Family Pyxicephalidae

Pyxicephalus Tschudi, 1838

bullfrogs, brulpaddas (A)

By L.H. du Preez

Currently accepted name: Pyxicephalus sp.
Red listing status:

Description

The generic name is derived from the Greek: pyxis = box; kephale = head. These large, stout-bodied ranids have a broad, heavy head and a wide gape. Two prominent tooth-like projections, separated by a smaller, central cusp, are present in the lower jaw. The toes are webbed and the inner metatarsal tubercle is enlarged and flange-like, serving as a spade when burrowing. Male Pyxicephalus are unusual in that they are larger than females and, especially in P. adspersus, highly territorial during the breeding period. Tadpoles form large schools that are guarded by territorial males (Lambiris 1989a; Passmore and Carruthers 1995).

Distribution

Pyxicephalus occurs in sub-Saharan Africa, ranging from Kenya southward to Eastern Cape Province in South Africa. Two of the three known species, P. adspersus and P. edulis, occur in the atlas region. The latter is found in the hot, dry, northeastern parts of the atlas region, while the former is widely distributed across the central parts.

Records were screened from those parts of the atlas region where the two species apparently occur in sympatry or parapatry; doubtful records were included only in the genus map and were omitted from the species maps. The atlas maps are reasonably accurate but not comprehensive.

Habitat

In the atlas region the genus inhabits the Savanna, Grassland, Nama Karoo and Thicket biomes where the species breed in shallow, ephemeral water bodies. P. adspersus is distributed mainly across the highveld, often on poorly drained clay soils, whereas P. edulis is found in lower-lying subtropical areas, usually on sandy substrates (Poynton and Broadley 1985b).

Life history

Despite their large size and the unique aspects of their reproductive biology, knowledge of the general biology of Pyxicephalus is far from complete. This is partly due to the unpredictability of their emergences and the relatively short time they spend on the surface when breeding. If conditions are unfavourable for breeding, the adults remain in a dormant state underground and are capable of surviving droughts lasting several years, without emerging to feed or breed.

Bullfrogs feed voraciously during their short time above ground. They prey mainly on insects and other invertebrates, but will take larger prey items such as other amphibians, reptiles, small birds and small mammals.

While aspects of the reproductive behaviour of P. adspersus have been well documented, including the territorial and lekking behaviour of adult males, guarding of tadpole swarms, and channel construction, little research has been conducted into the reproductive biology of P. edulis.

Conservation

P. edulus has a peripheral distribution in the atlas region and does not require special conservation attention, whereas P. adspersus is declining rapidly in certain areas and has been classified Near Threatened (Harrison et al. 2001).