Meeting Abstract

P1.159  Monday, Jan. 4  Decreased substrate diameter and increased surface compliance decrease climbing performance in snakes BYRNES, G.*; JAYNE, B.C.; University of Cincinnati byrnesgt@ucmail.uc.edu

Differences in the size, orientation and compliance of branches in arboreal habitats pose challenges for animal locomotion. For example, morphological constraints may limit the ability of an animal to conform to or grip narrow substrates. Successful vertical climbing also depends on the ability to press against the substrate and generate sufficient frictional forces, but this ability may be compromised by excessive surface compliance. Therefore, very narrow and compliant substrates would seem especially demanding for climbing animals. We varied the diameter and compliance of ropes independently to determine their effects on locomotor mode and performance during vertical climbing of juvenile boa constrictors. We measured rope deformation using a load cell and determined climbing velocity from video images. With decreased diameter and rope tension, locomotor performance of the snakes decreased significantly and the amount of rope deformation increased. The snakes used concertina locomotion on all surfaces, but the manner in which they pressed against the rope varied. On some large diameter stiff substrates, the lack of rope deformation implies that within each ventrally flexed gripping region the snake generated balanced opposing forces. By contrast, as substrate compliance increased and diameter decreased, the snakes used moment couples at successive pairs of gripping regions to deform the rope and increase its tension. This behavioral mechanism may compensate for morphological limitations on making the small radius of curvature required for gripping using only ventral flexion. Thus, these changes in behavior may allow the snakes to move on otherwise impassable narrow and compliant surfaces although locomotor performance is diminished compared to wider and stiffer surfaces.