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    The African clawed frog

    An unusual non-native frog with some unique talents, and a voracious appetite

    Compiled by Ryan Peek/Stillwater Sciences

    An African clawed frog captured at the steelhead smolt trap at the Freeman Diversion on the mainstem Santa Clara River. Photo: W. Sears.

     

    The Santa Clara River is home to a number of amphibians, including the non-native African clawed frog, known scientifically as Xenopus laevis, a native of the cooler regions of sub-Saharan Africa.  African clawed frogs are part of the family Pipidae, which includes the Surinam Toad (Pipa pipa) and several other species in which the young develop in capped pits in the dorsal skin on the female’s back before emerging as tiny froglets (Stebbins 2003). However, African clawed frogs breed through pelvic amplexus and scatter their eggs, similar to bullfrogs and native California red-legged frogs. African clawed frogs have flattened, smooth skin, and are usually almost completely aquatic and tongueless (Stebbins 2003). Pipidae species have no teeth and generally lack eyelids (Stebbins 2003, Beck 1994).  The term "Xenopus" is Latin for "peculiar foot," describing the enormous, webbed, five-toed, three-clawed rear feet.  African clawed frogs have smooth slippery skin (“laevis" means "smooth") which can be multicolored with blotches of olive, gray, brown, or gray, and the the underside of the frog is usually creamy white with a yellow tinge (Kaplan 1995, Chang 1998, Stebbins 2003).

    African clawed frogs are almost completely aquatic, only leaving water to migrate (Nieuwkoop and Faber 1994, Beck 1994, Kaplan 1995).  They breathe through highly developed lungs, instead of through their skin, as with most native California frogs (Kaplan 1995, Simmonds 1985).  This is a useful adaptation in areas where ponds dry up, particularly in dry years, forcing frogs to burrow into the mud (leaving a tunnel for air) and remain dormant for up to a year (Simmonds 1985).  African clawed frogs cannot hop; they can only crawl, but are excellent swimmers.  They live in warm, stagnant grassland ponds as well as in streams in arid and semi-arid regions, tolerating a wide variety of aquatic conditions, including extreme levels of acidity, low oxygen levels, and high water temperatures.  African clawed frogs are long-lived; some individuals have been recorded to survive for 15 years (Simmonds 1985).

    In 1987, the National Institute of Health discovered that the secretions produced from the African clawed frog's skin contains a type of antibiotic known as magainin, which protects the frog from bacteria that is found in the ponds and puddles the frog lives in.  Magainins are part of a family of antibiotics that help heal wounded skin rapidly (Grenard 1994).

    How did it get here?

    Distribution of the African clawed frog in Southern California and Arizona. Map served from the Amphibian Research and Monitoring Initiative - National Atlas for Amphibian Distributions.

    More info: Search for more information about the African clawed frog in the watershed knowledge base, Google, or NatureServe.

     

    In the 1940’s and 1950’s the African clawed frog was shipped throughout the world for use in human pregnancy tests, when it was discovered that female African clawed frogs laid eggs when injected with the urine of a pregnant woman.  The demand generated for the frogs through their use as a pregnancy assay spurred research into captive breeding of the frogs.  Eventually, African clawed frog were bred and reared in large numbers in captivity (Danoff-Burg 2002). The success of captive breeding programs, and their relatively simple care needs resulted in the development of a major pet trade for the species in the 1950’s and 1960’s.  The African clawed frog is now widely used in experimental biology.  Once new techniques for pregnancy detection were developed (during the 1950’s), African clawed frogs were intentionally released from laboratories around the world.  Significant releases have also likely occurred as a result of individual pet releases and escapees from aquariums (Danoff-Burg 2002).  They are now found in three of the world’s five Mediterranean-type regions – the Cape of Africa, California, and Chile, as well as the United Kingdom, Germany, and the Netherlands (Danoff-Burg 2002, Nieukoop and Faber 1994).  The species is now found in a number of other U.S. states as well. The African clawed frog was first found in Southern California in the late 1960’s and early 1970’s, and is known to inhabit most of the Santa Clara River corridor, including the estuary (USGS 2006).  The species is regularly captured at Freeman Diversion, near Saticoy.

    How is it impacting native species?

    As a “sit and wait” predator, adult African clawed frogs feed on essentially whatever prey/food items they encounter (similar to the non-native bullfrog).  In the Santa Clara River system, this may include a wide range of native aquatic invertebrates and vertebrates, including tadpoles and juvenile amphibians, young arroyo chub (Gila orcutti), the federally endangered unarmored threespine stickleback (Gasterosteus aculeatus), and the (also federally endangered) tidewater goby (Eucyclogobius newberryi) (Chamberlain 1997, Stebbins 2003, Lafferty and Page 1997).  Predators do not appear to find African clawed frogs distasteful, and in South Africa they are eaten by large fish, turtles, frogs, snakes, aquatic insects, and birds (Chamberlain 1997).  Potential predators of African clawed frogs in California may include two-striped garter snakes (Thamnophis couchi hammondi), bullfrogs (Rana catesbeiana), and a number of amphibian eating bird species (Chamberlain 1997, Stebbins 2003). 

    What’s being done?

    There are no known efforts targeting control of the African clawed frog in Southern California.

    References

    Avila, Vernon L. and Frye, Patricia G. 1978.  Feeding behavior of the African Clawed frog (Xenopus laevis Daudin): effect of prey type.  Journal of Herpetology 12(3).

    Beck, Alan. 1994.

    Kaplan, Melissa. 1995. Natural History of the Upland Clawed Frog.

    Behler, John L. and King, F. Wayne.  The Audubon Society Field Guide to North American Reptiles and Amphibians (New York: Alfred A. Knopf) 1979 pp. 423-424.

    Breen, John F.  Encyclopedia of Reptiles and Amphibians (Neptune City, NJ: TFH Publications) 1974 pp. 442-451.

    Danoff-Burg, James A.  2002.  Introduced Species Summary Project - African Clawed Frog (Xenopus laevis).  Developed as part of the course: Invasion Biology - The Ecology, Influence, and Impact of Introduced Species.  Department of Ecology, Evolution, and Environmental Biology Columbia University, NY, NY.

    Garvey, N. 2000.  "Xenopus laevis" (On-line), Animal Diversity Web. Accessed March 28, 2006 at.

    Grenard, Steve.  Medical Herpetology (Pottsville, PA: NG Publishing) 1994 pp. 3-13.

    Halliday, Tim R. & Adler, Kraig eds.  The Encyclopedia of Reptiles and Amphibians (New York: Facts On File) 1986 pp. 43-44, 52.

    Kelley, Darcy B. 1998.

    Lafferty, K. D., and C. J. Page. 1997. Predation on the endangered tidewater goby, Eucyclogobius newberryi, by the introduced African clawed frog, Xenopus laevis, with notes on the frog's parasites. Copeia 1997(3):589-592.

    Mattison, Chris.  Frogs & Toads of the World (New York: Facts On File) 1987 pp. 64-65,152-153

    Nieukoop, P.D and Faber, J. 1994. Normal Table of Xenopus Laevis (Daudin). Garland Publishing, Inc., New York and London

    Rose, Walter.  The Reptiles and Amphibians of Southern Africa_ (Cape Town: Maskew Miller) 1950 pp. 23-34

    Simmonds, Mark P. 1985. African Clawed toad survey. British Herpetological Society Bulletin No. 13.

    United States Geological Survey (USGS).  2006.  Non-indigenous aquatic species website.  Accessed April 22, 2006.


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