Phrynobatrachus chukuchuku, Zimkus, 2009

Zimkus, Breda M., 2009, Biogeographical analysis of Cameroonian puddle frogs and description of a new species of Phrynobatrachus (Anura: Phrynobatrachidae) endemic to Mount Oku, Cameroon, Zoological Journal of the Linnean Society 157 (4), pp. 795-813 : 801-804

PHRYNOBATRACHUS CHUKUCHUKU SP. NOV.

Spiny puddle frog

Holotype: MCZ A-138127, adult male, Cameroon, Northwest Region, Mt Oku , near summit, 06°11 ′ N, 10°31 ′ E (WGS datum), 2800 m elevation, 17.viii.2006, D.C. Blackburn, K.S. Blackburn, P. Huang, and M. Talla.

Paratypes: MCZ A-138124, adult male ; MCZ A-138125, adult male; MCZ A-138126, adult female; MCZ A-138128, adult female; MCZ A-138129, adult male; MCZ A-138130, adult female; MCZ A-138131, adult male; MCZ A-138132, adult male; MCZ A-138133, juvenile; MCZ A-138134, adult male, same collection data as holotype .

Diagnosis: Phrynobatrachus chukuchuku sp. nov. is readily distinguished from all other Phrynobatrachus because males have a unique ventral coloration, including a black throat, dark brown to black pectoral and abdominal regions that extend just anterior to the hind limbs, and a light or white area on the proximal hind limbs in close proximity to the cloaca. The venter may be partially or completely covered with small spines or asperities. Females are lighter than males on the ventral side; their venters appear completely white or cream in color and generally lack any conspicuous markings. Small, white spots or asperities extend from above the eye to the insertion of the hind limbs and may be present in either sex. There are no prominent dorsal markings; chevronshaped glands are present but may be difficult to discern because of dark brown dorsal coloration. A thin vertebral line may be present. A lighter triangle over the snout is variably present ( Fig. 4 ). The tympanum is either indistinct or only scarcely visible with a supratympanic fold present. Like all Phrynobatrachus species , P. chukuchuku sp. nov. lacks manus webbing; pes webbing is absent or extremely rudimentary. A midtarsal tubercle, elongate inner metatarsal tubercle, and outer metatarsal tubercle are present. Both a median papilla and tongue cleft are present. Manus digit tips are not expanded or only slightly bulbous. Pes digit tips are bulbous or slightly expanded into small discs with circummarginal grooves. This species may be distinguished from other small Cameroonian Phrynobatrachus as follows: from Phrynobatrachus hylaios , P. manengoubensis , and P. werneri by much darker coloration, both on the dorsum and venter (not including the dark or black gular region found in males of these three species), as well as the presence of ventral spines; from P. calcaratus and P. cornutus by the absence of an eyelid cornicle; from Phrynobatrachus latifrons by lack of pes webbing and the presence of a black throat in males. This species also differs from other large-bodied Cameroonian Phrynobatrachus ( P. africanus , P. auritus , P. batesii , P. cricogaster , Phrynobatrachus natalensis , Phrynobatrachus plicatus , and P. steindachneri ) by absence of pes webbing.

Description of holotype: Adult male, snout–vent length 15.3 mm ( Fig. 3 ; Table 1). Miniaturized (snout–vent length <20 mm) Phrynobatrachus with oval, compact body shape and slender limbs; head slightly longer than wide; canthus rostralis rounded but distinct; loreal region straight to slightly concave; distance from naris to rostral tip less than half that from naris to anterior eye; internarial distance approximately equal to interorbital distance; tympanum indistinct, much smaller than diameter of eye; supratympanic fold present; premaxillary and maxillary teeth; tongue with median papilla.

Relative length of fingers: III > IV ± II > I; hand with large and oval palmar and thenar tubercle; fingers with round subarticular tubercles, no webbing present between manus digits; finger tips are not expanded or only slightly bulbous; tibiofibula slightly longer than femur; relative length of toes IV > III > V > II > I; no webbing present between pes digits; midtarsal tubercle present; conspicuous, elongate inner metatarsal tubercle; outer metatarsal tubercle present but significantly smaller than inner metatarsal tubercle; pes webbing absent or rudiments present on toe bases; expansion of pes digit tips varies from bulbous to slightly expanded into small discs with circum-marginal grooves variably present.

Dorsal skin smooth; venter (gular, pectoral, and abdominal regions) completely covered with small spines or asperities that appear whitish in the pectoral and abdominal regions; small, white asperities above the supratympanic fold and below the tympanum extending along the lateral sides; gular skin slightly thickened, causing multiple lateral folds.

Coloration: Colour (in ethanol) varies from medium to dark brown with some darker, brown spots. A thin, cream, vertebral line may be present as in the holotype ( Fig. 3 ). A paler triangle is often present on the snout ( Fig. 4 ). Chevron-shaped scapular glands forming an ‘X’ pattern are often outlined in darker brown but may difficult to detect because of dark dorsal coloration. White asperities are found on the flanks extending from above the eye and supratympanic fold to anterior of the hind limb; often these spots may be present on the upper lip from the rostrum to the insertion of the forelimb. Dorsal sides of hind limbs are barred; ventral sides vary in pigmentation with regions appearing cream or mottled.

