Bioacoustics of Sclerophrys superciliaris

Description. Large sized Amietophrynus species, with very robust body shape; females distinctly larger than males (maximum snout-urostyle-length – SUL – in males: 116.0– 128.4 mm , in females: 108.1–153.4 mm ); mean head width similar in both sexes, in males 38% of SUL, in females 39%; snout in lateral view short, slightly rounded; head without bony ridges; canthus rostralis distinct, angular; loreal region straight, slightly concave; distance eye-snout similar to eye diameter; nares closer to snout tip than to eye; eyelid in adult specimens of prominent triangular shape from dorsal and in lateral view, possessing a distinct prolongation in the middle; eyelid process in juveniles less distinct and almost absent in very small specimens; tympanum more or less distinct, positioned at a concave part of the cheeks; tympanum vertically prolonged, horizontal diameter smaller than eye diameter; dorsal skin smooth in adults, warty in juveniles; parotid glands very prominent, shaped like a slender drop, converging backwards, usually with a pointed tip (parotid length / parotid width ratio in males: 3.17, in females: 3.23); in some specimens posterior to parotids a glandular bulge extending to the groins as a dorsolateral fold; parotids distinctly bi-coloured: like flanks on lateral lower part and like back on dorsal surface; gland openings only on dorsal part of parotids (rarely extending onto the borderline of the colour transition); border between the two colours sharp; fingers and toes simple, not enlarged at the end; subarticular tubercles simple; relative length of fingers: III> I> II ≥ IV (mean length of finger I / length of finger III ratio in males: 88%, in females: 94%); manual webbing absent; femora short and slender; mean tibia length in both sexes 38% of SUL; inner and outer metatarsal tubercle present; relative toe length: IV> III> V> II> I; webbing rudimentary: 1 (0.5), 2 (1-0.5), 3 (2-1) or 3 (2- 1.25), 4 (2.75-2.75), 5 (1) or 5 (1.25); females growing larger than males; males with nuptial pads on fingers I and II. Boulenger (1888) mentions the presence of a tarsal fold in his description of the species, while Werner (1897) states that the tarsal fold is absent in Bufo laevissimus (current synonym of A. s. superciliaris , see below); a character also used within his bufonid key. A distinct tarsal fold was absent in all examined specimens, only an indistinct bulging of the skin has been observed in some specimens. In dehydrated specimens, this somehow concave skin might be mistaken for a tarsal fold. Juveniles possess a granular skin till they reach a size of about 40 mm ( Amiet & Perret 1969 ). The largest specimen still showing minuscule warts on the dorsum measured 46 mm (MHNG 917.99), in few subadult and predominantly smooth specimens, single tiny bulges were recognizable on the eyelids. The eyelid projection can be very small and almost absent in juveniles of A. s. superciliaris , forming only a very indistinct “swelling” on the eyelid. Colouration. Dorsum a pale yellowish colour or marbled orange yellow ( Figs. 3 b, c, e–g), extending from the tip of the snout, along the upper side of the parotids backwards to the abdominal region; a pair of dark spots on posterior third of back ( Figs. 3 a, c, e–g); additional smaller spots on anterior part of back or between eyes in few adult specimens ( Figs. 3 c, e); intense red lateral colouration from tip of snout, continuing beneath the canthus rostralis and along entire flanks; sometimes parts of flank colouration darker, red-purple; ventral colouration ranging from light to intense reddish colour ( Fig. 3 d); extremities dark purple; inguinal region rarely with small spots; upper hind limbs and feet with white transversal bars; anterior extremities dark purple ventrally; gular region coloured like venter; juveniles coloured like adults but with additional transversal bars on tibiofibula, usually less distinct in adults ( Figs. 3 a–c, e); juveniles with more spots in addition to the abdominal pair on anterior part of back and in the interorbital region ( Figs. 3 a; 4; 5), these dark spots of different structure than surrounding skin, “drier and softer”. Interorbital markings of juvenile specimens usually consist of a pair of small blotches (sometimes dissolved into