While most animals will try to avoid freezing at all costs, some species of frog are actively encouraging it.
The wood frog (Rana sylvatica) is one of a handful of freeze-tolerant animals with adaptations to cope with freezing for up for 4 weeks. And within hours of defrosting the frogs are back to their usual selves again.
Freezing is particularly dangerous to living things because the formation of ice crystals can cause damage to cell membranes. It also draws water out of cells and deprives them of oxygen. Special adaptations in the Wood frog allow it to cope with these stresses. Cryoprotectants are substances which help to reduce the damage caused by freezing, and include glucose and urea, the main constituent of urine. At sub-zero temperatures wood frogs mobilise these cryoprotectants, which reduce ice formation and maintain oxygen supply to tissues. Genes also have a role to play, and several novel proteins have been found in the tissues of frozen frogs, which are not produced under warmer conditions.
Understanding freeze-tolerant frogs has helped improve medical techniques, and for the first time organs have been successfully frozen and defrosted before transplantation. Frozen frogs may have revolutionised the organ donation and transplant system
Want to Know More?
- Wood Frogs
- Storey and Storey (1996) Natural Freeze Survival in Animals
- National Geographic: Antifreeze-Like Blood Lets Frogs Freeze and Thaw with Winters Whims
Featured image used under a creative commons licence from Wikimedia commons. Original image by Bryan Gratwicke.