Total calorimetry and temperature regulation in the nine-banded armadillo

Cold exposure in the nine-banded armadillo causes vigorous shivering and a rise in core temperature (Tc). The increase in metabolic rate and Tc depends upon exposure temperature, but may be as much as six times and 3 degrees C respectively (Johansen 1961). These findings might indicate an insensitivity to Tc, which is puzzling since internal temperature is thought to be the primary and regulated variable. It is suggested that positive feedback may play a role in temperature regulation in these animals. To investigate this problem two series of experiments were performed in the same species. Series 1. Measurements of changes in heat loss (direct calorimetry) and heat production (indirect calorimetry) following transferral from a thermoneutral to a cold environment. The difference between these measurements determines whether heat storage is positive due to the increased core temperature or negative due to reduction in the size of the core with the increased temperature. Series 2. Investigation of core thermosensitivity (body core cooling using colonic thermode) under different environmental conditions. The results of the first series showed that the rise in Tc was accompanied by positive heat storage in the body. The second series demonstrated core thermosensitivities similar to those previously reported for a variety of other homeothermic mammals.