Body Weight Cycles and Energy Balance in the Alpine Marmot (Marmota marmota)

Abstract

Hibernation in most mammals is accompanied by a pronounced seasonal body weight cycle. Fat is accumulated during summer and consumed during the following hibernation season. We investigated the annual time course of energy intake and energy expenditure and their interrelation with seasonal body weight fluctuations and hibernation in captive alpine marmots (Marmota marmota). All animals exhibited an annual body weight cycle with maximum weights in October and minimum weights after termination of hibernation, regardless of food availability during the hibernation season. Both energy uptake and expenditure reached highest values between June and August, when highest rates of body weight gain were observed. Between May and August energy intake exceeded the expenditure by an average of 383 ± 28.3 kJ/d. From September onward, when weight gain in marmots was reduced, the energy balance became less positive. During the normal hibernation season a negative energy balance was observed, even when food was available. Body weight gain in alpine marmots was achieved by a more than 100% enhanced food intake during the summer months. However, this surplus of energy intake could be only partly used for fat accumulation since energetic costs for digestion and catabolism were also considerably increased. The observed annual cycle of energy expenditure reflects to a large extent the metabolic constraints of fat catabolism. The drop in energy expenditure prior to hibernation is therefore at least partly caused by a decreased food intake and body weight gain and seems to be less likely an energy saving mechanism to facilitate further fat accumulation.