Frog freezes, flatlines, comes back to life
Wood Frog (Rana sylvatica) by telemudcat on flickr
Let’s suppose you’re a frog. And a real eccentric one too, who decided to live in areas where it’s cold and icy – even north of the Artic Circle. What would you do to survive? As a cold-blooded creature (ectotherm) your body temperature decreases when the ambient temperature drops. Unlike toads frogs can’t dig deep burrows to overwinter. If you decide to spend the winter on land you have to hibernate in damp leaf litter to prevent drying out. But when it turns subzero the ice reaches you quickly and as soon as it touches your water-permeable skin you start to freeze. Your heart stops beating, your brain stops working and in the end more than two thirds of your body water is frozen solid. In form of a frog-shaped ice-cube you lie on the ground.
Then it thaws – and you come back to life within an hour. You’re freeze tolerant.
Frozen Wood Frog
Laboratory studies have shown that wood frogs can survive: (a) the freezing of up to 65-70% of their body water; (b) a minimum body temperature of -6°C; and (c) uninterrupted freezing for >= 4 weeks (Jon Constanzo et al.)
How does the frog do it? Well, the North American wood frog (Rana sylvatica) is one of very few amphibians that hibernate in a frozen state. The liver of these animals makes glucose (dextrose), a natural antifreeze, which is circulated to the cells. This way the ice only forms in the extracellular spaces but not inside the cells. Without the glucose water would also be sucked out by the ice outside which would cause dehydrating and shrinking of the cell. The greatest wonder is that the frog freezes and thaws without serious damage to it’s tissues.
What could this frog possibly gain from turning into a “frog-sicle”?What could we humans learn from this Cryonic-Expert?
To learn more about this incredible creature watch the following video and check out the interview with the Expert Jon Constanzo at pbs.org
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