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Alaska Wood Frog (Rana sylvatica): Creature that Defies Extreme Freezing

Alaska Wood Frog

Alaska Wood Frog, scientifically called Rana sylvatica, is currently the hot topic in Experimental Biology due to its exceptional freeze tolerance. The wood frog, also known as tree frog, is indigenous to Northern Alaska and some parts of North America, particularly North Dakota, the Upper Midwestern states (Minnesota, Wisconsin, and Illinois), and to northeastern Alabama. A typical wood frog is smaller than the palm of our hand and in a five-year lifespan,  it spends almost three years in mostly solid frozen state!

Furry Frogs like Polar Bears?

The snow-covered Arctic world always brings the images of furry polar bears, reindeer, chubby seal, snowy owl, or the like. But, survival for a frog with no fur in the freezing Arctic? Yes, this is what Jon Costanzo along with other researchers has been researching on for more than two decades. In fact, he got interested in this unique species of frog when he came to know about its extreme freeze tolerance. His research has been published in The Journal of Experimental Biology where he explains how the wood frog was able to survive long winters in Alaska.

Living without the heart, beating?

During the winter, which starts in September in the Arctic, the Alaska wood frogs freeze themselves. More than two-thirds of their body water gets frozen and they virtually become semi solid. The absolutely incredible thing that the researchers tell us is that during this frozen state, the wood frog stops breathing! Can you imagine a living creature with a heart that doesn’t beat?

So, how they die in their sleep and come out alive when wake up?

Well, the scientists tell us that during the long winter hibernation, the wood frog almost entirely stops its bodily functions which include metabolic activity or waste production. For several times the frogs freeze and thaw during a typical winter. They do not freeze to death because of a substance called cryoprotectant: this is an anti-freeze protein that many Arctic insects, fish, and amphibians create in their bodies. This special protein helps them protect their body tissues from damage in the life-threatening Arctic winter. This life-saving protein lowers the freezing temperatures of vital cellular fluids like glucose or urea. And, the wood frog is found with higher concentration of cryoprotectant in it. This protein helps the frog come out alive and kicking after seven months of clinical death!

How the wood frogs keep their body alive?

During this long hibernation, as Don Larson, a graduate student at the University of Alaska, Fairbanks explains, “The individual cells are still functioning, but they have no way to communicate with each other.” In his experiment on these wonderful creatures, Larson discovered that at the beginning of the winter before the temperature falls below the freezing point, the wood frogs go through a pattern of freezing and thawing. As Larson believes, this thawing and freezing helps the frogs convert glycogen into glucose which essential for the life in the individual cells. High concentration of glucose inside the cells does not allow the cellular water to freeze and dehydrate.

At the end of the winter, the Alaska Wood Frog follows the same process in reverse. It starts breaking the glucose into glycogen. All the required glycogen is extracted from the glucose stored in September and the extra is disposed off through urination. The body goes back to its natural state with the primordial urge for self-preservation: the Alaska Wood Frogs desperately look for partners and start mating once meet the cherished ones.

Lessons from the Alaska Wood Frog?

Certainly there is something very important that modern medical science may learn from the wood frogs: how to freeze and unfreeze vital human organs before transplanting them without any damage done? May be the time is not that far when science would find out the secret formula from the wood frog and implement that in preserving human organs for transplants in future. As Costanzo tells, “[the ability to] freeze human organs even for a short period of time, that would be a major breakthrough because then these organs could be shipped around the world, which would greatly [improve] the donor-matching process”. The Alaska wood frog is certainly a wonder of Mother Nature: check out this video!





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