Fight versus flight: physiological basis for temperature-dependent behavioral shifts in lizards.

Previous studies have demonstrated that a behavioral shift from flight to aggressive behavior occurs at low temperatures in some lizards. Our data for the agamid lizard Trapelus pallida demonstrate how the effect of temperature on whole organism performance traits such as sprint speed (much lower performance at lower temperature) and bite force (largely independent of temperature) may explain the shift from flight to fight behavior with decreasing temperature. Moreover, our data hint at the physiological basis for this effect as isolated muscle power output, twitch and tetanus time traits, relevant to sprinting, appear to be strongly temperature-dependent muscle properties. Maximal muscle force production, on the other hand, appears largely independent of temperature. Unexpectedly, differences in the physiological properties of jaw versus limb muscle were observed that enhance the ability of the jaw muscle to generate maximal force at all temperatures tested. Thus our data show how behavioral responses may be determined by the limitations set by temperature on physiological processes.