Torpor, Hibernation, and Why It's Good I'm Not a Bear

   

Anonymous student unsuccessfully attempts torpor.

It's fully winter now, and yet again I have failed as a mammal.  I was unable to store sufficient weight to save me the trouble of foraging all winter long.  My grocery bills are higher, if anything, than they were in the summer.  I suppose this is not truly my fault; humans are not really built to hibernate.  What a shame though.  Based on how much I love to sleep (an amount I will not openly describe on any even remotely public forum), I think I could be quite good at hibernation.   My friend and I once dressed up as "Torpor and Hibernation" for a costume party.  We showed up in jammies and blankets and from time to time lay down on the floor to rest.  "What? It's part of the costume."  It didn't really work though--we couldn't get our heart rates low enough.

Torpor and hibernation are really pretty cool adaptations.  Torpor and hibernation are confusingly similar.  In both, the animal in question drops its hear rate and metabolism and hangs out is a sleep like state to conserve energy during winter, while food is scarce.  They differ from sleep in that way less energy is used by the body.  Think of it this way: if you climbed into bed in November and tried to stay there asleep until March, would you survive?  No.   (Although some might find the suggestion tempting).  Even while you sleep, you are using energy to stay alive, keep your heart beating, ect.  In torpor or hibernation, the animal can go a longer time without food, or living on the reserves of its fat, because their heart rate and metabolism are so low (body temperature drops as well) that they are hardly burning energy at all.  So even if you ballooned your belly like a bear every fall, I'm sorry, but you will never be able to hibernate.  You don't have the ability to drop your functions down like that.

The difference between the torpor and hibernation mostly relates to timing and the related degree of temperature or metabolism drop necessary.  Torpor is a state that may last only a few hours or a few days.  Hibernation is much longer term, months on end, with few, short waking periods if any, so the changes a body undergoes for hibernation are likely to be more intense.

I will warn you right now that those are very basic explanations of torpor and hibernation.  In the wild and wooly world of science there are always heated debates going on over terminology and who truly hibernates and who is a faker that deserves a different term.  (Watch those thinly veiled derisive repartees fly! No wonder science is so fun!)  There's also a summer version of torpor called estivation, but we won't get into that right now because I would rather talk about Arctic Ground Squirrels.

image : Jim McCarthy, USFWS; license : public domain

Arctic Ground Squirrels are a ridiculously adapted little rodent that live ridiculously cold places like the perma-frosted peaks of Denali, Alaska.  When ground squirrels go into hibernation, their bodies do something called supercooling, dropping their body temperatures below freezing (32 degrees F).  Every several weeks, the squirrels warm back up to a more typical mammal temperature of 98 degrees F by shivering and shaking for 12 hours at a stretch.  Then they drop back into their cold, dormant state.  Unsurprisingly scientists are perplexed about this unusual adaptation, and are still trying to figure out why and how it works.

Those who love weird animal adaptations like the ground squirrels' should consider researching the awesomeness of wood frogs--possibly my favorite animal of all time.  They have an alcohol in their cells that allows them to essentially "freeze solid" in the winter, then thaw in such a way that their inside thaws at about the same rate as their outsides!  (Actually, the fact that there is alcohol in the tissues means that they don't truly freeze solid because alcohols generally must be at a lower temperature to solidify than water.)  If this didn't happen, the extremities, like feet, would thaw before the heart did and, therefore, before there is blood flow to keep them from becoming frost-bitten and dead.  I wonder if it would be possible to keep a pet wood frog and let it "overwinter" in your freezer each year?  Hypothetically it would be possible, but ethically it might be dubious.

"Wood frog embryos in an icy wetland"

Mark Roth , U.S. Geological Survey, http://gallery.usgs.gov