Subspecies have been considered artificial subdivisions of species, pattern classes, or incipient species. However, with more data and modern phylogenetic techniques, some subspecies may be found to represent true species. Mitochondrial DNA analysis of the polytypic snake, Elaphe obsoleta, yields well-supported clades that do not conform to any of the currently accepted subspecies. Complete nucleotide sequences of the cytochrome b gene and the mitochondrial control region produced robust maximum-parsimony and maximum-likelihood trees that do not differ statistically. Both trees were significantly shorter than a most parsimonious tree in which each subspecies was constrained to be monophyletic. Thus, the subspecies of E. obsoleta do not represent distinct genetic lineages. Instead, the evidence points to three well-supported mitochondrial DNA clades confined to particular geographic areas in the eastern United States. This research underscores the potential problems of recognizing subspecies based on one or a few characters.

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Some aspects of the natural history of snakes of the colubrid genus Natrix have been well studied. With their extensive European distribution and relative abundance, their ecology, reproduction and behaviour are well known. Yet other facets of their biology remain poorly understood. These include knowledge of Natrix phylogeny, hypotheses explaining the current distribution of the three extant members of the genus, and their evolution and relationships. In this study we used molecular data, the nucleotide sequences of four protein-coding mitochondrial genes (3806 bp total), to provide a well-supported phylogeny for the genus Natrix . With these molecular data, evidence from the fossil record, and knowledge of palaeogeological events, we used two approaches in designing a time scale which we used to date the major events in Natrix speciation and intraspecific variation. Our data strongly support a phylogeny for the genus in which N. maura is basal with N. natrix and N. tessellata being sister species. The calibrated molecular clock suggests that N. maura diverged from the common ancestor of the three species 18-27 mya and that N. natrix and N. tessellata diverged 13-22 mya. Although the ranges of these estimates are large they support an early Miocene to late Oligocene origin for the three species. Intraspecific divergence is estimated to have commenced 5.3, 6.0 and 6.7 mya with evolutionary rates of 1 : 1.25 : 1.35% per million years for N. maura, N. natrix and N. tessellata , respectively.

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