Optimal hibernation theory

Abstract

Hibernation has received considerable attention from physiologists and natural historians, but theoretical and ecological treatments of hibernation are rarer. There is ample recent evidence that costs associated with hibernation affect the degree to which hibernation is expressed in nature, but we currently lack a quantitative framework under which to make predictions about how the costs and benefits of hibernation interact under various environmental conditions. Here, we attempt the first steps towards building an optimal hibernation theory for making specific predictions about the expression of hibernation (i.e. the depth and duration of torpor bouts), metabolic functioning, and the total period of hibernation in mammals and birds. Our current understanding of the costs associated with hibernation do not allow for parameterisation of optimal hibernation theory, but we hope this work provides a roadmap for physiologists and ecologists to collect the necessary data in the future.

Bat population recoveries give insight into clustering strategies during hibernation

“…Thermal imaging has shown that the maximum temperature of arousing M. myotis bats in a cluster of nine or more individuals increases steeply [50]. When few individuals arouse at the same time, they frequently do so in a cold arousal with increasing their temperature by less than 10 • C. Increase in body temperature is expensive for bats in torpor, as arousals cost most energy exerted during hibernation [1,2,15]. Though clustering reduces heat loss [16] and evaporative water loss [18], hibernating in large clusters could mean that bats risk disturbance from other individuals, resulting in cascading arousals.…”

“…Bat species in the temperate zone hibernate to save energy during the winter, when food is unavailable and environmental conditions are unfavourable. Hibernating animals in torpor reduce their metabolism, lower their body temperature close to the ambient temperature, slow their heart rate and breathing frequency, and modulate the immune response [1,2]. To reduce exposure to outside environmental conditions and predation risk, animals use natural caves, artificial galleries, cellars and other suitable places in buildings, rock crevices or hollow trees as shelters.…”

“…The choice of a specific roost in a hibernaculum is important for successful hibernation. For each bat, laboratory experiments show that there exists a minimal torpor temperature, usually between 1 and 10°C, where its energy expenditure is lowest [2]. Hibernating at lower than critical temperatures requires thermoregulation to prevent freezing and at higher temperatures bats conserve less energy resources [11,12].…”

Flexibility Is Costly: Hidden Physiological Damage From Seasonal Phenotypic Transitions in Heterothermic Species

“…Understanding how heterothermy comes with ecological and physiological costs for seasonal organisms will provide insights into the constraints and physiological processes underlying the reaction norms of phenotypic performances and fitness components to seasonal environmental change (Boyles et al, 2020). This will help us to better understand physiological processes such as circannual biological rhythms and reproductive cycles (Cayetanot et al, 2005).…”

“…We do not intend to provide an extensive review of the literature on the regulation of seasonal heterothermy but rather to shed light on putative physiological costs that have been overlooked so far and should be considered in future research. We propose that these costs should be better supported by experimental evidence to be further included in studies modeling the interactions between heterothermy and environmental changes (Boyles et al, 2020).…”