Chilled out animals
It’s not just humans that have had to adapt to life at low temperatures - other animals do too, of course. And evolution has endowed them with an array of mechanisms to enable them to cope - and flourish - in the freezing cold. Lloyd Peck studies them with the British Antarctic Survey in Cambridge, and he spoke to Chris Smith live in the studio...
Lloyd - There are some animals that can be put into liquid nitrogen and they go solid - they don't freeze, they vitrify, they go like glass and these are nematode worms and tardigrades. And you can take them down to below -90, they vitrify, you warm them up, they become liquid again and they function absolutely normally. That's not exactly living at low temperature but it's surviving very very low temperatures.
Chris - How do they do it?
Lloyd - They do it because they're very small and because their composition is one that allows them to go down to low temperatures very very quickly. And that means they don't have the problem of ice crystals growing in them because they cool so fast that they just turn into the equivalent of a glass.
Chris - So some bits of the body of a larger creature are going to be at a still relatively warm temperature when other bits are at a very low temperature and it's that that causes part of the problem then? Whereas if you're really small, you lose heat really quickly, everything gets cold all at once and you freeze solid?
Lloyd - That's just about the right answer, yeah. Once you get above a certain size then the cooling is at a rate whereby ice crystals can form. And those ice crystals are the real problem for organisms that are trying to live at low temperatures because the ice crystals break the cells, they break the tissues and that damage inside the animal is what kills them off at the low temperatures.
Chris - But there are some much bigger animals that do successfully freeze, aren't there, things like frogs that can tolerate being frozen absolutely rigid?
Lloyd - Yeah. The Canadian wood frogs are about the biggest. And in the wintertime they freeze and you can take them into the laboratory, you can take them down sub zero temperatures, they freeze solid. They're just like an ice lolly.
Chris - They don't taste as good I bet though?
Lloyd - Well, I've never licked one and tried to taste one, and I wouldn't advise anybody to try and do that. But their consistency is very much like a...
Chris - How do they do it then? How are they succeeding, whereas if I put my strawberries in my freezer they definitely don't re-emerge looking the way they went in?
Lloyd - The way that the frogs do it is they specifically allow the water that is outside their cells to freeze and they use a range of chemicals to stop the cells themselves freezing. So there cells stay completely intact and they use chemicals to do that are called cryoprotectants, and it's the freezing of the water outside the cells that makes them go solid. During the wintertime, their metabolic rates drop really low, they use very little energy. Come the spring, they can defrost but there cells have maintained a liquid environment throughout the whole of that. Other groups of animals, they use similar chemicals to these what are called cryoprotectants to stop the body freezing and they survive at low temperatures by staying liquid all the time, and they use those chemicals and call them antifreezes.
Chris - It's an interesting adaptation then; you either put yourself into a frozen state so you don't need to go find food when conditions are just not very amenable to life in general with the ability to thaw yourself out afterwards, or you do decide to stay liquid and you have to evolve to have some pretty clever strategies to do that. Can we use that science though, because I can think of lots of examples where actually working out how these animals are doing this could turn into much better ways to freeze my strawberries or popsicles and things?
Lloyd - Yeah, it's not so easy with things like strawberries. But we currently use the antifreeze from Antarctic fish to make our ice cream very smooth. And 10 or 15 years ago there were real issues with making ice cream smoother because you wanted to control the size of the ice crystals, and the technology we had then wasn't really very very good at doing it.
Chris - Is that what gives you smooth ice cream then, smaller ice crystals?
Lloyd - Yes. If you can keep the ice crystals small, the ice cream stays smooth. And what we do now is we get the ice crystals to a certain stage, we put in antifreeze that comes from Antarctic fish that we culture in biotechnology, and that keeps those ice crystals at the size that we want, and it makes our ice cream very very smooth compared to what it was.
Chris - So there you go, there's a bit of science you can lick. You wouldn't go near the frog, but you'll eat an ice cream from an ice fish.
Lloyd - That's right. And you are, in fact, licking a bit of what's come from the technology based around an ice fish, that's right.
Chris - But turning to Antarctica again, which is somewhere you’ve spent a lot of time studying, you have sitting on the table in front of you something that looks pretty awesome. It’s the size of a dinner plate, what's that?
Lloyd - Well actually, I've got two things on the table in front of me. One is about 5 mm across and that one is one of the biggest sea spiders in the UK. But next to it is the one that you were talking about before which is an Antarctic sea spider. I'm holding it up now; it's about a foot across, and it's not one of the biggest Antarctic sea spiders. The biggest ones that we get in the Antarctic are over 2 feet across and they're at least 5,000 times heavier than the biggest sea spiders that we have in the UK.
Chris - So why the difference then? This thing lives in very cold conditions, the other one lives in much warmer conditions but is a lot smaller, why?
Lloyd - The difference is that as the temperature goes down, the metabolic rates of animals that are cold-blooded and are the same temperature as their environment go down. The temperature slows down their chemical reactions in their bodies, it slows down their metabolic rates. So in Antarctica the metabolic rates of the animals living there are 20 to 30 times slower than animals in the tropics in the sea. There's also more oxygen in the water; there's roughly twice as much oxygen in the water in the Antarctic as there is in the tropics because it's more soluble at low temperatures.
Chris - But those animals don't scuttle around a lot slower despite having a lower metabolism do they?
Lloyd - They do.
Chris - I've seen them moving, they don't move very very slowly.
Lloyd - Absolutely. But if you compare them with a similar sized animal in temperate zones they're moving around 3 to 4 times slower than the similar animal...
Chris - And that's just energy?
Lloyd - That's a whole range of things but it's the slowed physiology. It's the energy available, and that more oxygen and that slower use of the oxygen means they can get up to 5,000 times bigger on a weight basis.