Fecal DNA metabarcoding reveals how sexual dimorphism and bite force influence seasonal changes in diets of diamondback terrapins (Malaclemys terrapin littoralis)

Diamondback terrapins (DBTs, Malaclemys terrapin ) exhibit pronounced sexual dimorphism, yet the functional consequences of this morphology for trophic ecology remain poorly resolved. We examined sex- and size-dependent dietary shifts using fecal DNA metabarcoding of DBTs captured from February-August over a three-year period and integrated these data with bite force measurements to assess biomechanical constraints on prey use. Diets differed markedly among demographic groups. Adult females uniquely consumed gastropods, and only during the reproductive period, whereas males and subadult females relied primarily on algae and crustaceans as food sources. Bite force scaled strongly with carapace length and head width, and only adult females exceeded the force required to crush periwinkle snail shells, indicating a clear performance threshold governing access to this resource. Early - season diets of all groups were dominated by marine algae containing floridean starch, suggesting an important and previously underappreciated carbohydrate source during winter months. Collectively, these findings demonstrate that trophic ecology in DBTs is structured by the interaction of morphology, performance capacity, and reproductive demands, with adult females exploiting a temporally-restricted, calcium-rich prey resource that is physically inaccessible to other demographic groups. This is the first report of the use of fecal DNA metabarcoding to elucidate diets of DBTs.