The influence of gender on thermoregulation in pouched mice ,

Saccostomus campestris display sexual disparity in the use of summer daily torpor in response to energy stress . The hypothesis that males may compensate for a limited heterothermic capacity with lower normothermic body temperatures by maintaining lower resting metabolic rates relative to females was tested. Furthermore, the influence of testosterone on torpor incidence in males was investigated. Body temperature (Ts) and oxygen consumption (V02 ) were measured at various ambient temperatures (Ta) and were compared between the sexes under food ad libitum and food restriction treatments. There were no significant differences in Tb and V02 between sexes under food ad libitum treatment. Under food restriction there were pronounced sex differences in the employment ofheterothermy. Females defended a lower setpoint T, for torpor (ca. 25°C), than males (ca. 29°C), and also employed torpor more frequently than males . Non-torpid males did, however show slight reduct ions in V02 under food restrictio n. The effect of testosterone on daily torpor was investigated by comparing minimum Tband torpor frequency of castrated mice implanted with testosterone-filled (experimental) and saline-filled (control) silastic capsules in response to food ad libitum and food restriction treatments. Testosterone inhibited torpor in males. The majority of control animals employed torpor under both food ad libitum and food restriction diets. It was concluded that although the animals were capable of shallow, summer torpor, it was confined to moderate ambient temperatures and was not used at low Ta's where several animals became pathologically hypothermic. Females derive energetic benefits from the use of torpor whereas males may partially compensate for their limited