Overview

Comprehensive Description

Description

Diagnosis: Typical body shape; large ranid frog; protruding eyes; dorsal ridges; large inner metatarsal tubercle.

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.

This account was taken from Rödel, M.-O. (2000), Herpetofauna of West Africa vol. I. Amphibians of the West African Savanna, with kind permission from Edition Chimaira publishers, Frankfurt am Main.
For references in the text, see here.

  • Rödel, M. O. (2000). Herpetofauna of West Africa, Vol. I. Amphibians of the West African Savanna. Edition Chimaira, Frankfurt, Germany.
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Distribution

Range Description

This species ranges from southern Somalia, Kenya and Tanzania, south to Mozambique, southern Malawi, southern Zambia, Zimbabwe, Botswana, northern and eastern South Africa and Swaziland.
There are also populations currently assigned to this species in northern Benin, northern Nigeria and northern Cameroon, and in Mauritania, Senegal and Gambia. There are no records in the poorly explored regions between Cameroon and Somalia, and so its occurrence in these areas is not indicated on the distribution map. However, it might occur in the intervening areas in the Central African Republic, Chad, South Sudan, the Democratic Republic of Congo and Uganda, and also in Togo, Burkina Faso, Ghana, Côte d’Ivoire, Mali and Guinea.

Its distribution in eastern and southern Africa needs re-examination in light of recent separation of Pyxicephalus edulis from P. adspersus. Many specimens have not been clearly assigned between these two species, and so the distribution map should be regarded as provisional. It occurs from sea level up to 1,500 m asl in South Africa.
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Distribution and Habitat

Habitats: According to Amiet (1973), plain marshy areas are preferred in northern Cameroon. Walker (1966) mentions flooded meadows and ditches. Altogether, this species is found in arid savannas where it apparently prefers sand and clay substrates (Lanza 1981, Poynton & Broadley 1985b, Lambiris 1989, Herrmann & Kabisch 1991). The range of Pyxicephalus edulis enters West Africa only peripherally. In Nigeria, this species inhabits an area stretching from northern Guinea to the Sahel savanna (Schiøtz 1963, 1967, Walker 1966, 1968).

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).

  • Rödel, M. O. (2000). Herpetofauna of West Africa, Vol. I. Amphibians of the West African Savanna. Edition Chimaira, Frankfurt, Germany.
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The species is widespread in Central and East Africa; they occur along the northeastern border of South Africa which indicates that P. edulis is also likely to occur in Botswana and Zimbabwe. It can also be found in northern and eastern Swaziland (Text from Minter et al., 2004, © SI/MAB Biodiversity Program).

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Physical Description

Morphology

The original description of this speciesby Peters (1854) is woefully inadequate, including only the following: "Pedibus longitudine corpori aequalibus; olivaceo-viridis, maculis fuscis, linea dorsali flava." This is translated by B. Zimkus to the following: "Foot length equal to the body; olive-green, dark spots, yellow dorsal line."

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Size

Males do not exceed 120 mm in snout–vent length (Text from Minter et al., 2004, © SI/MAB Biodiversity Program).

Males are up to 100 mm and females up to 145 mm in snout-vent length (Harper et al., 2010).

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Diagnostic Description

This is a large rotund frog with short legs. The dorsum is brown to green and covered in rough glands that are elongate or round. There are projections on the lower jaw that resemble teeth. The tympanum is small, but distinctly visible. The first finger is longer than the second. The toes are webbed only at the base (Harper et al., 2010).

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Look Alikes

Comparisons

This was previously considered a subspecies of P. adspersus, but the teeth-like projections and large size are distinctive (Harper et al., 2010).

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Ecology

Habitat

Habitat and Ecology

Habitat and Ecology
It inhabits flat areas in open grassy woodland and marshy areas in eastern and southern Africa, and in very dry savannah in West Africa. It has been recorded from riverine and woodland habitats in western Tanzania (Gardner et al. 2007). It is fossorial, only coming to the surface at the beginning of the rainy season. It breeds in shallow, well-vegetated seasonal pans (although it has also been found at a puddle without vegetation in northern Benin; Nago et al. 2006), as well as many man-made small waterbodies. It has been found in rice paddies in Mozambique. It is active at night during the breeding season. The males guard the tadpoles, protecting them from predation.

Systems
  • Terrestrial
  • Freshwater
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Habitat and Ecology

Jacobsen (1989) found that this species inhabits several bushveld vegetation types in the northeastern parts of the Savanna Biome, from sea level to an altitude of about 1500 m (Text from Minter et al., 2004, © SI/MAB Biodiversity Program).

