Trichobatrachus robustus Boulenger, 1900
Original Published Description:
Hairy Frog (English)
Trichobatrachus robustus is a large, West African species that is well known for the hair-like dermal papillae founds in males. This species is also notable for having claw-like terminal phalanges on their hind feet that cut through the skin.
This species occurs in lowlands from the Osamba Hills in eastern Nigeria to the Mayombe Hills in extreme western Democratic Republic of Congo. There are records from Nigeria, Cameroon, Equatorial Guinea, Gabon and the Democratic Republic of Congo. It is presumed to occur in Congo and in the Cabinda Enclave of Angola (Amiet and Burger, 2004).
The specific epithet is from the Latin 'robustus' meaning hard, solid, or robust, and it refers to the general size of the species.
According to the original description, the type material measured 110 mm in snout-vent length (Boulenger, 1900). Perret (1966) examined five males, ranging from 98.0-130.0 mm SVL, and two females, measuring 80.0 90.0 mm SVL. Means and ranges of the snout-vent length of 5 males and 7 females examined by Jones (1971) were 114.7 mm (100.4-124.9 mm) and 99.7 mm (88.5-112.7 mm), respectively. Males were 13% larger than females, and forelegs of males (22.8 mm; 17.1-26.0 mm) averaged 64% greater in diameter than the forelegs of females (12.3 mm; 11.3-14.0 mm).
Vomerine teeth are in two short transverse series betweent he rather large choanae. Head is larger, broader than long, and much depressed. Snout is very short, rounded, and with a distinct canthi and very oblique, slightly concave lores. Nostril is slightly nearer to the eye than the end of the snout. The interorbital space is slightly broader than the upper eyelid. The tympanum is moderately distinct and half of the diameter of the eye. The limbs are robust. The tips of digits are slightly swollen. The first finger is much longer than the second and as long as the third. The toes are half-webbed. The sub-articular tubercles and large. A feebly prominent, elongate, inner metatarsal tubercle is present. The tibio-tarsal articulation reaches the eye. The skin is smooth. Boulenger (1900) notes that the sides of body, back of thighs, and a stripe along the upper surfaces of the latter have hair-like papilla that are more developed in the female than in the male. However, Kükenthal (1927) examined specimens and notes that these hair-like appendages are found only in males.
Dorsum is olive-brown in color. A darker, black-edged broad band is present along the back, fading away behind and sharply defined in front by a black cross-bar between the eyes. A black canthal and temporal streak is present. Sides of the body and limbs are blackish. The lower parts are white; female has brown dots on the throat. Male has a pair of internal vocal sacs and three short ridges (two longitudinal and one transverse) of small horney black spines on the inner side of the first finger (Boulenger, 1900).
Outer metatarsals are bound together. Omosternum has a bony stype. Sternum is a cartilaginous plate, with style (Boulenger, 1900). Terminal phalanges are simple and obtuse; the terminal phalanges of toes II–V are distinctly claw shaped and bear markedly downturned, pointed tips (Blackburn et al., 2008).
Habitat and Ecology
It lives in fast-flowing rivers in lowland rainforest, and in secondary and agricultural habitats, including tea plantations. The tadpoles live in fast, even torrential, water, and at the foot of small waterfalls (Amiet and Burger, 2004).
It is rare around Yaounde, but much more common in the west of its range in Cameroon (Amiet and Burger, 2004).
Populations of this species are decreasing (Amiet and Burger, 2004).
Kükenthal (1912) concluded that the dermal "appendages" appear in males during the mating seaason and should be considered secondary sexual organs that are charged with sensory functions. The dermal papillae have also been hypothesized to increase the effective surface for respiration; Noble (1925) proposed that T. robustus males needed an enlarged respiratory surface due to possessing small lungs and a robust body.
The times of breeding of hairy frogs correspond to the seasons of heaviest precipitation, although they can breed at other times of the year. Sabater Pi (1966) reported 200 eggs produced by a female in November. Jones (1971) reported a total of 721 eggs produced by a female in 4 consecutive days in May, and two females additional females that expelled 720 and 150 eggs, respectively. Clusters and single eggs were expelled; of the 720 eggs expelled by one animal, 77.5% were in clusters of 2-23 eggs, and of the 150 eggs produced by another female, 64.7% were in clusters of 2-23 eggs.
Activity and Special Behaviors
Blackburn et al. (2008) showed that the bony claws of Trichobatrachus and Astylosternus are different both anatomically and functionally from those in all other vertebrates. Noble (1931) speculated that these "claws" might provide a ‘surer grip before leaping,’ while Durrell (1954) suggested that these claws are for defence as they can inflict ‘deep bleeding wounds.'
IUCN Red List Category and Justification of Conservation Status
The IUCN Red List (2010) categorizes this species as Least Concern in view of its wide distribution, its presumed large population, and because it is unlikely to be declining fast enough to qualify for listing in a more threatened category (Amiet and Burger, 2004).
It is presumably decreasing because of declining water quality, but it appears to be relatively tolerant of changes in the terrestrial habitats around its streams. It is subject to intense hunting pressure for food, and is often rare in the areas around villages. In the Rumpi Hills in Cameroon, local people eat the tadpoles (Amiet and Burger, 2004).
Conservation Actions and Management
It occurs in several protected areas (Amiet and Burger, 2004).
This large species is used as a food source and for cultural reasons (Gonwouo and Rödel, 2008; Mohneke et al, 2009).
- Astylosternus robustus — Noble, 1924 (synonym)