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A turtle under the ice. Photo: <a href="http://www.flickr.com/photos/90434877@N00/3206736457/">Richard Due</a>. Creative COmmons, some rights reserved
A turtle under the ice. Photo: Richard Due. Creative COmmons, some rights reserved

Natural Selections: How do turtles survive a winter underwater?

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Unlike frogs, turtles don't hibernate through the winter. In fact, sometimes you can see snappers and other species moving around under the ice. While their metabolism runs at very low ebb in the cold, they remain alert to changes in light and temperature that signal the coming spring.

How do they survive without oxygen? As Paul Smiths College biologist Curt Stager tells Martha Foley, they get energy from their body tissues, and their shells neutralize the resulting lactic acid build-up.

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Martha Foley: Winter turtles. So I've always assumed that turtles, like frogs, go down and stick their heads in the mud and go into some sort of semi-torpor and then come up in the spring.

Curt Stager: I always though the same thing, too. Then I had a chance conversation with one of my colleagues at Paul Smith's College, Bob Brell, and he said that someone had been seeing snapping turtles under the ice.

MF: Moving around?

They can spend month after month sitting in the mud or on top of the mud, barely breathing at all, their heart barely beating at all.
CS: Moving around. So I thought, wow, I'll start looking thigns up and It turns out that's not that uncommon. Painted turtles can be under there too. So that's really strange. Usually they're not that active. But also even those that are sitting there on the bottom, let's say snapping turtles, they have a reputation for being able to kind of shut their bodies down. They can spend month after month sitting in the mud or on top of the mud, barely breathing at all, their heart barely beating at all. And then you wonder, if they're shut down that much to conserve energy and whatever, without a lot of oxygen, how in the world do they not suffocate and how do they know when to come out of their rest if they're shut down? How do they know it's spring?

MF: Well I would say the ice goes away, and the sun starts shining on them, and somehow they sense the change of the season.

CS: So that was one of the neat new research tracks. People are realizing they're not completely shut down; anything they don't need is shut down, but things like sensitivity of their eyes to light, will stay. So they're actually vigilant, visually. If the light levels go up at all, their eyes pick it up and it starts turning on parts of their nervous system and their genes…They can kind of tell when the ice lid is gone. And they can go up to breathe if they wanted to.

MF: So if you get a big thaw in the middle of winter?

CS: That will be part of it, but then the other thing that has to happen is also the water temperature has to go up a little bit, and that speeds them up enough so they start moving. But then as part of that study it's like, 'ok, that's neat…but how do they survive under there?'  With so little oxygen, let's say a stagnant pond. One of the other kinds of study done on the snapping turtles, how they make it, is when you're down their without a lot of oxygen, if you shut yourself down, you can barely stay alive without oxygen and burn off a little bit of your body fat, sugars, and things. But if you do that, you build up a waste product, something that we get when you work out too hard and your muscles get cramped.

MF: Sure, your lactic acid builds up, right?

CS: Yes, the lactic acid builds up from that. The way they deal with it because they've got this heavy shell with a lot of calcium and carbonates in it that neutralize acids. So it actually helps maintain their body chemistry with their shell, so in addition to protection, their shell and actually their bones too will help maintain their body chemistry while they're living like this.

MF: What about a softshell turtle?

CS: That's kind of neat, too, because they don't have that heavy shell and they don't have so much calcium and carbonates to help counteract the acids.

MF: So they're not as common, either?

CS: One of the ideas is: the reason you won't find soft-shells in a stagnant pond, let's say, with the snapper, is that they can't do this low oxygen thing that builds up the lactic acid. When they're shut down, they still have to have oxygen in the water so this doesn't happen to them. One of the neatest things is there is another kind of turtle, the painted turtle, they have an even tougher time. They spend the winter on land, in their nest.

MF: The babies? Just the babies?

CS: Yeah, just the babies. They hatch out but they don't come out of the ground in the fall like the snappers do. They'll stay in their nest and have to deal with all of that stuff, and emerge in the spring.

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