Description
Astylosternus rheophilus is a long-bodied West African frog that is composed of two subspecies. Astylosternus rheophilus rheophilusmales range from 42.0 - 51.5 mm in snout–vent length with an average of 45.7 mm. The females are, on average, 1.5 cm larger than the males. Astylosternus rheophilus tchabalensis is smaller than A. r. rheophilus, ranging from 34.5 - 39.5 mm in snout–vent length with an average of 36.5 mm. This species has a long flat head with small rounded canthus rostralis. The tympanum to eye ratio is 75%. The dorsal integument is smooth or has small wrinkles. The male spines are fine and located around margins of the lower jaw and in the center of the throat. The hands have supplementary tubercles at the base of the finger that are slightly smaller on females. Hind feet have a small amount of webbing and the toe tips are not dilated (Amiet 1977). The last phalanx of toes II–V is recurved and can protrude through the ventral skin of the toe, likely used to defend the frog by scratching potential predators (Blackburn et al. 2008). Toes are fringed by a small ridge of skin. The males nuptial pad is single and thicker than in other species of the genus (Amiet 1977).

The tadpole's total length is 80 mm with a body length to total length ratio of 32.8 ± 1.7%. The ventral-fin-height to dorsal-fin-height ratio is 79.9 ± 6.8% and the keratodont formula is 1:2+2/2+2:1. The anterior lip papillae are short, round, and restricted to the corner of mouth. The posterior lip papillae are in two or three rows of about 20 - 30 uniform, slender, triangular papillae. The rostral gap is large and the jaw sheaths is massive and serrated, the upper jaw is arched with a large medial fang, and the lower jaw is narrowly V-shaped, without a visible notch (Griesbaum et al. 2019).

It can be difficult to distinguish a small female Astylosternus r. rheophilus from a large female Astylosternus montanus (Amiet 1977).

The dorsal coloration of adult A. r. rheophilus is yellow to brown with a long rectangular band down the middle of the back that extends onto each eye where it forms a small “horn” pattern. On each side of the rectangular mark, two parallel darker bands stretch from behind the eye to the groin. Those markings are more often present on females than males, and are often broken in larger pieces that follow the same linear arrangement. Between the mediodorsal band and the dark lateral bands, the background color is often much paler. The ventral coloration is pale white with the throat area covered by dense black mottling. The abdominal area is darkened by spots and can appear gray (Amiet 1977).

Adult A. r. tchabalensis dorsal coloration is more yellow than brown. The rectangular pattern found on A. r. rheophilus is more fragmented and in some cases not aligned longitudinally, but other individuals present a similar design to A. r. rheophilus. Ventral coloration is similar to A. r. rheophilus, but often slightly darker. The leg coloration is golden yellow on the ventral and dorsal side (Amiet 1977).

Tadpole dorsal coloration is pale to dark brown, the lateral sacs and ventral surfaces are more pale in coloration and more grayish, with fine brown speckling on the tail axis, fading ventrally. The fins are mostly beige and transparent, with tiny brown dots along the margin of the last third of the dorsal and ventral fin. The jaw sheaths is black (Griesbaum et al. 2019).

The two subspecies differ in size, coloration, and patterning. Female A. r. rheophilus also differ slightly in patterning from males (Amiet 1977). See above for more details.

Distribution and Habitat

Country distribution from AmphibiaWeb's database: Cameroon

	View distribution map in BerkeleyMapper.
	View Bd and Bsal data (20 records).

This species is found in the Cameroon Volcanic Line in southwestern Cameroon and southeastern Nigeria (Amiet 1977; Channing and Rödel 2019). It is found associated with submontane to montane forests and grasslands from 1300 - 2450 meters. Its presence has been confirmed through surveys in the following areas in Cameroon: Mt. Manengouba, Tchabal Mbabo, Mts. Bamboutos, Mt. Bana, Mt. Mbam, Mt. Nkogam, Mt. Santa, and Mt. Oku (Amiet 1977; Doherty-Bone and Gvoždík 2017; Herrmann et al. 2006; Tchassem et al. 2019, 2021); and in Nigeria: Mambilla Plateau (Arroyo-Lambaer 2015). The population on Tchabal Mbabo, Cameroon is referred to as A. r. tchabalensis.

