Phrynobatrachus latifrons Ahl, 1924
Original Published Description:
Ahl's River Frog (English)
Phrynobatrachus latifrons is a small species (SVL < 23 mm) of puddle frog distributed across West Africa. Members of this genus are identified by the presence of a midtarsal tubercle, elongate inner metatarsal tubercle, and outer metatarsal tubercle. This species is characterized by moderate webbing (2-2.5 phalanges free of webbing on toe IV), absence of eyelid spine, lack of enlarged discs of finger and toes, and a yellow throat in breeding males.
This species ranges very widely in West Africa in both the forest and the savanna zones from Senegal, east to northern Cameroon, including Benin, Burkina Faso, Cameroon, Côte d'Ivoire, Gambia, Ghana, Guinea, Liberia, Mali, Nigeria, Senegal, Sierra Leone, and Togo. It has not been recorded from Guinea-Bissau and Niger, but it almost certainly occurs in these countries.
This species is named for the Latin 'latus' meaning wide or broad and 'frons' meaning forehead, brow, or face.
The two populations of puddle frogs identified as P. aff. latifrons from the Democratic Republic of Congo and Tanzania are morphologically similar to the West African P. latifrons but differ from this species by 18–19% in mtDNA (Zimkus et al., 2010). In addition, the P. aff. latifrons populations differ from each other by 7–8%. Additional study is needed to determine if these species can be assigned to known species or if this group comprises one or two new species.
This small-sized species (SVL of males up to 20 mm; females up to 23 mm) is characterized by moderate webbing (2-2.5 phalanges free of webbing on toe IV), absence of eyelid spine, lack of enlarged discs of finger and toes, and a yellow throat in breeding males.
Adult males range in size from 14–20 mm (SVL) and weigh 0.3–0.8 g, with most 17–18 mm in length and weighing 0.5–0.7 g. Adult females measure 16–23 mm and weigh 0.4–1.2 g, with most measuring 19–21 mm and 1.0–1.1 g (Rödel, 2000).
This species has a rather pointed snout, and the skin is smooth with a number of large and rounded warts on the dorsum, particularly on the anterior part of the back, and central outer parts of thighs. Additional large comma-shaped warts converging towards the snout are found behind the eyes. The mean index head width/SVL is 0.26 ± 0.03 (N = 57). The tympanum is visible but very small and feebly defined. No eyelid cornicle is present. The tips of fingers and toes may be slightly enlarged, but digital discs are not present. Manual webbing is absent, and rudimentary webbing is present on the feet with 2-2.5 phalanges free on toe IV. The pedal webbing formula is: 1 (0) or (0.5); 2 i/e (1–0) or (0.75–0.5) or (0.5–0); 3 i/e (1) or (1–0.5); 4 i/e(2) or (1.5); 5 (0.5) or (1). A small inner metatarsal tubercle, an outer metatarsal tubercle, and a tarsal tubercle are present. Males have a subgular vocal sac that is not always clearly discernible.
The basic color of the dorsum varies from light gray brown, or darker brown to almost black. Almost black animals are found on darker soil, whereas those encountered on lighter substrates are beige. Breeding males may be bright yellow or green. Parts of the back, especially the warts, may be darker or even black. Dark transverse bands are always present on the thighs and shanks. A fine light mediodorsal line or a broad band, starting just at the snout tip or between the eyes may be present or lacking. These lines or bands may be white, orange, red or green. If they are red they usually show white or orange borders. Very rarely, the lines may be broken, sinus-shaped, zigzagged or ramified. The intensity of the colors apparently depends on the physiological status of the frog, e.g. the backs of breeding males with green dorsal bands may become plain green. However, this color may be "withdrawn" to the center of the back within a few minutes. A dark stripe starting at the snout tip extends above the nostrils to the eyes. Behind the eye, it crosses the tympanum and extends diagonally towards the belly, being occasionally interrupted above the base of the forearm. Another short dark band sometimes stretches from the groin to the back. The lower edges of the posterior thighs bear yellow longitudinal lines with black borders. These lines turn upward in the vent area, fusing occasionally above the anus. The throat and the rest of the venter are usually white; only a few females have throats mottled with black and white. The throats of breeding males are deep yellow. Black points occasionally appear on the throat and in the pectoral area (compare Ahl 1924a). The edge of the lower jaw often bears dark bars. The webs may be slightly pigmented. In alcohol, both the pattern and the warts often fade, so that it becomes difficult to distinguished them from other Phrynobatrachus species. However, the black lateral lines and the vertebral bands and lines usually remain visible, but being less distinct or faded.
