Western Nimba Toad
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
Life History, Abundance, Activity, and Special Behaviors
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
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
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).
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.
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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.
Written by Anna Chow and Kellie Whittaker (achow AT berkeley.edu), UC Berkeley
First submitted 2010-10-14
Edited by Kellie Whittaker (2012-04-14)
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