Family Hyperoliidae

Afrixalus Laurent, 1944

leaf-folding frogs, spiny reed frogs, blaarvouendepaddas (A)

By P.J. Bishop and M. Pickersgill

Currently accepted name: Afrixalus sp.
Red listing status:

Description

Afrixalus can be distinguished from the morphologically similar genus, Hyperolius, by the presence of a vertical pupil and minute asperities (dermal spines) on the body and limbs. The asperities are more conspicuous in males than in females, and their size and pattern of distribution is, in some cases, diagnostic at the species level. The genus name is derived from Greek: Afr = Africa; ixalus = bounding or springing.

They are commonly referred to as “leaf-folding frogs” because of their mode of oviposition, which involves depositing the eggs within an envelope created by gluing the edges of a leaf together around them (Poynton 1964; Lambiris 1989a; Passmore and Carruthers 1995).

Little morphological differentiation is apparent in certain of the species groups, resulting in considerable taxonomic confusion, but recent studies have demonstrated the diagnostic value of the advertisement call (Pickersgill 1984; Backwell 1991; Passmore and Carruthers 1995).

Distribution

The genus contains 29 described species distributed across sub-Saharan Africa. Five species, of which two are endemic, occur in the extreme eastern and southern parts of the atlas region.

Habitat

Afrixalus species occur in well-vegetated habitats which receive a relatively high rainfall, from seasonally moist open grassland and savanna to rain forest. They are found from sea level to altitudes in excess of 2000 m. They show a preference for ponds, marshes, vleis and pans which contain suitable vegetation for nest construction (Jacobsen 1989; Passmore and Carruthers 1995).

Life history

Relatively little is known about the biology of most Afrixalus species. All are nocturnal, although they may sometimes be seen basking, in full view, during the day. They are adept climbers, possessing terminal adhesive discs on all digits, and can leap through vegetation with ease. During the non-breeding periods, both sexes can be found in leaf axils of Strelitzia, palms and bananas.

During the breeding season, males call from elevated positions up to 2 m above the ground. Males of certain dwarf species have a two-part call, in which one part serves to attract the female, while the other facilitates spacing between neighbouring males.

The amplexing pair usually deposit unpigmented eggs, in small numbers, on a leaf which is subsequently folded by action of the hind legs, and sealed with the aid of an adhesive oviducal secretion, as the pair move along the leaf from base to tip (Passmore and Carruthers 1995).

The tadpoles are slender and dorsally depressed, with a long muscular tail and low tail fins. The dentition, which is reduced to a pair of rostrodonts and, at most, a single row of keratodonts, suggests a carnivorous diet, and tadpoles of several species raised in captivity seem to specialize on mosquito larvae: nine A. paradorsalis (a West African species) tadpoles in an aquarium devoured approximately 3000 immature mosquito larvae within 24 hours (M.P. pers. obs.). Mosquitoes are abundant in Afrixalus breeding habitats, including small ponds uninhabited by fish. As yet the role of Afrixalus tadpoles in the natural control of mosquitoes has not been explored. Adult mosquitoes figure highly in the diet of post-metamorphic Afrixalus (Wager 1965).

Conservation

Of the five species that occur in the atlas region, only two are endemic and all occur in areas that enjoy some degree of conservation management. The endemic species, A. knysnae and A. spinifrons, are nevertheless threatened. The ranges of some species overlap areas of high industrial, agricultural and urban development where suitable breeding sites are being drained and destroyed at an alarming rate. On the other hand, some agricultural practices, such as dairy farming, and some urban developments, such as golf courses, potentially provide additional areas of breeding habitat.