Relationships of Pocket Gopher (Thomomys bottae) Populations of the Lower Colorado River

Abstract

Two major genically differentiated geographic segments of Thomomys bottae meet along the lower Colorado River in California and Arizona. Maximum divergence recorded between adjacent populations is as high as 35% of the genome as measured by electrophoretic techniques. There is no detectable gene flow between north-south arranged subspecies on either bank of the river due to physiographic barriers. Indirect gene flow through adjoining populations peripheral to the river in the Salton Basin of California and along the Gila River of Arizona is apparent. Populations on opposite banks are remarkably similar genically, suggesting recency of common origin or occasional movement of individuals across the river. The genic pattern of population relatedness is distinct from that indicated by morphology. The genic data are interpreted as more likely reflecting the history of the populations in question whereas the morphology responds more directly to environmentally mediated selection regimes.