Genetic and morphometric assessment of an unusual tortoise (Gopherus agassizii) population in the Black Mountains of Arizona

Under recent regulatory designation of the U.S. Fish and Wildlife Service, desert tortoises (Gopherus agassizii) occurring east and south of the Color ado River constitute the Sonoran population, whereas those to the west and north form the Mojave population. These management units, distinguished by significant genetic, morphometric, and ecological differences, represent de ep phylogenetic subdivisions within G. agassizii and are of high conservati on value. We provide genetic and morphological profiles for an unusual tort oise population inhabiting the Black Mountains of Arizona, some 40 km east of the Colorado River. Both mitochondrial (mt) DNA and morphometric analyse s revealed predominately Mojavean features: ten of eleven Black Mountain to rtoises possessed Mojave mtDNA markers, and 24 of 37 animals exhibited Moja ve morphometric phenotypes. Our results indicate west-to-east movement of t ortoises across the Colorado River, though how or when a Mojave lineage bec ame established in the Black Mountains is difficult to ascertain. Active di spersal, river meander, and human transport (early or modern peoples) serve as plausible explanations. Future management of the Black Mountain tortois es should emphasize the population's Mojavean affinities.