Body mass dependent use of hibernation: why not prolong the active season, if they can?

Abstract

Summary1. Hibernation is the most effective means for energy conservation during winter in mammals. The drawbacks of deep and prolonged torpor include reduced immunocompetence, and consequently, hibernators should be selected to minimize torpor expression when climatic conditions or energy availability (e.g. food or fat stores) permit. Therefore, it seems surprising that some hibernators employ extraordinary long hibernation seasons, lasting well beyond periods with unfavourable conditions. 2. Because of their extended use of torpor, edible dormice (Glis glis) provide an ideal model for scrutinizing interactions between energy reserves (i.e. body fat stores) and thermoregulatory patterns. We used a multimodel inference approach to analyse body temperature data (i.e. use of torpor) from 42 entire hibernation seasons over 4 years in females in relation to body mass. 3. Body mass prior to hibernation did not affect the duration of the hibernation season, but animals hibernated for c. 8 months, that is, 2 months longer than required by environmental conditions. Fatter individuals aroused significantly more often, had a higher mean minimum body temperature during torpor and remained euthermic for longer periods than leaner animals. 4. Surplus energy was therefore not used to shorten the hibernation season, but to rewarm more frequently, and to allow shallower torpor bouts. These adjustments apparently serve to avoid negative effects of torpor and, perhaps equally importantly, to minimize the time active above-ground. We argue that maintaining a short active season, despite surplus energy reserves, may be explained by known beneficial effects of hibernation on survival rates (via predator avoidance). 5. Our data provide quantitative evidence that hibernation is a flexible tool within life-history strategies. We conclude that, apart from energetic necessities due to harsh environmental conditions, predator avoidance may be an important factor influencing patterns of hibernation and torpor in mammals. Thus, our study indicates that climatic conditions alone are not a good predictor of hibernation patterns or survival in hibernating species during global climate change.

Late-born intermittently fasted juvenile garden dormice use torpor to grow and fatten prior to hibernation: consequences for ageing processes

“…In addition to food limitation, cold exposure can also exert a modulating effect on torpor use [38,39]. However, when food availability was sufficient, juveniles used torpor less frequently, which also indicates that torpor has costs [40][41][42][43]. Costs of torpor could be related to increased exposure to reactive oxygen species during rewarming phases [44,45], a view not supported by this study, as we did not find any relation between torpor use and telomere loss during pre-hibernation.…”

Metabolic Flexibility: Hibernation, Torpor, and Estivation

“…Intraspecifically among hibernators, larger (and, presumably, fatter) animals spend less time torpid, spend that time at higher T b (313), and arouse more frequently (21). Contrary to the prediction that heterotherms should maximize energy conservation, these patterns suggest that, if energy stores allow, heterotherms minimize the amount time spent torpid.…”

“…In animals that hibernate at low T b (i.e., near 5 • C), the duration of torpor phases depends on body mass within (313) and among species (104). In woodchucks (313) and edible dormice (21), larger, fatter animals spend less time torpid, and have higher torpid T b . These results are at least analogous to the reduced frequency and depth of torpor in hibernating chipmunks with large, supplemented food caches ( Fig.…”

Seasonal Prevalence of Lyme Disease Spirochetes in a Heterothermic Mammal, the Edible Dormouse (Glis glis)

“…Although heterothermic lizards are known to perpetuate B. lusitaniae (2), any effects of heterothermia on the various LD genospecies remain unknown. It remains to be examined whether the observed loss results from a failure to survive extended periods of low body temperature (18), drastically reduced metabolic rates (19), or biochemical changes within their hosts associated with hypothermia (35)(36)(37). Alternatively, spirochetes may be nondetectable if they would reside in some core organs of their hibernating hosts and the migration to the skin would be delayed.…”

“…Edible dormice are obligate hibernators, and in Germany adults hibernate for 7 to 8 months, generally from the end of September until the end of May (17). During hibernation, body temperature is drastically reduced close to 0°C (18), and metabolic rate is reduced to a fraction of the euthermic values (19). As a fat-storing hibernator, dormice cease feeding and rely entirely on stored fat accumulated during the previous autumn for energy metabolism (20).…”