Phylogenetics and biogeography of the microendemic rodentXerospermophilus perotensis(Perote ground squirrel) in the Oriental Basin of Mexico

Phylogenetic relationships of the Mexican endemic and endangered Perote ground squirrel, Xerospermophilus perotensis (Rodentia: Sciuridae), were examined using 2 mitochondrial (cytochrome-b [Cytb] and 12S ribosomal RNA) and 2 nuclear (growth hormone receptor and interphotoreceptor retinoid-binding protein) genes for a total of 3,403 base pairs. Gene sequences were analyzed using maximum-likelihood and Bayesian models of phylogenetic inference. Independent analyses of the 4 gene sequences converged on essentially identical gene trees, all showing X. perotensis to be sister to X. spilosoma from San Luis Potosí, Mexico, and nested within other geographic samples of X. spilosoma. Given the current absence of diagnostic morphological characters to distinguish X. perotensis from X. spilosoma and the moderate level of Cytb sequence divergence between the 2 forms (3.6%, which is less than divergence values measured between other subspecies of X. spilosoma), X. perotensis is herein reduced to subspecies status as X. spilosoma perotensis. Based on molecular estimates of divergence times, phyletic diversification of the genus Xerospermophilus began near the end of the Pliocene and X. spilosoma perotensis diverged from other Mexican populations of X. spilosoma during Pleistocene times. Climate cycles during the Pleistocene and the final uplift of the Trans-Mexico Volcanic Belt may have played a major role in early diversification in this lineage.