Regulation of body temperature and energy requirements of hibernating Alpine marmots (Marmota marmota)

Abstract

Body temperature and metabolic rate were recorded continuously in two groups of marmots either exposed to seasonally decreasing ambient temperature (15 to 0 degrees C) over the entire hibernation season or to short-duration temperature changes during midwinter. Hibernation bouts were characterized by an initial 95% reduction of metabolic rate facilitating the drop in body temperature and by rhythmic fluctuations during continued hibernation. During midwinter, we observed a constant minimal metabolic rate of 13.6 ml O(2) x kg(-1) x h(-1) between 5 and 15 degrees C ambient temperature, although body temperature increased from 7.8 to 17.6 degrees C, and a proportional increase of metabolic rate below 5 degrees C ambient temperature. This apparent lack of a Q(10) effect shows that energy expenditure is actively downregulated and controlled at a minimum level despite changes in body temperature. However, thermal conductance stayed minimal (7.65 +/- 1.95 ml O(2) x kg(-1) x h(-1) x degrees C(-1)) at all temperatures, thus slowing down cooling velocity when entering hibernation. Basal metabolic rate of summer-active marmots was double that of winter-fasting marmots (370 vs. 190 ml O(2) x kg(-1) x h(-1)). In summary, we provide strong evidence that hibernation is not only a voluntary but a well-regulated strategy to counter food shortage and increased energy demands during winter.

Cooling rates and body temperature regulation of hibernating echidnas(Tachyglossus aculeatus)

“…Although the slope of the line, and thus the calculated C, will not be affected by a constant rate of heat production, it will be affected if MR varies with T b (Bakken and Gates, 1974), but in previous laboratory experiments, we were unable to find any relationship between T b and MR in hibernating echidnas (Nicol et al, 1992). A similar independence of MR from T b has been observed in a variety of hibernating rodents during thermoconforming hibernation at low T b (Buck and Barnes, 2000;Heldmaier and Elvert, 2004;Heldmaier et al, 1993;Ortmann and Heldmaier, 2000). Although some small hibernators show a temperature effect on hibernating MR, particularly at high T b (Geiser, 2004), the linearity of the semi-log plots of the echidna cooling curves (Fig.·5) implies that there is no significant change in echidna heat production or conductance during the cooling period.…”

Nocturnal hypometabolism as an overwintering strategy of red deer (Cervus elaphus)

“…A similar decrease of T set occurs during entrance into hibernation and has led to the suggestion that hibernation is an extension of thermoregulatory adjustments that normally occur during slow-wave sleep (16,17). The gradual decrease of T set during entrance into hibernation permits the shutoff of heat production and maximal reduction of MR, leading to the continuous decline of T c toward the low values close to ambient temperature (47).…”

Decrease in the red cell cofactor 2,3-diphosphoglycerate increases hemoglobin oxygen affinity in the hibernating brown bearUrsus arctos

“…During hibernation bear body temperature is downregulated only slightly, fluctuating from ϳ37°C to a minimum of 30°C, as found in brown and in black bears (Ursus americanus) (17,26,27,36,43), whereas O 2 consumption rate is downregulated by 75% (43). In comparison, in most smaller hibernators, such as ground squirrels and marmots, body temperature drops dramatically to values close to ambient temperatures (32,37,48), with a consequent strong Q 10 -induced depression of metabolic rate (where Q 10 is the rate coefficient for a 10°C change in temperature). In spite of substantial downregulation of ventilation and heart rate, most hibernators likely experience only slight or no hypoxia and in some ground squirrels arterial O 2 tension (PO 2 ) is normal during torpor (16).…”