Wood frogs have a creative adaptation to survive winter.
Think back to January and February, temperatures below freezing were common, snow was on the ground, and trees had long lost their leaves. For people, coats, hats, and gloves were needed to stay warm. These layers helped insulate the body from the cold and keep our body heat as close to our skin as possible rather than letting our body heat escape into the air. Wood frogs, and other amphibians in the Midwest; however, have a different strategy for getting through the winter months. Instead of keeping their body heat as close to their skin as possible, wood frogs have a evolved a unique adaptation to deal with the cold, they freeze!
A Clever Solution
Wood Frogs have one of the most expansive ranges of amphibians in North America, covering a wide array of ecosystems from Tennessee to just above the Arctic Circle in Alaska. This extensive range is mostly made of temperate forest and is prone to freezing during the winter. Frogs and other amphibians are cold-blooded animals, which means their internal body temperatures do not self-regulate. If the water in a frog’s skin cells begins to freeze and form crystals, it will damage the cells beyond repair, similar to frostbite in humans.
However, the wood Frog relies on a unique adaptation to survive the bitter cold of winter. Wood Frogs create a natural antifreeze by flooding their blood with sugar as the temperature drops, protecting their cells from the damaging ice crystals. It’s the same principle that gives the ice cream a smooth, creamy texture. Instead of being completely solid like an ice cube, the introduction of sugar in the ice cream making process keeps ice crystals from forming. The sugars act as an antifreeze, preventing ice cream from completely freezing. The sugar-flooding process will also slow down the wood frog’s metabolism, and enable the frog to survive several months without eating. Once the spring rolls around again, the frog will thaw, starting from its heart, and begin to revive bodily functions as if it had never been frozen.
While freezing and thawing do no serious harm to the frogs, there are however threats to their survival. The freezing process of wood frogs enables them to though out winters both through their unique adaptation to survive to be frozen and by being able to go several months without eating. But if temperatures don’t get low enough, wood frogs might not be in their frozen state and will need to consume insects and other bugs to stay alive. During winter, there are not many bugs and insects that wood frogs rely on for food. and a wood frog will die if it does not have enough to eat. With warming winters due to climate change, the likelihood of temperatures not going low enough for freezing to occur also goes up. This endangers the wood frog’s survival are temperatures in all seasons gradually increase.
Listen: The Nature Guys talk about wood frogs and how they freeze each winter
What humans can learn from freezing frogs
The study of life at low temperatures is full of practical applications. Among the more promising is the preservation of organs and tissues for human-to-human transplant. Many people need an organ transplant, be it a heart, liver, or kidney, to stay alive. The ability to freeze such organs, transplant them, thaw and revive the tissue would allow for their long-term storage and enable more people to receive such organs at a time when the kidney transplant waiting list has 93,000 people.
There is also the potential life-saving techniques called cryosurgery. Cryosurgery uses extremely cold temperatures for the removal of dangerous cells. By rapidly freezing cancerous cells, the water inside the cell will break the cell wall and destroy the abnormal cell tissue. Such surgery has been found to be most successful in the early stages of skin cancer and eye cancer.
The study of wood frogs is to study how nature got around the problem of surviving for long periods of time as an icicle. As that work continues, scientists will gain a better understanding of how cells survive low temperatures may be discovered, more applications could be discovered.