Thermoregulation and cold acclimation in a hibernator, Citellus tridecemlincatus

¹ Division of Biosciences, National Research Council, Ottawa, Canada

In the thirteen-lined ground squirrel, Citellus tridecemlineatus, the maintenance of body temperature and oxygen consumption in the cold is improved by acclimation to 18 and 6 C in the laboratory. Heat production at –30 C was greater in animals acclimated to 6 C, whether or not they had been previously hibernating, than in squirrels kept at 28 C. Oxygen consumption was correlated to body weight^0.41. This relationship was not significantly affected by changes in ambient temperature. Local heat flow from the dorsal thorax was similar at a given temperature in all acclimation groups but the thermal conductance was greater and the cardiac-subcutaneous temperature difference was smaller in squirrels acclimated to 6 and 18 C. Although shivering was equally high in warm- and cold-acclimated ground squirrels in the cold, nonshivering thermogenesis occurred in curarized cold-acclimated animals exposed to cold or injected with noradrenaline. The results of the study suggest that ground squirrels are regularly exposed to temperatures in their natural habitat which induce considerable cold acclimation.

Submitted on July 6, 1964

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