Presentation Abstract

Title: Assessing population structure and subspecific status of the Western Shovel-nosed snake across the Colorado and Sonoran desertscrub valleys of California and Arizona.
Session Title: Reptiles and Amphibians
Session Number: 15
Session Time: Sunday, Oct 14, 2012, 8:30 AM -12:20 PM
Presentation Time: Sunday, Oct 14, 2012, 8:50 AM - 9:10 AM
Author(s): Dustin A. Wood, Amy G. Vandergast, US Geological Survey, San Diego, CA, Contact: dawood@usgs.gov
Abstract Body: There is concern that the Tucson Shovel-nosed snake (Chionactis occipitalis klauberi) has experienced significant declines over the past 25 years, which has lead to a petition to list klauberi under the Endangered Species Act. An important question in evaluating that petition is whether klauberi is a distinct subspecies. Subspecific recognition within the Western Shovel-nosed snake has been based primarily on weak morphological differentiation, and is further complicated by the fact that klauberi purportedly forms a large zone of intergradation with the Colorado Shovel-nosed snake (C. o. annulata) across central Arizona. Results from our previous range-wide analyses, using morphology and mtDNA data, supported six monophyletic units; however, neither genetic nor morphological data were entirely concordant with the traditional subspecies taxonomy. In particular, representative samples of klauberi were marginally differentiated morphologically, yet genetically embedded in a mtDNA clade that included both klauberi and annulata. Given these inconclusive results, we developed a multi-locus strategy, using nuclear microsatellite loci, to provide a robust estimate of the genetic units within shovel-nosed snakes, with particular emphasis on the zone of intergradation between the klauberi and annulata subspecies. We use 11 microsatellite loci genotyped for 264 specimens and two Bayesian clustering methods to infer population structure without a priori subspecies assumptions. Analyses support five genetic clusters across the species range, with admixture between groups generally occurring along contact zones. Importantly, one of the clusters recovered was concordant with the distribution of klauberi, providing genetic support for taxonomic recognition. Finally, significant estimates of population differentiation between clusters are detectable and appear to be driven, at least in part, by isolation-by-distance. However, even after controlling for geographic distance there still appears to be a gene flow barrier between the Tucson Shovel-nosed snake and more western genetic clusters, suggesting factors other than geographic distance may be at play.



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