Lizard Thermoregulation: Operant Responses for Heat at Different Thermal Intensities

Abstract

Sceloporus cyanogenys, blue spiny lizards, regulated their intestinal temperature by turning a heat lamp on and off. With the intensity of the heat lamp set at 3 different levels, intestinal temperature was regulated as an inverse function of thermal intensity. Also, the highest single intestinal temperature at which lizards retreated from the heat decreased with increasing intensity. The variance of the distribution of intestinal temperatures at activation of the heat lamp at each intensity was significantly greater than the variance of the intestinal temperatures at retreat from the heat lamp. This result suggests that the thermoregulatory system mechanism effecting heat-escape responses is more sensitive to thermal intensity than the corresponding mechanism effecting heat-seeking responses. Heat seeking strategies also differed among the three intensities. These results are compatible with a model of coupled on-off set points for behavioral thermoregulatory responses on either end of a refractory range. The data suggest that these set points change in response to changing thermal intensity, and thus they are also consistent with an adjustable set point model of the thermostat. These results are not explained by a model that postulates a single fixed body temperature as the goal for the lizard's thermoregulatory behavior.