Meeting Abstract
P3.62 Jan. 6 Hydrodynamic stability of swimming turtles: correlations with shell shape? RIVERA, G.*; BLOB, R. W.; Clemson University grivera@clemson.edu
Hydrodynamic stability in swimming animals can be defined as the ability to resist recoil movements of the body and maintain a given trajectory. Morphological features, such as body depth and rigidity, have been suggested to affect recoil motions such as yaw. As all turtles have rigid bodies, interspecific comparisons of swimming performance avoid the complexity of distinguishing effects of shape and flexibility. We evaluated differences in longitudinal stability between turtles with different body shapes by measuring lateral recoil (i.e., yaw) during rectilinear swimming in two morphologically divergent species, domed painted turtles (Chrysemys picta) and dorsoventrally-flattened spiny softshells (Apalone spinifera). We expected the taller shells of C. picta to better resist lateral rotation and lead to lower yaw (greater stability) than in flatter A. spinifera. High-speed (200Hz) ventral-view videos were digitized to calculate yaw and limb kinematics. Yaw was measured as the maximum angle of displacement between the body midline and the linear path of travel. Motions of each limb were defined by the angle formed between the proximal segment (humerus or femur) and the body midline. Maximum yaw ranged from 8.4 to 16.4 degrees, with little difference between species means (A. spinifera=11.3; C. picta=11.8). In addition, maximum recoil for both species occurs when one set of contralateral limbs is at maximum protraction and the other at maximum retraction. It seems likely that the strong webbing of forelimb paddles in A. spinifera reduces differences in contralateral fore- and hindlimb thrust, thereby decreasing the torque that generates yaw and leading to recoil magnitudes similar to those of C. picta, in which the forefeet are much smaller than the hindfeet. Thus, despite different shell morphologies, these species show similar hydrodynamic stability.
