Forest frog
| Forest frog | ||||||||||||
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Forest frog ( Rana sylvatica ) |
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| Scientific name | ||||||||||||
| Rana sylvatica | ||||||||||||
| Le Conte , 1825 |
The forest frog ( Rana sylvatica , syn .: Lithobates sylvatica ), also known as the ice frog , is a North American amphibian species from the family of real frogs (Ranidae) and the genus Rana . It also belongs to the group of brown frogs and thus resembles the European species common frog , moor frog or agile frog in appearance, but also in some ecological requirements and behavior (see there).
The common name "forest frog" is also used for other frog species; compare, for example, the Australian forest frog .
Some authors put the species in a newly defined genus Lithobates under the name Lithobates sylvaticus (Le Conte, 1825).
features
Forest frogs are up to eight centimeters long, although the males remain significantly smaller. On the smooth to slightly rough back there are two raised glandular ridges and often smaller folds between them. The color of the upper side varies between yellow-brown, gray, orange, rose-red-brown and dark-gray-green; the females tend more towards the reddish hues. There may also be blackish or dark brown spots. In addition, many specimens from the west and north of the distribution area have a white line on the middle of the back. The light underside is yellowish or greenish-white and only occasionally with dark spots.
The dark, triangular temple spot that is typical of brown frogs is always present, within which the eardrum also lies, which is smaller in diameter than the eye. In front of the eyes, a dark stripe continues over the nostrils to the tip of the snout, so that the impression of a “robber mask” arises in the case of more strongly colored specimens. The males have paired internal vocal sacs , but only have a low “voice”, which they use for mating calls during the short spawning season in spring. In addition, in this phase, like many male frogs, they develop oestrus calluses on their thumbs.
Distribution, habitat and way of life
Humid forest areas are populated in northern North America between Alaska , all provinces of Canada and the northeastern United States . The forest frog also crosses the Arctic Circle and penetrates further north than any other North American frog . The northern tree line between Alaska and Labrador can serve as a guide . The habitats in the forest can be located at a greater distance from the nearest body of water.
Forest frogs like to spawn in bodies of water that do not have constant water in order to avoid fish in the ponds. It is one of the first frogs to migrate back to their spawning grounds in spring so that the tadpoles have enough time to develop before the water dries up. Forest frogs show a pronounced loyalty to their spawning water and 90% return to it.
Herons, owls, raccoons and also snakes are among their predators; they themselves feed on beetles, snails and spiders, among other things.
Mechanisms for increasing cold tolerance
In order to adapt to the cold conditions of its distribution area, the wood frog has developed the ability to freeze the body fluids between the tissue cells by around a third in winter at direct ambient temperatures of down to −5 ° C - hence the common name "ice frog". So that his body cells are not damaged by ice crystals that can be seen under the skin, he produces an endogenous anti-freeze from glucose and urea inside the cells when the frost sets in .
The physiological processes in detail: When ice crystals first form on the frogs' skin, adrenaline is released . This is followed by the formation of glucose from glycogen in the liver. Glucose then reaches concentrations of up to 300 mOsm in the frog's extracellular fluid. (The “normal” concentration is actually 5 mOsm.) The increased osmolarity has the consequence that water follows the gradient, flows out of the cell and the freezing point is also lowered. The formation of ice crystals now mainly takes place in the extracellular space and the membranes of the cells are not destroyed. Functions such as heartbeat, blood flow and breathing stop completely in this phase. The frog then thaws out again in spring.
While glucose production is only triggered by freezing the extracellular space, urea is generally accumulated during osmotic stress. Since a high urea concentration leads to hypometabolism , the accumulation of urea is used for general adaptation to dry living situations. Freezing is one of those "dry" episodes as there is ultimately no free water available. In addition to reducing metabolism, urea also serves as a protection against frost.
protection
The forest frog is currently not considered to be endangered due to its wide distribution and little is being done to provide additional protection for the forest frog. In the winter habitat, it can be particularly threatened by forestry work.
swell
Individual evidence
- ↑ American Museum of Natural History: Database "Amphibian Species of the World" ( Memento of the original from September 17, 2006 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- ↑ G. Heldmaier & G. Neuweiler: Comparative animal physiology. Springer, Berlin 2004. ISBN 978-3-540-21909-5 .
literature
- Vasconcelos, D. & Calhoun, AJK: Movement patterns of adult and juvenile Rana sylvatica (LeConte) and Ambystoma maculatum (Shaw) in three restored seasonal pools in Maine. Journal of Herpetology 38 (2004), 551-561, doi : 10.1670 / 157-03a .
- Berven, KA & Grudzien, TA: Dispersal in the Wood Frog (Rana sylvatica) - implications for genetic population structure. Evolution 44 (1990), 2047-2056, doi : 10.2307 / 2409614 .