several smaller spots), caudally converging towards each other and barely reaching the eyelids ( Figs. 4 b; 5). Exceptionally these blotches are fused ( Fig. 4 b), a pattern also reported by Andersson (1905). Boulenger (1887) describes a “very fine lighter vertebral line” in some juveniles. According to Amiet & Perret (1969) juveniles possess a brown-black gular colouration and breast, while adults show an overall pale belly. Perret & Mertens (1957) comment on the absence of the pair of dark spots on the posterior part of the back in two specimens. Werner (1898) mentions a female from Cameroon (referred to as Bufo laevissimus ) with pale red-brown upper surface and chocolate brown flanks. Colouration in preservation. Preserved specimens may loose their reddish colouration, which turns brownish. The typical reddish colouration was only observable where it remained covered between skin folds; in other specimens it completely disappeared. Nonetheless, in many specimens a clear differentiation between the lateral and dorsal colouration is recognizable. Very old specimens may be bleached out completely, lacking any colour pattern; e.g. even the pair of abdominal spots then may only be recognizable by a closer examination of the skin structure. Natural history. Amietophrynus s. superciliaris inhabits the forest floor in primary forest vegetation along small rivers ( Frétey & Blanc 2001 ; Lasso et al . 2002 ; Figs. 6 e–g). Akani et al . (2004) report the finding of the species in the rainy season in a pristine swamp site. But the species also inhabits secondary growth with dense vegetation or even plantations ( Amiet 1976a , 1986 ; Rödel et al. 2004). Occasionally the species can be seen in more open places searching for food ( Sanderson 1936a ). Similarly, local farmers in western Cameroon reported to the senior author on occasional findings of the species in plantations. During the late rainy season ( September 2010 ) M. Hirschfeld and M.- O . Rödel ( pers. obs. ) observed an adult male (SUL 124 mm ) in a near pristine part of the Ebo forest, Cameroon , over a period of four days. During this time the toad only moved about 25 m , the largest daily distance being about 15 m . During two consecutive nights the male climbed onto the top of two different bare rocks of 50–60 cm height, respectively and seemed to stay there motionless for the night. The other days it was observed sitting under a smaller tree, turning its body only once into another direction. According to Amiet (1976a) breeding males possess slightly hypertrophied anterior extremities and black callosities on fingers I and II. A. s. superciliaris males lack a vocal sac ( Perret & Amiet 1971 ) and the species is assumed to utter no advertisement call ( Perret & Mertens 1957 ; Tandy & Keith 1972 ). A published sonogram of a A. s. superciliaris vocalization is not regarded to show an advertisement call ( Amiet 1976a ). This vocalization, a dull buzzing noise, lasted for almost 1– 1.5 s, comprising a long series of pulses ( Amiet 1976a , b ). Amiet only observed movements of the flanks during sound emission, but no movements of the gular region ( Amiet 1976a ). Hence, Amiet doubts that this noise represents an advertisement call, as it can be heard on short distances only. However, it may function in short distance recognition ( Amiet 1976a , 1989 ). Clutches are deposited and tadpoles may develop in slowly running streams ( Amiet 1976a , 1986 , 1989 ; Gossmann et al. 2002 ; Figs. 6 e–f). Egg size ranges from 1.40–1.95 mm (N= 102, mean= 1.67, SD= 0.09). Amiet (1976a) assumes that reproduction takes place in the dry season (January – March) as most specimens have been found during that time and only at that time males show their nuptial dress. Juveniles have been found in January in Nigeria (M.- O . Rödel & A.B. Onadeko, pers. obs; Figs. 3 a; 6e) and Cameroon ( Schmitz 1998 ). Amiet & Perret (1969) report on juveniles (< 40 mm ) collected in February, May, June and July–October. According to Angel (1931) specimens in captivity feed on insects, snails, but also on frogs and tadpoles. Perret & Mertens (1957) mention beef meat as food in captivity. Affa’a & Amiet (1990) report on nyctotheres (Protozoa, Clevelandellida , Prosicuophora basoglui , Nyctotheroides ptychadenae ) found in adult A. s. superciliaris .