A large and compact ranid frog with a pointed head. Two collected males measured 51 mm each (SVL). A female measured 56 mm. Six continuous ridges start at the level of the eyes. A shorter additional pair runs parallel, median to the dorsolateral ridges. The tympanum is large, distinct and slightly concave. The skin is somewhat granular, at least during the breeding season. Males have paired lateral vocal sacs whose slits start below the corner of the mouth and end below the base of the foreleg. They also have enlarged thenar tubercles and swollen first fingers. Sturdy hind legs of moderate length. The thighs measure 0.5 of the SVL, the shank 0.6 and the foot, incl. longest toe, 0.7 of the SVL. The massive inner metatarsal tubercle is almost as long as the shortest toe (0.8–1.2). A small outer metatarsal tubercle is present. Webbing formula: 1 (0.5), 2 i (1), 3 i/e (1–0.5), 4 i (1), 5 (0).
Guibé & Lamotte (1957) and Perret (1966) give 42–52 mm (SVL) for males and 47–57 mm for females. Mertens (1940) gives a SVL of up to 60 mm.
Voucher specimens: SMNS 8955 1–4 + tadpoles.
Coloration: Besides frogs showing a brownish basic coloration, there are also gray ones. Numerous black or dark brown spots are present on the dorsal ridges. However, these spots are also found on the rest of the back and on the flanks. They often fuse into larger patches. Extremities with well-defined dark transverse bands. These bands are most conspicuous on the proximal part of the thighs. Their distal parts either show a yellow longitudinal line, bordered with black, or they are mottled in black and yellow. Besides, many frogs have larger areas bearing numerous tiny spots which gives them an altogether mottled appearance. All examined specimens had fine but distinct white to yellow vertebral lines. The dorsolateral ridges are also white to red, and their color extend to the upper part of the eye. Another light line emerging at the upper lip runs below the eye and stretches to the area below the tympanum. The pupil has a narrow yellow border. The tympanum is always two-colored, showing a light, egg like central marking pointing upward. The venter is whitish to gray. The throat occasionally shows dark spots. The webs are pigmented dark. In alcohol the colors turn somewhat gray or brown; otherwise, they are similar to the life coloration.
Voice: The short croaking and very loud advertisement call consists of many notes, each comprising approx. 6 pulses. Two distinct harmonies are discernible. The lower has a frequency range of approx. 0.9–1.4 kHz. Calling males are extremely sensitive to any kind of disturbance. Amiet (1974b) illustrates a sonagram of this species. He describes the call as a loud "dry" sequence of "crrra" sounds comprising 7–8 pulses each and lasting approx. 0.2 sec. They are uttered at intervals of 0.4–0.6 sec. The dominant frequencies are 0.5 and 3kHz.
Distribution and Habitat
Country distribution from AmphibiaWeb's database: Benin, Cameroon, Central African Republic, Chad, Congo, the Democratic Republic of the, Gambia, Ghana, Guinea, Mali, Mauritania, Nigeria, Senegal
Range: According to Frost (1985), the range of P. trinodis stretches from Senegal to Nigeria, Cameroon and R.D. Congo. Published records exist for the following countries: Senegal, Gambia, Guinea, Mali, Ivory Coast, Ghana, Nigeria, Cameroon, R.D. Congo, Chad, Central African Republic (Angel 1922, Andersson 1937, Mertens 1938a, 1940, Schiøtz 1963, 1964a, 1967, Perret 1966, 1981, Lamotte 1966, 1969, Wake & Kluge 1969, Amiet 1973a, 1974b, Hughes 1988, Joger 1990, Pauwels & Meirte 1996, Rödel 1996, 1998b, Joger & Lambert 1997). The records from East Africa published by Pfeffer (1893) and Loveridge (1930) most probably refer to other species.
Habitats: In the Comoé National Park, this species has exclusively been found in savanna habitats. This statement also applies to the rest of its range (Guibé & Lamotte 1957, Lamotte 1969), with arid to very arid savannas of the Sudan (Lamotte 1966, Perret 1966), Hughes 1988) and Sahel region (Schiøtz 1963, 1967, Perret 1981) being preferred. The population in the northern Guinea savanna of the Comoé National Park therefore marks the southern border of its range. This species apparently prefers small (Amiet 1973a, 1974b) and shallow ponds (Lamotte 1969).
