Periodicity and Energetics of Torpor in the Kangaroo Mouse, Microdipodops Pallidus

Abstract

The effects of three environmental temperatures and four food rations on the duration and periodicity of torpor were examined, the oxygen consumption of torpid and normothermic kangaroo mice was measured, and temperature profiles in their habitat were obtained during all seasons. Because of their fossorial and nocturnal habits, kangaroo mice need not face environmental temperature above 30°C or much below 0°C although temperatures in their Great Basin habitat normally fluctuate far outside this range. Torpidity affords a reduction in energy expenditure which increases as temperature decreases. At 5°C the oxygen consumption of torpid mice was less than one—sixtieth that of normothermic mice. When the animals were given seeds in excess each day, none became torpid at either 17° or 6°C, but when the daily ration was reduced to 1.5 g all individuals become torpid. The per cent time torpid and the duration of torpor cycles varied inversely with temperature. At 6°C the time in torpor increased when he daily food ration was reduced from 1.5 to 0.5 g but decreased slightly when food in excess was made available at longer intervals. Periods of torpor varied from a few hours to several days. The time in torpor was related to environmental temperature and food supply in such a way that the mice maintained body weight and accumulated food stores under all conditions tested. This suggests that in nature Microdipodops can regulate periods of torpor so as to conserve its stored seeds during both chronic and acute shortages of food.

Coping with chaos: unpredictable food supplies intensify torpor use in an arid-zone marsupial, the fat-tailed dunnart (Sminthopsis crassicaudata)

“…Other species are apparently capable of using torpor to manage unpredictable supplies of food (Brown and Bartholomew 1969) or water (Ibuka and Fukumara 1997). But what is important in our study is that we have controlled food intakes in a manner that induced torpor responses to a pattern of unpredictability, rather than simply providing a different level of energy restriction.…”

Timing of the daily temperature cycle affects the critical arousal temperature and energy expenditure of lesser long-eared bats

“…Laboratory studies under constant T a have found that whereas times of entry into torpor are variable and occur earlier in the active phase under conditions of energetic stress, times of arousal appear largely fixed according to an endogenous circadian rhythm (Tucker, 1962;Brown and Bartholomew, 1969;Geiser, 1986). By contrast, in wild animals, times of arousal frequently coincide with an initial period of passive rewarming during the day , suggesting that these arousals are triggered by a threshold level of exogenous rewarming (Schmid, 1996;Lovegrove et al, 1999;Körtner and Geiser, 2000).…”

Thermal Biology, Torpor, and Activity in Free‐Living Mulgaras in Arid Zone Australia during the Winter Reproductive Season

“…In a similar fashion, kangaroo mice (Microdipodops pallidus) increasingly employ torpor in response to food restriction, enabling them not only to maintain body mass but also to accumulate food stores (Brown and Bartholomew 1969). It therefore appears that, similar to hibernation, in some species, daily torpor can be used to shift energetic costs between seasons beyond simply balancing daily energy requirements.…”