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Natural antifreeze prevents frogsicles

Sugar and other chemicals keep Alaskan frogs from freezing completely

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A body full of natural antifreeze helps Alaskan wood frogs weather winter’s chill, biologists report August 21 in the Journal of Experimental Biology.

Less ice formed in the skin and muscles of Rana sylvatica frogs living in Alaska compared with those of the same species from Ohio, the researchers found. The Alaskan frogs’ ability to fend off the cold may stem from having more freeze-preventing chemicals in their blood and tissues.

Wood frogs’ range spans a broad swath of North America, from Georgia up through Canada and into Alaska’s Arctic forests. The average January low for the Alaskan frogs’ home is ‑28° Celsius. In Ohio, lows typically reach only ‑5°.

Scientists knew the frogs could withstand the cold, but no one understood how the animals living farther north had adapted so well to frigid temperatures. To find out, Jon Costanzo and his colleagues at Miami University in Oxford, Ohio collected wood frogs from the two regions and examined their bodies after freezing and thawing them in the lab.

The team found higher levels of sugar, urea — a waste product in urine — and another unidentified chemical in the Alaskan frogs. The researchers suggest that deploying these chemicals throughout the body lowers the Alaskan frogs’ freezing point so they don’t turn into frogsicles as temperatures drop.

A wood frog, Rana sylvatica (shown), survives freezing winter temperatures with a kind of biological antifreeze that prevent ice from forming in its blood. In this time-lapse video, a frog frozen for 24 hours takes 10 hours of thawing to spring back to life.
Credit: Jon Costanzo/CompanyofBiologists

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