Molecular phylogeography of the western hognose snake (Heterodon nasicus)

Background/Question/Methods Heterodon nasicus (western hognose snake) is broadly distributed from southeastern Alberta, Canada to northern Mexico.  The currently recognized subspecies (H. n. nasicus, H. n. kennerlyi, and H. n. gloydi,) designation, based on morphological characters, has not been reassessed with modern molecular methods.  The use of molecular tools will help to clarify the taxonomic status and population relationships of this broadly-distributed snake.  Understanding evolutionary relationships among, and genetic variation within, H. nasicus populations will provide important conservation information, as this species is endangered or threatened in various parts of its range. This study will test for concordance in previous morphology based systematic assessments (Eckerman 1997; Chiszar et al 2003) against that of the proposed mitochondrial DNA sequence analysis.  The secondary goal will be to assess how populations are genetically structured and to determine the regional historical forces responsible for the current distribution of the species.  Results/Conclusions Preliminary results and methods used for designing primers will be presented.  We anticipate that southern populations will be more genetically distinct than northern populations as a result of expansions northward into areas heavily impacted by the retreat of glaciers approximately 10,000 years ago.  Furthermore, we predict H. nasicus dispersed northward and subsequently eastward, coinciding with the Holocene Climatic Optimum and the Xerothermic period of grassland invasion.  If this pattern of dispersal is apparent, phylogenetic analyses will show northern and eastern populations to be the most derived.