Hibernation and Overwintering

My lab has long been interested in hibernation.  Indeed, it was an interest in hibernation that introduced me to my PhD supervisor, and other interests have naturally derived from there.

What is hibernation?

Depends on who you ask.  Every 4 years, a group of scientists from around the world gather for the International Hibernation Symposium to discuss research on hibernation and even at this meeting there is often healthy debate about the use of the term.  I will not contribute to the confusion over semantics too much, but suffice to say I belong to a group of people who argue that the term should refer to a period of an animal’s life when it engages in a profound reduction in metabolism typically associated with the winter period.  Some confuse hibernation with requiring a reduction in body temperature, but in many cases this is insufficient evidence.

Why do Animals Hibernate?

To save energy, typically during a predictable period when food availability is low.  Some animals migrate in the winter, others do not, so to survive when food is scarce, they reduce their energy needs.  I was interviewed by a science write a while back on this subject and she wrote a nice summary of the topic, I link here:


Do ectotherms hibernate?

Yes they do.  In the cases of reptiles it has often been referred to as brumation (Mayhew, 1965).  This blog does a great job of collating the arguments and literature, so I will link to it here: http://theobligatescientist.blogspot.ca/2010/11/do-reptiles-hibernate-or-brumate.html

My own research interests began with amphibian hibernation (all my PhD work was on amphibian overwintering behaviour and physiology). Many temperate amphibians spend up to 6 months every year at very low temperatures. Some frogs spend the winter submerged under the ice of frozen ponds and lakes.  Under these conditions, the overwintering environment becomes extremely hypoxic, often leading to the death of many of its inhabitants. At the same time, the water beneath the ice becomes stratified for temperature and oxygen, being warmer at the bottom than below the ice as well as being more hypoxic. I have shown that cold-submerged frogs can detect these oxygen and temperature gradients even during their overwintering torpor, and exhibit distinct preferences for both. If the overall oxygen level in the water falls too low, frogs will select temperatures as cold as possible to lower their metabolic requirements and alleviate the hypoxic stress. Thus, the overwintering frog provides us with some proof for the ecological relevance of hypoxia-induced hypothermia.

hibernating frog2.jpg

Endothermic Hibernation and Tb Set-Points

In order to hibernate, endotherms need to achieve, at minimum two major metabolic feats.  The first is to suppress or shut down normal thermoregulatory control.  For temperate zone hibernators, this has been well studied.  Whenever a ground squirrel or chipmunk or bear begins to enter torpor, the thermostat in the brain is gradually suppressed, otherwise the animal would never cool down.  The second thing is to actively suppress and control cell metabolism but at a low rate.  This is the subject of much of current hibernation biology and is the holy grail of comparative physiological research into hibernation.  If we can fully understand how natural hibernators change metabolism so profoundly, the hope is that we will have answers to assist in biomedical research and in sending humans into space, through induced hibernation.  At present, it is still a bit too soon to say, but every year comparative physiologists are making progress on this interesting question!




Levesque, D. L., and G. J. Tattersall. 2009. Seasonal changes in thermoregulatory responses to hypoxia in the Eastern chipmunk (Tamias striatus). Journal of Experimental Biology 212:1801-1810.

Levesque, D. L., and G. J. Tattersall. 2010. Seasonal torpor and normothermic energy metabolism in the Eastern chipmunk (Tamias striatus). Journal of Comparative Physiology B-Biochemical Systemic and Environmental Physiology 180:279-292.

Rollinson, N., G. J. Tattersall, and R. J. Brooks. 2008. Winter temperature selection in relation to dissolved oxygen concentrations in a natural population of Painted Turtles (Chrysemys picta). Journal of Herpetology 42:312-321.

Tattersall, G. J. 2004. Overwintering in cold-submerged frogs. Pages 349-359 in B. Barnes and H. Carey, editors. Life in the Cold: Evolution, Mechanisms, Adaptation, and Application. Institute of Arctic Biology, Fairbanks.

Tattersall, G. J., and W. K. Milsom. 2009. Hypoxia reduces the hypothalamic thermogenic threshold and thermosensitivity. Journal of Physiology (London) 587:5259-5274.

Boutilier, R. G., Tattersall, G. J. and Donohoe, P. H. 1999. Metabolic consequences of behavioural hypothermia and oxygen detection in submerged overwintering frogs. Zoology: Analysis of Complex Systems 102: 111-119.

Tattersall, G. J. and Boutlier, R. G. 1999. Behavioural oxyregulation by cold-submerged frogs in heterogeneous oxygen environments. Canadian Journal of Zoology 77: 843-850.

Tattersall, G. J. and Boutlier, R. G. 1999. Constant set points for pH and Pco2 in cold-submerged skin-breathing frogs. Respiration Physiology, 118: 49-59.

Tattersall, G. J. and Boutilier, R. G. 1999. Does behavioural hypothermia promote exercise recovery in cold-submerged frogs? Journal of Experimental Biology, 202: 609-622.

Tattersall, G. J. and Boutilier, R. G. 1997. Balancing hypoxia and hypothermia in cold-submerged frogs. Journal of Experimental Biology 200: 1031-1038.

Boutilier, R. G., Donohoe, P. H., Tattersall, G. J. and West, T. G. 1997. Hypometabolic homeostasis in over-wintering amphibians. Journal of Experimental Biology 200: 387-400.