UC Irvine

The musk turtle (Sternotherus minor) is common throughout the southeastern United States. In 1955 a morphologically atypical form confined to the Black Warrior River System in Alabama was discovered and accorded full species status as S. depressus, the 'flattened musk turtle.' Questions remain about the taxonomic status and evolutionary history of the flattened musk turtle because (1) the geographic distribution of S. depressus is nested within the range of S. minor; (2) the flattened shell might be a recently evolved anti-predator adaptation; and (3) reports exist of intergrades between S. depressus and S. minor. We generated and employed sequence data from mitochondrial DNA to address the phylogenetic distinctiveness and phylogeographic position of S. depressus relative to all other musk and mud turtles (Kinosternidae) in North America. The flattened musk turtle forms a well-supported monophyletic group separate from S. minor. Genetic divergence observed between S. depressus and geographic populations of S. minor is no less than that distinguishing many kinosternid congeners from one another. These molecular genetic findings bolster rationale for the taxonomic recognition of S. depressus and, hence, for special efforts to protect this federally threatened species.