Family Ptychadenidae

Ptychadena taenioscelis Laurent, 1954

Dwarf Grass Frog, Spotted-throated Ridged Frog, Kleingraspadda (A)

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

Currently accepted name: Ptychadena taenioscelis
Red listing status: Least Concern

Distribution

P. taenioscelis is distributed from Angola, northern Namibia (Caprivi), southeastern Zaire and Tanzania, southward through northern Botswana and Zambia to northern Mozambique. Within this range the distribution is reported to be patchy (Poynton 1964; Stewart 1967; Passmore 1976; Poynton and Broadley 1985b; Rödel 2000; Channing 2001). The taxonomic relationship between P. taenioscelis and the West African P. pumilio has been the subject of some debate in the literature (Perret 1979; Poynton and Broadley 1985b; Passmore and Carruthers 1995; Channing 2001). Advertisement calls recorded in Cameroon appear to be those of P. taenioscelis (N.I.P. unpubl. data), which suggests that this species has a wider distribution than described above.

In the atlas region the species has a peripheral distribution comprising a few scattered populations along the coastal plain of northern KwaZulu-Natal. It has been recorded as far south as Richards Bay (2832CC). Channing (2001) recorded this species in Limpopo Province and North West Province, but no records were obtained from these areas during the extensive survey carried out by Jacobsen (1989), nor during the atlas survey.

The populations entering the atlas region were assigned to a new species, P. smithi, by Guibé (1960), but were later placed in the synonymy of P. taenioscelis by Poynton (1964). Thus, although P. taenioscelis has not yet been collected in southern Mozambique, the Zululand populations are currently regarded as representing the southern periphery of this species.

The atlas map is based entirely on pre-1996 records; this is probably the result of inadequate sampling as well as a relative scarcity of breeding sites.

Habitat

In the northern parts of its range, P. taenioscelis inhabits river-valley savanna (moist woodlands) and open grasslands at medium elevations (Stewart 1967; Poynton and Broadley 1985b). In the atlas region it occupies Coastal Bushveld-Grassland, a mosaic of vegetation types containing lowland swamps, forest patches and patches of secondary woodland in a grassy matrix (Passmore 1978).

Life history

Nothing is known of the life history of P. taenioscelis outside of the breeding season. Dense breeding aggregations develop in summer, in shallow, boggy areas of vleis, seepages and inundated grassland (Passmore and Carruthers 1995). Like P. porosissima, this species continues to call during dry periods, though less intensely (Passmore 1978). During the day, adults remain close to the breeding site (Passmore 1978).

Calling begins early in the afternoon, and is characterized by frequent physical interactions between males as they establish a suitable spacing (0.4–1.5 m apart). Calling peaks between 18:30 and 21:00, and ends 3–4 hours after dark. Males call from exposed positions in wet mud or shallow water at the margin of the breeding site, sometimes submerged to the level of the axillae (Passmore 1976, 1978).

Eggs are laid and fertilized in the same way as described for P. oxyrhynchus. They are released two or three at a time, in water 5–10 mm in depth. Eggs sink slowly and accumulate debris on the jelly capsule (Passmore 1978).

Adults feed on a variety of terrestrial arthropods, primarily beetles, bugs, wasps and spiders (Passmore 1978).

Conservation

P. taenioscelis has a peripheral and patchy distribution in the atlas region and few data are available to assess its conservation status. Despite its tendency to form large breeding aggregations, it was never encountered during the seven-year period of the atlas survey; therefore, from a national perspective, the species may be threatened. Population surveys and monitoring in protected areas are strongly recommended. If P. taenioscelis has indeed declined within the atlas region, it is important to try to identify the contributing factors as these may also be affecting endemic species.

Current distribution map

Undated records;  pre-1996;  1996 to 2002;  2003 to present