Temperature effects on the biomechanics of prey capture in the frog Rana pipiens.

Movements of many animals are powered by a combination of active shortening of muscles and recoil of elastic structures. Movements that rely primarily on elastic recoil, such as the explosive locomotor and feeding movements of many ectotherms, have been shown to exhibit lower thermal dependence than muscle-powered movements because elastically powered movements circumvent the effects of temperature on muscle contractile dynamics. To determine if elastic recoil contributes to the ballistic mouth opening and tongue projection of the frog Rana pipiens, we examined feeding kinematics and dynamics of tongue and jaw movements at three ambient temperatures (10, 15, and 25°C) using 6,000 Hz image sequences. We found that ballistic mouth opening exhibits high instantaneous power (up to 1,783 W kg(-1) of muscle mass) and its dynamics have low thermal dependence (Q(10) values of 1.02-1.37), indicating the contribution of elastic recoil. The dynamics of tongue projection are more thermally dependent (Q(10) of 1.35-2.51) and likely involve muscle activity during the movement. Mouth opening during prey transport, as well as tongue retraction and mouth closing showed little evidence of elastic recoil and their dynamics show relatively high thermal dependence (Q(10) of 1.38-1.89). R. pipiens shows lower thermal robustness and power of tongue projection than ballistic-tongued Bufo terrestris which displays complete thermal independence, suggesting that in Rana tongue projection is not as tightly coupled to jaw depression as in toads. We propose that thermal experiments may be useful in probing for elastic mechanisms in other biomechanical systems.