The Alaskan Wood or Tree Frog That can Freeze During Winter

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alaskan tree wood frog

The Alaskan Wood or Tree Frog – The Anti Freezing Frog.

The wood frog (Lithobates sylvaticus or Rana sylvatica) has a large distribution in North America, reaching from the boreal forest of the north to the southern Appalachians, with multiple distinct populations, including the area of lowland eastern North Carolina.

The wood frog has earned biologists’ study over the last century because of its freeze tolerance.

The ecology & conservation of the wood frog has attracted research attention in modern years because they are often considered “obligate” breeders in short-lived wetlands (sometimes called “vernal pools”) that are themselves more susceptible to extinction than the species that breed in them.

Wood frogs vary from 51 to 70 mm (2.0 to 2.8 in) in length. Females are larger than males. Adult wood frogs are ordinarily brown, tan, or rust-coloured, & regularly have a dark eye mask. Individual frogs can alter in colour. The undersides of wood frogs are pale with a yellow or green cast.

The Alaskan Wood Frog Description

A small brown frog with a dark eye cover in the woods is likely to be a wood frog. No other varieties of frogs have a similar appearance to the wood frog in North America.

The Alaskan Wood Frog Habitat

The contiguous wood frog range is from north Georgia & northeastern Canada in the east to Alaska & southern British Columbia in the west. It is the most generally distributed frog in Alaska. It is also observed in the Medicine Bow National Forest.

Alaskan tree wood frogWood frogs are forest-dwelling animals that breed primarily in ephemeral, freshwater wetlands: woodland vernal pools. Long-distance movement plays a vital role in their life history. Individual wood frogs range broadly (hundreds of meters) amongst their breeding pools & neighbouring freshwater swamps, cool-moist ravines, and/or upland localities.

Genetic neighbourhoods of individual pool breeding populations increase more than a kilometer beyond the breeding site. Thus, conservation of this frog species requires a landscape (multiple habitats at relevant spatial scales).

The Alaskan Wood Frog Spring mating calls

Adult wood frogs spend summer months in wet woodlands, forested swamps, ravines, or bogs. During the fall, they move summer habitats & migrate to neighboring uplands to spend the winter. Some may remain in moist areas to spend the winter. Places of refuge tend to be in the upper organic bands of the soil, beneath leaf litter.

Adults ensure a short migration to thawed pools of water in early spring by spending the winter in uplands adjacent to breeding pools. Wood frogs are mostly active during the daytime & are rarely seen at night, except in breeding rituals. They are among the first amphibians to emerge for breeding right when the snow melts, accompanying spring peepers.

The Alaskan Wood Frog Feeding

Wood frogs eat a diversity of small, forest-floor invertebrates. Omnivorous, the tadpoles feed on plant detritus & algae & attack & eat eggs & larvae of amphibians, including wood frogs.

The wood frog’s feeding pattern, mostly similar to other frogs, is triggered by prey movement & involves a bodily lunge that closes with the mouth opening & an extension of the tongue onto the food or prey. The frog tongue is connected to the floor of the mouth near the jaw’s tip. When the mouth is shut, the tongue lies flat, stretched behind from its point of attachment.

During the feeding strike, the tongue is swung ahead as though on a pivot, so some piece of the ordinarily dorsal & posterior tongue covering makes contact with the prey. At this point in the feeding strike, the wood frog diverges considerably from more aquatic species, such as the green frog, leopard frog, & bullfrog. The wood frog makes a connection with the prey with just the tip of its tongue, mainly like a toad.

Cold tolerance

Like other northern frogs that enter dormancy or hibernation close to the surface in soil and/or leaf litter, wood frogs can endure the freezing of their blood & other tissues. Urea is collected in tissues in preparing for the winter, & liver glycogen is turned in large quantities to glucose in response to inner ice formation. Both urea & glucose act as anti-freezing agents (cryoprotectants) to restrict the amount of ice that builds and reduce the frog’s cells’ shrinkage.

