Meeting Abstract

101.6  Thursday, Jan. 7  Effects of temperature on the motor control of chameleon feeding ANDERSON, C.V.*; DEBAN, S.M.; University of South Florida cvanders@mail.usf.edu

Environmental temperature effects muscle contractile velocity and thus constrains the activity patterns of ectotherms. As temperature decreases, performance of muscle-powered movements such as locomotion and tongue protraction decline and hinder prey capture ability. Chameleons do not pursue prey but use ballistic tongue projection to ambush prey. We have shown that their specialized feeding mechanism, which incorporates rapid recoil of collagenous sheaths to power tongue launch, maintains high performance at low body temperature, despite the presumed effects of temperature on muscle dynamics. Tongue retraction performance, which relies on direct muscle power, is strongly affected by temperature. 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. To test an alternative hypothesis that chameleons maintain high projection performance via muscle fibers that can maintain contractile rate performance at low temperature, we imaged Chamaeleo calyptratus feeding at 15-35°C with simultaneous electromyographic recordings of the accelerator muscle (ACC) and retractor muscle (HG). We found a Q₁₀ <1.1 for elastically powered tongue projection rate and Q₁₀ >1.6 for muscle-powered tongue retraction rate. Between 15 and 25°C motor control parameters show Q₁₀ >2.0 for muscle times to peak activity and for latencies between muscle activity events and kinematic events. These EMG results suggest that muscle contractile rates for both the ACC and HG show a temperature effect that is typical for muscle. Results thus fail to support the hypothesis that chameleons maintain tongue projection performance by maintaining muscle contractile rate performance at low temperature, and lend support to the elastic recoil model.