AZIZI, E.; HORTON, J.M.; University of Massachusetts, Amherst: Patterns of appendicular and axial movements during aquatic walking in the salamander, Siren lacertina.

Most studies of salamander locomotion have focused either on swimming or terrestrial walking. These studies have shown that during swimming many salamanders tuck their limbs against the body and generate a traveling axial wave, which provides forward propulsion. During terrestrial walking many salamanders use a diagonal lateral sequence walk, where diagonal limb pairs are used synchronously and axial bending occurs mainly between two nodes located at the pectoral and pelvic girdles. In addition to the two locomotor modes described above, some salamanders also use limb-based locomotion while submerged underwater (aquatic walking). In this study we used video analysis to describe the kinematics of aquatic walking in Siren lacertina (n=4), an elongate salamander that lacks hindlimbs. We found that S. lacertina use an appendicular-undulatory gait, which combines alternating use of the forelimbs with a traveling undulatory wave. The average contact interval of each forelimb is about 50% of the stride cycle and forelimbs have little temporal overlap in contact intervals. By quantifying the relative timing and frequency of limb and tail movements we found that unlike the terrestrial gaits of most salamanders, axial and appendicular movements are decoupled during aquatic walking. In addition, we have found that walking velocity is independent of stride frequency and is mainly modulated by varying tail-beat frequency. Finally by comparing axial wavespeed, Froude effieciency, and distance traveled per tail-beat during swimming (forelimbs not used) and aquatic walking (forelimbs used) we conclude that the reduced forelimbs of S. lacertina do contribute to forward propulsion.