Relationships between reduced metabolic rate during hibernation and the body size and body temperature of hibernators have been nicely discussed elsewhere. Many aspects of bear physiology remain to be elucidated, including how their metabolism is regulated to enable them to endure such prolonged hibernation periods.Īn average reduction in metabolic rate to 4.4% of normal basal rates and a decrease in body temperature down to about 6 ☌ have been calculated from the data available for 50-80 species of mammals that hibernate. Within this framework, the hibernation of bears represents an extreme phenotype that can last for up to 6-7 months during which inactive animals do not eat, drink, urinate, defecate, or exhibit arousal episodes. To save energy during the prolonged period of winter fasting, hibernators rely essentially on decreased metabolic rates over extended periods of deep torpor characterized by physical inactivity, reductions of heart and breathing rates and decreased body temperature. Hibernation/torpor expression implies trade-offs – on one hand physiological costs such as reduced memory retention, reduced immunocompetence and accumulation of sleep debt, and on the other hand, the major benefit of substantial fuel/energy conservation. Hibernation has evolved in a variety of mammalian species as an adaptive strategy to survive harsh winter environmental conditions, including seasonal cold ambient temperatures and food shortages.
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