Associations between body morphology and hibernation in mammals

Hibernation is an extreme mechanism for conservation of energy, where metabolic rate and body temperature are substantially lowered for a long-term period. This is typically<br>performed in response to food shortages or cold temperatures, allowing the organism to survive these unfavourable conditions. Hibernation is periodically interrupted by arousals, where hibernating species return to normothermic levels of functioning for short periods, before returning to a torpid state. As hibernation is intrinsically a method for conservation of energy, as a strategy it potentially enables energy reserves to be allocated to other functions such as growth or reproduction. It may also allow hibernators to escape selection pressures enforced by cooler climates because they do not have to maintain normothermic body temperature. Here I investigate whether hibernation influences patterns in body morphology (size of appendages), brain size, metabolic rate and lifespan using a data set of 916 mammalian species. I demonstrate for the first time that, in contrast to non-hibernating species and mammals as a whole, hibernators do not demonstrate Allen’s rule in relation to tail length (shorter tails in cooler climates). This suggests that there is reduced selection against longer tails in cold climates for hibernating species. I also show that hibernators have smaller brains than non-hibernators, and infer this is related to the high energetic cost of growth and maintenance of a large brain. Finally, I relate various aspects of hibernation to basal metabolic rate and lifespan, and provide explanations as to why no significant relationship is observed. This research is important as it directly highlights how different selective pressures affect various hibernating species and offers insight into the evolution of body morphology in relation to hibernation.<br><br>