That's hot: golden spiny mice display torpor even at high ambient temperatures

Golden spiny mice (Acomys russatus) living in the Judean desert are exposed to extended periods of food and water shortage. We investigated their thermal and metabolic response to three weeks of 50% food reduction at ambient temperatures of 23, 27, 32 and 35 °C by long term records of metabolic rate and body temperature in the laboratory. At all ambient temperatures, A. russatus responded to starvation by a reduction of daily energy expenditure. At 32 and 35 °C, this metabolic adjustment fully compensated the reduced food availability and they maintained their energy balance at a slightly reduced body mass. At lower ambient temperatures, they could not fully compensate for the reduced food availability and kept a negative energy balance. The reduction of daily energy expenditure was largely achieved by the occurrence of daily torpor. Torpor even occurred at high ambient temperatures of 32 and 35 °C during which metabolic depression was not associated with a marked decrease of body temperature. The results show that the occurrence of daily torpor is not necessarily linked to cold exposure and the development of a pronounced hypothermia, but may even occur as depression of metabolic rate in a hot environment.