Frozen Frogs: How Tiny Amphibians Survive in Alaska

A researcher from the University of Alaska Fairbanks is conducting what is thought to be the first live field study of wood frogs - freeze tolerant amphibians who can survive extremely low temperatures until the spring thaw.

"Alaska wood frogs spend more time freezing and thawing outside than a steak does in your freezer, and the frog comes back to life in the spring in better shape than the steak," Don Larson, the lead author of a recent paper detailing this freeze-tolerance, joked in a recent release.

But culinary humor aside, Larson has revealed some striking findings about the tiny amphibians.

In subarctic Interior Alaska, where temperatures can remain below freezing for more than six months, these frogs winter simply by allowing themselves to get frozen. Cells traditionally die when frozen because ice formation pulls water out of the cells, desiccating them and leading to death.

"Imagine what happens when you suck on a freeze pop," said Larson. "After you've sucked out all the sweet stuff, you're left with just ice."

And "just ice" sure isn't living. However, past studies of wood frogs has revealed that their cells are capable of holding a remarkable amount of glucose, which serves as an extra supply of "sweet stuff," effectively preventing the freeze-pop effect.

Interestingly, Larson's field study revealed that wood frogs in the wild were surviving colder temperatures than ever thought.  Data showed an almost 10-fold increase in glucose capacity compared to lab samples, with a nearly 100 percent survival rate.

So how was this happening? Larson theorizes that repeated on-off flash freezing can help build up a "freezer-burn" like layer of additional protection around cells.

"In the field in early Autumn it's freezing during the night, thawing slightly during the day, and these repeated freezing episodes stimulate the frogs to release more and more glucose," Larson said. "It's not warm enough for long enough for the frog to reclaim much of that glucose and over time it accumulates giving the frog more protection against cell damage."

According to Larson, understanding this feat may help humans one day preserve organs for extended periods of time, aiding transplant banks.

"If science can figure out how to freeze human organs without damage it would allow more time to reach people in need of organs."

The study was published in the Journal of Experimental Biology.