Life History, Abundance, Activity, and Special Behaviors
Spawn: Single floating films composed of rather large eggs with black and white poles. Including the jelly the eggs measure 8.5 to 8.7mm. The undeveloped egg measures approx. 4mm. The tadpoles hatch within a day.
Tadpoles: Freshly hatched larvae have exterior gills, and their BL can reach 4.4 mm. Their forelegs emerged at a BL of 12–13 mm (TL: 34 mm). The largest tadpole showing no signs of hind limbs measured 21 (BL; TL: 42 mm). Tadpoles collected in ponds had fully developed hind limbs when they measured 13–23 mm (BL; TL: 32–41 mm). The SVL of freshly metamorphosed frogs was 13–17 mm. In the wild, they metamorphosed after three weeks. The basic color of the rather rapidly growing tadpoles is beige to drab brown, and their heads are more pointed than those of other Ptychadena tadpoles. The dorsal part of the tail fin inserts at the level of the spiracle. Ventral and dorsal part of the tail fin are broad, robust and transparent, converging abruptly near the tip so forming a tail filament. Older tadpoles are heart-shaped. The oral disc shows moderately massive serrated horny beaks, surrounded laterally and caudally by single rows of papillae. The papillae are densely packed at the corners of the mouth. Keratodont formula: 1 / 1+1 // 2.
Another tadpole morph hatches from apparently similar eggs. With their longer and more muscular tail axis, they appear more elegant than the morph described above. The flanks of these tadpoles are almost parallel. The tail fin of this morph inserts at the same level, but its borders converge evenly towards the tip of the tail, without forming a tail filament. The papillae surrounding the oral disc are less numerous, but larger. The long slender horny teeth are bicuspid. Metamorphosing frogs do not differ at all from the first morph. Lamotte et al. (1958) give the following keratodont formula for ovoid larvae whose caudal fins converge evenly: 1 / 1+1 // 2. However, they illustrate an animal whose formula is 1 // 2. The number of intestinal slings quoted in various tadpole descriptions is virtually useless because it often only depends on the respective diet (see Babok 1903a/b).
Biology: The large inner metatarsal tubercles indicate that this species digs itself into the soil to survive the dry season. I have not yet succeeded in collecting any individuals during this period. The use of subterranean refuges during the dry season has also been suggested by Lamotte (1969), Amiet (1973a) and Perret (1981). When the savanna ponds are partially filled after the first rains, P. trinodis appears immediately, and the clutches are usually deposited within the first night after rainfall. Similar observations were made by Amiet (1973a, 1974b) in northern Cameroon. However, he observed the breeding period to last just one single week. At Comoé National Park, active animals are found throughout the rainy season. Calling males usually sit in shallow water or in the vegetation on the banks. Their choruses set in at long intervals. Most often they start immediately after Hoplobatrachus occipitalis has finished calling.
During the beginning of the rainy season P. trinodis is one of the most dominating Ptychadena species at most savanna ponds. Later on, these frogs apparently avoid those ponds where P. schubotzi and P. bibroni prevail. P. trinodis is then virtually restricted to small and tiny waters which often lack any vegetation. Lamotte (1969) underlines the degree to which this species is related to water during the rainy season. As the animals only betray their presence by their calls, that are uttered at night or during periods of rainfall (Amiet 1973a), I can neither conform nor refute this statement. However, calling males are heard throughout the rainy season. The highly variable sizes of larvae of the same stage possibly indicate that unfavorable conditions induce smaller animals to metamorphose earlier and therewith to avoid the risk of desiccation.
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.
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 2001-05-07
Edited by Arie van der Meijden (2002-02-08)
Species Account Citation: AmphibiaWeb 2002 Ptychadena trinodis <http://amphibiaweb.org/species/4962> University of California, Berkeley, CA, USA. Accessed Oct 22, 2017.
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Citation: AmphibiaWeb. 2017. <http://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 22 Oct 2017.
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