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First published online October 18, 2006
Journal of Experimental Biology 209, 4203-4213 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02488

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Aquatic turning performance of painted turtles (Chrysemys picta) and functional consequences of a rigid body design

Gabriel Rivera^*, Angela R. V. Rivera, Erin E. Dougherty and Richard W. Blob

Department of Biological Sciences, Clemson University, 132 Long Hall, Clemson, SC 29634, USA

View larger version (130K): [in a new window]   Fig. 1. Ventral view of a painted turtle with 19 digitized landmarks. The number 8, visible on the plastron, was used for identification purposes. R and L refer to the right and left sides of the turtle, respectively. Note that because the ventral view is reflected by a mirror, the left side of the animal appears on the left side of the image. Scale bar, 1 cm.

View larger version (118K): [in a new window]   Fig. 2. Representative kinematic profiles for three modes of swimming performed by painted turtles, with still images from a high-speed video indicating the position of the limbs (humerus and femur) at specific times during the locomotor sequence. Circles, forelimbs; triangles, hindlimbs; open symbols, right side of the body; closed symbols, left side. A decrease in the angle with midline represents limb protraction and an increase in the angle represents limb retraction. Arrows in the first still image of each sequence indicate the direction of movement during the sequence. (A) Representative kinematic profile of a painted turtle during level rectilinear swimming. Note the synchronous movements of contralateral fore- and hindlimbs and the alternating movements of the ipsilateral fore- and hindlimbs. (B) Representative kinematic profile of a turtle during a forward turn. This 82° turn had an average linear velocity (Uavg) of 1.83 L s-1, resulting in an R/L of 0.24. The turtle propels itself forward using alternating movements of the hindlimbs. The inboard forelimb (open circle) is held in a protracted position for the entire turn and acts as a pivot. The outboard forelimb (closed circle) moves approximately in phase with the contralateral hindlimb, as in rectilinear swimming. (C) Kinematic profile of a backward turn. This 113° turn had an average linear velocity (Uavg) of 0.86 L s-1, resulting in an R/L of 0.0091. The turtle used synchronous protraction of the hindlimbs to begin moving backward (not plotted). While moving backward, the right forelimb was retracted while the left hindlimb was protracted. During this time the other set of contralateral limbs were held motionless, after which the outboard hindlimb retracted to accelerate the turn.

View larger version (5K): [in a new window]   Fig. 3. Relationship between average tangential velocity (Uavg) and length-specific minimum radius (R/L) for forward and backward turns. Open symbols represent forward turns (N=43, solid regression line); closed symbols represent backward turns (N=7, broken regression line). Both relationships are significant (see text for regression statistics).

View larger version (4K): [in a new window]   Fig. 4. Relationship between the length-specific minimum radius of the turning path (R/L) and average angular velocity (avg). Open symbols represent forward turns (N=43); closed symbols represent backward turns (N=7). Neither relationship is significant (see text).

View larger version (8K): [in a new window]   Fig. 5. Comparison of turning performance for three rigid-bodied taxa. (A) Length-specific minimum radius of the turning path (R/L). (B) Average turning rate (avg). Closed circles indicate the single minimum value, open squares indicate the single maximum value, closed squares indicate the mean of all values, and closed triangles indicate the mean of the minimum 20% of values (A) or maximum 20% of values (B). Values for boxfish (N=12) are from Walker (Walker, 2000); values for beetles (N=119) are from Fish and Nicastro (Fish and Nicastro, 2003); values for turtles are from this study and include only forward turns (N=43). Data are graphed on a log10 scale.

View larger version (7K): [in a new window]   Fig. 6. Comparison of turning rate, avg, with respect to size among a broad range of taxa graphed on a log10 scale. The line connects the beetle and submarine (USS Albacore), both of which have rigid bodies. Other rigid-bodied taxa appear to the left of the line. Modified from Fish and Nicastro (Fish and Nicastro, 2003) with permission. Value of avg for turtles based on this study; position of boxfish data point moved to reflect avg rather than max.