Survival, aging, and life-history tactics in mammalian hibernators

Hibernation is commonly viewed as an adaptation that simply allows animals to survive periods of food shortage and climatically harsh conditions. Here, we review accumulating evidence suggesting that hibernation is part of a specific "slow-paced" mammalian life-history tactic that is associated with increased survival, retarded physiological aging, increased maximum longevity, low rates of fecundity, and long generation times. We argue that these traits can be explained if the primary function of hibernation-at least in many species-is the reduction of extrinsic mortality risks, namely predation, under environmental conditions that are not lifethreatening, but do not favor reproduction. According to this view, hibernation is but one element of a life-history strategy that maximizes fitness by bet-hedging, i.e., reducing the risk oflosing offspring by spreading lifetime reproductive effort over a number of temporally separated bouts. Further, increased survival and spreading of reproductive bouts should allow hibernators to produce young at times when climate and food resources are optimal for the rearing of offspring.