Xenopus muelleri (Peters, 1844)
Idwi lika-Müller (Zulu)
|Species Description: Peters, W. C. H. (1844). Über einige neue Fische und Amphibien aus Angola und Mozambique. Monatsberichte der Königlichen Preussische Akademie des Wissenschaften zu Berlin 1844: 32–37.|
© 2016 Dr. Joachim Nerz (1 of 9)
A medium-sized clawed frog with button-like protruding eyes situated dorsally. Body flattened. Adults measure 38–60mm (SVL). The subocular tentacles are well developed, reaching about 0.6–1 of the eye diameter. The skin is almost smooth. Starting at the posterior border of the eye, a double line of elongate unpigmented flat sensory tubercles (lateral line sense organs) is arranged in roughly alternating order. The outer line comprises 20–29 tubercles set at right angles to the body axis. The inner one runs parallel to the latter, comprising about 16–20 tubercles. Furthermore, 3–7 pairs of these tubercles appear in the neck region, and 10–14 ones are found on the border of the lower jaw, set at right angles to the mouth. Like all of the dorsal surface, this part of the skin is scattered with numerous minute asperities which are equally unpigmented. Some of these may also be found on the fingers which are covered with numerous minute grooves. On breeding males, the outer part of the fingers is black. The dermal lobes above the vent are better developed in females. The web of the hind limbs is fully developed. Toes 3–5 have black horny claws. Metatarsal tubercle without claw. 2n = 36.
According to Stewart (1967), males from Malawi reach a SVL of 58 mm, females 72 mm. Concurring measurements were published by Nieden (1923), Poynton (1964a), Arnoult & Lamotte (1968), Lamotte & Xavier (1981) and Lambiris (1988). Poynton & Broadley (1985a) even specify a SVL of up to 80 mm. Smaller frogs, concerning animals from Cameroon, were measured by Mertens (1938a); SVL: males 38 mm; females 57 mm) and by Perret (1966); SVL: males 40–49 mm; females 54–63 mm). Nieden (1915) mentions a specimen from Tanzania showing traces of a fourth claw.
Coloration: Dorsal parts of body and limbs drab olive with large black patches that are sometimes vaguely defined. The iris shows a silver-grey glimmer. The venter is whitish to orange yellow. Some darker patches occasionally appear on the throat and on the thighs. A single female had the belly scattered with black spots. Distinctive ventral designs were reported from Ghanian frogs (Poynton 1964c). According to Loumont (1984), the dorsal patches of animals from Tanzania, Malawi and Zimbabwe are often arranged in two longitudinal rows. Mertens (1955b) mentions a female from Tanzania whose venter showed smoky-gray patches and a young specimen whose venter was plain white. In alcohol the dorsum turns almost completely gray olive, and the original black patches are hardly visible. The venter turns gray white, and black spots remain visible.
Voice: So far, it has not yet been registered at Comoé National Park. According to Schiøtz (1963), the call sounds like a rather low "pink-pink" resembling the sound produced by a spoon knocking against a pan. According to Vigny (1979), animals from Malawi produce a sequence of rattling "trra-trra" calls lasting 0.15–0.21 sec, the dominant frequency being 1.1 kHz. She describes two types of calls. Picker (1983) has also published sonagrams. These calls lasts 0.15 to 0.20 sec, comprising 5–6 pulses (dominant frequency: 0.8–0.9 kHz). Wager (1986) describes the call as "turrr", comparing it to the sound produced by a pencil vibrating against a glass pane. According to Lambiris (1988), two soft calls per second are uttered under water. Passmore & Carruthers (1995) report short "metallic" calls produced under water at intervals of 0.15 seconds. The vocal apparatus of the male has been examined by Loumont (1981).
Distribution and Habitat
Country distribution from AmphibiaWeb's database: Angola, Benin, Botswana, Burkina Faso, Cameroon, Central African Republic, Chad, Congo, Congo, the Democratic Republic of the, Cote d'Ivoire, Ghana, Kenya, Malawi, Mozambique, Namibia, Nigeria, South Africa, South Sudan, Swaziland, Tanzania, United Republic of, Uganda, Zambia, Zimbabwe
This species inhabits savanna ponds of highly variable size. During the dry season, X. muelleri is found at the banks of rivers. The data found in the available literature almost exclusively refer to savanna habitats (e.g. Schiøtz 1967, Walker 1968, Joger 1981, Hughes 1988, Böhme et al. 1996). Only Schiøtz (1963) mentions a dry forest habitat where X. muelleri occurs in syntopy with Silurana tropicalis. However, the two species were never found in the same pond, thus resembling very much the situation in Comoé National Park. The data concerning the preferred habitat types are somewhat contradictory. For example, small ephemeral ponds are mentioned by Noble (1924), Loveridge (1933), Schiøtz (1963), Joger (1981, 1982) and Böhme et al. (1996), whereas Walker (1968), Broadley (1971), Lamotte & Xavier (1981), Poynton & Broadley (1985a), Lambiris (1988), and Passmore & Carruthers (1995) refer to permanent ponds and lowland rivers as preferred habitats. According to Channing (1989) X. muelleri in Namibia inhabits pans and deep pools, often even in the presence of large fish. Finally, Arnoult & Lamotte (1968) state
semi-permanent waters. It is very difficult to decide which habitat type is really preferred, as most studies exclusively refer to the actual state of the respective habitat, which may have appeared totally different as it was colonized by clawed frogs. Residuary puddles are mentioned quite regularly, but these are often situated in the dry beds of brooks and rivers. In the Comoé National Park, large but temporary pools are apparently preferred, at least during the breeding season.
