Seasonal Study of Spontaneous Daily Torpor in the White-Footed Mouse, Peromyscus leucopus

Seasonal pattern and energetics of short daily torpor in the Djungarian hamster, Phodopus sungorus

“…Peromyscus Lynch et al (1978b) could observe torpor only when T, was below 3 ~ C and in caged individuals torpor only rarely occurred at Ta as high as 15 to 17 ~ C. In both studies highest frequency of torpor was observed during winter months but sometimes Peromyscus were also found torpid during summer months. This is completely different from our observation in Phodopus, where torpor was exclusively observed during winter months but then it occurred even at room temperature.…”

“…In Peromyscus leucopus Tre during torpor was found ranging from 12 to 22 ~ C and was apparently related to changes in T~ with lowest torpor temperatures at -10 and highest torpor temperatures at + 10 ~ C T, (Gaertner et al 1973). In the same species Hill (1975) reported torpor temperatures between 16.8 and 27.7 ~ C and Lynch et al (1978b) observed mean minimum T~e ranging from 18.0 to 26.6 ~ C, but no measurements at varying T~ are available to illustrate eventual thermoregulatory control during torpor. In Perognathus californicus Tucker (1965a, b) observed torpor following rationing of food and found Tro ranging from 10.6 and 34~ at T, between 5 and 26 ~ C, and Tr~ in torpor apparently varied as function of T,.…”

“…In fact, most previous investigations of shallow daily torpor were made following food or water deprivation of small mammals in the laboratory, and there are only few reports indicating that shallow daily torpor may also occur spontaneously in field animals, sufficiently supplied with food. In the white-footed mouse, Peromyscus leucopus, Gaertner et al (1973), Hill (1975) and Lynch et al (1978b), showed that spontaneous daily torpor is a seasonal phenomenon, preferrably occurring at low ambient temperature during winter months even in the presence of excess food. In the Djungarian dwarf hamster, Phodopus sungorus, a similar seasonality of incidental torpor has been reported in hamsters kept at room temperature, fed ad libitum, but subjected to seasonal variations in photoperiod (Figala et al 1973;Heldmaier and Steinlechner, in press).…”

Differential reproductive response to short photoperiod in deer mice: role of melatonin

“…Short photoperiod is ineffective in causing either testicular regression or other physiological adjustments (body weight, pelage, torpor) in mice obtained from Georgia populations Gram et al 1982), which breed in the fall and winter months (Golley 1962). In contrast, males obtained from Connecticut populations, which breed in the spring and summer months, respond to short days with gonadal regression and an assortment of concomitant physiological adjustments (Lynch et al 1978;Lynch and Gendler 1980). Melatonin treatment mimics the effects of short photoperiod in Connecticut mice but has no effect on either testicular function or other physiological parameters in Georgia mice (Gram et al 1982;Heath and Lynch 1982;Carlson et al 1989).…”

Brown fat and nonshivering thermogenesis in the gray mouse lemur (Microcebus murinus)

“…Torpor bouts are induced by both cold exposure and food or water restriction (8,31). In addition, DT frequency and/or depth often show seasonal changes with a reduction in summer (12,29). The metabolic cost of arousal from torpor is high and can reach 80% of the total energy expenditure of DT (11).…”