BECHTEL, B.F.; ASHLEY-ROSS, M.A.*; Wake Forest University: Kinematics of the transition between aquatic and terrestrial locomotion in the newt Taricha torosa

Newts are capable of locomotion in both aquatic and terrestrial environments. The movements of swimming involve primarily the axial musculature, which generates traveling waves of lateral undulation. In contrast, walking uses the paired limbs to generate force against the ground and propel the body forward. We examined the transition between swimming and terrestrial walking by videotaping newts walking both up and down a ramp that had its lower end immersed in water, and its upper end out of the water, supported so that it was inclined at 15 degrees to the horizontal. When ascending the ramp, newts first approached it by swimming, then used the limbs to walk while still in water, and finally left the water using a normal terrestrial walking gait. The reverse of this sequence was observed when newts descended the ramp. In both directions, newts used a lateral sequence walk with a duty factor of approximately 75% when out of the water. Timing of footfalls was more variable in water, and generally featured shorter duty factors. Limbs were held in a more extended position in water. In sequences showing the transition from walking to swimming, limbs would often proceed through 1-2 complete protraction-retraction cycles without making contact with the substrate before being folded against the body for axially driven swimming. Newts began generating traveling waves lateral undulation after the entire body was immersed in water.