Slide 1
A wood frog survives ice in part of its body water
Wood frogs survive winter conditions that freeze part of their body water. This is freeze tolerance, not every cell becoming a solid block.
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Ice forms mainly outside cells, where its effects can be managed. Avoiding destructive ice inside cells distinguishes surviving freezing from simply being damaged by cold.
Slide 2
Stored carbohydrate becomes cell-protecting glucose
As freezing begins, a wood frog converts glycogen, a stored carbohydrate, into glucose, a sugar. The dissolved sugar helps protect cells during the freezing process.
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The response involves the liver and circulation before full freezing develops. Timing matters because protective compounds must reach tissues while transport through the body remains possible.
Slide 3
Normal activity and circulation fall during freezing
A frozen wood frog is not feeding or hopping. Its normal activity and circulation are profoundly reduced during the frozen state.
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This is a seasonal survival strategy, not an extra period of active life. The animal relies on stored resources and must tolerate stresses associated with freezing and thawing.
Slide 4
Warming allows surviving tissues to resume activity
When conditions warm, a surviving frog thaws and resumes activity. Recovery depends on tissues remaining functional through the cold period.
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Repeated natural freeze-thaw cycles affect protective chemistry. Research on wild frogs therefore adds information that one short laboratory freeze cannot fully represent for every population.
Slide 5
Temperature, duration and condition still limit survival
Wood frog populations differ in the cold conditions they experience. Survival limits depend on temperature, duration and the animal's condition.
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The adaptation should not be generalized to all frogs. Many amphibians find places that avoid severe freezing rather than tolerating ice within their bodies.
Sources
- Amphibians at Denali
National Park Service
- Host-parasite ecophysiology of overwintering
University of Alaska Fairbanks