MEHTA, Rita; Univ. of California, Davis: Evolution of Constriction Motor Patterns in Snakes

Behavior results from the integration of morphology, physiology, and biomechanics. Any one of these levels can be examined to gain insight into patterns driving behavioral variation across species. My research takes an integrative approach to test hypotheses concerning the evolution of constriction behavior in snakes. Constriction, a prey immobilization technique, varies among lineages, but detailed kinematics of the constriction posture along with variation in the underlying epaxial muscle activity pattern remains unknown. I studied kinematics and epaxial motor patterns during constriction in a basal snake Loxocemus bicolor and two intermediate snakes Python molurus and Boa constrictor to test whether the variation in constriction kinematics corresponds with underlying epaxial muscle activity patterns. L.bicolor used lateral bends to coil around mice. Lateral bending corresponded with unilateral muscle activity patterns. Python molurus and Boa constrictor used mainly ventral bends to loop around prey. Ventral bending corresponded with bilateral muscle activity. In all three lineages the epaxial muscles fired during coil formation and intermittently during sustained constriction. Viewed in the context of a snake phylogeny these results suggest that the ancestral pattern of constriction involved lateral bending and that pythons and boas use a derived posture. The evolution of different motor patterns may have been driven by prey size.