#53 - Critters Surviving Extremes
After my recent trip to Antarctica, I became interested in the extremophiles, the critters that it seems can survive almost anywhere.
Heat
There are only so many neat tricks for surviving in extreme heat. Elephants' ears aren't just big and good for flapping away flies. They are thin and filled with fine veins. Flapping their ears creates evaporative cooling. Other critters will lick saliva onto the legs and bodies to take also take advantage of evaporative cooling. Some of them, including the elephants and humans, will vasodilate their capillaries near the skin's surface to move the hot blood to somewhere it can cool off.
Camels, gazelles, and several of their relatives use a neat trick. The veins (blood delivery) and arteries (blood return) run side-by-side. This allows arterial blood, especially that which circulated through the nostrils, to pre-cool the veinous blood bound for the brain.
When it gets too hot, it's only the extremophiles that survive, like the worms living at deep-ocean volcanic vents. At the first level, they generate and fill their cells with a sugar called trehalose. Basically, vitrifying their cells into a glass-like structure, so that they don't break down in the heat. Then the crazy little dude called a tardigrade goes one step farther. It will actually exude all of its water, so that its cells don't boil, and can survive heat up to 150°C in this state. Cool it down, drip some water on it, and they're back in gear.
Cold
These little guys, most less that 0.5mm long, are also the kings of cold. Using the same trick. They can survive being frozen in Antarctica or exposed to outer space. Warm them up, dribble on a little water, and they recover almost instantly.
But micro-life isn't the only one with cold tricks up their sleeve. Ever see flamingos or gulls standing on one leg? They can stand in freezing water. But in the reverse of the camel's trick, they have built-in heat exchangers in their legs. They use the hot heart blood to pre-warm the returning cold blood before it reaches their body and heart which would cause excessive cooling.
There are three main strategies for dealing with deep cold.
Dehydration: like the tardigrade above. If it doesn't have any water in its body to freeze and turn into damaging ice crystals, it's fine.
Anti-freeze: Again, sugars comes into play, typically glucose and glycerol. The liver of certain frogs, turtles, or the Antarctic cod--when trapped in the ice--will produce large quantities of these sugars and pump them into the cells. Nature's anti-freeze.
Metabolic shutdown: The tree frog, the caterpillar phase of an Arctic Wooly Bear moth, and a few others can completely shut down their metabolism. Nothing. No heartbeat, no breaking, nada! The caterpillar can survive multiple seasonal freezes down to -70°C until it thaws into a breeding season that has the most favorable conditions for success.
And there's one screwy one, the Antarctic Ice Fish. They evolved to not have any hemoglobin in their blood (the only vertebrate that can claim that). Hemoglobin causes blood to become all viscous when it gets too cold, so they decided not to bother with the stuff. They have to pump far more blood around to move the oxygen they need to the individual cells, but it gains them tolerance for a few crucial degrees below freezing to prowl the Antarctic waters.
So, next time you're feeling cold, consider plasticizing your cells with glycerol and entering a long period of cryogenic stopped metabolism. Of course, I'm left to wonder, will they still dream?
