It surely isn’t the time to be thinking about this, but it has crossed my mind (numerous times) during the course of the week.
Ever wondered how animals manage to survive in the cold of winter without warm mittens and scarfs? Since they don’t come in beetle size, luck would have it that they’re specially adapted to life challenges thrown their way in sub-zero temperatures.
Animals employ a number of tactics to survive in harsh, cold environment. One, used by say birds, is to get your ass feathers out of there. But seriously, for animals that do not migrate, a more robust, terminator approach is needed. I’ll focus on three methods employed, namely preemptive ice crystal formation, supercooling and antifreeze deployment.
This method is the ninja method I would use if I were a beetle or a fish living under the Arctic ice. The idea behind this principle is to prevent formation of ice all together. For ice crystals to form, they need something to start from. (Artificial snow needs nuclei for crystals to form as well). And animals use that to their advantage. By excluding nuclei (which serve as starting points for crystal formation) from their tissues (extracellular spaces and cells), they can allow their tissue temperatures to reach sub-zero values and not freeze. However, should a nuclei appear, no animal can move fast enough to escape the wrath of ice sludge. Milk shake anyone? This method is often complemented by anti-freeze method, by accumulating glycerol or some other substance with anti-freeze properties. I turn to those next.
A method known to many from various every day scenarios, like sprinkling of salt on roads in winter, or putting anti-freeze liquid into your car. Certain organic molecules like glycerol or some glycoproteins prevent ice crystals not from forming, but from becoming too large. As ice crystals grow, they can damage cell wall, which can have deletarious consequences. These molecules lower the temperature where these crystals start to grow.
Preemptive formation of ice crystals
This is a method where animals form crystals (sounds, silly and counter productive, huh? Bare with me), but not in the cells. Rather in extracellular spaces. How does this help, one might ask? As it turns out, by supplying nuclei (pl. for nucleus, as you might have figured out by now) to the intracellular space, crystals start to form, excluding solutes. This raises the osmotic pressure in the extracellular level which causes water to move out of the cells (through membranes) by osmosis which in turns rises osmotic pressure in the cells, lowering the freezing point! This protects the cells from forming ice crystals that can damage it.
Different cell types are differently resistant to ice crystal formation. This is why they can deep freeze blood and sperm, but not Disney. Another valid point! The speed of ice crystal formation is also essential. Faster = smaller crystals = better.