Midwest Fish & Wildlife Conference 2019

AUTHORS: Alex Ochoa, Michael Broe, H. Lisle Gibbs – Ohio State University

ABSTRACT: Small isolated populations of endangered species can experience genetic costs through the loss of adaptive variation and/or the accumulation of deleterious mutations through genetic drifts.  The endangered Eastern Massasauga Rattlesnake (Sistrurus catenatus) occurs in isolated populations with small effective sizes throughout its range in the U.S. and Canada, but little is known about the levels of adaptive genetic variation in existing populations.  Here, we used DNA capture probes and Next Generation Sequencing to assess the genetic diversity of venom genes in 93 Eastern Massasauga Rattlesnakes from 12 populations in Ohio, Pennsylvania, New York, Illinois, and Ontario.  Specifically, we characterized the genetic diversity of genes encoding PLA2, BPP, CRISP, SVSP, and SVMP venom proteins, as well as an additional set of ~1400 non-toxin and neutral loci.  Within populations, we find that variation—defined as the presence of nonsynonymous single nucleotide polymorphisms in venom genes—is common and not related to effective population sizes, as determined from neutral genetic markers.  This suggests that small populations of this species still retain high levels of adaptive genetic variation despite the impact of strong genetic drift. In contrast, levels of population divergence in toxin and non-toxin loci are similar, thus making the roles of selection versus genetic drift in maintaining population differences in venom gene alleles uncertain.  Broadly, we discuss the implications of our results for management activities for this endangered snake from a conservation genetics perspective.