Life History, Abundance, Activity, and Special Behaviors
X. muelleri spends the dry season in the bank zone of the rivers, migrating into the savanna as soon as heavy rainfall sets in. I have found them in the gallery forest only during those migrations. As X. muelleri reappears almost immediately even in ponds far away from the permanent rivers, it seems highly probable that some frogs survive the dry season in the mud of those ponds. In Nigeria, Schiøtz (1963) found animals under humid layers of leaf litter in the dry season. According to Noble (1924) they buried themselves in the mud when ponds dried out. If it happens to rain at night, the frogs often move between different ponds. Drift fences with pitfall traps arranged at one pool have shown that even well-filled ponds are often left and/or re-colonized by these animals. Short migrations made by adult specimens are referred to in Walker (1968), too. According to this author, the species call both during day and night.
Reproduction apparently takes place exclusively in a rather restricted number of ponds, so I seldom succeeded in recording tadpoles of X. muelleri (Rödel 1998b). They seem to be comparatively common in large ponds, but occur occasionally in puddles containing less than 200 l or in residuary ponds, e.g. those found in the dry beds of seasonal brooks. As the tadpoles inhabiting large ponds always form larger swarms whereas those found in puddles are less numerous or even solitary, it is highly probable that the latter have been washed accidentally into these habitats during periods of heavy rainfall. Like the tadpoles of S. tropicalis, those of X. muelleri filter their food in mid-water, swimming either on the spot, or moving forward rather slowly. In flight, however, these animals can reach astonishingly high speeds, jumping occasionally even above the surface. According to Stewart (1967) and Lambiris (1988), the tadpole of this species usually swim horizontally. In Comoé National Park I observed them always with the head directed downward. Stewart (1967) confirms that swarms of 20–30 specimens are found mostly in mid-water.
The observations made by Joger (1982) apparently speak in favor of a rather extended breeding season: he found various stages of development in one and the same pond. At Comoé National Park, tadpoles occur throughout the rainy season. The breeding ponds in Ghana are said to dry up before September (Arnoult & Lamotte 1968). In Nigeria, Walker (1968) found numerous mummified tadpoles, mainly during the months of November-December. Noble (1924) identified green algae and diatoms as food items in the alimentary tracts of tadpoles. Adults’ stomachs contained arthropods and small Xenopus tadpoles. Haagner & Haagner (1997) report on storks preying on X. muelleri in Natal.
In 1993, two weeks after the rainy season had set in, we found a larva measuring 60mm (TL) whose limbs had not yet emerged. Two weeks later, the tadpole metamorphosed, having reached a length of 21.8 mm. Some example measures and weights (TL in mm, weight in g): 42/ 0.24; 45/ 0.48; 48/ 0.75; 55/ 0.68; 58/ 1.44; 63/ 1.53; 68/ 1.38; 72/ 1.75. Metamorphosis set in when the tadpoles had reached a TL of more than 5 cm. The largest tadpole ever collected in Comoé National Park measured 100mm, showing fully developed hind limbs. Freshly metamorphosed young measured more than 20 mm. The largest tadpole collected by Noble (1924) measured 87mm. Stewart (1967) writes that the length of the tentacles corresponds to more than ¼ of the TL. According to Lambiris (1988), tadpoles reach a TL of 70 mm, whereas Arnoult & Lamotte (1968) mention animals measuring 98 mm (TL). According to the latter, the tentacles begin to emerge at a TL of 7 mm (BL: 2.5 mm). At this stage, exterior gills have already been reduced almost completely. Freshly metamorphosed animals are reported to measure 40 mm (SVL, Arnoult & Lamotte 1968).
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Originally submitted by: Marc-Oliver Rödel (first posted 2001-02-21)
Edited by: Vance T. Vredenburg (2023-05-31)
Species Account Citation: AmphibiaWeb 2023 Xenopus muelleri: Idwi lika-Müller (Zulu) <https://amphibiaweb.org/species/5258> University of California, Berkeley, CA, USA. Accessed Sep 30, 2023.
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Citation: AmphibiaWeb. 2023. <https://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 30 Sep 2023.
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