Frog-sicles? Antifreeze made from turtle pee?

Click to see a frozen frog thaw out and spring to life!

My college zoology teacher once started off a class by putting what was, by all appearances, a frozen turtle on his lab bench.  He had just pulled it out of the freezer, he said, and assured us that it would be active again by the end of our 90-minute class.  As I recall, he admitted sheepishly that it was still inert as we filed out at the end of our lesson in ectothermy, or “cold-bloodedness,” but he invited us to return after our next class to see it unharmed and shuffling with vigor. I took his word for it and now I really with I’d gone back to see it for myself.

To be sure, animals have some amazing weapons in their battles with winter. Obviously the low temperatures are challenging but, for endotherms like mammals and birds, it’s really the lack of food and dehydrating conditions that are hardest. Food becomes scarce because it’s hard for plants to photosynthesize in the cold, dry air and shortened, winter days.

Many birds, for example, aren't really migrating to leave the cold behind. They just came up from the tropics to fatten themselves and their chicks on the springtime explosions of insect populations.  When these birds head south, they’re really heading back home. 

Even if a frog or turtle had the stamina to hop or lumber to the tropics, it’d be spring again by the time they got there so they have to face winter’s challenges head-on. Many adult turtles burrow into the mud at the bottom of their ponds where it’s at least a little above freezing. Breathing may cease, heart rates all but stop and everything slows so much that they can survive for months in a true suspended animation.  Other turtles stay at the surface and, with natural “antifreeze”(perhaps derived from their urine), remain unfrozen at temperatures well below 32°F. Some can even survive small amounts of ice in their systems. 

Some frogs, like the land-dwelling wood frog, can tolerate quite a bit of freezing.  They survive the experience by dehydrating their vital organs and moving water into the spaces between cells and organs where it can freeze and expand without causing injury. Breathing and circulation stop completely and, essentially, they've become frog-sicles.  When things warm up in, say, February, they’ll thaw out and start calling for a mate. I will pass on the opportunity to make a joke about her being cold-hearted or giving them the cold shoulder.  Wait, I think I failed to pass on that opportunity. 

Strictly speaking, none of this is truly hibernation which involves a form of thermoregulation that only mammals can do (there’s some debate about a bird or two). Still, the word has been so abused by public and scientists alike that you need not trouble yourself with the differences between hibernation, torpor, dormancy, diapause, aestivation or brumation. 

Suffice it to say that animals have amazing ways to shut themselves down when times get tough. Bat hearts beat at near-freezing temperatures. Bears sleep for six months without peeing. At least one rodent is really only active for four months out of twelve. Nature’s just full of surprises, isn’t it?

Why is any of this important? Scientists hope that some of their discoveries might be of use in medicine.  Perhaps bears can show us how to help preserve bone strength and muscle mass in bed-ridden people.  Maybe we can use amphibians’ natural antifreezes to help us in organ transplants or even interstellar travel.  For now, it’s just plain interesting and that’s enough for me.