Conservation genetics of the yellow-blotched sawback Graptemys flavimaculata (Testudines: Emydidae)

Abstract

Turtles within the genus Graptemys are increasingly becoming a group of conservation priority due to (1) the number of species endemic to single Gulf of Mexico rivers and (2) human alterations of riverine habitat. The yellow-blotched sawback (Graptemys flavimaculata) is a federally threatened species that is endemic to the Pascagoula River system of southeastern Mississippi, USA. Currently, there is nothing known about genetic variation and population structure in G. flavimaculata. We used microsatellite data to analyze population genetic structure, assess historical demography, and determine effective population size at six sites throughout the Pascagoula River system. Considerable genetic diversity was found within each site (mean allelic richness: 6.65–8.08) and two analyses found no evidence of genetic bottlenecks. All of the pairwise FST values, while low (average = 0.026), were significant, with most sites possessing one or more private alleles. Pairwise FST values with the Escatawpa River site were larger (0.030–0.047), which likely reflect its historical isolation. Genetic distance was correlated to geographic distance between sites, with the exception of the Escatawpa River site; a similar pattern was also found with estimates of recent rates of migration among sites. While an analysis of molecular variance indicated that most variation was partitioned within rather than among sites, STRUCTURE analysis strongly supported the recognition of two distinct groups (mainstem Pascagoula vs. Escatawpa), with the possibility of additional substructure within the mainstem Pascagoula.