The need for speed: functional specializations of locomotor and feeding muscles in Anolis lizards.

Muscles often perform diverse mechanical roles within an organism. Tuning of contractile properties may therefore provide an opportunity for muscles to better perform their different roles and impact their associated whole-organism performance. Here, we examined the muscle contractile physiology of a jaw and a leg muscle in five Anolis species to determine whether consistent physiological differences are found in these muscles. We found that these jaw and leg muscles exhibited consistent patterns of variation across species, which may be related to the functional use of each muscle. In particular, we found that each muscle had differentially increased different measures of muscle speed. Although the jaw muscles had faster peak contractile velocities than the leg muscles, the leg muscles had faster twitch times and faster contractile velocities under intermediate loads. We also found that the jaw muscles exerted higher specific tensions and had a greater curvature to their force-velocity relationship. The consistent patterns across five species suggest that these jaw and leg muscles have specialized in different ways. Examination of these contractile property variations may help illuminate important features relating to performing their individual functional roles.