Habitat and Ecology
It lives in wooded and open savanna, secondary forest, heavily degraded former forest (farm bush), agricultural areas, and inselbergs in rainforest. It avoids closed primary rainforest. It breeds in temporary ponds, puddles, and roadside ditches.
Typical P. accraensis were found in the rainforest zone of the Ivory Coast, both in areas disturbed by man and in those parts of the primary forest at the Tai National Park where vegetation happens to be rather scanty (e.g. on Inselbergs). Hughes (1988) quotes P. accraensis for any habitat in Ghana, but this probably shows that he does not distinguish savanna and forest forms. Schiøtz (1967) considers P. accraensis a "farm bush" element of the fauna, i.e. occupying an intermediary position between savanna and forest species. Lamotte (1967b) quotes both savanna and forest locations, but the latter are reported to prevail. Different types of water bodies are colonized at different seasons.
It is an extremely common species (Rödel and Schiøtz, 2004).
Populations of this species are stable (Rödel and Schiøtz, 2004).
The diet of this species consists mainly of arthropods, although they will consume almost anything (Rödel, 1995). One collected male was swallowing a Kassina tadpole measuring 15 mm while still in the net. At Lamto, adult P. accraensis mainly preyed on ants (Barbault, 1974).
During the day, single males will call from concealed calling sites on the floor, between tufts of grass or from floating aquatic plants. At night, they are also met on the plain ground or on grass leaves, up to 30 cm above the soil. Amplectant pairs perform a headstand underwater while spawning. The female clings to aquatic plants during egg laying. In this position, a single egg layer is spread over the water surface (Linsenmair, pers. comm.). As a consequence of this behavior, the film is almost always attached to grass. Clutches are also found even when it does not rain at all for a longer period. However, the frogs usually spawn after rainfall. The intensity of precipitation apparently plays a minor part, and it does not always trigger reproduction. Many pairs spawn simultaneously. The egg films are often concentrated in a few areas of the pond. Shallow shady sites bearing a rich vegetation are preferred spawning sites. Females normally lay two clutches consisting of 267 ± 130 eggs with a mean egg diameter of 0.9 mm (N = 93; Barbault and Trefaut Rodriguez, 1979, Barbault 1984). At Lamto, population sizes have proved to vary considerably during a given year, which may be a result of the succession of two generations within the same year, or the humidity dependent migrations (Rödel, 2000).
The creaking advertisement call starts as a sequence of rapid pulses whose frequency ranges from 2.45–4.82 kHz. This phase lasts about 0.4 sec. After a short pause (0.2 sec), several notes comprising 3–7 pulses are uttered (frequency range: 1.88–5.14 kHz). The duration of a single note ranges from 0.33-0.44 sec, and that of the pauses separating the single pulses is 0.01–0.20 sec; those between the notes last 0.14–0.16 sec. 4–5 click sounds lasting 0.01 sec may precede the call. They are uttered at intervals of 0.23-0.43 sec. Their frequency ranges from 3.11–5.13 kHz. The duration of the longest call recorded was 17.55 sec. However, the call sometimes ends much earlier or even breaks off after the first phase. This happens quite frequently when the frogs call from their refuges during the day in the dry season. To the human ear, the call of P. accraensis sounds quite similar. Schiøtz (1964) has published a sonagram that he refers to this species. 3–5 notes, each comprising 1–3 pulses form units that are uttered at short intervals. These calls last up to 7 sec, with up to 35 pulses per second. The frequency intensity maximum lies between 2–4 kHz. Except for its duration, this call shows a structure that resembles, to a large extent, that of the P. latifrons I recorded. Schiøtz (1964) recorded these calls in a savanna in Sierra Leone. The call of P. gutturosus is quite similar, but it begins with a long buzzing sound, whereas a few clicks are uttered towards the end. Females lay 300 to 1300 eggs are laid as a single surface layer, most frequently attached to vegetation in shallow water zones.
The eggs are light sand yellow, and their diameter, incl. the jelly, is 2.2–2.3 mm and 0.8 mm.
Juveniles of this species fed throughout the dry season, thus maturing for the beginning of the next rainy season (Rödel 1995). The larvae usually prefer the bottom of the deeper zones of ponds, as well as more vegetated sites. They may be found throughout the rainy season (Rödel 1998b).
