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1 German Institute of Human Nutrition, D-14558 Bergholz-Rehbrücke; and 2 Philipps University, D-35032 Marburg, Germany
Body temperature and
metabolic rate were recorded continuously in two groups of marmots
either exposed to seasonally decreasing ambient temperature (15 to
0°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
O2 · kg
1 · h1
between 5 and 15°C ambient temperature, although body temperature increased from 7.8 to 17.6°C, and a proportional increase of
metabolic rate below 5°C ambient temperature. This apparent lack of
a Q10 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
O2 · kg1 · h1 · °C1)
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
O2 · kg1 · h1).
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.
thermal conductance; metabolic rate; body temperature-ambient temperature gradient; thermoregulation; hibernation physiology
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