UC Riverside

Movement is a fundamental aspect of animals. Natural and sexual selection act on the ability of an animal to effectively move through the environment in order to find and acquire mates, eat food, and escape from predators. It is generally thought that faster animals sire more offspring, acquire more mates, and evade predators more effectively. Effectively escaping through complex, three-dimensional environments is a principal driver of terrestrial animal biomechanics. However, the integrated, underlying suites of mechanisms including the interacting morphological components by which animals achieve successful performances are varied and contentious. Novel morphological structures increase performance of an ecologically relevant task in a descendent compared to its ancestor, often leading to adaptive radiation. The adhesive toe pad of geckos involves novel morphological structures that permit locomotion on inclined and inverted surfaces. The intricate method by which geckos employ the adhesive system has many cascading trade-offs on locomotion. Using a pad-bearing, secondarily terrestrial gecko from Namibia (Rhoptropus afer), I quantified the intimate relationships between gecko toe pads, habitat use, and the biomechanics of locomotion.

I tested the hypothesis that the adhesive toe pad morphology of R. afer corresponds to the physical structures used during escape behavior in the field. The size of the adhesive toe pad varies in relation to structural habitat use. Second, I brought the same individuals into the laboratory to quantify how they coordinate sprint speeds on ecologically relevant surfaces. Using high-speed video and path analysis, I found that this secondarily terrestrial gecko sprints using an integrated, but behaviorally flexible, suite of muscle group contributions. While many geckos are thought to power locomotion through specialized climbing muscles located near their center-of-mass, I found that R. afer mainly use ankle extensor muscles to power locomotion. Finally, I tested the hypothesis that the adhesive toe pad alters the coordination of locomotion, predicting individuals will alter relative contributions of muscle groups within limb segments to accommodate the toe pad when in use. I found that individuals vary in their use of toe pads, individuals alter limb segment coordination during toe pad use, and toe pads enhance sprint speed on level surfaces.