Description
Trichobatrachus robustus is the only species of the frog family, Arthroleptidae, in which males are typically larger than females, with male snout–vent lengths averaging 130 mm compared to 90 mm in females (Channing and Rödel 2019). This species has a compact body and a short, broad head with a distinct canthus rostralis. Trichobatrachus robustus has a tympanum to eye ratio of 50% (Boulenger 1900). The dorsal integument is smooth to granulated and covered with small, round tubercules (Amiet 1977). In breeding males, the upper surfaces of the thighs and lower flanks have long hair-like papillae made of vascularized skin (Boulenger 1900; Noble 1925). Tubercles on the feet are weakly developed, and an elongate inner metatarsal tubercle is present (Boulenger 1900). The toe tips are slightly dilated (Boulenger 1900) with extensive webbing (Amiet 1977). The last phalanx of toes II–V is recurved and can protrude through the ventral skin of the toe to defend the frog by scratching potential predators (Durrell 1949; Blackburn et al. 2008). The males have a paired internal vocal sac, and, at least during breeding season, mature males have a nuptial pad comprising three short but robust ridges—two longitudinal and one transverse—of stiff and heavily keratinized spines on the first finger (Boulenger 1900).

The dorsal coloration is olive-brown, with a broad, dark, black-edged band along the back, sharply defined in front, and forming a black cross-bar between the eyes. The side of the body and limbs are black. The ventral coloration is white, with the females having brown speckling on the throat (Boulenger 1900).

Trichobatrachus robustus may be unique among frogs in having sexually dimorphic lungs. Females have a typical anuran lung with a thin, narrow diverticulum on the posterior lung. In males, this diverticulum is robust with circular muscles extending along its length. Noble (1925) used this dimorphism as part of his argument that males required additional surface area of the skin—i.e., the “hairs—for cutaneous respiration.

Distribution and Habitat

Country distribution from AmphibiaWeb's database: Angola, Cameroon, Congo, Congo, the Democratic Republic of the, Equatorial Guinea, Gabon, Nigeria

	View distribution map in BerkeleyMapper.
	View Bd and Bsal data (25 records).

Trichobatrachus robustus is primarily associated with streams in the southern Cameroon Volcanic Line and the Atlantic Equatorial Coastal forest from southern Nigeria to Northern Angola (Channing and Rödel 2019), where it can be found at elevations from 26 - 1458 meters (IUCN 2022). Its presence has been confirmed through surveys in the following areas: Nigeria: Cross River National Park (Onadeko et al. 2010), Ikpan Forest (Rahman et al. 2020), Obudu Plateau (Shiøtz 1963; Lea et al. 2005), and Osomba (Shiøtz 1963); Cameroon: Banyang Mbo (Blackburn et al. 2008), Mt. Nlonako (Herrmann et al. 2005), Mt. Kupe (Portik et al. 2016), Mt. Oku (Doherty-Bone and Gvoždík 2017), Mamfe (Amiet 1978; Parker 1936), and Nkonsamba (Amiet 1975; Perret and Mertens 1957); Gabon: Monts Birougou National Park (Dewynter et al. 2018), Monts Doudou (Burger et al. 2004), and Crystal Mountains National Park (Rodel and Pauwels 2003); Equatorial Guinea: Monte Alen National Park (Lasso et al. 2002) and Rio Muni (Jones 1971); Republic of the Congo: Mayombe (Laurent 1940); Angola: Serra do Pingano region (Ernst et al. 2014).

Life History, Abundance, Activity, and Special Behaviors
Eggs are deposited as clutches attached to stones below water and are guarded by males (Perret 1966; Channing and Rödel 2019). During the breeding season, likely from April-June (Jones 1971), males are primarily aquatic and females are found in forest leaf litter (Channing and Rödel 2019). Males grow long, highly vascularized papillae on their flanks and thighs (Noble 1925), leading to the common name “Hairy Frog.” These papillae are thought to allow for increased gas exchange during a time when the frog is experiencing increased metabolic activity (Noble 1925; Robischon 2017). However, there have never been field-based ecological or physiological studies of T. robustus.

