Kinematics of level terrestrial and underwater walking in the California newt, Taricha torosa

Abstract

Salamanders are acknowledged to be the closest postural model of early tetrapods and are capable of walking both in a terrestrial environment and while submerged under water. Nonetheless, locomotion in this group is poorly understood, as is underwater pedestrian locomotion in general. We, therefore, quantified the movements of the body axis and limbs of the California newt, Taricha torosa, during steady-speed walking in two environments, both of which presented a level surface: a treadmill and a trackway that was submerged in an aquarium. For treadmill walking at a relative speed of 0.63 snout-vent lengths (SVL)/sec, newts used a diagonal couplets lateral sequence walk with a duty factor of 77%. In contrast, submerged speeds were nearly twice as fast, with a mean of 1.19 SVL/sec. The submerged gait pattern was closer to a trot, with a duty factor of only 41%, including periods of suspension. Environment appears to play a critical role in determining gait differences, with reduction of drag being one of the most important determinants in increasing duration of the swing phase. Quantitative analysis of limb kinematics showed that underwater strides were more variable than terrestrial ones, but overall were strikingly similar between the two environments, with joint movement reversals occurring at similar points in the step cycle. It is suggested that the fundamental walking pattern appears to function well under multiple conditions, with only minor changes in motor control necessary.