High Connectivity Observed in Populations of Ringed Sawbacks, Graptemys oculifera, in the Pearl and Bogue Chitto Rivers Using Six Microsatellite Loci

Graptemys oculifera is endemic to the Pearl River drainage system in Louisiana and Mississippi, and due to this limited range it is vulnerable to environmental changes. Many impacts to this drainage system are due to anthropogenic activities, and alterations may negatively impact the connectivity among populations of G. oculifera. Previous studies show populations below the Ross Barnett Reservoir might be undergoing population declines, suggesting limited movement among populations. In addition to anthropogenic effects, the drainage geomorphology might also play a role in shaping population connectivity, as the sister species of G. oculifera, G. flavimaculata, contains two distinct populations (mainstem Pascagoula and Escatawpa River) and possible subpopulations within the Pascagoula (upper Leaf River, upper Chickasawhay River, and lower sections of the Pascagoula River). We used six polymorphic microsatellite loci to analyze the population genetics of G. oculifera at eight sites in the Pearl River drainage. The STRUCTURE program found support for one genetic group; however, our AMOVA analysis detected small but significant genetic differentiation in our three-group analysis. Both the MIGRATE and Isolation-by-Distance analyses supported a stepping stone model of gene flow, not panmixia. We suggest management agencies should consider these genetic data when developing management plans. Although we did not detect any influence of the reservoir on population connectivity, likely due to the long generation times of turtles, we suggest mark–recapture and/or radio-telemetry studies be performed on populations near the reservoir to determine if cross reservoir movements occur.