Winterschlaf des Alpenmurmeltieres (Marmota marmota) [Hibernation des marmottes alpines].

Résumé

The most important adaptation of marmots for inhabiting harsh alpine habitats is their ability to hibernate. By reducing metabolic rate to 3-5 % of the summer level, body temperatures may decrease to 2.6° C. However, marmots can remain in this state with extremely low energy consumption only for a limited period of time. They regularly interrupt torpor after approximately 12 days and rewarm for about one day to body temperatures of on average 34.5° C, which is still 3.7° C below the average body temperature during summer. During deep torpor marmots remain sensible against external stimuli and again increase metabolic heat production below a critical temperature threshold in order to avoid a further decrease of body temperature and the risk of death from exposure to cold. In natural hibernacula, such temperature conditions exist for most of the hibernation period. An endogenous circannual rhythm and the seasonal changes of daylength as an external Zeitgeber play an important role for regulating the annual changes of body mass and readiness to hibernate. Marmots fuel their metabolism during winter entirely from body fat accumulated during summer and lose on average one third of their autumn body mass. The herbivorous marmots emerge from hibernation long before the thaw is completed and hence continue to depend on fat reserves after termination of hibernation. The total energy requirements during the fastening period cannot be decreased sufficiently by solely reducing metabolic rate, particularly not by juveniles which have only 3 month available for accumulating fat reserves for a hibernation period of 6-7 month. In order to further reduce their energy demands marmots hibernate in groups of up to 20 individuals. They reduce individual heat loss to the cold environment by huddling close together and synchronizing their regular changes from torpor to high body temperatures. In addition, the most vulnerable juveniles are located in the middle of the huddling group and related adult group members actively warm juveniles during winter by slightly increasing their body temperatures or by additional interruptions of torpor.