After surviving 90 years buried in the frozen soil of Siberia, a tiny salamander has turned the spotlight on one of the miracles of the natural world. We are only beginning to learn how animals adapt to extremes.
One autumn day in the early 20th century, a tiny Siberian salamander (Randon sibiricus) burrowed beneath the surface of the Siberian soil, in search of protection from the frosty climate and the coming winter. This was part of the animal’s natural yearly cycle, for winter temperatures in Siberia can plunge as low as -70 degree Celsius. Consequently, cold-blooded animals, such as salamanders, newts and frogs, must find protection if they are going to last through the long winter until the arrival of spring.
This particular winter must have been extremely harsh, as the animal was literally frozen solid, even though it had buried itself very deeply. The 12-cm-long amphibian was found by a gold prospector in a block of ice at a depth of nearly 9 m. When told of the find, Russian biologists hurried to the site. After freeing the animal from the ice, they were surprised to see signs of life. Eventually, the salamander stirred and set off in search of new adventures on the Arctic tundra.
Daniil Berman and his colleagues from the Biological Institute in Magadan, eastern Siberia, used radiocarbon dating to find out how long the salamander had lain in its burrow. This procedure analyses the amount of carbon-14, a radioactive carbon isotope which is naturally present in the soil and corresponds to the carbon-14 content of the atmosphere. Based on the amount of decay recorded in the carbon-14, they concluded that the creature had slept for 90 years.
Few animals can survive such extreme conditions, for each organism contains a high proportion of fluids, which freeze at low temperatures. For example, the human body consists of up to 60% water. If it freezes, ice crystals form in the cells, causing irreparable internal damage to the cell membranes. Ice crystals outside the cells act like a pump to draw the body’s vital water from its cells.
To wake up after 90 years in a deep freeze requires incredible survival strategies. If we look closely at the Siberian salamander, we find that it has a relatively strongly developed liver, which makes up about a third of its body weight and stores plenty of glycogen (carbohydrates), also known as animal starch. When winter sets in, the liver converts these stored carbohydrates into glycerine, an alcohol compound. The presence of glycerine lowers the crystallisation temperature of water, preventing the formation of ice crystals in the animal’s body. The glycerine acts as a natural anti-freeze, allowing the salamander to burrow into the permafrost (permanently frozen soil), where it can wait for spring. Another example is the North American wood frog (Rana sylvatica), which also endures extreme cold in winter. This amphibian can tolerate temperatures as low as -8 degree Celsius. Its natural anti-freeze system makes use of glucose, a form of sugar.
Scientists are interested in the ways organisms adapt to extreme living conditions. Even though cellular anti-freeze has been identified, its uses are limited. At present, it only possible to preserve some tissue and cells – for example, blood vessels, sperm, embryos and red corpuscles – in liquid nitrogen (at -196 degree Celsius). However, vital organs such as the liver or heart cannot survive such treatment. Such studies have important implications for the field of biotechnology; in agriculture, for example, the principle of cellular anti-freeze may be useful in the development of frost-resistant plants.