For days, even weeks weeks at a time during its period of winter hibernation, over 60 percent of the frog’s body freezes; it stops breathing and its heart stops beating. Its physical processes like metabolic activity and waste production come to a halt. “For all intents and purposes, they are dead,” said Don Larson, a Ph.D. student at Fairbanks, Alaska. As per his research, wood frogs can survive long winters where temperatures range between -9C to -18C. In fact, it can go through 10 to 15 freeze/thaw cycles over the course of a single season.
Researchers have discovered that the reason for this the miraculous phenomenon is the high concentration of cryoprotectants in the wood frog’s tissues. These are solutes – including glucose and urea – that lower the freezing temperature of the frog’s cells, helping them survive. In most animals, exposure to subzero temperatures for a long time could cause cellular shrinkage. During this process, water is pulled from the body’s cells to form ice, eventually sucking them dry and killing the cell. But with wood frogs, cryoprotectants help the cells resist shrinkage.
“The solutes tend to depress the freezing point,” said Jon Costanzo of the Department of Zoology at Miami University in Ohio. “It limits the amount of ice that actually forms in the body at any part.” Costanzo has been researching wood frogs for the past 25 years – he wanted to understand how the frog could function on a physiological and chemical level.
Thanks to the incredible wood frogs, medical researchers have discovered ways that living organs and tissues can be frozen and unfrozen without damaging them, which have had serious implications in areas like organ transplants. “There’s an obvious parallel between what these frogs are doing to preserve all of their tissues simultaneously and our need to be able to cryopreserve human organs for tissue-matching purposes,” Costanzo explained. “If you could 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.”