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Wood frog

life science Maturity 5-7 Next article →

The wood frog, known scientifically as *Lithobates sylvaticus*, is a remarkable amphibian species.

Wood Frog
Wood Frog

It is found across a massive portion of North America. Its range stretches from the boreal forests of Canada to the southern Appalachians. In the west, it reaches from Alaska to southern British Columbia. This frog is highly significant to biologists because of its unique survival skills. It can tolerate freezing temperatures that would kill most other animals. It is also a very terrestrial frog, meaning it spends much of its life on land.

WoodFrog DarienLakesStatePark 2020-06-16 (02)
WoodFrog DarienLakesStatePark 2020-06-16 (02)

Because it relies on specific types of wetlands, it is a key species for studying ecology.

To survive harsh winters, the wood frog uses a complex biological process. As winter approaches, the frog accumulates urea in its body tissues. It also converts liver glycogen, which is stored energy, into glucose, a type of sugar. Both urea and glucose act as cryoprotectants. These substances help limit ice formation and prevent cells from shrinking too much.

Ranasylvatica
Ranasylvatica

When the frog freezes, ice forms in its body water. The frog can tolerate the freezing of 65% to 70% of its total body water. During this time, the frog has no detectable heartbeat, breathing, or brain activity. It remains in this frozen state for an average of 193 days. This allows it to survive in extreme environments like Interior Alaska.

Wood frogs have different physical characteristics depending on their environment and season. Most adults are brown, tan, or rust-colored to help them hide. They often have a dark mask over their eyes.

Wood Frog from White Clay Creek, Delaware
Wood Frog from White Clay Creek, Delaware

Their skin color can actually change based on sunlight exposure. Sunlight can cause their skin to darken. Some individuals have been observed changing from light brown to dark brown. Their underparts are usually pale with a yellow or green tint. In northern populations, the belly might have a mottled pattern. These variations help them blend into the forest floor.

Scientists have discovered specific evolutionary adaptations that make this freeze tolerance possible. One key mechanism involves a specific enzyme called SERCA 1. This enzyme is a protein pump that helps manage calcium in cells. In wood frogs, a series of seven amino acid substitutions allows this pump to function at very low temperatures.

Wood Frog, floating
Wood Frog, floating

This is different from related species like the green frog, which cannot work as well in the cold. Researchers have also found that Alaskan wood frogs have larger liver glycogen reserves. They also produce more urea than frogs in warmer areas. These specific adaptations help them survive the most extreme northern climates.

Reproduction for the wood frog is an intense and rapid event. They are known as "explosive breeders" because many frogs mate within a single week.

This usually happens in early spring right as the snow melts. Males move through the water making duck-like quacking sounds to attract females. When a male finds a female, he uses a hold called amplexus. He clasps her from behind her forearms to hold her until she lays her eggs. The female attaches the eggs to underwater plants or fallen branches. Often, many eggs are laid together in large groups to increase their chances of survival.

Wood frogs prefer to breed in ephemeral wetlands known as vernal pools. These are freshwater pools that are not permanent and eventually dry up. This habitat provides a special advantage against predators. Most fish cannot live in these temporary pools, so the eggs and tadpoles are safer. However, there is a risk that the pool might dry up before the tadpoles can grow into frogs. The tadpoles are omnivores that eat algae and plant bits. They must grow quickly to reach the next stage of life before the water disappears.

The life cycle of the wood frog is closely tied to the health of the forest. Most young frogs are philopatric, meaning they stay near the pool where they were born. Only about 20% of juveniles move away to find new breeding sites. Because they rely on these specific pools, the species is sensitive to environmental changes. For example, road salts used for de-icing can be toxic to larvae. Studies show that salt can cause lower weight and physical abnormalities in tadpoles. Protecting the wide landscape of forests and wetlands is essential for their survival.

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🖼️ Images & Media (8)
File:Wood Frog.jpg
Wood Frog.jpg
File:WoodFrog DarienLakesStatePark 2020-06-16 (02).jpg
WoodFrog DarienLakesStatePark 2020-06-16 (02).jpg
File:Wood Frog, floating.jpg
Wood Frog, floating.jpg
File:Wood Frog from White Clay Creek, Delaware.jpg
Wood Frog from White Clay Creek, Delaware.jpg
Wood Frogs calling in spring.ogg
File:Wood Frog in Kabekona Lake.jpg
Wood Frog in Kabekona Lake.jpg
File:Ranasylvatica.JPG
Ranasylvatica.JPG
File:Woodfrog tadpole.jpg
Woodfrog tadpole.jpg
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