METAMORPHIC AND SPEED EFFECTS ON HINDLIMB KINEMATICS DURING TERRESTRIAL LOCOMOTION IN THE SALAMANDER DICAMPTODON TENEBROSUS

Abstract

The kinematics of the hindlimb during terrestrial treadmill locomotion in Dicamptodon tenebrosus were compared between larval and metamorphosed individuals at different speeds. Coordinates of marker points on the salamander's midline, pelvic girdle and left hindlimb were digitized from high-speed videos (200 fields s-1). These yielded kinematic variables describing trunk flexion, pelvic girdle rotation, femoral protraction/retraction and knee flexion/extension. A three-way analysis of variance tested for mean differences among individuals, speeds and metamorphic stages for each variable. No significant overall effects of metamorphosis were found, although several variables showed significant stage x individual effects. Multivariate analyses revealed that the variance in kinematics of the larvae was significantly greater than that of the metamorphosed salamanders. Several variables showed significant speed effects or strong trends, among them stride length (increases with speed), cycle duration (decreases), contact interval (decreases) and phase variables describing the relative timing between minimum/maximum angles and the beginning of stance/swing phase. Such changes with speed are consistent with those shown for diverse arthropods and tetrapods and suggest that changes in stride length and timing events during a stride represent a general mechanism for effecting an increase in locomotor speed.