The kinematics of larval salamander swimming (Ambystomatidae: Caudata)
We studied the kinematics of straightforward, constant velocity swimming in larval Ambystoma mexicanum and Ambystoma maculatum. The larvae were filmed at 200–320 frames/s and their filmed images were digitized for computer analysis. The maximum sustainable velocity we recorded was 18.7 lengths/s, which compares favorably to the maximum speed reported for similarly sized anuran larvae. The Ambystoma, however, differed greatly from tadpoles in the form of the propulsive wave in their bodies. Specifically, the maximum amplitude at the tail tip, at swimming speeds >6 lengths/s, was exceptionally high, exceeding 30% of body length; at high speed, the position of minimum amplitude was well posterior to the otic capsules and produced considerable yaw at the head; and the length of the propulsive wave in the body shortened as speed increased. All of these features characterize poor mechanical efficiency during constant velocity swimming, and indeed two measures of efficiency (propeller efficiency and stride length) confirmed the locomotor superiority of tadpoles and sub-carangiform fishes to Ambystoma larvae. The drag induced by exposed gills and limbs may account in part for the inferior performance of the salamanders. Ambystoma larvae are designed for anguilliform movement among the rocks and vegetation of the substrate, and for high acceleration over short distances, such as those used during a lunge at prey. The mechanical inferiority of Ambystoma larvae during sustained, constant velocity swimming is consistent with their microhabitat shift away from open water situations in the presence of subcarangiform fishes.