Hybridization and low genetic diversity in the endangered Alabama Red-Bellied Turtle (Pseudemys alabamensis)

Pseudemys alabamensis is one of the most endangered freshwater turtle
species in the United States due to its restricted geographic distribution
in coastal Alabama and Mississippi. Populations of P. alabamensis are
geographically isolated from one another by land and salt water, which
could act as barriers to gene flow. It is currently unknown how
differentiated these isolated populations are from one another and whether
they have experienced reductions in population size. Previous work found
morphological differences between Alabama and Mississippi populations,
suggesting that they may be evolutionarily distinct. Other Pseudemys
turtles such as P. concinna and P. floridana occur naturally within the
same geographic area as P. alabamensis and are known to hybridize with
each other. These more abundant species could threaten the unique genetic
identity of P. alabamensis through introgression. In order to evaluate the
endangered status of P. alabamensis and the level of hybridization with
other species, we used mitochondrial and nuclear microsatellite markers to
assess genetic variation within and among populations of P. alabamensis
throughout its range and estimate admixture with co-occurring Pseudemys
species. In P. alabamensis, we found no variation in mitochondrial DNA and
observed an excess of homozygosity in the microsatellite data. Our results
indicate evidence of genetic differentiation between Alabama and
Mississippi populations of P. alabamensis, and low estimated breeding
sizes and inbreeding for two populations (Fowl River, Alabama and Biloxi,
Mississippi). Our results also support admixture of P. alabamensis with P.
concinna/P. floridana. Based on our results, P. alabamensis is highly
endangered throughout its range and threatened by both low population
sizes and hybridization. In order to improve the species’ chances of
survival, focus should be placed on habitat preservation, maintenance of
genetic diversity within both Mississippi and Alabama populations, and
regular population monitoring activities such as nest surveillance and
estimates of recruitment.