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.
Syntypes: BMNH, 2 specimens: one male, one female, "Benito River", Equatorial Guinea (Boulenger 1900).
Snout to vent length of approximately 110 mm; large head (broader than long); short rounded snout; nostril is somewhat nearer the eye than the tip of the snout; vertical pupils; notched tongue; two rows of vomerine teeth located between relatively large choanae; distinct tympanum that is approximately half the diameter of the eye; webbed pedal digits; bound lateral metatarsals; omosternum has a bony style; sternum is a cartilaginous plate lacking a style; simple terminal phalanges; subarticular tubercles are large; olive brown dorsally, with dark black bands between the eyes and on the dorsum.
The males of this species are much larger than the females. The males have a paired internal vocal sac and three short ridges (two longitudinal and one transverse) of small black spines along the inner surface of the first manual digit. There is a narrow posterior diverticulum of the lung that apparently occurs only in males. The male also has dermal papillae extending along the lateral surfaces of the body and proximal hindlimbs (Boulenger 1900; Noble 1925; Perret 1966)
The specific epithet is from the Latin 'robustus' meaning hard, solid, or robust, and it refers to the general size of the species.
Distribution and Habitat
Trichobatrachus robustus is known from Equatorial Guinea, Cameroon, the Democratic Republic of Congo, and Nigeria. In 1998, it was collected in Southwest Cameroon by the ALSCO Biodiversity Conservation Initiative (Herrmann and Herrmann 2002).
Trichobatrachus robustus is thought to be terrestrial, returning to the water for breeding. Stomach contents have included slugs, myriapods, spiders, beetles, and grasshoppers.
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).
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).
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).
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).
Habitat and Ecology
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).
Life History and Behavior
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.'
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.
IUCN Red List Assessment
Red List Category
Red List Criteria
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).
Life History, Abundance, Activity, and Special Behaviors
Egg masses are laid on rocks in streams. The tadpoles of this species are reported to be quite muscular. They are carnivorous and their mouths contain several rows of cornified teeth.
Noble (1925) hypothesized that the dermal papillae of the males increased 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.
Populations of this species are decreasing (Amiet and Burger, 2004).
Life History, Abundance, Activity, and Special Behaviors
The status of this species is unknown.
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).
Relevance to Humans and Ecosystems
This large species is used as a food source and for cultural reasons (Gonwouo and Rödel, 2008; Mohneke et al, 2009).
The hairy frog (Trichobatrachus robustus), also known as the horror frog or Wolverine frog, is a Central African species of frog in the Arthroleptidae family. It is monotypic within the genus Trichobatrachus. Its common name refers to the somewhat hair-like structures on the body and thighs of the breeding male.
The species is about 11 cm long from snout to length. The large head is broader than long, with a short rounded snout. Males are much larger than females. The former have a paired internal vocal sac and three short ridges of small black spines along the inner surface of the first manual digit. Breeding males also develop – somewhat hair-like – dermal papillae that extend along the flanks and thighs. These contain arteries and are thought to increase the surface for the purpose of absorbing oxygen (comparably to external gills of the aquatic stage), which is useful as the male stays with his eggs for an extended period of time after they have been laid in the water by the female.
The species is terrestrial, but returns to the water for breeding, where egg masses are laid onto rocks in streams. The quite muscular tadpoles are carnivorous and feature several rows of horned teeth. Adults feed on slugs, myriapods, spiders, beetles and grasshoppers.
The hairy frog is also notable in possessing retractable "claws" (though unlike true claws, they are made of bone, not keratin), which it may project through the skin, apparently by intentionally breaking the bones of the toe. In addition, the researchers found a small bony nodule nestled in the tissue just beyond the frog's fingertip. When sheathed, each claw is anchored to the nodule with tough strands of collagen, but, as Gerald Durrell discovered firsthand, when the frog is grabbed or attacked, the frog breaks the nodule connection and forces its sharpened bones through the skin.
This is probably a defense behavior. Although a retraction mechanism is not known, it has been hypothesized that the claws later retract passively, while the damaged tissue is regenerated.
Amphibian researcher and biologist David Wake of the University of California, Berkeley, says that this type of weaponry appears to be unique in the animal kingdom, (although the Otton Frog possesses a similar "spike" in their thumb). Also David Cannatella, a herpetologist at the University of Texas, Austin, questions whether the bony protrusions are meant for fighting. They could allow a frog's feet "to get a better grip on whatever rocky habitat they might be in," he says.
It is found in Cameroon, Democratic Republic of the Congo, Equatorial Guinea, Gabon, Nigeria, and possibly Angola. Its natural habitats are subtropical or tropical moist lowland forests, rivers, arable land, plantations, and heavily degraded former forest.
T. robustus is threatened by habitat loss, but is not considered endangered.
Relation with humans
This species is roasted and eaten in Cameroon. They are hunted with long spears or machetes. The Bakossi people traditionally believed that the frogs fall from the sky and, when eaten, help childless human couples become fertile.
- Amiet, J.-L. & Burger, M. (2004). "Trichobatrachus robustus". IUCN Red List of Threatened Species. Version 2012.2. International Union for Conservation of Nature. Retrieved 26 June 2013.
- "Trichobatrachus ". Integrated Taxonomic Information System.
- Frost, Darrel R. (2013). "Trichobatrachus Boulenger, 1900". Amphibian Species of the World 5.6, an Online Reference. American Museum of Natural History. Retrieved 26 June 2013.
- The Bafut Beagles
- Legrand N. Gonwouo & Mark-Oliver Rödel (20 February 2008). "The importance of frogs to the livelihood of the Bakossi people around Mount Manengouba, Cameroon, with special consideration of the Hairy Frog, Trichobatrachus robustus". SALAMANDRA 44 1: 23–34. ISSN 0036-3375.
- AmphibiaWeb: Trichobatrachus robustus
- NewScientist news service: 'Horror frog' breaks own bones to produce claws Retrieved on June 9, 2008.
- Blackburn, David C.; Hanken, James & Jenkins, Farish A. Jr. (2008): Concealed weapons: erectile claws in African frogs. biology letters (published online). doi:10.1098/rsbl.2008.0219 – PDF