P. latifrons reaches sexual maturity at the age of 4–5 months, living only for further two months (Rödel, 2000).
Tadpoles are ovoid in shape, and a feeble constriction is discernible on a level with the spiracle. The respective parts show a conspicuous red pigmentation. The basic color of the very tiny tadpoles is dark red-brown. The tail fin is transparent or finely spotted, starting dorsally on the last quarter of the body and converging evenly towards the tip of the tail. On live animals, the serrated horny beaks seem to be very narrow. If the skin has contracted, e.g. on animals prepared for SEM photos, the beaks appear more voluminous. The keratodont formula is 1 / 1+1 // 2+2 or 1+1 // 2+2. These variations have been recorded within the offspring of a single pair. Additional yet very short and more caudal tooth rows may precede the papillae. All the tooth rows are arranged on the outer edges of dermal folds. The horny teeth have short broad bases. They bear a short semicircular "crown" with 4–5 tips. The mouth is surrounded by a single row of cone-shaped papillae followed by a variable number of filamentous ones. Freshly hatched tadpoles with external gills, do not yet possess oral discs. Their BL is 1.1–1.4 mm (TL: 3.7–4.1 mm). Reared in captivity for two months, they measured 6 mm BL, and 17 mm TL, possessing fully developed hind legs. A few days later, the first young frogs, of approx. 6 mm, left water. Tadpoles captured in ponds and possessing developed hind legs measured 8–10mm. According to my observations, the forelegs emerge at a BL of 7 mm (TL: 12 mm). Six weeks after the beginning of the rains, the first young frogs were observed on the edges of the ponds. They measured 7–7.5 mm, and their coloration was already as variable as in adult frogs.
Activity and Special Behaviors
During the dry season, P. latifrons lives on the riverbanks and near those forest ponds that still contain water. The frogs inhabiting forests, particularly the humid tracks of large mammals, are diurnal, while those living on the riverbanks are strictly nocturnal. During the day, these frogs seek refuge under stones and dead wood or in crevices on the very edges of water bodies where the temperature may be 35 °C at most, compared to 40 °C outside these refuges. At night, the frogs forage for prey in a very limited area bordering open water, feeding mainly on arthropods. Some individuals always seem to hunt in the same area. Complexly structured bank sectors usually harbor more frogs. Habitat choice and activity period are apparently humidity dependent (Rödel ,1995). After rainfall, many individuals leave the river area, cross the gallery forest, and arrive at the savanna ponds recently filled with water. This “migration” or habitat shift may be a result of many factors. First, rising water level of the river may directly threaten the frogs. Second, the soil is much more humid after rain, and these frogs may therefore not be restricted to foraging at the edge of the river. Lastly, when the savanna ponds are full, P. latifrons may begin its reproduction phase. During extended dry periods, P. latifrons is found more frequently in the forest, particularly on the edges of pools and on riverbanks, waiting to mate with those females that contain mature eggs during the dry season. This species is mostly diurnal during the rainy season, although males may call at night when sympatric species are less common and their voices are not drowned out (Rödel, 2000).
Evolution and Systematics
Mitochodrial sequence data from 12S rRNA, valine-tRNA, and 16S rRNA fragment, as well as combined sequence data from mitochondrial and nuclear (RAG-1) genes indicate that P. latifrons is the sister species of a group that contains P. cf. hylaois and P. aff. latifrons (Zimkus et al., 2010). The two populations of puddle frogs identified as P. aff. latifrons from the Democratic Republic of Congo and Tanzania are morphologically similar to the West African P. latifrons but differ from this species by 18–19% in mtDNA. In addition the P. aff. latifrons populations differ from each other by 7–8%. Additional study is needed to determine if these species can be assigned to known species or if this group comprises one or two new species.
It is a very adaptable species that is not facing any significant threats (Rödel and Schiøtz, 2004).
Conservation Actions and Management
It occurs in many protected areas (Rödel and Schiøtz, 2004).
- Phrynobatrachus latifrons latifrons — Ahl, 1924 (synonym)
- Phrynobatrachus latifrons togoensis Ahl, 1924 (synonym)
- Hylarthroleptis accraensis Ahl, 1925 "1923" (synonym)
- Hylarthroleptis albolabris Ahl, 1925 "1923" (synonym)
- Phrynobatrachus albolabris — Deckert, 1938 (synonym)
- Phrynobatrachus accraensis — Deckert, 1938 (synonym)
- Phrynobatrachus parogoensis Loveridge, 1955 (synonym)