concatenation-based studies by estimating clade ages under the multispecies coalescent model. Returning to the shallow depths of chapters 1 and 2, I evaluate the age and topology of the Asiatic Naja radiation and the Naja melanoleuca species complex, and weigh the two markers’ ability to resolve shallow radiations under the coalescent model.