BLOB, R.W.*; WILLEY, J.S.; LAUDER, G.V.; Clemson Univ.; Clemson Univ.; Harvard Univ.: Swimming in painted turtles: particle image velocimetry reveals different propulsive roles for the forelimb and hindlimb.

Because most of their body axis is fused to a rigid shell, turtles rely primarily on the limbs to generate propulsive forces. Kinematic data indicate that swimming freshwater turtles rotate the palms of both manus and pes perpendicular to flow during the thrust phase of the stroke, forming a propulsive paddle. However, in emydids (e.g., sliders, painted turtles) movements at other joints differ substantially between the forelimb and hindlimb; moreover, hindfeet are larger than forefeet and have more extensive webbing between digits. How do these morphological and kinematic differences affect the contributions of emydid forelimbs and hindlimbs to aquatic thrust? To evaluate differences in propulsive function between the forelimb and hindlimb in swimming emydids, we used particle image velocimetry (PIV) to visualize the wake behind swimming painted turtles (Chrysemys picta) in two perpendicular planes: parasagittal (XY) and horizontal (XZ). Consistent with predictions based on differences in fore- and hindfoot size, forces produced by the hindlimb (calculated from PIV analyses of jet momentum) typically exceed those produced by the forelimb, often by a factor of two or more. Fluid jets produced by the limbs also differ substantially in orientation. Hindlimb jets are oriented almost directly posteriorly with a slight upward component, but forelimb jets have strong lateral and downward components. These results indicate markedly different roles for the fore- and hindlimbs in swimming painted turtles. Forward propulsion depends overwhelmingly on thrust generated by the hindlimbs. Though forelimbs seem to contribute little to propulsive thrust, the lateral forces they produce are likely important to stability and maneuverability in swimming emydids.