© 2011 Dr. Peter Janzen (1 of 8)
Description: A large, very compact ranid. Males reach 83–120 mm (SVL), females 85–110 mm. Females reach just 50% of the male weight. The lower jaw of the broad mouth bears two characteristic long projections (tooth like structures) which point dorsally. Nuptial pads appear on the first finger of the male. The skin is faintly warty, and the warts are rather rounded. The lateral ridges are short, never stretching from the head to the end of the body. The habitus changes considerably as growth proceeds. Young frogs are sturdy and almost plump. Adult animals are dorsoventrally flattened, resembling a flat cake. The eyes move more and more towards the center of the frontal region, and in adults are very protruding. The tympanum is distinct, large and high-oval in shape. Webs are found exclusively on the hind feet. They either leave free the first phalange of the fourth toe (as on animals from Zimbabwe, see Lambiris 1989), or the webbing formula reads 1 (0), 2 i (0.5), 3 i (1.5), 4 i/e (2), 5 (0.5) (as on an animal of unknown origin shown in Fig. 43; see reference below). Finger and toe tips are not enlarged. The inner metatarsal tubercle is transformed into a large shovel whose length surpasses that of the shortest toe.
Coloration: The dorsum of adult animals is more or less uniform yellow green to drab olive green. Males tend to be more greenish, whereas females are often more olive brown. A pale vertebral stripe and light lines on the ridges and warts are more common in females. The young often bear a bright, light green vertebral stripe, gold-brown speckles and black markings on their dark green skin. Forming black bars, these markings also appear on the lips and extremities. Lower lip, finger-tips and venter are uniform white or cream. Males have dark yellow throats. On some individuals, the venter is completely yellow. A dark patch is often present in the center of the tympanum. The webs are darkly pigmented.
Voice: A loud "whoop" lasting about 0.11 to 0.29 sec, with the dominant frequency of this frequency modulated call being 0.45–0.60 kHz. Additionally, there are components of 0.3–0.4 and 0.6–0.9 kHz (Channing et al. 1994). Passmore & Carruthers (1995) describe the call as a short deep "yop" uttered at irregular intervals.
Distribution and Habitat
Country distribution from AmphibiaWeb's database: Angola, Benin, Botswana, Burkina Faso, Chad, Kenya, Malawi, Mali, Mauritania, Mozambique, Nigeria, Tanzania, United Republic of, Zambia, Zimbabwe
Range: This species does not occur at Comoé National Park. In southern Africa, the ranges of the two species have not yet been neatly defined, mainly due to the ancient confusion of P. edulis and P. adspersus. In the northern range of the species, all former P. adspersus records will be in fact P. edulis. However, it may well be that P. "edulis" from West Africa is specifically distinct from those in Southern Africa (Böhme pers. comm). Records are available for the following countries: Nigeria, Cameroon, Somalia, Kenya, Tanzania, Malawi, Zambia, Zimbabwe, Mozambique, Botswana, Namibia, Angola (Günther 1868, Lönnberg 1910, Nieden 1915, Loveridge 1925, 1930, 1933, 1936, 1942, 1957, Schiøtz 1963, 1967, Poynton 1964c, 1991, Laurent 1965, Perret 1966, Walker 1966, 1968, Stewart 1967, Broadley 1971, Amiet 1973, ?Stevens 1974, Böhme 1975, Lanza 1981, Parry 1982, Poynton & Broadley 1985b, Branch 1988, Lambiris 1988, 1989, Herrmann & Kabisch 1991, Poynton & Haake 1993, Simbotwe & Mubemba 1993, Channing et al. 1994).
