Meeting Abstract
Two important metrics of aquatic locomotor performance are hydrodynamic stability and the ability to execute turns. Stability can help reduce the energetic costs of steady swimming, and rapid execution of turns in a limited space can facilitate successful prey capture and escape from predators. In human-engineered aquatic vehicles, stability and turning performance can be improved via a rudder, which can be oriented parallel to the long axis of the vehicle to act as a stabilizing keel, or adjusted to redirect oncoming water flow, changing the balance of forces and turning the vehicle. Similar to human-engineered vehicles, turtles possess a rigid body and a posteriorly directed midline structure, the tail, which could be used like a rudder during swimming. However, in many turtles, tail length is sexually dimorphic, with males having significantly longer tails than females. We examined whether turtle tails might function similarly to the rudders of boats, and the implications of such use for swimming performance in males versus females, by comparing stability and maneuverability of male painted turtles (Chrysemys picta) under two conditions: normal swimming, and swimming after the tail had been secured inside the shell with tape (a proxy for the highly-shortened tails of females). In general, turtles were more stable in trials with full tail use, especially in positional displacements such as heave and sideslip. Also, whereas turning rate was not affected by tail use, full use of the tail allowed turtles to have a substantially smaller turning radius. Thus, much like boat rudders, turtle tails may facilitate the execution of tight turns. Moreover, this structural difference between male and female turtles might contribute to differences in their swimming performance.
