Abstract
In the genus Thomomys, external phenotypic differences account for much of the variation among currently named species. Allozyme and mitochondrial studies of the Mexican species, T. umbrinus, have shown strong discordance between genetically defined clades and current species taxonomy. In this study, I analyzed mitochondrial and nuclear DNA sequences, chomosomes, and morphological characters, and used ecological niche modeling to investigate the phylogenetic status of a phenotypically divergent subspecies of T. umbrinus, T. u. atrovarius. Although quantitative morphometrics provided little discrimination among groups within T. umbrinus, the molecular data indicated that there are three allopatric clades. The Pacific coastal clade (T. u. atrovarius) is diagnosable based on multiple characters, including nuclear genotype, habitat preference, and qualitative morphological characters. Accordingly, I resurrect Allen’s (1898) species Thomomys atrovarius to represent members of this clade, which occurs in the Pacific coastal region of western Mexico.
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