Cryopreserving the Creepy
Houseflies seem to have a mysterious power to transcend the cold. Give them a little heat, and they'll behave in January as if it were August. Earlier this winter, an acquaintance heated up an outbuilding that had been chilled to 20 below, and found the place buzzing with dozens of thawed-out flies within just a few hours.
Many northern buggy beasts can live in deathlike dormancy through bitter cold, then thaw into pestiferous life as soon as temperature permits. Arctic woolly bear caterpillars can stay frozen solid, at temperatures down to -50oC (-58oF), for as long as ten months without damage. Our multilegged denizens aren't the only ones to master the freeze-thaw life cycle. It's possible to find frozen frogs, showing all the vital signs of granite, burrowed into the equally frozen mud in some Interior lakes.
Normally, freezing is deadly for living things. Ice crystals burst through cell and capillary walls, disrupting delicate structures at all levels from subcellular to whole organs. Even when freezing doesn't rip and break an organism, it provides other stresses. No fluid flow means no transfer of oxygen and no disposal of wastes, problems that usually mean no life.
Some animals get around these problems by operating internal furnaces---the mammalian technique---and growing furry or fatty protections against the cold. So-called cold-blooded animals, the exotherms, don't have that option. Many instead use variants on the antifreeze theme, producing chemical protectants that keep ice from forming in their body fluids just as antifreeze keeps water from freezing in a car's cooling system. Polar marine fishes are full of antifreeze, and so are many cold-adapted insects. This evolutionary adaptation means their life-sustaining fluids can be supercooled, staying liquid at temperatures below those at which they should freeze.
The antifreeze chemicals in the fishes and many northern spiders, mites, and insects are proteins that block the effects of ice nucleators, particles that provide binding sites where water molecules begin the process of setting up the orderly lattices of ice crystals. Nucleators turn out to be important also to the animals that get through the cold months by freezing solid. Their chances of surviving freezing are better if ice growth begins in the fluids not contained within cell membranes, such as urine or blood plasma. They are also better off if the freezing proceeds slowly and the crystals formed are small, as in good ice cream. To accomplish these ends, the animals synthesize nucleating agents when external cues trigger the process, such as declining temperatures and daylength. The nucleators provide binding sites for the ice lattice formation to begin, and help set off the freezing process in the right places and at the right speeds to produce the safer kinds of crystals.
Little ice crystals tend to agglomerate into bigger ones, as happens in ice cream stored too long. To prevent that, animals that freeze solid also produce enough antifreeze to block the refreezing of little crystals into bigger ones.
Many freeze-tolerant animals also produce other useful chemicals known as cryoprotectants. (That term is a fine technical cop-out---all it means is that these substances protect cell structures and membranes against various effects of chilling.) The cryoprotectants regulate cell volume during freezing and also seem to protect vital proteins and enzymes from the denaturing effects of very low temperatures.
Finally, the cells and organs of frozen animals are capable of surviving for a long time without oxygen. As their metabolic rates drop to one to 10 percent of their normal resting rates, their needs for energy and waste removal drop accordingly.
So, our winter-surviving creepers and buzzers are little less than chemical and physical marvels, capable of survival feats well beyond human capacities. Swat we must, no doubt, but now I'll do so with a little more respect.
