Meeting Abstract

17.2  Sunday, Jan. 4  Temperature gradients in the dorsolongitudinal flight muscles of Manduca sexta may yield functional gradients. GEORGE, N.T.*; DANIEL, T.L.; Univ. of Washington, Seattle ntgeorge@u.washington.edu

During muscle contraction, heat is produced as chemical energy is converted into mechanical work. Many large insects with active flight muscles use this byproduct to elevate flight muscle temperature, thereby achieving higher mechanical power output during flight. Contractile heat production paired with convective and radiative heat loss necessarily lead to a temperature gradient, but the functional consequences of such a gradient remain unknown. Because force generation of muscle depends on temperature, subunits experiencing lower temperatures could function differently than those at higher temperatures. This is particularly relevant to the flight musculature of Manduca sexta. The dominant flight muscles (dorsolongitudinal muscles: DLMs) are divided into five subunits, each separately innervated. We measured two important aspects of temperature dynamics in the DLMs during tethered flight: (1) using a hypodermic thermocouple probe, we showed that there is a strong temperature gradient in the dorso-ventral direction, with a mean difference of 8.8C (a max of 10C; n = 7) across 5 mm, (2) using standard electromyography, we showed that the 5 subunits of the DLMs are activated nearly simultaneously (max time difference = 2 ms, 5% of cycle time; n = 3). Therefore, the muscle bundles do not appear to employ a spatial offset in timing to correct for the thermal gradient that they generate. Taken together, the observation of simultaneous activation and a strong thermal gradient suggest that the dorsal-most subunits may function differently from warmer, more ventrally located units.