RIVERA, G; Clemson University, Clemson: Morphological variation in a species of freshwater turtle (Pseudemys concinna) inhabiting different flow regimes

Species with populations that inhabit a wide range of environments frequently display morphological variations that correlate with differences in environmental parameters. Water velocity is a critical feature of aquatic habitats that could impose selection for drag-reducing morphologies. This possibility has been suggested for several species of fishes, in which populations in lotic habitats have more streamlined body shapes than those in lentic habitats. Freshwater turtles provide a novel test of such correlations because they spend a substantial amount of time out of water; thus, selection pressures for hydrodynamic efficiency may be weaker than in fully aquatic fishes. To determine whether this is the case, I assessed intraspecific morphological variation in the river cooter (Pseudemys concinna) between two physiographic regions of Alabama, the Piedmont and the Coastal Plain. These regions exhibit dramatically different stream flow velocities that might place different hydrodynamic demands on turtles, with the high-elevation Piedmont characterized by higher flow rates than the flat Coastal Plain. I used geometric morphometrics to analyze three-dimensional landmark data collected from museum specimens. A principal components analysis (PCA) of the landmark data showed separation between the two groups and a Goodall�s F-test found significant differences in their overall shape. Upon comparison of the groups, two primary differences emerge: (1) the carapace is flatter in the Piedmont specimens, and (2) the posterior end of the carapace is wider in the Piedmont specimens. These differences would be predicted to enhance swimming performance in faster flowing water, suggesting a correlation between shape and hydrodynamic environment in a semi-aquatic organism.