Freeze tolerance and the dynamics of ice formation in wood frogs

Cooled wood frogs at controlled rates while monitoring the heat released as ice formed, measuring how much of the body water froze, how fast, and what proportion of animals recovered.

Studied in

Lithobates sylvaticus

Sample size

frogs frozen and thawed under measured cooling regimes

Around two-thirds of the frog’s body water froze, in extracellular spaces, over a period of many hours, and the animals recovered on thawing. Faster cooling and deeper freezing reduced survival sharply.

• Laboratory cooling regimes are more uniform than a natural leaf-litter winter.
• Recovery was scored over days; longer-term consequences were not followed.

• Freeze tolerance

  Freeze-tolerant animals make themselves freeze on purpose, at the highest sub-zero temperature they can manage. A slow freeze starting at −1 °C is survivable; a sudden one at −8 °C is not.

• Wood frog

  A frozen wood frog has ice through roughly two-thirds of its body water, no heartbeat and no breathing, for weeks — and thaws into a working frog. The ice is outside its cells, and it is flooded with glucose.