Zootaxa 4138 (3): 549–569 ISSN 1175-5326 (print edition) http://www.mapress.com/j/zt/ Article ZOOTAXA Copyright © 2016 Magnolia Press ISSN 1175-5334 (online edition) http://doi.org/10.11646/zootaxa.4138.3.7 http://zoobank.org/urn:lsid:zoobank.org:pub:C7391621-50DB-4070-9BCF-3D00B49F291C A cryptic new species of Indigo Snake (genus Drymarchon) from the Florida Platform of the United States KENNETH L. KRYSKO1,5, MICHAEL C. GRANATOSKY2, LEROY P. NUÑEZ1,3 & DANIEL J. SMITH4 1Florida Museum of Natural History, Museum Road, Dickinson Hall, University of Florida, Gainesville, Florida 32611 USA. E-mail: KLK: [email protected], LPN: [email protected] 2Department of Evolutionary Anthropology, Duke University, Durham, North Carolina 27708, USA. E-mail: [email protected] 3School of Natural Resources and Environment, 103 Black Hall, University of Florida, Gainesville, Florida 32611 USA. 4Department of Biology, University of Central Florida, 4000 Central Florida Blvd, Orlando, Florida 32816, USA. E-mail: [email protected] 5Corresponding author Abstract Indigo Snakes (genus Drymarchon) occur from northern Argentina northward into to the United States, where they inhabit southern Texas and disjunct populations in Mississippi, Florida and Georgia. Based on allopatry and morphological dif- ferences Collins (1991) hypothesized that the two United States taxa—the Western Indigo Snake, D. melanurus erebennus (Cope, 1860), and the Eastern Indigo Snake, D. couperi (Holbrook, 1842)—deserved full species recognition. Building upon this hypothesis with molecular and morphological analyses we illustrate that D. couperi is split into two distinct lin- eages. Based on the General Lineage Concept of Species, we describe the lineage that occurs along the Gulf coast of Flor- ida and Mississippi as a new species, Drymarchon kolpobasileus. The new species is distinguished from D. couperi by a suite of morphological features, including a shorter and shallower head, deeper and shorter 7th infralabial scales, and short- er temporal scales. Overall, the presence of a deep 7th infralabial scale provides the best univariate identifier of D. kol- pobasileus sp. nov. This study illustrates the usefulness of using both morphological and genetic data in refining accurate descriptions of geographical distributions. Key words: Colubridae, D. couperi, D. melanurus, Drymarchon kolpobasileus sp. nov., Indigo Snakes, morphology, phy- logenetics, Pleistocene, Pliocene, Serpentes, United States Introduction With the advancement of molecular and analytical tools, the definition of a species is becoming more agreed upon among modern systematists (Wiens 2007; Pyron & Burbrink 2009). Although there have been more than 20 species concepts (some very similar) since Mayr’s (1969) Biological Species Concept, de Queiroz (1998, 2007) made an invaluable contribution by taking common criteria among the different concepts and applying them to a unified concept, the General Lineage Concept of Species. Under this philosophical view, the primary criterion for recognizing a species is that it exhibits a separately evolved metapopulation or lineage, where an inclusive population is made up of connected subpopulations in an ancestor-descendant series (de Queiroz 1998, 2007). Secondary operational criteria (although not necessary) include that the lineage exhibits intrinsic reproductive isolation, diagnosability, or monophyly, which may provide further evidence for lineage separation (de Queiroz 1998, 2007). Thus, species are well-supported genealogical lineages in terms of population structure (Wiens 2004; Ereshefsky & Matthen 2005; de Queiroz 2007; Shaffer & Thomson 2007; Wiens 2007). Indigo Snakes (genus Drymarchon, with five currently recognized species; see Wüster et al. 2001) occur from northern Argentina northward into the United States, where they inhabit southern Texas and disjunct populations in Mississippi, Florida and Georgia (Krysko et al. 2016). Based on known allopatry (approximately 1000 km, see Moler 1992) and a difference in supralabial scale shape (Fig. 1; originally proposed by Baird & Girard 1853 and Accepted by A. Bauer: 9 Jun. 2016; published: 18 Jul. 2016 549 illustrated by Conant 1958), Collins (1991) hypothesized that the two United States taxa previously considered as subspecies within D. corais (Boie, 1827)—the Western Indigo Snake, D. melanurus erebennus (Cope, 1860), and Eastern Indigo Snake, D. couperi (Holbrook, 1842)—deserved separate species recognition (Krysko et al. 2016). The names D. couperi and D. melanurus have now been in use for more than 25 and 15 years, respectively (see Collins 1991; Wüster et al. 2001; Wallach et al. 2014; and Powell et al. 2016). A recent multi-locus phylogenetic study (Krysko et al. 2016) using both mitochondrial (mtDNA) and single copy nuclear (scnDNA) DNA suggests that not only are D. melanurus and D. couperi genetically distinct and recognizable as separate species based under the General Lineage Concept of Species, but also that D. couperi as currently recognized represents two distinct genetic lineages and separate species (Fig. 2). These molecular data suggest that D. melanurus from Texas and Mexico initially diverged from Drymarchon populations in Florida and Georgia about 5.9 million years ago (Ma); 95% Highest Posterior Density [HPD] = 2.5–9.8 Ma; during the late Blancan of the Pleistocene through the Hemphillian of the Miocene) (Krysko et al. 2016). During this time, western Drymarchon likely utilized a Gulf coast corridor and followed suitable habitat eastward during a glacial maximum when sea levels dropped and previously submerged land on the Florida Platform was exposed (Krysko et al. 2016), a range expansion hypothesis originally proposed by Auffenberg & Milstead (1965). Subsequently, the two well-supported genetic lineages in Florida and Georgia (termed Atlantic and Gulf lineages after Soltis et al. 2006) had diverged from each other about 2 Ma (95% HPD = 0.7–3.7 Ma; during the Irvingtonian of the Pleistocene through the Blancan of the Pliocene) (Krysko et al. 2016). This later divergence illustrates a common biogeographic distributional break in peninsular Florida, corresponding to historical sea level changes caused by Milankovitch cycles (Randazzo & Jones 1997; Hine 2013; Krysko et al. 2016). The identified extreme glacial minimum between 2.7–3.2 Ma incorporates much of the 95% HPD for the divergence date estimate between the Atlantic and Gulf lineages (Krysko et al. 2016). During this time, sea level was about 22 m higher than present day (Miller et al. 2012) and peninsular Florida consisted of a series of subaerially exposed islands on the Florida Platform (Lane 1994; Randazzo & Jones 1997; Miller et al. 2012; Hine 2013; Krysko et al. 2016). Thus, Krysko et al. (2016) hypothesized that the Gulf Lineage (as well as many other distinct plants and animals) evolved on these islands or a single large island, which would have been surrounded by saltwater acting as a physical barrier to gene flow from closely related populations (i.e., the Atlantic Lineage) still in contact with the mainland to the north. Despite dozens of Milankovitch cycles (Hine 2013) along with associated forming of physical barriers (i.e., sea level fluctuations, high elevation sand ridges, and/or insufficient habitats) since their initial lineage diversification, these two lineages have likely come in and out of contact with each other many times, yet today they still illustrate near discrete geographic distributions (Krysko et al. 2016). Voucher specimens confirm that Drymarchon was once widespread in the Coastal Plain of the southeastern United States, from southeastern Mississippi, southern Alabama, southern Georgia, and southward into the Florida Keys (Krysko et al. 2010, 2016). Krysko et al. (2016) noted that the Alabama voucher consists of a late Pleistocene fossil from the Bogue Chitto Creek Site, Dallas County (Dobie et al. 1996; Holman 2000), and only unverifiable observations of live snakes have been reported from Alabama (Löding 1922; Haltom 1931; Neill 1954; Mount 1975). However, there is a single non-fossil specimen (MMNS 1199) collected on 16 November 1939 by W.H. Young from southern Wayne County, Mississippi (United States Fish and Wildlife Service 2008; B. Jones, personal communication). It is currently unknown to which lineage of Drymarchon this specimen is associated. This specimen is one of three collected in Mississippi during a faunal survey directed by Fannye A. Cook from 1936– 1941; two specimens from Wayne County and a third specimen from Forrest County (Cook 1954; B. Jones, personal communication). The other Wayne County specimen and the Forrest County specimen have been lost, and the last Drymarchon in Mississippi was found in Forrest County in 1955 by William Turcotte (B. Jones, personal communication). Although both the Atlantic and Gulf lineages of Drymarchon are well-supported genealogical lineages in terms of population structure (Krysko et al. 2016), a new species description was delayed in order to acquire secondary operational criteria to provide further evidence for separately evolved lineages. In this paper, we conduct morphometric analyses to illustrate reliably detectable diagnosable differences (in addition to molecular evidence) between these two cryptic lineages, and revise the taxonomy of Drymarchon in the southeastern United States. 550 · Zootaxa 4138 (3) © 2016 Magnolia Press KRYSKO ET AL. FIGURE 1. Proposed differences in supralabial morphology between the A) Western Indigo Snake, Drymarchon