The African clawed frog (Xenopus laevis, also known as platanna) is a species of South African aquatic frog of the genus Xenopus. It can grow up to 12 cm long with a flattened head and body, but no external ear or tongue. Its name derives from the three short claws on each of its hind feet, which it probably uses to stir up mud to hide it from predators.
The species is found throughout much of Africa, and in isolated, introduced populations in North America, South America, and Europe.
These frogs tend to live 5 to 15 years but some have been recorded to live to be nearly 30 years. They shed every season, and eat their own shed skin.
Although lacking a vocal sac, the males make a mating call of alternating long and short trills, by contracting the intrinsic laryngeal muscles. Most unusually, females also answer vocally, signaling either acceptance (a rapping sound) or rejection (slow ticking) of the male.
They also swim very fast, and can eat smaller fish, such as minnows and guppies. When they eat, the food is not actually held down very well, and occasionally, the fish, or bug, can actually escape before being forced back into the mouth by the frog's front hands.
Xenopus oocytes provide an important expression system for molecular biology. By injecting DNA or mRNA into the oocyte or developing embryo, scientists can study the protein products in a controlled system. This allows rapid functional expression of manipulated DNAs (or mRNA). This is particularly useful in electrophysiology, where the ease of recording from the oocyte makes expression of membrane channels attractive. One challenge of oocyte work is eliminating native proteins that might confound results, such as membrane channels native to the oocyte. Translation of proteins can be blocked or splicing of pre-mRNA can be modified by injection of Morpholino antisense oligos into the oocyte (for distribution throughout the embryo) or early embryo (for distribution only into daughter cells of the injected cell).
X. laevis is also notable for its use as the first well-documented method of pregnancy testing when it was discovered that the urine from pregnant women induced X. laevis oocyte production. Human chorionic gonadotropin (HCG) is a hormone found in substantial quantities in the urine of pregnant women. Today, commercially available HCG is injected into Xenopus males and females to induce mating behavior and breed these frogs in captivity at any time of the year.
In 2007, these frogs invaded a pond in San Francisco, where much debate exists on how to terminate these creatures and keep them from spreading. It is unknown if these frogs entered the San Francisco ecosystem through intentional release or escape into the wild.
Because these frogs are immune to the fungi Batrachochytrium dendrobatidis (a chytridomycota) and B. dendrobatidis has been traced back to the habitat of Xenopus laevis in Africa, many scholars believe it is the source of the worldwide frog population crash. Due to its extensive use in obstetrics and research, it appears Xenopus laevis has carried B. dendrobatidis with it out of Africa to all over the world, causing chytridomycosis and eventually death in native frogs naïve to the fungi.