This study examined the genetic divergence of cytochrome oxidase I ( Cox1 ) and the molecular phylogenetic relationships among allopatric populations of five morphospecies of brush-tailed mice ( Calomyscus ). The genus Calomyscus had long been considered a single species, Calomyscus bailwardi ; however, currently, eight geographical species are recognized on the basis of karyotypic, morphologic, and restriction fragment length polymorphism differentiation. Molecular approaches (DNA sequencing) have recently been used to examine the level of genetic differentiation, but this research has principally been restricted to cytochrome b sequences throughout the ranges of C. baluchi and C. hotsoni . To further examine the relationships among species of Calomyscus , we evaluated five morphospecies using DNA sequences. Specimens of Calomyscus were collected from 13 sites in Iran and Pakistan. A total of 637 base pairs of a mitochondrial gene ( Cox1 ) was amplified and sequenced. Analyses using maximum parsimony, maximum likelihood, and Bayesian inference provided similar results and placed the representatives of the five morphospecies into five well-supported clades, each corresponding to one of the recognized morphospecies. Furthermore, our molecular data expanded the known distribution of C. elburzensis from northeast to central Iran (Razavi Khorasan, Northern Khorasan, and Yazd provinces) and identified the Yazd population as a geographic isolate with ties to the Elburz Mountains.

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