Phrynobatrachus pakenhami Loveridge, 1941
Original Published Description:
Pakenham's River Frog (English)
Phrynobatrachus pakenhami is medium-sized species (SVL 37-51 mm) of puddle frog endemic to Pemba Island, Tanzania. Members of this genus are identified by the presence of a midtarsal tubercle, elongate inner metatarsal tubercle, and outer metatarsal tubercle. Phrynobatrachus pakenhami is characterized by its almost smooth skin, a visible tympanum, and distinct digital discs on the toes. Males exhibit a grey throat with minute asperities, as wel as asperities on the head and anterior truck, and weak lateral folds when the vocal sac is deflated. In females, asperities are found only in proximity to the vent, and the throat has brown blotches.
This species is known only from the northern part of Pemba Island, Tanzania, where it has been recorded at Machengwe Swamp, Wete and Ngezi Forest Reserve (Pickersgill and Howell, 2008).
This species is named for its collector, Mr. R.H.W. Pakenham, who studied the fauna of Zanzibar and Pemba, writiing "The Birds of Zanzibar and Pemba."
It has been suggested that this species is a synonym of Phrynobatrachus acridoides, genetically its sister species, but recent surveys indicate that it differs both in vocalizations and ecology (Zimkus et al, 2010; Pickersgill and Howell, 2008). Phrynobatrachus nigripes, described by Pickersgill (2007) as a 'dwarf' species, is a synonym of this species with the specimens being juveniles and sub-adults.
Phrynobatrachus pakenhami is morphologically very similar to P. acridoides, with both having almost smooth skin, a visible tympanum, and distinct digital discs on the toes. Males exhibit a grey throat with minute asperities, as wel as asperities on the head and anterior truck, and weak lateral folds when the vocal sac is deflated. In females, asperities are found only in proximity to the vent, and the throat has brown blotches.
Loveridge (1941) reported that males are between 33-35 mm, and females are 33-36 mm in length; the female holotype measured 36 mm, and the male measured 35 mm. Pickersgill (2007) found males to be 25-30 mm, and females measured 31-36 mm.
This species is rather stocky and has an obtusely pointed snout. The head width, femur, tibia, and foot are 34-37%, 43-50%, 48-56%, and 48-51% of the snout-vent length, respectively. The eye diameter is approximately the same as the snout length, somtimes slightly less. The tympanum is visible, measuring 40-60% of the diameter of the eye. Fingertips are swollen or exhibit small digital discs. Well-developed digital discs are present on all toes. Pedal webbing is moderate with 2-3 phalanges on toe IV free of web, and up to 1.5 phalanges free of web on toes III and V. The tibiotarsal articulation of the adpressed hind limb is somewhat variable, reaching midway through the eye, anterior to the eye, ot just passed the tympanum. The skin is almost smooth with scapular glands in a "W" shape. Males exhibit asperities on the throat, and weaker asperities over the head and anterior trunk. Weak lateral folds are visible when the vocal sac is deflated. Females exhibit asperities in proximity to the vent and on the sacral region of the dorsum only. Males do not exhibit femoral glands (Pickersgill, 2007).
Dorsum is grey or brownish grey, more or less uniform. A lighter triangle is often present on the snout. A broad, light vertebral area may be present. A broad, transverse interorbital bar may be present. Darker brown patches are superimposed on the scapular warts. Hind limbs may be uniform or transversely barred with broad, light-edged dark bands. The upper lip is either uniform grey or with barring. Venter is whitish with some minute, brown spots. The palms and soles of the feet are grey in colour. The throat in males is dark grey, and females are marked with brown blotches, which may give a dark cast to the throat (Loveridge, 1941; Pickersgill, 2007).
Phrynobatrachus pakenhami is morphologically most similar to P. acridoides. According to Loveridge (1941), the latter can be distinguished by the barring (brown and white) present on the lower jaws, and the smaller body size (23-27 mm). However, he used these characters to distinguish P. pakenhami from what he believed was P. acridoides on Pemba Island, and this species is not believed to be found on the island. Pickersgill (2008) reported that apart from the advertisement call and slightly larger size, there is little to distinguish P. pakenhami from P. acridoides.
Habitat and Ecology
It lives in the leaf litter of the forest floor, as well as iin forest fringes and clearings. It has not been found in areas away from the forest (Pickersgill and Howell, 2008).
It is a common species in Ngezi Forest Reserve. It is not clear that it survives elsewhere on the island, although intensive surveys have not yet been carried out (Pickersgill and Howell, 2008).
Populations of this species are believed to be reduced in size due to loss of the indigenous broadleaf lowland forest in Pemba, largely for agriculture (Pickersgill and Howell, 2008).
It breeds in pools, marshes, puddles and roadside ditches in and near tropical evergreen lowland forest (Pickersgill and Howell, 2008).
The advertisement call of P. pakenhami is much coarser than that of P. acridoides. Antiphonal chorusing occurs in this species. Males were recorded with frequencies ranging between 1.05-2.5, with dominating frequencies between approximately 1.05-1.45 kHz and 1.63-2.1 kHz. Calls lasted 0.74-0.77 seconds for two recorded males with 26-28 pulses per call and 33-36 pps. (Pickersgill, 2007).
Evolution and Systematics
Mitochodrial sequence data from 12S rRNA, valine-tRNA, and 16S rRNA fragment, as well as combined sequence data from mitochondrial and nuclear (RAG-1) genes indicate that P. pakenhami and P. acridoides are sister species (Zimkus et al., 2010). These two species are in turn sister taxa to P. francisci and P. bullans.
IUCN Red List Category and Justification of Conservation Status
The IUCN Red List (2009) categorizes this species as Endangered because, although it can withstand a limited degree of habitat modification, its Extent of Occurrence is less than 5,000 km2, it occurs in fewer than five locations, and the quality and extent of its forest habitat on Pemba is declining (Pickersgill and Howell, 2008).
There has been widespread introduction of clove trees throughout the island, and it seems not to be present in clove thicket, only indigenous broadleaf lowland forest. It is now intrinsically at risk because of the small size of its remaining distribution (Pickersgill and Howell, 2008).
Conservation Actions and Management
This species occurs in the Ngezi Forest Reserve, which was established in northwest Pemba in the 1950s to save one of the last remaining stands of indigenous forest and covers 1440 hectares. The protecion of this forest is essential to the long-term survival of this species (Pickersgill and Howell, 2008).
- Phrynobatrachus nigripes Pickersgill, 2007 (synonym)