BLOB, R.W.*; PACE, C.M.; WESTNEAT, M.W.: Testing functional correlates of habitat specialization: swimming and walking in spiny softshell and slider turtles.

Although many freshwater turtles frequently travel long distances over land, several species are morphologically specialized for swimming and spend little time out of water. To test the impact of locomotor specialization on limb kinematics and motor control, we used EMGs and high-speed video to compare hindlimb motor patterns during swimming and walking in the generalized turtle Trachemys scripta (red-eared slider) and the aquatic specialist Apalone spinifera (spiny softshell). Kinematic distinctions between the species indicate that aquatic specialization need not impede terrestrial locomotion. For instance, in both swimming and walking, femoral excursion is nearly twice as great in softshells (70-75�) as in sliders (35-40�). However, in softshells the knee is held significantly straighter during walking than during swimming, suggesting that softshell knee extensors may operate at shorter lengths less optimal for force generation during walking. Motor patterns of softshells and sliders also show several differences; however, the modulation of motor patterns between swimming and walking is similar in both species. In both sliders and softshells, the knee extensor femorotibialis shows a second burst during walking that correlates with a protractive phase of knee extension. In addition, the timing of femoral protractor activity does not change significantly between swimming and walking in either species. Together, our analyses of hindlimb kinematics and muscle activity in these species suggest that measurements of muscle length changes may indicate key distinctions in how habitat specialists and generalists modulate muscle function between behaviors. NIH 5F32NS10813-01/02 to RB and ONR N000149910184 to MW.