AMPHIBIAWEB
Petropedetes johnstoni
family: Petropedetidae

© 2005 Dave Blackburn (1 of 1)
Conservation Status (definitions)
IUCN (Red List) Status Near Threatened (NT)
CITES
Other International Status None
National Status None
Regional Status None

Country distribution from AmphibiaWeb's database: Cameroon

 

View distribution map using BerkeleyMapper.

   

From the Encyclopedia of Life account:

Etymology

This species was named in honor of Mr. Henry Hamilton Johnston, who collected the type specimen.


Author: Zimkus, Breda
License: http://creativecommons.org/licenses/by-nc/3.0/

Taxonomic Notes

According to Barej et al. (2010), molecular investigation of populations of P. johnstoni from Bioko Island may reveal that mainland populations belong to a separate evolutionary lineage, and if so, the name P. newtonii would be available for this island populations (sensu Tympanoceros newtonii du Bocage, 1895).


Author: Zimkus, Breda
License: http://creativecommons.org/licenses/by-nc/3.0/

Distribution

This species is known only from the lowland, coastal plain of south-western and southern Cameroon, Gabon, and Equatorial Guinea, including Bioko Island (Barej et al., 2010).


Author: Zimkus, Breda
License: http://creativecommons.org/licenses/by-nc/3.0/

Morphology

This is a medium-sized Petropedetes with a slender body shape. A conical papilla is present on the tongue; vomerine teeth are in two slightly oblique series behind the the line of the choanae. The snout is rounded to slightly pointed in lateral view. Canthus rostralis is sharp. Loreal region is concave. The nostrils are closer to snout-tip than to eye (Boulenger, 1887). Mean head width in males is about 41% of SUL, in females about 38%; eye diameter about 1.5 times eye-narial distance (Barej et al., 2010). A distinct, round tympanum is present, which is smaller than the eye in both sexes (tympanum / eye in males: 0.49–0.63; in females: 0.45–0.48). The tympanic papilla of breeding males is close to upper border of tympanum and is comparatively slim. A supratympanic fold is present and distinct. Fingers are slender with T-shaped fingertips. The relative length of fingers is as follows: III > IV > II >I. Manual subarticular tubercles are single; palmar tubercle and thenar tubercle are also present. Manual webbing is absent. Forearm hypertrophy is weakly developed. Carpal spikes are present in males, and spinosities are found on the upper arm, throat and breast. A few minuscule spines are preesnt on supratympanal gland. Dorsal skin is granular and covered in small warts; fewer larger warts are arranged in more or less longitudinal rows on the dorsum, and the flanks exhibit few large warts. The ventral skin is smooth. Mean femur length in males is 53% of SUL, in females about 51%. Mean tibia length in both sexes is 61% of SUL. Mean foot length in males is 79% of SUL, in females 78%. Pedal subarticular tubercles are single and according to Boulenger (1887), rather feeble and oval in shape. Hind limbs are slender. Femoral glands are very large in males; these are larger and more prominent in males than in females (femoral gland /femur length in males: 0.28–0.46, in females: 0.25–0.27). Relative length of toes is as follows: IV > III > V > II > I. Webbing is rudimentary with the following formula: 1 (1) 2 (1-1) 3 (2-2) 4 (3-3) 5 (2) (Barej et al., 2010).

According to Amiet (1973) the tympanic papilla is shorter than the tympanum diameter and thickened at its tip, but Barej et al. (2010) state that this character is hard to verify in preserved specimens, as the papilla is then often shrunken. Amiet (1983) remarked that skin on throat and basis of the arms is smooth, showing no trace of spinosities, but this observation was not consistent with some specimens examined by Barej et al. (2010).

Dorsum is brownish with small dark spots, marking larger warts. The color on the flanks is the same as the back, often with larger spots than on back. Iris is speckled with gold and silver. Throat is marbled blackish. Belly is whitish with minuscule dark speckles (recognizable only under the microscope). Hind limbs dorsally with large spots that are almost bar-like dark. Femoral glands are bright orange in males. Color after preservation is as in life, but color is pale. Boulenger (1888) mentioned a dark interorbital bar; Barej et al. (2010) noted that this bar was often incomplete.


Author: Zimkus, Breda
License: http://creativecommons.org/licenses/by-nc/3.0/

Size

Snout-urostyle length is 28.5–45.6 mm in males and 28.1–47.8 mm in females; sexes are approximately the same size (Barej, 2010). The holotype, a female, measred 31 mm from snout to vent (Boulenger, 1887).


