Natures wonders: Frozen frogs and more (Introduction)

by David Turell , Thursday, November 17, 2022, 21:18 (735 days ago) @ David Turell

A definite survival technique explained:

https://www.nationalgeographic.com/animals/article/animals-freeze-then-thaw-explained?r...

"The wood frog is one of the most frequently studied animals on Earth that freezes. When temperatures drop in the fall, it nestles in leaves and lets the cold creep into its body until it fully succumbs—heart, brain, and all. But it’s not the only species that essentially dies and then comes back to life.

"Thousands of insect larvae freeze and thaw, and some go back and forth every day depending on the weather. Young painted turtles manage to freeze without the same methods as the wood frog. And then there are tardigrades, which dehydrate completely and wait for spring.

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"This transition requires major changes in biochemistry. The frog’s microRNA molecules reorganize cells to protect them from damage. Ice then slowly forms around the outside of organs and cells. At the same time, the frog’s liver pumps out incredible amounts of glucose—a syrupy liquid that acts like antifreeze for vital organs—that seeps everywhere including the insides of cells to keep them from shrinking and dying.

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"But it’s not the only way animals freeze. According to new research published in the journal Science of the Total Environment, painted turtle hatchlings freeze as microRNA reorganize their metabolism in a way that requires significantly less glucose than wood frogs. And as adults, they don’t freeze so much as hold their breath. The adults hibernate underwater in mud where they can survive up to four months without breathing.

***

"Ice needs something to form around, otherwise known as a nucleating agent, which can be as small as a piece of dust or a cholesterol molecule. But if an insect or animal can ward off the formation of ice crystals, their frozen blood remains liquid.

"That’s a big if. Outside of a very controlled laboratory, our world is full of nucleating agents, Tessier says. The Arctic ground squirrel has been shown to outrun freezing by eliminating all potential nuclei for crystals to form.

"'Different insects have evolved different wants to accomplish this same goal. Gall fly larvae freezes solidly in the winter when it’s subzero and thaws when it warms, even over the course of 24 hours. Gall moth larvae, on the other hand, stay liquid during the day and night, Storey says.

"Gall fly larvae use sugar like the wood frog to buffer its cells from the damaging effects of subzero temperatures. Gall moth larvae use sugar to prevent freezing, essentially supercooling to as cold as negative 36 degrees Fahrenheit.

"Tardigrades, the microscopic invertebrates found in Earth’s most extreme environments, have found an inventive way to prevent water in their cells from freezing: They just expel it."

Comment: How did these tricks evolve? By steps a little colder each time. You get to a critical point when it freezes, and this is where the mechanism should work. But real cold is not the state of frozen. I think these are designed mechanisms.