Alaskan tree wood frog

Frogs can survive many freeze/thaw episodes during winter if no more than about 65% of the whole body water freezes.

The Alaskan Wood Frog Reproduction

The Alaskan Wood Frog primarily breeds in temporary pools rather than continual water bodies such as ponds or lakes. This is assumed to protect the adult frogs & their offspring (eggs and tadpoles) from predators by fish & other predators of continual water bodies. Adult wood frogs appear from hibernation in early spring and migrate to nearby pools. There, males chorus, uttering duck-like quacking sounds.

A male approaches a female & clasps from her behind & her forearms before hooking his thumbs together over her in a hold called “amplexus,” which is continued until the female lays the eggs—females lay eggs attached to the submerged under the soil, typically vegetation or branches laying on the ground. Most commonly, females lay eggs alongside other egg clusters, creating extensive collections of groups.

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Some benefit is conferred to pairs first to breed. Clutches closer to the centre of the raft absorb heat & develop quicker than those on the periphery & have more shelter from predators. If pools dry before tadpoles transform into froglets, they die. This constitutes the danger of counterbalancing the antipredator protection of temporary pools. By breeding at the start of spring, wood frogs improve their offspring’s chances of metamorphosing before pools dry out.

The larvae experience two development stages: fertilisation to free-living tadpoles & free-living tadpoles to juvenile frogs. Through the first stage, the larvae are adapted for accelerated development. Their growth depends on the temperature of the water & has a higher death rate. The second stage of growth features rapid development & growth. It depends on environmental circumstances, including food availability, temperature, & population quantity.

Following metamorphosis, a small portion (less than 20%) of juveniles will disperse, forever leaving the environment of their natal pools. The bulk of offspring tends to prevail or return to the same area, returning to their natal pool to reproduce. Most frogs reproduce only once in their lives.

Alaskan tree wood frog

However, some will breed two or three times, usually with differences according to age. The larvae & tadpole success is essential in wood frogs populations because they affect the following generations’ gene flow and genetic variation.

The Alaskan Wood Frog Conservation status

Although the wood frog is not an endangered or threatened species, several parts of its range urbanisation are fragmenting communities. Several scientific studies have shown that under specific thresholds of forest cover loss or over specific road density thresholds, wood frogs and other common amphibians begin to “drop out” of formerly inhabited areas.

Another conservation concern is that wood frogs fundamentally depend on smaller, “geographically isolated” wetlands for reproducing. In the United States, these wetlands are unprotected largely by federal law, leaving states to tackle preserving pool-breeding amphibians.

The wood frog has a complicated lifecycle that depends on multiple habitats, damp lowlands, & adjacent woodlands. Their habitat protection is, therefore, complicated, requiring combined, landscape-scale preservation.

Wood frog development in the tadpole stage is negatively influenced by road salt polluting freshwater ecosystems.

Alaskan tree wood frog

The Alaskan Wood Frog Facts

Do Alaskan tree frogs freeze in winter?

According to a new scientific study, the wood frog of Alaska lives nearly seven months a year in a frozen state. Each September, the wood frogs of Alaska do an extraordinary thing: They freeze. They do not freeze completely solid, but they do freeze mostly solid—two-thirds of their body water changes to ice.

Can frogs live after being frozen?

When in its partially frozen state, as much as 70% of the water in a frog’s body is able to be frozen, write researchers Jack Layne & Richard Lee in their 1995 article in Climate Research. Frogs can survive all wintertime like this, experiencing cycles of freezing & thawing. If it gets too cold, though, they’ll die.

How does the wood frog survive winter?

Most animals that hibernate during snowy winter months have thick coats of fur or fat layers to guard them. Therefore this tiny amphibian has adjusted by freezing & thawing itself depending on the outside temperature.

How long do Alaskan wood frogs live?

The Alaskan Tree or Wood Frog lives for around 3 years.
Adulthood may be reached in one to two years, depending on the sex & frog population. A wood frog’s lifespan in the wild usually is no longer than three years.

Further reading

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