SICB 2015: The Mechanics of Arboreal Locomotion

Anolis equestris. Photo courtesy of Day’s Edge Productions.

The ability to move through complex arboreal habitats is critical to anoles, yet we know very little about the physiological mechanisms that underlie arboreal locomotion. Kathleen Foster, a graduate student in Tim Higham’s lab at UC-Riverside, presented an outstanding talk at SICB this week on the kinematics of locomotion in Anolis equestris. (Yep, Kathleen gave both a poster and a talk at this meeting!)

The relationship between the force a muscle can produce and the length of that muscle determines how force is generated at different positions of a limb – at different joint angles, the muscle will have a different length. But, this is extremely difficult to study in anoles, as standard surgical techniques aren’t possible in such small muscles. Kathleen is focusing on the muscles of the hindlimb, and she first determined that tendon strain did not contribute to the force-length relationship in these muscles. This result indicated that in vivo measures of muscle length should provide relevant information on limb kinematics. Next, she addressed how muscle function changes as lizards move on different substrates, using the gastrocnemius (a muscle in the “calf” of the hindlimb). Her preliminary data showed that this muscle is more active on a broad, flat perch than a small, narrow perch, that the active length of the gastrocnemius is more optimal on a flat perch, and that the maximum force generated by the gastrocnemius is greater on a flat perch. Together, these results indicate that the gastrocnemius contributes more to locomotor propulsion on a flat perch than a small perch.

And, because Kathleen has shown that tendon strain doesn’t significantly contribute to differences in muscle length in lizards, she can now study smaller species. This will allow her to examine the physiological differences underlying locomotor adaptations among ecomorphs!