Abstract
Aquatic organisms exhibit tremendous diversity in body design and modes of propulsion that can strongly influence locomotor performance. Understanding how such differences affect locomotor performance is a major focus of research in integrative organismal biology and can provide insight into the evolutionary origins of such variation. Turtles are unique among extant tetrapods (i.e., amphibians, reptiles, birds, and mammals) in that they possess rigid bodies. In turtles, the vertebrae are fused dorsally with a bony carapace, precluding movement of the axial skeleton between the base of the neck and the tail. As a result of their immobilized axial skeleton and reduced tail, thrust in swimming turtles is generated exclusively by the movements of fore- and hind-limbs. Despite the potential constraints of a rigid body on locomotion in turtles, over 100 extant species inhabit aquatic environments. Moreover, these turtles display considerable variation in shell and propulsor morphology and have evolved two different modes of propulsion (four-limbed rowing vs. forelimb flapping). My dissertation is a collection of three studies that examined the interaction between morphology and hydrodynamic performance (maneuverability, stability, and drag) in freshwater turtles. First, I described the patterns of limb movements used to produce turns and quantified turning performance, comparing results to that of other rigid- and flexible-bodied animals. Second, I assessed kinematics and hydrodynamic stability during straight-line swimming. I also compared data I collected from freshwater turtles to previous data collected from two species of sea turtles to assess how the different modes of propulsion used by the two groups affect stability. Finally, I examined the relationship between habitat (environmental flow regime), morphology (shell shape), and performance (hydrodynamic drag) among intraspecific populations of the large riverine turtle Pseudemys concinna. Specially, I tested for threedimensional differences in shell shape between turtles from slow- and fastflowing habitats, while concomitantly testing whether the carapace and plastron demonstrate the same propensity for environmentally correlated differences. I also used physical models to test whether morphological differences of the shell confer reductions in drag, and provide preliminary data regarding the potential role of phenotypic plasticity in generating the morphological variation observed in turtles between the two flow regimes. Data from these studies provides insight into the evolutionary origins of intra- and inter-specific variation in shell shape.