Author: Zimkus, Breda
License: http://creativecommons.org/licenses/by-nc/3.0/

Diagnostic Description

This is a medium-sized Petropedetes with a slender body. The tympanum is round and distinctly smaller than the eye diameter (smallest distinct tympanum in the genus). Breeding males exhibit a slim tympanic papilla that is closer to the upper border of tympanum, a carpal spike, spinosities on the upper arm, throat and breast, some minuscule spines on the supratympanal gland, and prominent, bright orange femoral glands. Webbing is rudimentary (Barej et al., 2010).


Author: Zimkus, Breda
License: http://creativecommons.org/licenses/by-nc/3.0/

Comparisons

P. johnstoni is easily differentiated from other Central African congeners by its rudimentary webbing. P. palmipes and P. perreti are both fully webbed; P. cameronensis and P. juliawurstnerae are half-webbed. The presence of a distinct tympanum and a tympanal papilla distinguishes P. johnstoni from P. cameronensis and P. palmipes, which lack these characters. The small but distinct tympanum and the large femoral glands differentiate P. johnstoni from P. euskircheni, P. parkeri and P. vulpiae, which are all species with reduced webbing. Furthermore, P. johnstoni seems to be strictly restricted to lowland localities in coastal areas, while the other species live inland or are montane (Barej et al., 2010).


Author: Zimkus, Breda
License: http://creativecommons.org/licenses/by-nc/3.0/

Habitat and Ecology

It lives in lowland forest and mangrove forests, and can tolerate a limited degree of habitat disturbance (Amiet, 2004).


Author: Zimkus, Breda
License: http://creativecommons.org/licenses/by-nc/3.0/

Population Biology

It is a common species.


Author: Zimkus, Breda
License: http://creativecommons.org/licenses/by-nc/3.0/

Advertisement Call

The call is very characteristic and can be heard from far away (du Bocage 1903).


Author: Zimkus, Breda
License: http://creativecommons.org/licenses/by-nc/3.0/

Reproduction

Amiet (1989, 1991) assumed that tadpoles of this species were terrestrial because he discovered an egg clutch on a large leaf in the forest, some centimetres above the ground, and a male was sitting close to the clutch during daytime.


Author: Zimkus, Breda
License: http://creativecommons.org/licenses/by-nc/3.0/

Tadpole morphology

One tadpole of this species, collected at Musola (500–700 m) on Bioko Island, was described by Barej et al., (2010). The tadpole (Gosner stage 41) has fully developed hind limbs (18.6 mm) and rudimentary webbing. The vent tube is regressed. Body length is 11.3 mm (total length 26.3 mm), and its femoral glands were already 1.8 mm long. Barej et al. (2010) assume the identity of this species because no other Petropedetes species from Bioko exhibits rudimentary webbing (P. cameronensis possesses half-webbed feet). Its body is broad and slightly flattened. The flanks are not parallel, rather slightly convex. Nostrils are closer to the eye than to the snout tip. Tail axis is long and very muscular. No tail fins are visible. The end of is tail shrunken, in life probably pointed. Kkeratodont formula is as folows: 3+3//1+1:2; the upper three rows are interrupted by the upper jaw sheath.


Author: Zimkus, Breda
License: http://creativecommons.org/licenses/by-nc/3.0/

Phylogenetics

A genetic comparison of a fragment of the mitochondrial 16S rRNA gene (611 bp, including gaps) by Barej et al. (2010) found that interspecific comparison between P. johnstoni and all other Central African Petropedetes taxa resulted in uncorrected p-distances that ranged between 3.85%-9.03% with this species most closely related to P. vulpiae.


Author: Zimkus, Breda
License: http://creativecommons.org/licenses/by-nc/3.0/

IUCN Red List Category and Justification of Conservation Status

The IUCN Red List (2010) categorizes this species as Near Threatened because its Extent of Occurrence is probably not much greater than 20,000 km2, and the extent and quality of its habitat is probably declining, thus making the species close to qualifying for Vulnerable (Amiet, 2004). This account only took into account populations within Cameroon.


Author: Zimkus, Breda
License: http://creativecommons.org/licenses/by-nc/3.0/

Threats

It is threatened by the loss of forest habitat due to agricultural development, logging and expanding human settlements (Amiet, 2004).


Author: Zimkus, Breda
License: http://creativecommons.org/licenses/by-nc/3.0/

Conservation Actions and Management

It occurs in Korup National Park, and possibly in a few other protected areas (Amiet, 2004).


Author: Zimkus, Breda
License: http://creativecommons.org/licenses/by-nc/3.0/