Meeting Abstract

51.5  Thursday, Jan. 6  Effects of temperature on in vitro muscle dynamics of chameleon feeding muscles ANDERSON, C.V.*; DEBAN, S.M.; Univ. South Florida, Tampa cvanders@mail.usf.edu

Despite the strong effect of body temperature on muscle contractile velocity, and thus movement performance, chameleons are known to feed using high-powered ballistic tongue projection at low body temperature. In Chamaeleo calyptratus ballistic tongue projection, which uses rapid recoil of collagenous sheaths to power tongue launch, exhibits a weak effect of temperature, while tongue retraction, which relies on direct muscle power, exhibits a strong effect of temperature. Motor patterns of the tongue projector muscle, the accelerator (ACC), and tongue retractor, the hyoglossus (HG), both increased in latency between onset of muscle activity and associated movements as temperature drops. We hypothesize that chameleons maintain high performance at low temperature as a result of minimal thermal effects on peak isometric muscle force and the elastic recoil of collagen. Further, we hypothesize that both the ACC and HG experience strong thermal effects on dynamic contractile properties, resulting in the increased latency between their activity and associated movements. To test these hypotheses, we examined in vitro muscle dynamics for the ACC and HG at 15-35°C. Both ACC and HG muscles showed a significantly larger effect of temperature on dynamic properties (Q₁₀ = 1.6-2.6) than on static properties (Q₁₀ = 1.3-1.4). These results reject the alternative hypothesis that chameleons maintain tongue projection performance by maintaining muscle contractile rate performance at low temperature, and are consistent with an elastic recoil mechanism underlying high performance at low temperature. The decoupling of muscle dynamics from projection performance suggests that selection for fast muscles with low Q₁₀ values is unlikely. This is consistent with published comparisons of locomotor and tongue muscles of chameleons and other taxa.