Freeze Tolerant Frogs!

Since a lot of our posts seem to be about cool organisms and how they can be beneficial to humans, I thought about one that I was interested in a few years ago. There's an amphibian that undergoes freeze-thaw cycles due to its surrounding arctic environment and lives through it! Normally, animals would migrate to warmer climates or hibernate for the winter, but the North American wood frog (Rana sylvatica) buries in the leaves and allows itself to freeze in suspended animation. They are able to survive weeks at a time without a beating heart and brain activity. When the temperature drops, urea concentrates in the tissues and their liver produces mass amounts of glucose and packs it into the cells to prevent intracellular ice formation. When water turns into ice, it forms ice crystals, which are harmful to cells causing shrinkage and cell death. Obviously, this must be avoided in order to survive freeze thaw cycles. Therefore, the urea and glucose are used as a cryoprotectant to lower the freezing temperature in the tissues. However, it has been suggested that enduring many freeze thaw cycles could result in significant energy depletion and be fatal to the frog. Applications for this freeze tolerant ability include aiding human organ transplants and cryopreservation of whole humans.

http://voices.nationalgeographic.com/2013/08/21/how-the-alaska-wood-frog-survives-being-frozen/

http://news.nationalgeographic.com/news/2007/02/070220-frog-antifreeze.html

https://www.youtube.com/watch?v=Fjr3A_kfspM


They are able to do this with special proteins in their blood called nucleating proteins.