Meeting Abstract

17.3  Sunday, Jan. 4  Effects of temperature on dynamic properties of active and passive caterpillar muscle: Q₁₀ less than 1? WOODS, W. A. Jr.*; TRIMMER, B. A. ; Tufts University; Tufts University william.woods@tufts.edu

Caterpillars are soft-bodied terrestrial climbers that accomplish a wide variety of complex movements over a broad range of ambient temperatures using several hundred muscles. We examined temperature dependence of passive and dynamic characteristics of Manduca sexta ventral interior longitudinal muscle, a comparatively large muscle known to serve alternately as a locomotor and as a damper during each crawling strain cycle. At temperatures of 20 to 30 °C, we recorded passive tension at resting length, peak force after stretching, and peak force under tetanic stimulation of individual muscles in saline mimicking hemolymph. Surprisingly, all changes in these parameters were inversely related to temperature. Resting tension declined linearly by 25% as temperature increased (Q₁₀ = 0.75). Under linear stretching from 90 to 110% of resting length, peak force dropped by similar percentages at all strain rates from 0.1 to 1.6 lengths s^-1 as temperature increased (Q₁₀ = 0.54). Peak force reached during 4 s tetanic stimulations diminished by fivefold over the same temperature range. To examine how these unexpected temperature responses might affect stimulus patterns required for crawling at different temperatures, we subjected muscles in vitro to strain cycling and stimulation similar to those previously determined during crawling in vivo at 23-25 °C. As preparation temperature was reduced from 25 to 20 °C, the portion of the strain cycle where positive work was done shifted in the same manner as when stimulus duration was increased at a fixed temperature. These results raise the possibility that crawling caterpillars may employ different stimulus patterns at different temperatures.