Trichobatrachus robustus is also remarkable for the presence of subdermal claws in their hind feet that become functional by piercing the ventral skin to be used as a defense mechanism (Durrell 1954; Blackburn et al. 2008).

To date, there are no reported observations of advertisement calls in T. robustus (Amiet 2017).

Durrell (1960) reported that T. robustus would eat neonate mice in captivity.

Trends and Threats
This species is experiencing decreasing population trends due to declining water quality, although it appears to be adaptable to some habitat degradation. Additional threats are intense hunting pressure for food, international trade, and Bd infections (IUCN 2021).

Relation to Humans
In Cameroon, the tadpoles are often eaten (Gonwouo and Rödel 2008). Cameroonian traders collect this species for international trade to the USA and Japan (IUCN 2021). Adults of the species are hunted in many places in Cameroon, sometimes with the use of specialized spears (Blackburn et al. 2008; Gonwouo and Rödel 2008).

Comments
The genus Trichobatrachus is most closely related to the genus Astylosternus. A recent mitochondrial phylogenetic study of these two genera found two distinct clades of Astylosternus, one in West Africa and one in Central Africa. Trichobatrachus robustus was found to be sister to the Central Africa Astylosternus rendering the genus paraphyletic (Rödel et al, 2012). Dubois et al. (2021) recently considered Trichobatrachus to be a synonym of Astylosternus.

References

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Amiet, J.-L. (1978). ''A propos d'Hyperolius platyceps Boulenger, H. kuligae Mertens et H. adametzi Ahl (Amphibiens Anoures).'' Annales de la Faculté des Sciences du Cameroun, 25, 221-256.

Amiet, J.-L., Goutte, S. (2017). Chants d'amphibiens du Cameroun. Locus Solus Publishing House, Chateaulin, France. [link]

Amiet, J.L. (1975). ''Ecologie et distribution des amphibiens anoures de la région de Nkongsamba (Cameroun).'' Annales de la Faculté des Sciences de Yaoundé, 20, 33-107.

Blackburn, D. C., Hanken, J., Jenkins Jr, F. A. (2008). "Concealed weapons: erectile claws in African frogs." Biology Letters 4, 355–357. [link]

Boulenger, G. A. (1900). ''A list of the batrachians and the reptiles of the Gaboon (French Congo) with descriptions of new genera and species.'' Proceedings of the Zoological Society of London, 1900, 443-456.

Burger, M., Branch, W.R., Channing, A. (2004). "Amphibians and reptiles of Monts Doudou, Gabon: Species turnover along an elevational gradient." Monts Doudou, Gabon: A Floral and Faunal Inventory with Reference to Elevational Variation. Fisher, B.L., eds., California Academy of Sciences, San Francisco, California, USA, 145–186.

Channing, A., Rödel, M.-O. (2019). Field Guide to the Frogs and Other Amphibians of Africa. Penguin Random House South Africa, Cape Town, South Africa.

Dewynter, M., Frétey, T., Jongsma, G. F. M., Bamba-Kaya, A., Pauwels, O. S. G. (2018). "L’herpétofaune du site Ramsar des Monts Birougou (Gabon): catalogue illustré des espèces." Les Cahiers de la Fondation Biotope, 18, 1–50. [link]

Doherty-Bone, T. M., Gvoždík, V. (2017). "The amphibians of Mount Oku, Cameroon: an updated species inventory and conservation review." ZooKeys, 643, 109–139. [link]

Dubois, A., A. Ohler, and R. A. Pyron (2021). "New concepts and methods for phylogenetic taxonomy and nomenclature in zoology, exemplified by a new ranked cladonomy of recent amphibians (Lissamphibia)." Megataxa, 5, 158-161. [link]

Durrell, G. (1954). The Bafut Beagles. Rupert Hart-Davis Ltd., London, UK.