This species inhabits flooded grasslands and shrubland up to 1500 m (Harper et al., 2010).

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Associations

Food items include a variety of invertebrates and small vertebrates, including frogs. Several bird species, Nile Monitors Varanus niloticus and humans are known to prey on this species (Text from Minter et al., 2004, © SI/MAB Biodiversity Program).

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Life History and Behavior

Behavior

Activity and Special Behaviors

P. edulis spends up to 10 months of the year in a dormant state beneath the soil surface (Mitchell 1946), the species products a cocoon to prevent desiccation (Text from Minter et al., 2004, © SI/MAB Biodiversity Program).

This is a fossorial species that is seen only in the rainy season (Harper et al., 2010).

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Reproduction

Advertisement Call

The advertisement call was described by Channing (2001) as sounding like “the barking of a small dog."

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Flat, low-lying areas in open, grassy woodland, that become flooded after heavy rain or contain shallow, seasonal pans, constitute prime breeding habitat and support large breeding populations. Channing et al. (1994a) found this species breeding in rice paddies in Mozambique. Breeding takes place at night after heavy rain. No aggressive behaviour was observed in a breeding population near Beira (Text from Minter et al., 2004, © SI/MAB Biodiversity Program).

Breeding takes place in shallow pools with ample vegetation. Females lay several thousand eggs singly and scattered. Males guard tadpoles (Harper et al., 2010).

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Conservation

Conservation Status

IUCN Red List Assessment


Red List Category
LC
Least Concern

Red List Criteria

Version
3.1

Year Assessed
2013

Assessor/s
IUCN SSC Amphibian Specialist Group

Reviewer/s
Stuart, S.N.

Contributor/s
Channing, A., Poynton, J., Howell, K. & Minter, L.

Justification
Listed as Least Concern because, although it is also eaten in parts of its range, it has a wide distribution, is tolerant of a broad range of habitats and has a presumed large population.

History
  • 2009
    Least Concern
  • 2004
    Least Concern
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IUCN Red List Category and Justification of Conservation Status

More detailed studies of habitat requirements, breeding biology, duration of the larval stage and development are recommended for this species (Text from Minter et al., 2004, © SI/MAB Biodiversity Program).

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Population

Population
It is a common species in East Africa and is quite common in South Africa.

Population Trend
Unknown
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Life History, Abundance, Activity, and Special Behaviors

Eggs: According to Passmore & Carruthers (1995), numerous heavily pigmented single eggs are deposed in shallow (P. adspersus?) or deep water (P. edulis). Herrmann & Kabisch (1991) report on 900 (max. 3500) eggs which are deposited as a surface layer in two subsequent charges. At a water temperature of 29 °C, the tadpoles hatch within 20 hours. As these authors describe animals from Malawi, these frogs are most probably P. edulis.

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.
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Threats

Major Threats
The major threat through most of its range is harvesting of frogs for local consumption. This species is sometimes also found in the international pet trade but at levels that do not currently constitute a major threat. In western Tanzania, much of the miombo woodland area is increasingly threatened by habitat degradation following conversion to agriculture or overharvesting (see Gardner et al. 2007).
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Management

Conservation Actions

Conservation Actions
There are large populations in many protected areas.
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Relevance to Humans and Ecosystems

Benefits

Uses

In Burkino Faso, P. edulis is one of many frog species that are traded and it is the second most consumed frog species. In Malanville, Benin, it is the third most commonly "caught and traded frog." Because villagers are employed to catch and prepare frogs, and because they are an "important international trading item", frogs are an integral part of the economy in areas with large frog populations. Aside from their value as an essential food source, they may also be used for cultural reasons and as traditional medicine in areas where Western medicine is not available. The overexploitation of frogs has lead to villagers observing high decline rates in several species of frog, P. edulis having the highest reported rate among them. (Mohneke, 2010)

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Wikipedia

Edible bullfrog

The edible bullfrog (Pyxicephalus edulis) is a species of frog in the Ranidae family. It is found in Botswana, Cameroon, Gambia, Kenya, Malawi, Mozambique, Nigeria, Senegal, Somalia, South Africa, Swaziland, Tanzania, Zambia, Zimbabwe, and is possibly found in; Benin, Burkina Faso, Central African Republic, Chad, Democratic Republic of the Congo, Ivory Coast, Ghana, Guinea, Mali, Namibia, Sudan, Togo, and Uganda. Its natural habitats are dry savanna, moist savanna, subtropical or tropical seasonally wet or flooded lowland grassland, swamps, intermittent freshwater lakes, intermittent freshwater marshes, arable land, pastureland, ponds, canals and ditches, and man-made karsts.

Immature specimen

References[edit]

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