Genetic Diversity and Population Structure of the Texas Tortoise (Gopherus berlandieri): Implications for Conservation

Abstract

The Texas tortoise ( Gopherns berlandieri) is a state threatened species in Texas. Expanding agricultural practices and urban development are major causes of habitat degradation for G. berlandieri. In order to provide genetic data that can inform conservation planning for this species, genetic variation, population structure and its underlying processes were examined in the U.S. populations of G. berlandieri. An a priori hypothesis for geographic pattern in its population structure as shaped by the Nueces River basin was tested. A total of 127 individuals representing nine sampling areas were genotyped for 11 microsatellite loci. Assignment tests, F-statistics, and analysis of molecular variance (AMOV A) indicate that G. berlandieri forms weak population differentiation into northern and southern populations with a boundary at southern Duval County. A test of isolation by distance and indirect estimation of Nm suggest recent gene flow between two populations. Estimation of the extent of recent migration appears to be complicated by human translocation of the tortoises. A lack of concordance between the detected population structure boundary and the Nueces River basin did not support the a priori hypothesis. Gopherus berlandieri is weakly differentiated due to ongoing migration as evidenced by a pattern of isolation by distance. Given the limited population structure and continuous habitat degradation, designation of two management units may not be warranted. Conservation efforts rather should emphasize connectivity between the populations to maintain genetic diversity in both Populations.