Wood frog

The Wood Frog, otherwise known as Lithobates sylvaticus, is a terrestrial frog found throughout North America [5]. In Greek Litho translates to "a stone", bates translates to "one that walks", and sylvaticus meaning "amidst the trees" [6]. They belong to the Order Anura and the Family Ranidae [2]. This species of frog is common and is not currently under any threat of extinction [5].

Description

This is a photo of an adult Wood frog.

The Wood frog is a comparatively small frog. Fully grown adults are 1.5 to 3.25 inches in length [5]. Females are typically larger and more brightly colored than their male counterparts [5]. They can differ in color, but bodies typically range from a light tan to a dark brown [4]. Their most distinct feature is the coloration around their eyes. The Wood frog has two black markings that extend back from their eyes, resembling a mask [6]. The underbelly is white and sometimes has small grey marks [4]. This frog has two distinct ridges that run down their back. These ridges are known as Dorsolateral folds [6].

Anatomical diagram of an adult Wood frog.

Range and Habitat

This map shows the geographical range for Lithobates sylvaticus.

Wood frogs have a very large range. They are found in Canada and North America [5]. Their range goes as far south as the Appalachian mountains and as far north as Alaska [6]. They can also be found in smaller populations in Alabama and Idaho [5]. The Wood frog is the only frog that lives in the Artic Circle, this is due to their ability to freeze [5].

Wood frogs typically like both deciduous and coniferous forests [6]. They gravitate towards forests with a closed canopy to keep out sunlight and keep in moisture [2]. This species likes lots of leaf litter and wood debris on the forest floor for shelter [4]. Especially in the winter, Wood frogs can go upland and seek refuge in the leaf litter while they hibernate [3]. When they are not breeding, they can be found in an moist forested areas, ravines, bogs or forested swamps. When spring comes they migrate into forested wetlands or other protected bodies of water to breed [2].

During mating season, these frogs find temporary pools of water of vernal pools [6]. These can be any cut off water sources like streams or ponds, and can even be in ditches. These are preferably free of fish to increase survivability of the offspring [6]. Wood frogs are diurnal and are rarely seen at night but often heard in loud choruses during mating season [5].

Cold Tolerance

Wood frogs are one of the only species of frog to live in the Artic Circle, this is due to their ability to freeze [4]. These frogs "freeze over" in the winter, this serves as hibernation [5]. The freezing process works by releasing large amounts of glucose into their bloodstream, this keeps their body cells from freezing, but not their other bodily fluids [4]. The distribution of liver glycogen enhances the survival of cells, tissues, and organs. This was seen by experimentally adding additional glucose to the Wood frog which increased its tolerance to freezing [1]. This glucose distribution raises the osmotic pressure of the body fluids, which in turn reduces the amount of ice that forms at any given temperature [1]. The Wood frog also creates and antifreeze using their urea [5]. These cryoprotectants keep the water within their cells from freezing because this would indeed kill them [5]. As winter ends the frogs will begin to thaw and begin the breeding process [5].

Diet

As tadpoles, Wood frogs only eat algae and other frog larvae, but as they grown into their adult stages they become omnivores [4]. While inhabiting the forests, they feed on a variety of small invertebrates that they find on the forest floor. With their long tongue they can catch insects including, arachnids, worms, slugs, and snails [5]. The Wood frog is not particular about its diet and will eat just about anything that's the size of its mouth [3]. These frogs are often seen as easy prey, and are eaten by snapping turtles, raccoons, skunks, coyotes, foxes, and birds [5].

Reproduction

Wood frogs will leave their leaf litter refugee after "freezing off" to find a vernal pool for breeding [6]. This process typically begins as early as March and as late as April [4]. The male frogs will make a crocking noise to attract a mate when they are ready, this is typically at night [3]. While the male is on the back of the female they will both simultaneously release their gametes, sperm and egg, into the water [3]. The eggs are now fertilized, and can continue to grow in the water [3]. Each female can lay 1,000 to 3,000 eggs per season [5]. To prevent the eggs from drifting downstream the egg mass attaches itself to nearby vegetation [3]. It takes the eggs about one week until they hatch, once hatched they are in their tadpole stage [3]. This stage can last at least two months, and is likely to be longer if nutrient availability is low [3]. After the two months, the tadpoles have transformed into froglets [3]. These froglets are only about ten centimeters long and it takes two more years until they before adult Wood frogs [3]. After two years, the Wood frog is fully matured it may began to mate, and the process begins again [3]. Wood frogs have a life span of about 3 years [5].

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References

[1] Costanzo, Jon P., et al. “Cryoprotectants and Extreme Freeze Tolerance in a Subarctic Population of the Wood Frog.” PLOS ONE, vol. 10, no. 2, Feb. 2015, p. e0117234. PLoS Journals, doi:10.1371/journal.pone.0117234.

[2] Integrated Taxonomic Information System - Report. (n.d.). . https://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=775197.

[3] Preston, B. (n.d.). The Biology of the Wood Frog. Nature North. http://www.naturenorth.com/spring/creature/woodfrog/wf2.html.

[4] Wild things in your woods. (n.d.). . Cornell University. https://cpb-us-e1.wpmucdn.com/blogs.cornell.edu/dist/a/7804/files/2018/05/Wood-Frog-23xt0xr-11v8dab.pdf.

[5] Wood frog. (n.d.). . National Wildlife Federation. https://www.nwf.org/educational-resources/wildlife-guide/amphibians/wood-frog#:~:text=Wood%20frogs%20are%20found%20in,lay%20eggs%20in%20vernal%20pools.

[6] Wood Frog. (n.d.). . Virginia Herpetological Society. https://www.virginiaherpetologicalsociety.com/amphibians/frogsandtoads/wood-frog/wood_frog.php.