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Lessons learned from frogs that freeze and thaw

NSF Award:

Physiological Mechanisms in Anuran Adaptation to Extreme Cold  (Miami University)

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A team of NSF-funded researchers has shown that Alaskan wood frogs (Rana sylvatica) survive the Alaskan Interior's harsh winter temperatures by freezing their body fluids. The ability to survive freezing at temperatures as low as -16 degrees Celsius (3.2 degrees Fahrenheit) rank the wood frog among the most cold hardy of all vertebrate animals.

The project provides details on the molecular, biochemical and physiological mechanisms for cold tolerance among populations of ectotherms (animals dependent on external sources for body heat) in different settings. Research on adaptive responses related to freeze tolerance may provide important clues in the development of technologies related to the cryopreservation of human tissues and organs. (Cryopreservation involves preserving cells or whole tissues using sub-zero temperatures.)

Although researchers have identified some of the mechanisms underpinning freezing adaptation in vertebrate ectotherms, it is unclear how animals from northern populations survive at extremely low temperatures. The wood frog is the most northerly distributed amphibian in North America and can even be found north of the Arctic Circle. Research indicates that profound freeze tolerance in Alaskan wood frogs derives, in part, from high levels of urea and glucose accumulated before and/or during freezing. These "cryoprotectants" serve to limit ice formation and cellular stress and injury incurred when the frogs freeze and thaw.

When the researchers compared the Alaskan wood frogs with a well-studied frog population from southern Ohio, they found that the Ohio frogs also accumulated cryoprotectants, but to a much lesser extent. The Ohio frogs were also less able to mobilize glucose quickly during freezing. The Alaskan frogs retained elevated levels of glucose long after thawing. This evidence suggests that when wood frogs moved into high latitudes, their freeze tolerance was achieved, at least partly, by enhancing their cryoprotectant system.

 

Images (1 of )

  • a frozen wood frog
  • a researcher collects wood frogs near fairbanks, alaska
A frozen wood frog.
Jon P. Costanzo, Miami University
A researcher collects wood frogs near Fairbanks, AK.
Jon P. Costanzo, Miami University

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