Hibernation

Abstract: We derive a general model, based on principles of biochemical kinetics and allometry, that characterizes the effects of temperature and body mass on metabolic rate. The model fits metabolic rates of microbes, ectotherms, endotherms (including those in hibernation), and plants in temperatures ranging from 0° to 40°C. Mass- and temperature-compensated resting metabolic rates of all organisms are similar: The lowest (for unicellular organisms and plants) is separated from the highest (for endothermic vertebrates) by a factor of about 20. Temperature and body size are primary determinants of biological time and ecological roles.

Abstract: ▪ Abstract Although it is well established that during periods of torpor heterothermic mammals and birds can reduce metabolic rates (MR) substantially, the mechanisms causing the reduction of MR remain a controversial subject. The comparative analysis provided here suggests that MR reduction depends on patterns of torpor used, the state of torpor, and body mass. Daily heterotherms, which are species that enter daily torpor exclusively, appear to rely mostly on the fall of body temperature (Tb) for MR reduction, perhaps with the exception of very small species and at high torpor Tb, where some metabolic inhibition may be used. In contrast, hibernators (species capable of prolonged torpor bouts) rely extensively on metabolic inhibition, in addition to Tb effects, to reduce MR to a fraction of that observed in daily heterotherms. In small hibernators, metabolic inhibition and the large fall of Tb are employed to maximize energy conservation, whereas in large hibernators, metabolic inhibition appears to be em...

Abstract: Mammals normally maintain their core body temperature (CBT) despite changes in environmental temperature. Exceptions to this norm include suspended animation–like states such as hibernation, torpor, and estivation. These states are all characterized by marked decreases in metabolic rate, followed by a loss of homeothermic control in which the animal's CBT approaches that of the environment. We report that hydrogen sulfide can induce a suspended animation-like state in a nonhibernating species, the house mouse ( Mus musculus ). This state is readily reversible and does not appear to harm the animal. This suggests the possibility of inducing suspended animation-like states for medical applications.

Abstract: For many animals, the best defense against harsh environmental conditions is an escape to a hypometabolic or dormant state. Facultative metabolic rate depression is the common adaptive strategy of anaerobiosis, hibernation, and estivation, as well as a number of other arrested states. By reducing metabolic rate by a factor ranging from 5 to 100 fold or more, animals gain a comparable extension of survival time that can support months or even years of dormancy. The present review focuses on the molecular control mechanisms that regulate and coordinate cellular metabolism for the transition into dormancy. These include reversible control over the activity state of enzymes via protein phosphorylation or dephosphorylation reactions, pathway regulation via the association or dissociation of particle-bound enzyme complexes, and fructose-2,6-bisphosphate regulation of the use of carbohydrate reserves for biosynthetic purposes. These mechanisms, their interactions, and the regulatory signals (e.g., second messenger molecules, pH) that coordinate them form a common molecular basis for metabolic depression in anoxia-tolerant vertebrates (goldfish, turtles) and invertebrates (marine molluscs), hibernation in small mammals, and estivation in land snails and terrestrial toads.

Abstract: Hibernation and daily torpor are usually considered to be two distinct patterns of heterothermia. In the present comparison we evaluated (1) whether physiological variables of torpor from 104 avian and mammalian species warrant the distinction between hibernation and daily torpor as two different states of torpor and (2), if so, whether this distinction is best based on maximum torpor bout duration, minimum body temperature ($T_{b}$), minimum metabolic rate during torpor, or the reduction of metabolic rate expressed as percentage of basal metabolism (BMR). Initially, animals were grouped into species displaying either daily torpor or prolonged torpor (hibernation) according to observations from original sources. Both cluster and discriminant analyses supported this division, and further analyses were therefore based on these two groups. Frequency distributions for all tvariables tested differed significantly (P < 0.001) between daily torpor and hibernation. The average maximum torpor bout duration was 355...