Family Ptychadenidae

Ptychadena sp.

grass frogs, ridged frogs, graspaddas (A)

By L.R. Minter and N.I. Passmore

Species account was published under the name:
          Ptychadena Boulenger, 1918
Red listing status:

Description

The genus name is derived from Greek: ptyche = folds; adenos = gland. These sharp-snouted, streamlined frogs have well-developed hindlimbs and moderate to extensive webbing between the toes. These features allow them to move rapidly through dense grass, across open spaces, and through water. They can be distinguished from similar genera such as Afrana and Strongylopus by the presence of a pair of lateral, external vocal sacs in males, and six or more continuous longitudinal ridges on the dorsal surface. The pupil is horizontal and vomerine teeth are present, touching the anterior corners of the choanae (Poynton 1964; Stewart 1967; Poynton and Broadley 1985b; Passmore and Carruthers 1995).

Distribution

This large African genus of about 44 tropical and sub-tropical species occurs throughout sub-Saharan Africa, Madagascar, Seychelles and the Mascarene Islands. Most species have extensive ranges. The highest species diversity occurs in the tropics and none of the species is endemic to the atlas region. The genus is not represented in the southern and western parts of the atlas region (Poynton and Broadley 1985b; Channing 2001).

Habitat

Several sylvicolous species occur in the tropics, but in the southern third of Africa the majority inhabit sub-tropical, low-altitude savanna. A few extend into temperate, moderate- to high-altitude grassland habitats (Stewart 1967; Passmore 1978; Poynton and Broadley 1985b).

Life history

Surprisingly little is known of the natural history of many Ptychadena species, despite their abundance and wide distribution. The taxonomy is still in flux and basic aspects of biology of the majority of species, such as the structure of the advertisement call and tadpole morphology, are inadequately described or totally unknown. Much original information may be found in the works of Wager (1965) and Stewart (1967), while detailed studies of the vocalizations and reproductive behaviour of South African Ptychadena were carried out by Passmore (1976, 1977a, 1978).

Because they live in relatively moist environments, Ptychadena species are active at the surface for most of the year. They are known to retreat into deep mud cracks or bury themselves in the soil during dry periods. Their diet consists of a wide variety of insects and arachnids, as well as earthworms, snails, tadpoles and other frogs (Barbour and Loveridge 1928; Inger and Marx 1961; Passmore 1978; Channing 2001).

Explosive episodes of breeding follow heavy rain. In some species calling is dependant on rain, while others continue to call during dry periods. Breeding sites include temporary rain pools, vleis, inundated grassland and sedge pans. There is little differential utilization of available aquatic habitats, although rivers, streams and reedbeds are not used for breeding (Passmore 1978).

Call sites are located close to or in shallow water, and are usually concealed by grass or other vegetation, although some species call from exposed positions on the perimeter of the breeding site. Temporal variation in calling activity occurs, with some species peaking in the early evening, while others are most active around midnight or early morning (Passmore 1978). A complex vocal repertoire is present in most species, comprising up to four structurally and functionally different call types (Passmore 1976, 1977a, 1978).

The eggs are fertilized before they are deposited in shallow water. Using his feet as a funnel, the male directs his sperm onto the eggs as they leave the cloaca of the female (for more details see P. oxyrhynchus species account). The eggs are released in small clumps and float on the surface, sinking if disturbed. Larval growth is rapid, especially in species inhabiting arid areas, and froglets leave the water after 3–6 weeks (Stewart 1967; L.R.M. unpubl. data).

Conservation

In terms of their global distribution, none of the species in the atlas region appears to be under threat. However, from a national perspective, species such as P. mascareniensis, P. taenioscelis and P. uzungwensis have limited peripheral distributions within the atlas region and their breeding habitat may require protection. The taxonomic status of populations assigned to P. taenioscelis needs to be confirmed (see species account).