Description
This viviparous toad has a restricted range in the Mount Nimba region of Guinea, Côte d'Ivoire, and Liberia. Two subspecies have been denoted, one from Guinea and Côte d'Ivoire and one from Liberia: N. occidentalis occidentalis is generally smaller in body size (females average 20.5 mm SVL, males average 18.0 mm) compared to N. occidentalis liberiensis (females average 28.7 mm SVL, males average 22.4 mm). Females of N. occidentalis liberiensis have significantly longer feet than females of N. occidentalis occidentalis, even when corrected for differing body size (Sandberger et al. 2010).

Most individuals have brown to black dorsal surfaces and white venters without distinct borders between the dark and light areas. N. occidentalis liberiensis sometimes has brown dots on the venter, while N. occidentalis occidentalis has a uniform venter. The dorsum may be uniform or may show an irregular mixture of lighter and darker browns. The snout and eyelids are lighter in color. Legs are light brown with irregularly bordered dark stripes or dots (Sandberger et al. 2010).

Juveniles have a brighter, golden-brownish dorsum that may have blackish spots or figures. Juveniles also have a black lateral line, bordered by white, that runs from the tip of the snout through the eye and on into the groin area. In juveniles, legs are yellow to brown with white stripes. As the toads mature, the dorsum and legs become darker and the contrast between colors fades (Sandberger et al. 2010).

Distribution and Habitat

Country distribution from AmphibiaWeb's database: Cote d'Ivoire, Guinea, Liberia

View distribution map in BerkeleyMapper.

N. occidentalis occidentalis inhabits montane grassland in the Mount Nimba region of Guinea and Côte d'Ivoire, while N. occidentalis liberiensis is found in the Liberian region of the Nimba mountain range (Sandberger et al. 2010). The two subspecies are separated by a forested mountain ridge and about 7.5 km distance (Sandberger et al. 2010). This species is only found above 1200 m a.s.l. up to the highest montane grasslands at about 1600 m a.s.l (Lamotte 1959; Sandberger et al. 2010); the most recent records in Guinea are primarily from above 1600 m a.s.l. (Hillers et al. 2008), while those from Liberia are from above 1200 m a.s.l. (Sandberger et al. 2010). During the dormant period toads are underground, while during the active period they prefer to hide in a thick layer of grass roots (Hillers et al. 2008).

Life History, Abundance, Activity, and Special Behaviors
Toads are dormant and hide underground during the dry season, which lasts approximately from November to March (Lamotte 1959). They become active at the first rains (Lamotte 1959). Calling can begin in July, in the middle of the rainy season, but most calling occurs in early or mid-September (Sandberger et al. 2010). Calls are faint and sound like a short, metallic "bing," with an initial part of higher frequency and greater energy followed by a second, longer part of slightly lower frequency and lower energy: 3319 Hz followed by 2775 Hz for N. occidentalis occidentalis, vs. 3565 Hz followed by 3477 Hz for N. occidentalis liberiensis (Sandberger et al. 2010). Advertisement call duration is quite short, lasting 0.018 seconds (Sandberger et al. 2010). A male-male aggressive "rasping" call was recorded for N. occidentalis occidentalis, of slightly longer duration (0.126 sec) than the advertisement call (0.018 sec) (Sandberger et al. 20100. Although Schiøtz (1964) reported a third type of call for N. occidentalis occidentalis, consisting of a slow chirp with modulated frequency, Sandberger et al. (2010) did not detect this in their survey.

This species is viviparous (Angel and Lamotte 1944, 1948; Xavier et al. 1977, 1986). Endocrinology of this toad has been extensively studied by Xavier and her colleagues. Females produce clutches of 4-35 eggs in N. occidentalis occidentalis, and 6-24 in N. occidentalis liberiensis. Ova are small; 0.5-0.6 mm in diameter. Ovulation and fertilization occur before females retreat underground for the dry season on Mt. Nimba from October through April (Lamotte 1959). The gestation period lasts nine months; during the last two months of development, fetuses are nourished by secretions of the oviductal epithelium (Xavier et al. 1977, 1986). Fetuses have papillae around the mouth, presumed to facilitate ingestion of nutritive mucopolysaccharide secretions (Wake 1993). The adult parents emerge to forage in April at the beginning of the rainy season, with gravid females emerging first, then non-gravid females, and finally males (Lamotte 1959). Parturition occurs in June or July, yielding 4-35 fully metamorphosed froglets, each approximately 7.5 mm SVL long and weighing 45 mg (Xavier et al. 1986). Mating begins at the end of August before dormancy (Lamotte 1959).

Trends and Threats
This species is in imminent risk of extinction (Hillers et al. 2008). It is protected under CITES Appendix I. It has a very limited range (Lamotte 1959; Lamotte and Sanchez-Lamotte 1999; Stuart et al. 2008). Population numbers have been decreasing, most likely due to habitat loss as well as degradation from iron ore exploration and mining (Stuart et al. 2008); the type locality for N. occidentalis liberiensis is now an open cast mining pit (Sandberger et al. 2010). A proposed new mining project in the central area of the range presents a significant threat (Hillers et al. 2008). Mining also compacts the soil and renders it unsuitable for burrowing (Sandberger et al. 2010). Montane grassland fires may also be a threat, changing the vegetation and ground cover and particularly eliminating the thick layer (>10 cm) of grass roots in which these toads prefer to live (Hillers et al. 2008). The most viable populations aqpear to be those at Mont Sempére, Grands Rochers, and Mont Richard Molard (Hillers et al. 2008), and a new population has been reported from the Ivorian side of Mt. Nimba (Sandberger et al. 2010). It is thought that this species is present in at least one protected area, the Mount Nimba Strict Nature Reserve (Rödel et al. 2004).

