Defining population structure for the Mojave desert tortoise
Conservation Genetics, 11 (5):
1795-1807 (2010)DOI: 10.1007/s10592-010-0073-0
Abstract
We used highly variable microsatellite markers to identify population structure, movement, and biological boundaries for populations of the desert tortoise, Gopherus agassizii, in the Mojave and Colorado Deserts of the southwestern United States. The Mojave desert tortoise (listed as “threatened” by the U.S. Fish and Wildlife Service) has a large geographic range, long generation time, low population densities, and little above-ground activity. Additionally, the dispersal patterns of individual tortoises are virtually unknown, making indirect methods to assess movement among populations valuable. Using Bayesian assignment tests, we detected hierarchical structuring within the Mojave desert tortoise. Three basal groups were identified, and these corresponded to the mitochondrial DNA haplotypes reported in 1989. Additional population structure was evident within each basal unit, and this structure corresponds with major geographic barriers. Our analyses suggest that gene flow among populations was historically high because levels of population differentiation were low across the range. Geographic distance explained a large proportion of variation in genetic distance (68%), which pinpoints that dispersal is limited only on a regional scale. In light of these new analyses of the genetic population structure of the Mojave desert tortoise, we make new recommendations for the number and locations of recovery units for conservation of this species.