Phylogenetic, population genetic, and morphological analyses reveal evidence for one species of Eastern Indigo Snake (Drymarchon couperi)

Accurate species delimitation and description are necessary to guide effective conservation management of imperiled species. The Eastern Indigo Snake ( Drymarchon couperi ) is a large species in North America that is federally-protected as Threatened under the Endangered Species Act. Recently, two associated studies hypothesized that Drymarchon couperi is two species. Here, we use diverse approaches to test the two-species hypothesis for D. couperi . Our analyses reveal that (1) phylogenetic reconstruction in Krysko et al. (2016a) was based entirely on analysis of mitochondrial DNA sequence data, (2) microsatellite data demonstrate significant nuclear gene flow between mitochondrial lineages and a clear isolation-by-distance pattern across the species entire range, and (3) morphological analyses recover a single diagnosable species. Our results reject recent conclusions of Krysko et al. (2016a,b) regarding species delimitation and taxonomy of D. couperi , and we formally place Drymarchon kolpobasileus into synonymy with D. couperi . We suggest inconsistent patterns between mitochondrial and nuclear DNA may be driven by high dispersal of males relative to females. We caution against species delimitation exercises when one or few loci are used without evaluation of contemporary gene flow, particularly species with strong sex-biased dispersal (e.g., squamates) and/or when results have implications for ongoing conservation efforts.