Meeting Abstract
As nocturnal fliers, bats must maintain a rapid wingbeat frequency in the face of thermal conditions that likely result in net heat loss from their poorly-insulated wings. Because rate-related processes in muscle slow at cooler temperatures, temperature effects in the wing muscles may impair flight performance. Bats maintain a proximal-to-distal temperature gradient during rest and activity: continuous measurements of internal muscle temperature during wind tunnel flights indicate that the distal wing muscles of Carollia perspicillata operate at up to 12°C below core body temperature (Tb), while the more proximal pectoralis muscle remains near Tb during flight. Thus, during normal flight, different muscles of the flight apparatus may operate at vastly different temperatures. We predicted that the contractile properties of the pectoralis would be specialized to operation near Tb, and thus more sensitive to temperature than those of the extensor carpi radialis longus (ECRL), a distal wing muscle. We previously measured the contractile properties of the ECRL in C. perspicillata at 22, 27, 32, and 37°C in vitro, and here measure the same properties over that temperature range for the pectoralis. Both muscles decline in performance below 37°C, but pectoralis performance was more sensitive to declining temperature than the ECRL for shortening velocity and several time-dependent isometric properties. Isometric force production is also highly thermally sensitive in the pectoralis. These results support our prediction that a proximal, thermally insulated muscle will be highly temperature sensitive, while a distal, thermally variable muscle will be less temperature sensitive, and suggest that endotherms compensate for temperature effects due to regional variation in body temperature.
