Interaction between temperature and hypoxia in the alligator.

Hypoxia elicits behavioral hypothermia in alligators. Under normoxic conditions, the selected body temperature is 27.8 +/- 1.2 degrees C. However, when inspired O2 is lowered to 4%, selected body temperature decreases to 15.4 +/- 1.0 degrees C. The threshold for the behavioral hypothermia is between 4 and 5% inspired O2, the lowest threshold measured so far in terrestrial vertebrates. This study assessed the physiological significance of the behavioral hypothermia. The body temperature was clamped at 15, 25, and 35 degrees C for measurements of ventilation, blood gases, metabolic rate, plasma lactate, and acid-base status. Hypoxia-induced changes in ventilation, acid-base status, oxygen consumption, and lactate were proportional to body temperature, being pronounced at 35 degrees C, less at 25 degrees C, and absent at 15 degrees C. The correlation between selected body temperature under severe hypoxia and the measured parameters show that behavioral hypothermia is a beneficial response to hypoxia in alligators.