Freeze Survival: North American Frogs' Cryogenic Adaptation

Several North American frog species, including the wood frog, spring peeper, and gray treefrog, possess the remarkable ability to survive being frozen solid for extended periods. During winter, up to 65% of their body water turns to ice, their hearts stop, and all visible signs of life disappear, yet they thaw and resume normal activities when spring arrives. This freeze tolerance is achieved through sophisticated biochemical preparations: their livers produce massive amounts of glucose (up to 250 times normal levels), along with urea and other cryoprotectants that protect cellular structures while allowing ice to form safely between cells. These frogs can endure multiple freeze-thaw cycles, with Alaskan wood frogs surviving temperatures as low as -18°C for over seven months. This adaptation varies geographically within species and has attracted significant medical research interest for potential applications in organ preservation, treatments for ischemia, and cryonic preservation technologies.

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