The new ice queen is… a frog

The tree frog survives long and harsh winters in Canada and the northern United States, and can completely freeze, thaw, and return to activity numerous times without harm.

By: Maya Givon

The tree frog Lithobates sylvatica is a species of the frog family that is common in North America, and was even chosen as the national amphibian of the state of New York, an honorable title without a doubt. The unprecedented cold waves that hit the region recently caused a lot of damage, but the national frog apparently survived them without difficulty, as it has an unusual ability to cope with freezing temperatures.

Plants and animals have different strategies for dealing with cold. Many of them avoid it by migrating or by finding a hiding place for the winter, or they go into hibernation in a relatively warm place, and delay their life cycle until the return of favorable conditions for their existence. But there are also those who do not run away or hide, but endure the stagnation.

Dealing with low temperatures by resisting freezing is a complex strategy: when the temperature drops below zero, the water in the blood freezes and forms small ice crystals. These may cause damage to the blood vessels, damage the function of the cells and lead to dehydration. An animal that is able to freeze and thaw must be able to protect its body from these damages.

The tree frog survives long and harsh winters in Canada and the northern United States, and can completely freeze, thaw, and return to activity numerous times without harm. During the stasis, her tone changes from brown to bluish, core activity ceases, and up to 65% of the amount of water in her body becomes solid. All physical activity, including breathing, stops, the metabolism drops and so the glacier-frog spends the winter in suspended animation until the air warms up again.

How does she do it? Two mechanisms help the frog: the first is control and control over the freezing process. The frog is able to create proteins that encourage freezing, and actually initiates the start of freezing from a controlled source in its body, so it can control the process and slow it down, thus allowing the body to adapt to the situation more gradually than in spontaneous freezing, which can be extremely fast. The second mechanism includes the production of a substance that prevents freezing: the frog stores sugars in high concentration inside the cells, so that the water leaves the cells and leaves a concentrated sugar solution in them, which prevents freezing and damage. Only the space between cells freezes.

Biologists hypothesize that these strategies are actually a combination of the frogs' adaptation strategies to dry conditions. Most amphibians have skin that is extremely permeable to water and therefore they also lose water very easily. Frogs that live on land have the ability to lose up to 50% of the fluids in their body and recover - an ability that does not exist in vertebrates.

The exact mechanisms that allow the frog to freeze and recover are still being investigated, and many questions are still open: How does the animal survive for a long time without oxygen? What are the triggers that start the freezing process - and more importantly, the thawing process? The road to a full understanding of these puzzles is still long, but the potential uses that can develop as a result of them excite the imagination...

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