African Clawed Frog (Xenopus laevis*)

Photo by Cecil Schwalbe

Photo by Cecil Schwalbe

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Description

One of five introduced amphibians in the 100-Mile Circle, the African Clawed Frog, a native of southern and north-central Africa, grows to a SVL of 143 mm, has a flattened body and head, and the digits of the hind feet are long and fully webbed, the three inner toes of which end in sharp, black claws.  The digits of the front feet lack webbing and do not possess claws, although the tips of the digits in breeding males are blackened.  The eyes are oriented high on the head, and African Clawed Frogs lack vocal sacs and distinct tympana.  Dorsally this frog is gray to olive, brown, or yellow-brown, often with a scattering of darker markings.  Ventrally it is cream–colored, sometimes with some dark spots or mottling.

The African Clawed Frog was widely used in many regions of the world in the 1930s, 40s, and 50s in human pregnancy testing; they have also been in the pet trade in many areas of the United States and are still used by many laboratories in biomedical, developmental, and molecular biological research.  Frogs were released or escaped in many regions and became established in some areas around the world.  The only known localities for the African Clawed Frog in Arizona and the 100-Mile Circle are ponds at the Arthur Pack Desert Golf Course, 9101 North Thornydale Road in northwestern Tucson.  The species has been documented at that site since the 1960s, and still persists there.  Although confined to this one golf course in Arizona, in other states the species has sometimes spread beyond the initial introduction site.  These are highly aquatic frogs that do not disperse readily overland, but may move if their pond is drying up or perhaps during heavy rains or flooding.

African Clawed Frogs pose a predation threat to native aquatic organisms.  In California, in particular, the species is considered a significant pest species and breeds in many localities.  Front limbs that are used to fork prey into the mouth and the clawed hind limbs that can act as shredders make the African Clawed Frog an efficient predator of relatively large prey.  They are known to feed upon tadpoles and metamorphs of a number of native anuran species in California, and they can also take small fish.  However in their native Africa, they feed primarily on aquatic invertebrates, although larger frogs will readily cannibalize smaller African Clawed Frogs and tadpoles.

Breeding has not been investigated in Arizona; however, in California the African Clawed Frog breeds from January to November, with most reproduction occurring from March to June.  The male’s advertisement call, given underwater by day or night, is a metallic two part trill, about 0.5 second in duration and repeated as much as 100 times per minute.  The call can be heard by following this link: http://www.californiaherps.com/frogs/pages/x.laevis.sounds.html

Clutches, which may contain as many as 17,000 eggs, are deposited as single eggs or in small clusters on submerged plants or other structure.  Eggs hatch within two or three days, and in the laboratory tadpoles metamorphose in ten to twelve weeks.  The tadpoles are distinctive in that they possess a pair of tentacles on the snout, similar to those seen in catfish.

African Clawed Frog populations in Africa often persist with stable endemic infections of the fungal skin disease, chytridiomycosis that is killing amphibians of many species around the world.  Weldon et al. (2004) proposed an Out-of-Africa scenario for the disease, whereby the pathogen originated in Africa and was spread around the globe when African Clawed Frogs were exported for human pregnancy testing.  However, no African specimens of Xenopus examined tested positive for the disease before 1938 (specimens from as early as 1879 were examined), and other hypotheses for the origin of the disease cannot be ruled out.

The IUCN lists this frog as a species of least concern on the Red List.  As an invasive exotic with a potential to adversely affect native aquatic organisms, possession of the African Clawed Frog is prohibited by Arizona Game and Fish Department regulations.  The African Dwarf Clawed Frog (Hymenochirus boettgeri), common in the Arizona pet trade, is very similar to the African Clawed Frog, but only grows to about 63 mm SVL, the digits on the front feet are webbed, and the eyes are positioned on the side of the head.

Suggested Reading:

Brennan, T.C., and A.T. Holycross. 2006. Amphibians and Reptiles in Arizona. Arizona Game and Fish Department, Phoenix, AZ.

Crayon, J.J. 2005. Xenopus laevis (Daudin, 1802) African Clawed Frog.  Pages 526 in: M.J. Lannoo (editor), Amphibian Declines: The Conservation Status of United States Species.  University of California Press, Berkeley.

Elliott, L., C. Gerhardt, and C. Davidson. 2009. The Frogs and Toads of North America. Houghton Mifflin Harcourt, Boston and New York.

McCoid, M.J., and T.H. Fritts. 1993. Speculations on colonizing success of the African clawed frog Xenopus laevis Pipidae in California. South African Journal of Zoology 28:59-61.

Weldon, C., du Preez, L. H., Hyatt, A. D., Muller, R., and Speare, R. 2004. Origin of the amphibian chytrid fungus. Emerging Infectious Diseases 10: 2100-2105.

Author: Jim Rorabaugh

For additional information on this species, please see the following volumes and pages in the Sonoran Herpetologist: 2002 Aug:89; 2005 Mar:29.

 

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