Frogs of the United States and Canada, 2-vol. set

Family Pipidae

Family Pipidae Xenopus laevis (Daudin, 1802) African Clawed Frog ETYMOLOGY laevis: from Latin meaning ‘smooth.’ NOMENCLATURE Synonyms: Complete synonymy in Amphibian Species of the World 5.1, an online reference. IDENTIFICATION Adults. This species is streamlined for living in the water, with a narrow dorsoventrally flattened head and smooth globular gray body. The ground color is olive to brown, finely spotted to marbled or with large round or irregular spots in yellow or dark tints. A lateral line system is obvious on the sides of the body, looking like a line of stitches. The eyes face upward. There are no eyelids nor does it possess a tongue or visible tympanum. The front legs are small in relation to the rear legs; front toes are not webbed. The hind legs are long and muscular, and the hind toes are fully webbed with claws on the tips, hence its common name. Venters are immaculate yellowish white to densely spotted. The body is covered with mucous making it difficult to handle. Males have black roughened areas on the ventral surfaces of the forelimbs during the breeding season; females have large cloacal lips whereas those of males are barely discernible. Females are larger than males, normally averaging 90 to 100 mm SUL whereas males average 60 to 80 mm SUL. In California, McCoid and Fritts (1989, 1995) reported males to 80 mm SUL and females 65–119 mm SUL. Larvae. The larvae are easily recognized by their tentacles and transparent body. They actually look more like young catfish than tadpoles. Heads are flattened and nearly translucent, and the body is almost completely transparent with only slight indications of pigment (transparent in daylight and darker at night). Viscera are visible through the skin. In high concentrations of algae, the tadpole can take on a green appearance. Eyes are black. Larvae have a very long tail with a whip-like tip and high tail fin. Maximum length is 80 mm. Eggs. The eggs are pale brown and very small, averaging 1.1 to 1.2 mm in diameter inside a firm capsule 1.6 mm in diameter. Hatching occurs in 24 hrs. DISTRIBUTION The African Clawed Frog is indigenous to central and southern Africa, from Uganda and adjacent Sudan to South Africa. A variety of subspecies are recognized, with those in the United States most Distribution of Xenopus laevis XENOPUS LAEVIS 829 remove oxygen from water via the skin. As such, it can remain submerged for long periods. The short front limbs help push food into the mouth and circulate water across the lateral line system, which detects both vibrations and chemicals in the water. The rear legs are used for locomotion. In its native range, it occupies ponds and lakes in a wide variety of climatic conditions, from low tropics to high mountains (to 2,300 m). Feral populations in southern California inhabit both lentic and lotic waters, especially man-made impoundments and canals in highly disturbed areas. The biology of Xenopus is reviewed by Tinsley and Kobel (1996) and du Preez and Carruthers (2009). Populations of African Clawed Frogs can be small to large. For example, McCoid and Fritts (1980b) estimated population size at two ponds as 602 and 494 adult frogs. Dispersal may occur downstream within a stream system or during sheet-flooding events, but most dispersal is probably human-mediated. African Clawed Frogs can move overland when ponds dry and move to the next available water, but normally they do not leave the water. Frogs in drying ponds are capable of excavating deeper holes to maintain water longer and lower the surface water temperature (McCoid and Fritts, 1980b). Activity occurs yearround , although aestivation can be induced in the laboratory. When aestivating, frogs maintain a likely X. l. laevis. The species was introduced into the United States in large numbers beginning in the 1930s to 1940s in connection with human pregnancy tests. Others were sold as pets. In 1970–71, for example, more than 200,000 African Clawed Frogs were imported into the United States. Populations were first reported in California in 1968 (St. Amant and Hoover, 1969; Mahrdt and Knefler, 1972, 1973; St. Amant et al., 1973; Bury and Luckenbach, 1976; Lemm, 2006), with periodic accounts of African Clawed Frogs being captured elsewhere across the continent (Colorado, Florida, Massachusetts, North Carolina , Texas, Virginia, Wisconsin; Zell, 1986; in Tinsley and Kobel, 1996; Kraus, 2009). They are now established in most drainages of southern California and in the Tucson and Phoenix...