Behaviour 2019
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Underdeveloped Cloacal Bursae and Age-dependent Surfacing Postures in Diamond-backed Terrapins
Megan P. Wright1, Jadyn M. Sethna1, Ollie Shinn1, Joseph R. Mendelson1,2. 1Georgia Institute of Technology, Atlanta, Georgia, United States; 2Zoo Atlanta, Atlanta, Georgia, United States

Malaclemys terrapin is a species of turtle that lives in brackish waters along the eastern coast of the United States from Cape Cod to Texas. We documented distinctive underwater postures during surfacing in hatchling versus yearling individuals. Hatchlings approach the water’s surface in horizontal postures, while yearlings approach in a more vertical posture. Because cloacal bursae play a role in controlling buoyancy in freshwater turtles, we investigated their potential role in determining surface postures. We discovered that cloacal bursae are absent in M. terrapin, but present in their close relatives that we examined, Trachemys and Graptemys. We attribute this absence to the brackish habitats of this species. We posit that horizontal postures in the hatchlings create a broader visual target to both aerial and aquatic predators and that the younger turtles likely do not have the strength, muscle or lung-volume coordination, or sufficient bone density to adopt the more visually streamlined vertical posture at the surface.