Hormones and hibernation: possible links between hormone systems, winter energy balance and white-nose syndrome in bats

Hibernation allows mammals to survive in cold climates and during times of reduced food availability. Drastic physiological changes are required to maintain the energy savings that characterize hibernation. These changes presumably enable adjustments in endocrine activity that control metabolism and body temperature, and ultimately influence expression of torpor and periodic arousals. Despite challenges that exist when examining hormonal pathways in small-bodied hibernators, bats represent a potential model taxon for comparative neuroendocrinological studies of hibernation due to their diversity of species and the reliance of many species on heterothermy. Understanding physiological mechanisms underlying hibernation in bats is also important from a conservation physiology perspective due to white-nose syndrome, an emerging infectious disease causing catastrophic mortality among hibernating bats in eastern North America. Here we review the potential influence of three key hormonal mechanisms - leptin, melatonin and glucocorticoids - on hibernation in mammals with an emphasis on bats. We propose testable hypotheses about potential effects of WNS on these systems and their evolution.