Genetic Analysis and Captive Breeding Program Design for the Eastern Massasauga Sistrurus catenatus catenatus

Abstract

The eastern massasauga Sistrurus catenatus catenatus is a declining species for which a captive breeding program was established in 2006. To effectively manage wild and captive populations, an understanding of genetic diversity within the species is necessary. We analyzed mitochondrial DNA sequences of 186 individuals: 109 wild snakes from 34 U.S. and Canadian counties and districts, all 52 breeding program members (23 of known and 29 of unknown origin), 18 other captives of unknown origin, and 7 outgroup representatives of desert massasauga S. c. edwardsii, and western massasauga, S. c. tergeminus. Statistical parsimony, maximum likelihood, and maximum parsimony analyses all identified eastern massasaugas as divergent from western and desert massasaugas. We found 18 different haplotypes among eastern massasaugas, comprising three geographically and genetically differentiated NADH dehydrogenase II (ND2) subunits that potentially reflect post-Pleistocene range expansion from unglaciated into formerly glaciated regions. Snakes of unknown origin could all be assigned unambiguously to these ND2 subunits. To maintain natural genetic variation, preserve diversity in captive lineages, and allow future augmentation or reintroduction, the Association of Zoos and Aquariums is managing these three geographic ND2 subunits separately within the Eastern Massasauga Species Survival Plan breeding program.

Origin of a cryptic lineage in a threatened reptile through isolation and historical hybridization

“…We conclude that these clusters east of the Mississippi River have not been isolated for a sufficient time following the post-glacial colonization of their present range to show evidence of being evolutionarily independent lineages. These conclusions differ from those of Ray et al (2013) in terms of the number and geographic location of potential conservation units within S. catenatus. That study was limited to a single mtDNA locus, whereas our analyses used 41000 nuclear DNA loci.…”

“…Because BFD* relies on SNAPP, this analysis was subject to similar computational demands as those described above. Therefore, we again chose three individuals to represent each group identified in our clustering analyses (S. tergeminus, Iowa, West and East -see clustering results below), and also included three samples to represent the Central group proposed by Ray et al (2013) based on previous mtDNA analyses (these 'Central' samples were included as part of the Eastern group in the current analyses). These samples were used to test alternative models that ranged from a fully differentiated five-lineage model to a two-lineage model in which S. tergeminus and S. catenatus were included as the only two recognized taxa.…”

“…Although mtDNA alone can reveal phylogeographic patterns that are consistent with genome-wide patterns (Barrowclough and Zink, 2009), analyses based on multiple nuclear DNA markers often provide a more reliable estimate of the true phylogeographic history of a species (Edwards and Bensch, 2009). In addition, Ray et al (2013) used a clade support metric (the gsi statistic; Cummings et al, 2008) to define conservation units that is less stringent than our more conservative approach in which we assessed and required differentiation across a series of metrics including clade support values, branch lengths and BFD* analyses.…”

“…For example, Kubatko et al (2011) found no evidence for phylogeographic structure based on a multilocus analysis of 20 nuclear DNA markers, although the number and geographic range of samples analyzed was limited. In contrast, Ray et al (2013) analyzed a much larger and more widespread set of samples with a single mitochondrial DNA (mtDNA) locus and identified three geographically separate mtDNA lineages (Western, Central and Eastern). These designations are currently being considered for use in a captive breeding program for this species (Ray et al, 2013).…”

“…In contrast, Ray et al (2013) analyzed a much larger and more widespread set of samples with a single mitochondrial DNA (mtDNA) locus and identified three geographically separate mtDNA lineages (Western, Central and Eastern). These designations are currently being considered for use in a captive breeding program for this species (Ray et al, 2013). However, given that this inference is based on a single mtDNA locus, it is unclear whether this pattern represents variation across the genome as a whole, and hence whether it provides an accurate representation of the phylogenetic history of this species.…”