For the entire winter, the wood frog is like a lump of hard, frigid, icy stone carved in the shape of a frog. What does a hibernating wood frog look like? There is no muscle movement. So on the one hand, the wood frog’s body allows ice to form around the outsides of cells and organs and on the other hand, it prevents ice from forming inside the cells-thus avoiding the lethal damage suffered by most animals when they freeze. This syrupy sugar solution prevents the cells from freezing and binds the water molecules inside the cells to prevent dehydration. The eyes turn white because the lens freezes.Īt the same time, the wood frog’s liver produces large amounts of glucose that flushes into every cell in its body. Ice crystals form between layers of skin and muscle. How do they pull this off?Īt the beginning of winter, ice quickly fills the wood frog’s abdominal cavity and encases the internal organs. They’ve accomplished what would seem to be a biological miracle. Yet wood frogs have evolved ways to freeze solid for up to eight months each year. The result is pervasive and deadly internal damage. And ice severely injures cells by drawing out water and causing dehydration, scrambling the interior structure of cells and fracturing the cell walls. When blood freezes, there is no mechanism to deliver oxygen and nutrients to organs, so extreme metabolic damage occurs. Why is freezing so dangerous? Several things can happen: If ice crystals form inside an animal they can puncture blood vessels. These frogs need permanent water that won’t dry out.įor most other animals, survival depends on protecting themselves from any condition that could freeze their flesh. By contrast, frogs that hibernate underwater take longer to become active, so they must breed later. Researchers have found that wood frogs spend the winter frozen! This amazing strategy allows wood frogs to become active very early in spring, because the land thaws and warms more quickly than the ice-covered lakes The newly active frogs can mate and lay eggs in small ponds and even in melt water pools that dry up by midsummer. The leaves, duff and overlying snow give some insulation from extreme cold, but the frogs are not protected from subfreezing temperatures as they would be if they chose the underwater strategy. They hibernate by nestling down into the leafy litter on the forest floor. Most frogs survive northern winters by hibernating deep under water, in ponds, lakes and streams-they are cold and dormant but their body temperature never falls below freezing. Biologists have studied wood frog hibernation and what they’ve learned is truly astonishing. This mystery has intrigued scientists for a long time. How do these delicate little creatures endure the intense, protracted, iron-cold subarctic winter? Remember, frogs are cold blooded, so their body temperature is about the same as the surrounding air. This is the winter world in which the wood frog must survive. Almost certainly, there were hibernating wood frogs near Prospect Creek when that record was set. Prospect Creek, just south of the Brooks Range, had the coldest temperature ever recorded in Alaska-minus 80 degrees Fahrenheit. Winter brings some of the earth’s coldest temperatures: it is not unusual to have temperatures of minus 50 degrees Fahrenheit. Summer days stretch to 24 hours and temperatures can climb into the 90’s. The northern forests of Alaska and Canada have some of the most dramatic temperature ranges in the world. The most remarkable thing about wood frogs happens not in the summer when they transform from tadpoles to frogs, but in the winter when they hibernate. Wood frog's winter habitat: Boreal Forest
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