Life History, Abundance, Activity, and Special Behaviors
Tadpoles: According to Wager (1986), the tadpoles of P. edulis are quite similar to those of P. adspersus. The latter he figured with ovoid bodies whose dorsal tail fin inserts at the level of the body end. The dorsal part of the tail fin is somewhat broader than the ventral one. The laterad section of the oral disc (keratodont formula: 2 / 3+3 // 3) is lined laterally by many and caudally by two rows of papillae. The horny beaks are moderately massive and serrated. Lamotte & Xavier (1981) show a tadpole with a slender body whose tail fin, which is somewhat broader dorsally, inserts at the level of the body end and whose pigmentation is almost uniform. Herrmann & Kabisch (1991) report freshly metamorphosed frogs to measure 20 mm (SVL). The larval developmental period is said to last 15–18 days. Haas (1999a) investigated the skeletal development of P. adspersus tadpoles during metamorphosis. He gives a developmental time of 17 days at 29 °C (Haas 1999a, b).
In Tica, Mozambique, Pickersgill (pers. comm.) observed tadpoles of P. edulis to form swarms similar to those of P. adspersus (Van Wyk et al. 1992a, b). These swarms are most probably meant to maximize the chances of survival of the individual swarm members. Even if they should attract certain predators by their sheer size, the chance of escaping their attacks might be considerably higher as long as the tadpole remains within the swarm. It pays to join a swarm as long as individual benefits can be derived independently of what is happening on the level of the entire group or population. The above mentioned studies further give hints that the tadpoles might assist each other by turning up the substrate when the swarm moves. The males of P. adspersus guard and defend the tadpole swarms swimming across shallow sectors of the ponds. If the latter are separated from the main pond as the water level sinks, the males will dig a channel enabling the young to move to deep water. Kok & DuPreez (1989) describe a channel whose length amounted to 3.2 m (width: 5 cm; depth: 2–5 cm). Freshly metamorphosed P. edulis are almost immediately capable of wolfing down siblings of the same size (Amiet 1973, Passmore & Carruthers 1995).
Biology: These frogs (P. adspersus and P. edulis) spend most of the year buried in the substrate, appearing only when the rains set in (Perret 1966, Böhme 1975). In order to survive the dry season, both young and adult frogs produce cocoons formed by shed skin-layers and soil particles sticking to it (Parry 1982). The frogs are thus capable of reducing their evaporation rate by 50% (Loveridge & Grayé 1979, Poynton & Broadley 1985b). In Cameroon, the breeding season of P. edulis is very short (Amiet 1973). The Nigerian frogs observed by Schiøtz (1963) were both diurnal and nocturnal towards the end of the rainy season. In that region, Walker (1966) found the first animals in April/May, i.e. after rainfall had set in, and again in June/July. During the latter period, they were somewhat more common and exclusively nocturnal.Channing et al. (1994) report on males calling in rice fields with a water level of 30 cm. In this case, single males sit amidst the vegetation in deeper water. They never form leks like those of P. adspersus, and males do not show any aggressive interactions (compare Picker 1983a, Haagner 1990). The eggs of P. adspersus are fertilized outside the water, i.e. the female raises her body end at the very moment of oviposition.
Pyxicephalus edulis deposits its eggs beneath the surface, similar to most other ranids. At this stage, the amplectant pairs are occasionally floating in deeper water, too. Herrmann & Kabisch (1991) describe females stimulating their mates by rhythmic movements of their warty backs. According to these authors, the eggs are deposited as a surface layer. Wherever the two Pyxicephalus species happen to occur in syntopy, they appear at different times (Amiet 1973b).
Loveridge (1933, 1942) reports on a case of mismating with a toad. He writes that this species mainly feeds on various arthropods, that are occasionally quite aggressive, but also on diverse vertebrates including tadpoles, on young Pyxicephalus, on frogs nearly as large as themselves, and on a lizard (Loveridge 1936). Walker (1966) even mentions a bird caught by this frog.
Rödel, M. O. (2000). Herpetofauna of West Africa, Vol. I. Amphibians of the West African Savanna. Edition Chimaira, Frankfurt, Germany.
Written by M.O. Roedel (roedel AT biozentrum.uri-wuerzburg.de), Post-Doc at the University of Wurzburg, Department of Animal Ecology and Tropical Biology, Wurzburg, Germany
First submitted 2001-05-02
Edited by Meredith Mahoney and Tate Tunstall (2003-02-17)
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