RIVERA, A.R.*; RIVERA, G.; BLOB, R.W.; Clemson University, SC: Aquatic Turning Performance of a Rigid-Bodied Vertebrate, the Painted Turtle (Chrysemys picta)

The rarity of rigid body designs among aquatic vertebrates suggests that such designs may carry costs that impair functional performance. Although rigid bodies are expected to incur less drag and are more stable during rectilinear locomotion than flexible bodies, previous studies have suggested that aquatic turning performance may be reduced as a trade-off for such stability. In this study, we tested the effect of a rigid design on aquatic turning performance in a species of semi-aquatic turtle, the painted turtle (Chrysemys picta). Sixty turns by yearling turtles were recorded in lateral and ventral views using two synchronized high-speed video cameras (150 Hz). For each turn, we measured the limb motions that produced the turn and evaluated two parameters of turning performance, agility (turning rate) and maneuverability (space required to execute a turn). We identified three distinct patterns of limb movements used to execute turns. The most common pattern involved extending the forelimb on the inside of the turn perpendicular to the body, increasing drag and thereby effecting rotation to that side. Two less common patterns of limb movements appear to be differentially employed to balance the speed and/or direction of movement upon entering a turn. Comparisons of turning data from turtles vs. data from flexible-bodied animals support previous findings of reduced turning performance in animals with rigid bodies. However, when compared with rigid-bodied fishes such as boxfish, painted turtles have higher turning rates. Differences in turning performance between turtles and boxfish may be related to differences in the structure of limbs vs. fins that could enhance thrust production in turtles, and differences in body height that might cause greater resistance to rotation in fishes.