Behavioral regulation of internal temperature in the lizard Tiliqua scincoides

Abstract

To study behavioral thermoregulation in the lizard, Tiliqua scincoides, two animals were implanted with two thermodes astraddle the preoptic region of the brainstem. These and four others without thermodes wandered between warm and cold environments, keeping the brain or colonic temperature cycling about a mean preferred temperature of 29.3 C during activity. When inactive, they voluntarily moved to a cool place and let their internal temperatures drop. When put into a hot test chamber, the lizards returned to a neutral environment when their colonic temperatures reached a reproducible level, designated the colonic exit temperature. Increasing the temperature of the test environment decreased the colonic exit temperature, the difference being highly significant when increasing the ambient temperature from 40 to 55 C. Warming the rostral brainstem by circulating water of 42 C through the thermodes also lowered the colonic exit temperature significantly at an ambient temperature of 40 and 45 C. Cooling the brainstem by 25 C water caused an increase of the colonic exit temperatures. We believe that the behavioral regulation of the internal temperature in Tiliqua scincoides is activated by a combination of brain and peripheral temperatures.