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Ernst, R., Nienguesso, A.B.T., Lautenschläger, T., Barej, M.F., Schmitz, A., Hölting, M. (2014). "Relicts of a forested past: southernmost distribution of the hairy frog genus Trichobatrachus Boulenger, 1900 (Anura: Arthroleptidae) in the Serra do Pingano region of Angola with comments on its taxonomic status." Zootaxa, 3779, 297–300. [link]

Gonwouo, L. N., Rödel, M. O. (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, 23–34. [link]

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IUCN SSC Amphibian Specialist Group. (2017). "Trichobatrachus robustus." The IUCN Red List of Threatened Species 2017: e.T54443A18361006. https://dx.doi.org/10.2305/IUCN.UK.2017-2.RLTS.T54443A18361006.en. Accessed on 03 February 2022.

Lasso, C.A., Rial, A.I., Castroviejo, J., De la Riva, I. (2002). ''Herpetofauna del Parque Nacional de Monte Alén (Río Muni, Guinea Ecuatorial).'' Graellsia, 58(2), 21–34. [link]

Laurent, R. (1940). "Trois interessants Batraciens recoltes par M. Vleeschovwers an Mayombe." Revue de Zoologie et de Botanique Africaines, 33, 279–281.

Lea, J. M., Luiselli, L., Politano, E. (2005). "Are there shifts in amphibian faunal composition in Nigerian landscapes undergoing long-term degradation? A case study from a montane environment." Revue d'écologie, 60, 65–76. [link]

Noble, G. K. (1925). ''The integumentary, pulmonary, and cardiac modifications correlated with increased cutaneous respiration in the Amphibia: a solution of the 'hairy frog' problem.'' Journal of Morphology and Physiology, 40(2), 341-416.

Onadeko, A. B., Rodel, M. O., Egonmwan, R. I., Saliu, J. K. (2010). "Herpetological surveys of south-western and south-eastern regions of Nigeria." Zoologist, 8, 34–43. [link]

Parker, H.W. (1936). "The amphibians of the Mamfe Division, Cameroon. I. Zoogeography and systematics." Proceedings of the Zoological Society of London, 106, 135-163.

Perret, J.-L. (1966). ''Les amphibiens du Cameroun.'' Zoologische Jahrbücher für Systematik, 8, 289-464.

Perret, J.-L. and Mertens, R. (1957). ''Étude d’une collection herpétologique faite au Cameroun de 1952 á 1955.'' Bulletin de l’Institut fondamental d’Afrique noire, Série A, 19, 548-601.

Portik, D. M., Jongsma, G. F. M., Kouete, M. T., Scheinberg, L. A., Freiermuth, B., Tapondjou, W. P., Blackburn, D. C. (2016). "A survey of amphibians and reptiles in the foothills of Mount Kupe, Cameroon." Amphibian & Reptile Conservation, 10, 37–67. [link]

Rahman, M. M., Nneji, L. M., Adeniyi, A. C., Chen, J., Eniang, E. A., Oladipo, S. O., Olatunde, O., Onadeko, A. B., Kilunda, F. K., Ayoola, A. O., Adedeji, B. E., Nneji, I. C., Akwaowo, N. U., Ugwumba, A. A. A., Jin, J.-Q., Yin, T., Peng, M.-S., Olory, C., Eninekit, N., Che, J. (2020). "Amphibian assemblages and diversity patterns in two forest ecosystems of South-Eastern Nigeria." African Journal of Ecology, 58, 815–827. [link]

Robischon, M. (2017). "Surface-area-to-volume ratios, fluid dynamics & gas diffusion: four frogs & their oxygen flux." The American Biology Teacher, 79(1), 64–67. [link]

Rodel, M. O., Pauwels, O. S. (2003). "A new Leptodactylodon species from Gabon (Amphibia: Anura: Astylosternidae)." Salamandra, 39, 139–148. [link]

Schiøtz, A. (1963). ''The amphibians of Nigeria.'' Vedenskabelige Meddelelser fra Dansk Naturhistorisk Forening, 125, 1-92.

Species Account Citation: AmphibiaWeb 2022 Trichobatrachus robustus: Hairy Frog <https://amphibiaweb.org/species/1506> University of California, Berkeley, CA, USA. Accessed Dec 18, 2024.

Citation: AmphibiaWeb. 2024. <https://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 18 Dec 2024.

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