Family Hyperoliidae

Kassina Girard, 1853

kassinas, chikwarikwari (S), vleipaddas (A)

By P.J. Bishop

Currently accepted name: Kassina sp.
Red listing status:

Description

The genus is named for John Cassin (1813–1869), an ornithologist at the Academy of Natural Sciences, Philadelphia, Pennsylvania, USA. These medium-sized frogs are slow moving and prefer to walk or run, rather than hop or jump. Their dorsal coloration usually consists of round, or elongated, dark brown, regular patches, bordered by a thin pale line on a light brown to yellow background. The pupil is vertical and some species possess discs on fingers and toes. The fingers lack webbing and there is only a small amount of webbing between the toes. The skin of these frogs contains bioactive amines and peptides that may serve as a toxic deterrent to predators and leave a characteristic smell on one’s hands (Roseghini et al. 1988).

The tympanum is indistinct, while the vocal sac in males is obvious and sub-gular, protected by a distinct gular disc. When inflated, the vocal sac is usually paired. The frogs of this genus produce unusual advertisement calls that contain rapid upward sweeps in frequency. They begin calling in the late afternoon, well before sunset, and may continue until sunrise.

The nektonic tadpoles have tails with characteristically high fins and a flagellum, and can easily be mistaken in the field for small fish. The fins are often coloured with bright yellow or red infusions.

Distribution

The genus Kassina is widely distributed throughout sub-Saharan Africa, but is absent from extremely arid areas. Eleven species are currently recognized, of which two occur in the central and eastern parts of the atlas region.

Habitat

Kassina species occur in Forest (but not in the atlas region), Savanna and Grassland biomes. They favour permanent, standing water, such as forest pools, marshes and dams with emergent and/or floating or overhanging vegetation. Some species also breed in temporary water bodies such as shallow pans, vleis and flooded grassland.

Life history

During dry periods, individuals take shelter in disused termitaria, burrows in the soil, the axils of banana or Strelitzia leaves, and under rocks or damp vegetation.

Males begin calling in dense choruses at the beginning of the summer rainy season and continue for most of the summer months. In some species, these choruses can be heard over a distance of several kilometers. Usually individuals start to call in the late afternoon from concealed sites in dense undergrowth. As the evening progresses, males move towards the breeding site and call from more exposed positions. The characteristic upward sweep in call frequency plays an important role in call recognition by females (Passmore and Carruthers 1995; P.J.B. and N.I. Passmore unpubl.data).

The larger females locate males using acoustic cues. The females initiate amplexus, which is axillary. Females direct movement to the oviposition site where up to 600 eggs are laid (Rödel 2000).

Conservation

The Kassina species in the atlas region are widespread, locally abundant, and do not require special conservation attention at present. Although commercial Eucalyptus plantations pose a major threat to these species in coastal areas of KwaZulu-Natal, farm-dam construction and irrigation seem to be advantageous to other populations.

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