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Zombie Frogs: These frogs freeze for months, then come back to life

Essentially, these frogs freeze to death for half a year and come back to life when the weather is warmer.

Every September the frogs of the Alaskan forests do something unique; they lower their body temperature until they are completely frozen. Two-thirds of their body water turns to ice, and they become completely immobile, so much so that if we were to pick up a frog in this state and bend one of its legs, it would simply break. But there is something even more surprising, and that is that they can survive in this state for more than half a year.

Frogs freeze for months

It is well known that there are species that prepare themselves to get through the harsh winters; many of these species dig burrows and go into them to hibernate until the warmth emerges again. But Alaskan wood frogs take this behavior to the extreme; they not only hibernate, but also cryogenize.

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It is to be expected that truly amazing physiological mechanisms take place within their bodies. Starting with the most extraordinary response that seems to go totally against life, their hearts simply stop beating. The most immediate consequence is that blood no longer flows through the rest of their bodies, and their glucose levels shoot through the roof.

“At the organismal level, they are essentially dead,” says Don Larson of the University of Alaska, Fairbanks. “The individual cells are still functioning, but they have no way to communicate with each other.”

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In their cryopreserved state, Alaskan wood frogs can withstand extreme temperatures as low as -17°C for seven long months. And then, when spring peeks above ground, the frogs simply return to life by thawing their organisms and continuing their daily lives.

Excessively long freezing periods

Frogs are abundant in areas around the Arctic Circle, and it was previously known that some species are capable of remaining frozen for a couple of weeks at a temperature of -6°C; however, Alaska has much more extreme weather conditions than that. For this reason, the researchers became interested in the frogs of this region and proved their theories; Alaskan frogs can cryogenically freeze for excessively long periods of time of up to seven months.

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During the research that lasted more than two years, in which they analyzed specimens of Alaskan wood frogs, they discovered that the frogs do not freeze for good, but do so gradually. They spend a week to two weeks, freezing at night and thawing during the day until the temperature drops below freezing.

This is how they remain frozen for long seven months until spring arrives and the frogs simply spring back to life. Then they rush to the nearest pond and begin their mating season, which makes sense since they only have five months to ensure that their species has enough offspring to survive in harsh Alaska.

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Story originally published in Spanish in Ecoosfera

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