Latitudinal Differences in the Hibernation Characteristics of Woodchucks (Marmota monax)

Abstract

There is little information on the phenotypic flexibility of hibernation characteristics within species. To address this issue, we observed differences in hibernation characteristics of three free-ranging populations of woodchucks (Marmota monax) distributed along a latitudinal gradient from Maine to South Carolina. Data from free-ranging animals exhibited a direct relationship between latitude and length of the hibernation season. As expected, woodchucks in the northern latitudes hibernated longer than those in the southern latitudes. Also, the length of interbout arousals decreased with increase in latitude, whereas the length of torpor bouts and the number of arousals increased. Thus, we observed phenotypic plasticity in hibernation characteristics based primarily on latitudinal temperature differences in each population. Further analysis revealed a direct relationship between latitude and total time spent in torpor. Maine animals spent 68% more time in torpor than South Carolina animals. However, total time spent euthermic did not differ among the three populations. The "cost-benefit" hypothesis of hibernation may help to explain these results. It assumes that hibernators avoid the physiological stress of torpor by staying euthermic as much as possible. Woodchucks in each population maximized time spent euthermic, utilizing torpor only at the level needed to survive winter hibernation and to commence reproduction in the spring.

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.…”

Modelling mammalian energetics: the heterothermy problem

“…For a species with readily predictable torpor bout lengths and hibernation seasons of a set length, such as the Holarctic ground squirrels (family Sciuridae, tribe Marmotini, [142]), this would often cover the winter months only (eg. [143]), although this may also change based on latitude or local climate conditions [144,145]. Such obligate hibernators, must undergo significant pre-hibernation fattening before entering into torpor [30,105,146,147].…”

The Hibernation Continuum: Physiological and Molecular Aspects of Metabolic Plasticity in Mammals

“…We note that the plasticity within individuals to orchestrate diverse patterns of metabolic activity and T b , as seen with dwarf lemurs moving among different tree holes with different insulating properties (FIGURE 3, C-E; Ref. 14); dormice engaging in daily torpor, hibernation, and estivation (93); highly variable T b patterns of ground squirrels preparing for hibernation during fall (71); seasonal changes in torpor bout duration and frequency of arousal that leads to reproducibly longer periods of torpor mid-hibernation season (23); and variable patterns of woodchuck hibernation depending on environmental conditions (97); taken together with the intermediate torpor utilization patterns of the Patagonian opossum (24) and tenrecs described above are consistent with the view that the metabolic plasticity observed among mammals represents a continuum of possible phenotypes rather than fixed discrete patterns. It is reasonable to infer that the apparent clustering of features, such as minimum T b and metabolic rate during torpor or maximum torpor bout length, into apparently distinct pattern groups for daily torpor and hibernation (70) may reflect optimal conditions for energy conservation given specific conditions of ambient temperature and body size taken together with strategies for avoiding predation and enhancing reproduction (79,96).…”