(Photo: Michael Zahniser)
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The wood frog (Lithobates sylvaticus) is a resilient creature. You can find it as far south as Alabama and as far north as Alaska and northern Canada. It's the only frog that lives in the wild north of the Arctic Circle.
How does an amphibian survive the harsh winters of those frozen lands? It freezes. Scientists working in Alaska found that local wood frogs can freeze solid for up to 7 months. When the ice melts, the frogs thaw and, amazingly, are still alive! Deborah Netburn wrote about this phenomenon last year in the Los Angeles Times:
"On an organismal level they are essentially dead," said Don Larson, a graduate student at the University of Alaska, Fairbanks who studies frogs. "The individual cells are still functioning, but they have no way to communicate with each other."
Larson is one of several researchers who published their findings in the Journal of Experimental Biology. They found that the frogs produce a lot of glucose during the winter, which keeps their cells viable:
The researchers also discovered that the frogs don't freeze once and stay frozen. Instead they spend a week or two freezing at night and thawing during the day, until the temperature drops permanently below freezing.
Larson thinks this thawing and freezing patterns helps the frogs convert more of the glycogen stored in their liver into glucose. This is essential because it is the high levels of glucose in the frogs' cells that keep them alive throughout the long, cold winter.
The glucose's main function is to keep water inside the cells. Frostbite in humans is caused when the water in our blood outside turns to ice. That hyperconcentrates the fluid around the cells and tissues, which in turn draws water out of the cells. Eventually the cells get so dehydrated that they die.
Larson offers this analogy: "If you put a potato in salty water, the whole potato kind of shrivels up because all the water from the potato goes to the higher concentration of salinity, but if you add a bunch of salt to a potato, it would retain its water," he said.
By making the cells super sweet with glucose, the frogs keep the water from leaving their cells.
This clip from the PBS series The Living Edens shows a time-lapse video of the process.
-via Oddity Central