title: 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.
authors.affiliation: German Institute of Human Nutrition, D-14558 Bergholz-Rehbrücke, Germany. ortmann@www.dife.de
authors.forename: S
authors.initials: S
authors.lastname: Ortmann
authors.forename: G
authors.initials: G
authors.lastname: Heldmaier
mesh_terms: D000818:Animals; D001831:Body Temperature / Q000502:physiology; D001833:Body Temperature Regulation / Q000502:physiology*; D004734:Energy Metabolism / Q000502:physiology*; D006605:Hibernation / Q000502:physiology*; D008392:Marmota / Q000502:physiology*