Life History, Abundance, Activity, and Special Behaviors
The breeding season is not well known, but it is hypothesized that they breed mainly from July–September. The males call at night and during the day from cavities near streams, with a call described by Amiet as "rrou" lasting 0.2 second (Amiet 1977).

On Mt. Mbam, Astylosternus rheophilus was found sharing the same breeding streams as A. montanus (Tchassem et al. 2019), and it was found at the same site as A. diadematus in Ngel Nyaki Forest Reserve, Nigeria (Arroyo-Lambaer 2015).

Trends and Threats
The population trend is decreasing due to habitat loss and degradation within its restricted range due to smallholder agricultural activities, subsistence wood extraction, human settlement and pollution (IUCN 2021).

Comments
Preliminary genetic studies have found two clades in the genus, a West African Clade and a Central African clade (Portik et al. 2019). Astylosternus rheophilus is likely found in the Central African clade (Allen et al. unpubl data).

References

Amiet, J.-L. (1977). ''Les Astylosternus du Cameroun (Amphibia Anura, Astylosterninae).'' Annales de la Faculté des Sciences de Yaoundé, 23/24, 99-227.

Arroyo-Lambaer, D. (2015). "Conserving amphibian diversity: a species inventory and gene flow studies in fragmented montane forest, Mambilla Plateau, Nigeria." Doctoral Dissertation. University of Canterbury. School of Biological Sciences.

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

Bogart, J. P. and Tandy, M. (1981). ''Chromosome lineages in African frogs.'' Monitore Zoologico Italiano, N.S. Supplemento, 15(5), 55-91.

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]

Griesbaum, F., Hirschfeld, M., Barej, M. F., Schmitz, A., Rohrmoser, M., Dahmen, M., Mühlberer, F., Liedtke, H.C. Gonwouo, N.L., Doumbia, J., Rödel, M. O. (2019). "Tadpoles of three western African frog genera: Astylosternus Werner, 1898, Nyctibates Boulenger, 1904, and Scotobleps Boulenger, 1900 (Amphibia, Anura, Arthroleptidae)." Zoosystematics and Evolution, 95, 133–160. [link]

Herrmann, H. W., Schmitz, A., Herrmann, P. A., Böhme, W., Koenig, Z. F. A. (2007). "Amphibians and reptiles of the Tchabal Mbabo Mountains, Adamaoua Plateau, Cameroon." Bonner zoologische Beiträge, 55, 27–35. [link]

IUCN SSC Amphibian Specialist Group. (2017). "Astylosternus rheophilus." The IUCN Red List of Threatened Species 2017: e.T54424A95848815. https://dx.doi.org/10.2305/IUCN.UK.2017-2.RLTS.T54424A95848815.en. Accessed on 02 February 2022.

Portik DM, Bell RC, Blackburn DC, Bauer AM, Barratt CD, Branch WR, Burger M, Channing A, Colston TJ, Conradie W, Dehlin JM, Drewes RC, Ernst R, Greenbaum E, Gvozdík V, Harvey J, Hillers A, Hirschfeld M, Jongsma GFM, Kielgast J, Kouete MT, Lawson LP, Leaché AD, Loader SP, Lötters S, van der Meijden A, Menegon M, Müller S, Nagy ZT, Ofori-Boateng C, Ohler A, Papenfuss TJ, Rößler D, SinschU, Rödel MO, Veith M, Vindum J, Zassi-Boulou AG, McGuire JA (2019). ''Sexual dichromatism drives diversification within a major radiation of African amphibians.'' Systematic Biology , 68(6), 859-875. [link]

Tchassem F., A. M., Doherty-Bone, T. M., Kameni N., M. M., Tapondjou N., W. P., Tamesse, J. L., Gonwouo, L. N. (2021). "What is driving declines of montane endemic amphibians? New insights from Mount Bamboutos, Cameroon." Oryx, 55, 23–33. [link]

Tchassem Fokoua, A. M., Gonwouo, L. N., Tamesse, J. L., Doherty-Bone, T. M. (2019). "Value of forest remnants for montane amphibians on the livestock grazed Mount Mbam, Cameroon." Amphibian & Reptile Conservation, 13, 68–81. [link]

Species Account Citation: AmphibiaWeb 2022 Astylosternus rheophilus <https://amphibiaweb.org/species/1489> University of California, Berkeley, CA, USA. Accessed Oct 11, 2024.

Citation: AmphibiaWeb. 2024. <https://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 11 Oct 2024.

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