Males have a black throat, as well as dark brown to black pectoral and abdominal regions. A light coloured area is present on the proximal hind limbs anterior to the cloaca, and other portions of the limbs in close proximity to the elbows and knees are often light coloured in males, whereas the remaining portions are brown. The lower jaw is often lined with lighter brown or even white. The venter in males may be partially or completely covered with small spines or asperities that appear white in the pectoral and abdominal region, whereas those in the gular region are black. The venter of females is immaculately white or cream, and the lower jaw is normally lined with the brown dorsal colour. Ventral asperities are not present in females.

Variation: Descriptive morphometrics of P. chukuchuku sp. nov. are provided in Table 1. Morphological proportions in paratypes are generally consistent with those in the holotype. All specimens have a snout–vent length less than 20 mm. Females are significantly larger than males (t -test: P = 0.0089; Table 1). A paler triangle on the snout is often present, but some specimens exhibit a rudimentary band or spot ( Fig. 4 ). In addition, snout shape varies slightly; some specimens appear rounded ( Fig. 4B ), whereas others are slightly pointed or triangular ( Fig. 4F ). Webbing varies from completely absent to rudimentary. Expansion of pes digit tips may vary slightly amongst toes of an individual from bulbous to slightly expanded into small discs.

Distribution: Phrynobatrachus chukuchuku sp. nov. is known only from grasslands near the summit of Mt Oku (2800 m; Fig. 5 ). Such grasslands do not occur in other highland areas of the Cameroon Volcanic Line, such as Mt Kupe (summit 2064 m), Mt Nlonako (summit 1825 m), Mt Manengouba (summit 2411 m), Tchabal Mbabo (highest elevation approximately 2380 m), or Obudu Plateau (highest elevation approximately 1700 m). Near the summit of Mt Oku habitat loss is occurring, with overgrazing by cattle, goats, and horses owned by local people. Fire is also a potential threat to the habitat of the species.

Etymology: The specific epithet is derived from Cameroonian pidgin English. The phrase, ‘chuku-chuku’ means ‘spiny’ or ‘thorny’ and refers to the minute spinules visible on the ventral sides of males of this species.

Sequence divergence: Phrynobatrachus chukuchuku sp. nov. differs from 12 Cameroonian species of Phrynobatrachus by mitochondrial (12S rRNA, valine-tRNA, and 16S rRNA) sequence divergence of 4.94–18.69% ( Table 2). No sequence divergence was detected amongst the three P. chukuchuku sp. nov. sequences.

Differential diagnosis: Phrynobatrachus chukuchuku sp. nov. is morphologically most similar to other small Cameroonian species, such as P. latifrons , P. calcaratus , P. cornutus , P. hylaios , P. manengoubensis , and P. werneri . Phrynobatrachus latifrons has distinct webbing and males exhibit a yellow throat, whereas P. chukuchuku sp. nov. generally lacks webbing and males possess a black throat. The newly described species can be easily differentiated from P. calcaratus and P. cornutus because it does not have an eyelid cornicle. Of the miniaturized Cameroonian species mentioned, the new species is genetically closest to P. werneri and P. manengoubensis with a 4.94–5.54% difference in the mtDNA examined. Phrynobatrachus werneri and P. hylaios differ from P. chukuchuku sp. nov. by much darker coloration, both on the dorsum and venter (not including the dark or black gular region found in males), as well as the presence of ventral spines in males. Numerous morphological characteristics differentiate P. chukuchuku sp. nov. from other Cameroonian Phrynobatrachus species. Phrynobatrachus africanus , P. auritus , P. batesii , P. cricogaster , P. natalensis ( Smith, 1849) , P. plicatus ( Günther, 1858) , and P. steindachneri are all substantially larger than this new species. In addition, P. africanus , P. auritus , P. batesii , P. cricogaster , P. natalensis , P. plicatus , and P. steindachneri have moderate to extensive pes webbing with 1.5–3.5 phalanges free of webbing on the fourth toe, whereas P. chukuchuku sp. nov. either lacks or has only a rudimentary web. The mtDNA of the new species, P. chukuchuku sp. nov., was compared to all other Phrynobatrachus known to occur in Cameroon, except for P. hylaios for which tissue was not available. Phrynobatrachus chukuchuku sp. nov. differed from 12 Cameroonian species of Phrynobatrachus by mtDNA sequence divergence of 4.94–18.69%; interspecific pairwise 16S divergences in a group of Madagascan frogs revealed similar differentiation amongst species, ranging from 1 to 16.5% with a mode at 8% ( Vences et al., 2005).

Figures

Figure 3. Holotype of Phrynobatrachus chukuchuku sp. nov. (MCZ A- 138127) in A, dorsal, B, ventral, C, lateral views. Typical gular coloration of P. chukuchuku sp. nov. exhibited by adult male (MCZ A- 138127; D), in comparison to adult female (MCZ A-138130; E). Scale bars = 1 mm.

Figure 4. Variation of interorbital line and dorsal head coloration amongst paratypes of Phrynobatrachus chukuchuku sp. nov. A, MCZ A-138124, B, MCZ A-138125, C, MCZ A-138126, D, MCZ A-138129, E, MCZ A-138130, F, MCZ A-138132. Scale bars = 1 mm.

Figure 5. A, map illustrating topography of Cameroon and neighbouring countries. Inset shows position of Cameroon within Africa. Black star indicates position of Mt Oku. B, topographic map of portion of Bamenda Highlands (magnification of rectangle in Fig. 3A), showing the single known locality of Phrynobatrachus chukuchuku sp. nov. at Mt Oku (black star). Black circle indicates position of Lake Oku.