Molecular Evolution in Thomomys: Phyletic Systematics, Paraphyly, and Rates of Evolution

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Abstract
The phylogenetic relationships among extant members of the bottae-group of Thomomys (subgenus Megascapheus, sensu Thaeler, 1980) are examined in the context of their relationships to two species of the talpoides-group (subgenus Thomomys) by electromorphic biochemical analyses. a basic dichotomy of the extant species is supported. The phyletic position of the four bottae-group species is such that bottae and townsendii form a sister-group relative to umbrinus and this triad forms a sister-group relative to bulbivorus.T. bulbivorus is a monophyletic taxon; T. umbrinus is also monophyletic, although it may comprise more than one biological species. T. townsendii is monophyletic but stems from one geographic populational unit of T. bottae; thus bottae is a paraphyletic taxon in relation to townsendii. Differential rates of molecular change across sampled populations are ascribed to historical and population processes, such as hybridization, population size, and degree of geographic isolation.