Systematics of the Eastern Ratsnake Complex (Elaphe obsoleta)

Abstract

The eastern ratsnake, Elaphe obsoleta currently includes seven highly variable and taxonomically confusing subspecies. Recently, maximum likelihood and maximum parsimony phy- logenetic analyses of two mitochondrial gene sequences suggested that the complex of E. obsoleta (including E. bairdi) is composed of four distinct evolutionary lineages found in four geographical areas: 1) an eastern clade located east of the Apalachicola River and the Appalachian Mountains, 2) a central clade located west of the Apalachicola River and the Appalachian Mountains and east of the Mississippi River, 3) a western clade located west of the Mississippi River, and 4) E. bairdi is located in southwest Texas and northeastern Mexico. With respect to this phylogeographic hy- pothesis, the former seven subspecies of E. obsoleta do not represent distinct evolutionary lineages. In this paper, the morphology of Elaphe obsoleta and E. bairdi is compared to the results of the previous molecular study. Univariate and multivariate analyses of 67 morphological characters scored from 1006 specimens provided statistical support for the recognition of the same four evolutionary lineages identified in the phylogeographic study. Specimens can be classified morphologically by using canonical discriminant function analysis into the four molecular clades more accurately than they can be grouped into subspecific categories. Moreover, the identification of these subspecies proved difficult when using the traditional characters ascribed to them. In light of the corroborating molecular and morphological evidence, it is suggested that the recognition of the subspecies of E. obsoleta be discontinued. Instead, the four molecular clades should be recognized as four species: 1) eastern clade = E. alleghaniensis, 2) central clade = E. spiloides, 3) western clade = E. obsoleta, and 4) E. bairdi = E. bairdi.