In Liberia, mining has significantly impacted habitat, with the type locality for the subspecies N. occidentalis liberiensis now an open mining pit. Most individuals have been found south of the former Mount Alpha; surveys in 2007 encountered 14 adults and 16 juveniles, while surveys in 2008 detected 17 adult females (of which 16 were pregnant) and 5 adult males. Toads were found only at localities where mining had been abandoned after 10 years, and were not found at localities that had been mined for 30+ years. Localities with toads had soil that was not compacted, as judged by the presence of holes and cracks in the substrate. No toads were observed at localities with heavily compacted soil (Sandberger et al. 2010).

Possible reasons for amphibian decline

General habitat alteration and loss
Mining

Comments
Species authority: Angel (1943).

Nimbaphrynoides liberiensis, originally described by Xavier (1978), is now considered a subspecies of N. occidentalis (Sandberger et al. 2010). Size and color differences were noted between the two subspecies but genetically and acoustically the subspecies cannot be distinguished (Sandberger et al. 2010). The greatest genetic differences between the two taxa, found in the cyt b gene, were about 2% (Sandberger et al. 2010). Captive breeding experiments showed that N. occidentalis liberiensis males and females had an 80% successful live birth rate, while heterogeneous pairings of N. occidentalis liberiensis males and N. occidentalis occidentalis females were not viable (only 1 of 16 pairings produced a pregnant female, and those offspring were born dead) (Xavier 1978); the reverse combination of Liberian females and Guinean males was apparently not attempted (Sandberger et al. 2010).

References

Angel, F. (1943). ''Description d’un nouvel amphibien anoure, ovo-vivipare de la Haute-Guinée Française (Materiaux de la mission Lamotte, au Mont-Nimba) (2e note).'' Bulletin du Muséum National d’Histoire Naturelle, 15, 167-169.

Angel, F. and Lamotte, M. (1944). ''Un crapaud vivipare d’Afrique Occidentale Nectophrynoides occidentalis Angel.'' Annales des Sciences Naturelles, Zoologie, 6, 63-89.

Angel, F. and Lamotte, M. (1948). ''Nouvelles observations sur Nectophrynoides occidentalis Angel. Remarques sur le genre Nectophrynoides.'' Annales des Sciences Naturelles, Zoologie, 11, 115-147.

Hillers, A., Loua, N.-S., and Rödel, M.-O. (2008). ''Assessment of the distribution and conservation status of the viviparous toad Nimbaphrynoides occidentalis on Monts Nimba, Guinea.'' Endangered Species Research, 5, 13-19.

Lamotte, M. (1959). ''Observations écologiques sur les populations naturelles de Nectophrynoides occidentalis (Fam. Bufonidae).'' Bulletin de Biologie France Belgique, 4, 355-413.

Lamotte, M., and Sanchez-Lamotte, C. (1999). ''Adaptation aux particularités climatiques du cycle biologique d’un anoure tropical, Nectophrynoides occidentalis Angel, 1943 (Bufonidae).'' Alytes, 16, 111-122.

Sandberger, L., Hillers, A., Doumbia, J., Loua, N., Brede, C., and M. Rödel (2010). ''Rediscovery of the Liberian Nimba toad, Nimbaphrynoides liberiensis (Xavier, 1978) (Amphibia: Anura: Bufonidae), and reassessment of its taxonomic status.'' Zootaxa, (2355), 56-68.

Schiøtz, A. (1964). ''The voices of some West African amphibians.'' Vedenskabelige Meddelelser fra Dansk Naturhistorisk Forening, 127, 35-83.

Stuart, S., Hoffmann, M., Chanson, J., Cox, N., Berridge, R., Ramani, P., Young, B. (eds) (2008). Threatened Amphibians of the World. Lynx Edicions, IUCN, and Conservation International, Barcelona, Spain; Gland, Switzerland; and Arlington, Virginia, USA.

Wake, M. H. (1993). ''Evolution of oviductal gestation in amphibians.'' The Journal of Experimental Zoology, 266, 394-413.

Xavier, F. (1977). ''An exceptional reproductive strategy in Anura: Nectophrynoides occidentalis Angel (Bufonidae), an example of adaptation to terrestrial life by viviparity.'' Major Patterns in Vertebrate Evolution. M.K. Hecht, P.C. Goody, and B.M. Hecht, eds., Plenum, New York, 545-552.

Xavier, F. (1978). ''Une espèce nouvelle de Nectophrynoides (Anura, Bufonidae) des Monts Nimba, N. liberiensis n.sp. I - description de l'espèce.'' Bulletin de la Société Zoologique de France, 103, 431-441.

Xavier, F. (1986). ''La reproduction des Nectophrynoides.'' Traité de Zoologie Amphibiens, 14, 497-513.

Species Account Citation: AmphibiaWeb 2012 Nimbaphrynoides occidentalis: Western Nimba Toad <https://amphibiaweb.org/species/368> University of California, Berkeley, CA, USA. Accessed Dec 26, 2024.

Citation: AmphibiaWeb. 2024. <https://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 26 Dec 2024.

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