Thermal effects on the dynamics and motor control of ballistic prey capture in toads: maintaining high performance at low temperature.

Temperature has a strong influence on biological rates, including the contractile rate properties of muscle and thereby the velocity, acceleration and power of muscle-powered movements. We hypothesized that the dynamics of movements powered by elastic recoil have a lower thermal dependence than muscle-powered movements. We examined the prey capture behavior of toads (Bufo terrestris) using high speed imaging and electromyography to compare the effects of body temperature (11-35°C) on the kinematics, dynamics and motor control of two types of movement: (1) ballistic mouth opening and tongue projection, which are powered by elastic recoil, and (2) non-ballistic prey transport, including tongue retraction and mouth closing, which are powered directly by muscle contraction. Over 11-25°C, temperature coefficients of ballistic mouth opening and tongue projection dynamics (Q(10) of 0.99-1.25) were not significantly different from 1.00 and were consistently lower than those of prey transport movements (Q(10) of 1.77-2.26), supporting our main hypothesis. The depressor mandibulae muscle, which is responsible for ballistic mouth opening and tongue projection via the recovery of elastic strain energy stored by the muscle prior to the onset of the movement, was activated earlier and for a longer duration at lower temperatures (Q(10) of 2.29-2.41), consistent with a slowing of its contractile rates. Muscle recruitment was unaffected by temperature, as revealed by the lack of thermal dependence in the intensity of activity of both the jaw depressor and jaw levator muscles (Q(10) of 0.754-1.12). Over the 20-35°C range, lower thermal dependence was found for the dynamics of non-elastic movements and the motor control of both elastic and non-elastic movements, in accord with a plateau of high performance found in other systems.