A West African species of Acanthixalus, morphologically similar to the only other known member of the genus, the central African A. spinosus. The only substantial difference seems to be the wider head of male A. sonjae (Schiřtz 2007, pers. comm.). The head has a long, pointed snout, with canthi and slightly concave lores. Eyes are protuberant and bear rhomboid-shaped pupils. The tympanum is absent. Paired, oval subgular glands are present,extending longitudinally. The body is stout and flattened with quite warty skin dorsally and on the extremities. In addition, a transverse row of bigger warts in the neck area gives the appearance of a "crown"; four particularly large warts are present in the shoulder area; and two particularly large warts are visible on the sacral region. Ventrally the skin is granular. Both hands and feet are webbed, and fingers and toes bear enlarged discs. Males bear a pair of subgular glands and numerous hook-shaped tarsal spines, and have larger digital discs, but possess no vocal sacs (Rödel et al. 2003).
The dorsum and extremities are yellow-green and bear numerous white warts with black spines. Three black crossbands as well as black spots and lines are present on the dorsum, as well as a transverse black band on the sacral region. A single black triangular mark is located between the eyes, and paired black triangles are visible on the shoulders, with each triangle apex pointing towards the posterior. Black transverse bands are also present on the upper lip, femur and tibula fibula. Flanks are green to white. Ventral surfaces are gray brown with black markings and white warts lacking black spines. Gular glands (present on males) are beige-colored. The anal region is bright yellow. Finger and toe discs are white with a black spot above and beige below; heels are orange to yellow. This frog is capable of metachrosis, with colors darkening almost to black in the sunlight, within a few minutes. The iris is black with white stripes radiating outward (Rödel et al. 2003).
Juveniles are more brightly colored, with the dorsal ground color often being yellow to orange, and the ventral side orange as well. Juveniles also have four enlarged yellow warts on the neck (Rödel et al. 2003).
Tadpoles are similar to those of A. spinosus but have longer tails. The body is compact, rounded dorsally and slightly depressed laterally. Eyes are very small and lateral. The oral disc is subterminal, with a tooth formula 1: 2 + 2/ 3, wide serrated, curved jaw sheaths, a single row of lateral papillae on either side and two rows of caudal papillae (medially uniserial). The spiracle is sinistral and the vent is medial. The tail tip is broadly rounded (Rödel et al. 2003).
Tadpoles taken directly from treeholes were a fleshy violet color, which quickly changed to black in the sunlight. In some tadpoles, the tail tip is almost transparent (Rödel et al. 2003).
Distribution and Habitat
Country distribution from AmphibiaWeb's database: Cote d'Ivoire, Ghana
This species is known from a few localities in southwestern Côte d'Ivoire (Rödel et al. 2003). It has also been found in Ghana, within the Krokosua Hills Forest Reserve and the Ankasa Conservation Area (Rödel et al. 2005). It may also occur elsewhere (Schiřtz 2007, pers. comm.), perhaps across the border into Liberia (IUCN 2006). It occurs in both primary and secondary forest (Rödel et al. 2003).
Life History, Abundance, Activity, and Special Behaviors
Acanthixalus sonjae lives and breeds in water-filled cavities of trees, like A. spinosus (Rödel et al. 2003). It is difficult to find (Schiřtz 2007, pers. comm.).
Clutches are attached to the walls or ceiling within a water-filled tree cavity. The egg masses are flat immediately after oviposition, changing to hemispheric soon thereafter and measuring 2-4 cm in diameter. The mean clutch size was 9.3 eggs. Eggs are whitish gray with a darker pole. One female in captivity oviposited three clutches within 21 days (Rödel et al. 2003).
Tadpoles first orient horizontally within the egg, changing to a head-up vertical position as development progresses. They begin dropping into water 11-14 days post-oviposition. Metamorphosis is complete within three months. Tadpoles have been reported to be at least partly carnivorous (Rödel et al. 2003).
Trends and Threats
It occurs within several protected areas. In Côte d'Ivoire: Taď National Park (Rödel et al. 2003), Haute Dodo Classified Forest (Rödel and Branch 2002), Cavally Classified Forest (Rödel and Branch 2002). In Ghana: Ankasa Conservation Area and the Krokosua Hills Forest Reserve (Rödel et al. 2005).
Possible reasons for amphibian decline
General habitat alteration and loss
Habitat modification from deforestation, or logging related activities
Intensified agriculture or grazing
Genetic analysis (using mitochondrial 16S RNA) points to differences between A. sonjae and A. spinosus at a level comparable to species differences in other amphibian groups, and A. sonjae appears to be separated from A. spinosus by a gap of 1700 km (Schiřtz 2007, pers. comm.).
IUCN, Conservation International, and NatureServe. (2006). Global Amphibian Assessment: Acanthixalus sonjae. www.globalamphibians.org. Accessed on 21 August 2008.
Rödel, M.-O., Gil, M., Agyei, A.C., Leaché, A.D., Diaz, R.E., Fujita, M.K., and Ernst, R. (2005). ''The amphibians of the forested parts of south-western Ghana.'' Salamandra, 41, 107-127.
Rödel, M.O., Kosuch, J., Veith, M., and Ernst, R. (2003). ''First record of the genus Acanthixalus Laurent, 1944 from the Upper Guinean Rain Forest, West Africa, with the description of a new species.'' Journal of Herpetology, 37(1), 43-52.
Schiřtz, A. (2007). Treefrogs of Africa: Addenda and Corrigenda 2007. Personal communication, available as .pdf file from http://zoologi.snm.ku.dk (english/staff/schiřtz/list of publications).
Written by Kellie Whittaker and Arne Schiřtz (kwhittaker AT berkeley.edu), UC Berkeley
First submitted 2008-08-21
Edited by Kellie Whittaker (2008-09-30)
Citation: AmphibiaWeb: Information on
amphibian biology and conservation. [web application]. 2013. Berkeley, California:
(Accessed: May 24, 2013).
AmphibiaWeb's policy on data use.