Photographer: Brian Gratwicke Source:commons.wikimedia.org Copyright: (CC BY 2.0)
Frogs of the genus Xenopus are the only frogs with clawed toes and the African clawed frog is the largest species with adults reaching up to 5 inches in length. Usually they are greenish-grey with brown to black spotting or mottling. All species of the Pipidae family are tongue less, toothless and fully aquatic. Since they lack tongues, they use their hands to shove food in their mouths and down their throats and a hyobranchial “pump” to suck things in their mouth. The powerful legs and large claws on their feet help this frog family to tear up pieces of large food. They lack true ears but have lateral lines running down the length of the body and underside, which is how they can sense movements and vibrations in the water.
The African clawed frog is a threat to native amphibians and fish since it preys upon tadpoles and fish fry. In South Africa, mass migrations lead to large numbers of clawed frogs invading houses and clogging up irrigation pipes. Migrating individuals in Africa also invade fish farms, consuming both fish and fish food, and are difficult to keep out. In Chile, nonindigenous X. laevis are consumed by several species of native birds. Populations in California have been the most studies nonindigenous populations. The African Clawed Toad in California has been associated with the population decrease of the Western Toad (Bufo boreas). Even though feeding on fish is rare for Xenopus laevis it has been observed to feed on the federally endangered Tidewater Goby (Eucyclogobius newberryi) and locally endangered three spine stickleback (Gasterosteus aculeatus). African clawed frogs also carry a rather diverse parasite load and individuals from nonindigenous populations in California harbor a variety of parasites; however, there are no studies to verify if these parasites pose a direct threat to nonindigenous ecosystems. Also, they are carriers of the virulent amphibian fungus Batrachochytrium dendrobatidis. The impact of these hardy, adaptable, invasive frogs is not fully understood; but so far it has become an unwelcomed animal in the ecosystems it is present in.
These frogs spend most of their life-cycle in the water, only to leave when there is a drought. When a drought occurs, they will burrow into the drying mud. They can survive up to a year without food. Larvae are mid-water suspension feeders and have little pigmentation. Their diet consists of a wide range of animals including fish, crustaceans, insects, and other frogs. They will also scavenge on dead frogs, fish, birds, and small mammals. The lifespan of Xenopus laevis ranges from about 5 to 15 years but they have been recorded to live up to 25 years.
In 1960s Arizona, Xenopus laevis was intentionally introduced into man-made ponds. It was also found in several localities in California in the late 1960s and re-collected in new counties in 1989. For Florida in 1964, 200 African clawed frogs were released into Hialeah (Red Road) Canal, Hialeah, Mimi-Dade County, Florida, by an animal importer. In 1972, a "large number" of late-stage larval X. laevis was collected from an artificial pond in Wisconsin. In June 1990, a single X. laevis was found under a submerged log in a relic beaver pond in Colorado. The water was partially frozen and slushy. It has also been collected in artificial and natural ponds from North Carolina, Massachusetts and Virginia by the 1990s. The wide range and variety of habitats this frog is found in, suggests it will continue to expand and can potentially become established in any state.
Africa
U.S. Present: AZ, CA, CO, FL, KY, MS, NC, TX, VA, WI
U.S. Habitat: Natural or artificial ponds, and can be found in slow-moving creeks. Never in fast-moving bodies of water.
This is one of the most-studied species of frogs, considered one of the model systems of developmental biology. It is hardy and breeding can be easily induced in the laboratory. Xenopus laevis early development has been studied by developmental biologists for decades and its genome has been fully sequenced. Because it makes a hardy and popular pet, it can also be found in aquariums worldwide.
The aquarium/pet trade is a main factor to the introduction of Xenopus laevis to the United States, because most laboratory specimens do not make it out into the environment. If this frog is kept as a pet it should remain so until the end of its life. They are resistant to several chemicals but they are not able to inhabit ponds with predatory fish and Xenopus laevis is prey for indigenous garter snakes, Thamnophis couchi hammondi, fish, and the nonindigenous bullfrog, Rana catesbeiana . The presence of any other these predators can prevent the establishment of the African clawed toad.
Kuperman, B. J., V. E. Matey, R. R. Fisher, E. L. Ervin, M. L. Warburton, L. Bakhireva, and C. A. Lehman. 2004. Parasites of the African clawed frog, Xenopus laevis, in southern California, U.S.A. Comparative Parasitology 71(2):229-232.
Maddin & al. 2009. The anatomy and development of the claws of Xenopus laevis (Lissamphibia: Anura) reveal alternate pathways of structural evolution in the integument of tetrapods. Journal of Anatomy, no 214 (4): pp 607-19
Measey, G. J., & Channing, A. 2003. Phylogeography of the genus Xenopus in southern Africa. Amphibia Reptilia, 24(3):321-330.
Tinsley, R. C. 1996. Parasites of Xenopus. Pp.233-261. In: R. C. Tinsley and H. R. Kobel (editors). The Biology of Xenopus. Clarendon Press for The Zoological Society of London, Oxford. 440 pp.
Trueb, L. 2003. Common platanna, Xenopus laevis. Grzimek's Animal Life Encyclopedia, Volume 6, Amphibians. 2nd edition. M. Hutchins, W. E. Duellman, and N. Schlager, eds., Gale Group, Farmington Hills, Michigan.
Woodward, Susan L., and Joyce Ann. Quinn. 2011. African Clawed Frog. Encyclopedia of Invasive Species: From Africanized Honey Bees to Zebra Mussels. Santa Barbara, CA: Greenwood, 201-204. Print.
Internet References
http://www.bcb.uwc.ac.za/presents/focuson/frogs/xenopu.htm
http://amphibiaweb.org/cgi/amphib_query?account=amphibiaweb&where-genus=Xenopus&where-species=laevis
http://nas.er.usgs.gov/queries/FactSheet.aspx?SpeciesID=67
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