What special tricks do creatures living in cold areas have?

★ Short-term quick freezing will freeze animals such as toads and fish, but if they are warmed up in time, they will not be fatal.

★ Freezing can cause ice crystals to form in the water within cells, causing damage to the cells such as rupture and leading to the death of the animal.

★ In order to resist freezing, animals such as the North American wood frog, Greenland moth, and water bear have a set of unique tricks for "resurrection after ice."

Recently, a hilarious video became a hot topic. A woman from Jilin accidentally caught a toad while casting a net to catch fish. The temperature was below -20℃, and the toad was frozen into an "ice sculpture" in an awkward posture after just a few jumps... Fortunately, the woman immediately put it back into the water, and the toad finally recovered and swam away.

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There are many short videos with similar content, such as a person opening a freezer and taking out a fish wrapped in ice and frozen hard. After an explanation, he throws the fish into the water. When the ice on the fish slowly melts, the fish comes back to life!

Animals such as toads and fish can indeed be revived within a short period of time after being quickly frozen. This is mainly because only the surface of their bodies is frozen, and their internal organs have not yet been frozen and damaged. If the time is too long, they will still die.

So, what causes animals to die from freezing?

The damage caused by freezing to biological organisms is mainly to cells. If the body of an animal is frozen, the cell fluid in the cells of the animal will freeze. When water turns into ice, its volume will increase, and sharp ice crystals will often be produced, which will cause cells to be "burst", causing irreversible damage to the body.

Fish caught in winter cannot live in the ice. | Tuchong Creative

In addition, when cells freeze, the exchange of substances between cells will stop. More importantly, it means that there is no water in the organism, almost all metabolism will stop, and the carrier of organic life - protein will also denature, and the animal will lose its life.

However, there are also many small animals that can survive freezing. To this end, they can be said to be eight immortals crossing the sea, each showing their magical powers. The following are some typical ones.

01

The forest frog that comes with its own "antifreeze"

Many members of the wood frog family are relatively "cold-resistant", such as my country's Northeast Wood Frog and Heilongjiang Wood Frog, which have strong cold resistance. However, their relatives in Alaska, Rana sylvatica, also known as the "North American Wood Frog", can actually freeze themselves for 8 months, and when the spring comes, they are still like normal frogs, and they are still in good health and eat everything they want.

Although it does not have the unique skills of the North American wood frog, the Northeast wood frog is also very resistant to cold. | Tuchong Creative

Frogs are cold-blooded animals, and their body temperature changes with the temperature. Most cold-blooded animals will freeze to death if they cannot maintain their body temperature after the temperature drops to freezing point. So how does the North American wood frog prevent damage caused by freezing?

The secret of the North American wood frog's cold resistance is that it has two antifreeze substances. One is urea and the other is glucose. During the freezing process, the North American wood frog can release urea and glucose into the blood and transport them to various organs throughout the body through the blood. When the concentration of these two substances in the body increases, the freezing point of body fluids can be lowered to slow down the freezing of the body.

When the ambient temperature drops below freezing, the body surface of the North American wood frog will slowly be covered with a layer of ice, and its body will slowly freeze. At this time, the ice nucleation protein in its body will be activated. The function of this protein is to freeze the ice outside the cell, thereby preventing the formation of larger ice crystals inside the cell to avoid cell damage. When the water outside the cell freezes, the water inside the cell will seep outward due to the osmotic pressure, causing the cell to dehydrate, thereby avoiding damage when the body is frozen.

Few people live in the cold Alaska | Tuchong Creative

The freezing period in Alaska not only has a temperature close to -20 degrees Celsius, but also lasts for up to eight months. During this period, the North American wood frog needs its specialized liver to survive.
The huge liver is also the key factor in its successful "freezing". The North American wood frog uses the liver to store sugar as energy to sustain life. When the long winter ends and the temperature rises, the ice in the North American wood frog gradually melts and it can wake up again.

02

The tenacious and long-lived tiger moth

In the Canadian Arctic Archipelago, Greenland and Russia's Wrangel Island, there is a moth: Gynaephora groenlandica, known as the Greenland moth. It also has an extraordinary ability to resist freezing.

Insects generally have a short life cycle and are afraid of cold, but the larval period of the Greenland moth is as long as 7 years. Living in high-latitude areas, it is very cold most of the time, and plants only germinate for a short period of time in a year. Its larvae can only use this short window period to eat and replenish the energy for metamorphosis. It will not pupate until the summer of the seventh year, and then metamorphose in the spring of the second year. After metamorphosis, the female moth can hardly fly, and relies on the pheromone it emits to attract male moths to mate. After mating, the female moth will lay eggs, and when the eggs hatch, another 7-year cycle will begin.

After research, scientists found that this insect can withstand temperatures as low as -70°C. When the temperature drops, it will excrete excess water from its body to maintain a very high concentration of body fluids. At the same time, the larvae's host plant contains an alkaloid called pyrrolizidine, which causes the larvae to produce juvenile hormone. Some scientists believe that this alkaloid can help the larvae expel excess water from their cells, thereby enhancing their ability to resist freezing.

Plants containing pyrrolizidine are harmless to insects but are hepatotoxic to humans. | Tuchong Creative

03

The water bear is so strong that it is unfair

When talking about "tough" creatures, many people may think of tardigrades. This little guy can easily survive in outer space or boiling water.

A scientist once conducted an experiment in which he placed a tardigrade in liquid air at -200 degrees Celsius for 20 months, then placed it in liquid nitrogen at -253 degrees Celsius for more than 26 hours, and then soaked it in liquid helium at -272 degrees Celsius for 8 hours. He thought that this would kill the tardigrade, but after fishing it out, he found that the ice in its body melted quickly and it soon revived.

Water bear | Tuchong Creative

When water bears encounter a harsh environment, they curl up and expel most of the water in their bodies, entering a state called "cryptoecology". At this time, the water bears are like being paused. There is also a damage-inhibiting protein in the water bears' bodies, which can act as a "shield" to protect the cells from damage when the water bears' cells may be damaged. The ability of animals to resist freezing is the result of their adaptation to the environment during tens of millions of years of evolution. Scientists have gained a lot of inspiration from their research on them, and these achievements are contributing to the benefit of mankind. Maybe one day, when the "cryonics freezing" technology matures, interstellar travel will no longer be a dream.

Author | Li Weiyang, science writer

His works have been published on Guokr.com, State Forestry Administration, China National Geographic, "Bowu" magazine, Juvenile Science Magazine, etc.

Review | Huang Chengming, Researcher, Institute of Zoology, Chinese Academy of Sciences

Editor | Jiang Fan

Editor | Ding Zong

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