Family Hemisotidae

Hemisus marmoratus Peters, 1854

Mottled Shovel-nosed Frog, Marbled Snout-burrower, Gemarmerde Graafneuspadda

By L.R. Minter

Currently accepted name: Hemisus marmoratus
Red listing status: Least Concern

Photo by Sharp A; I. Sharp, 2013. URL: FrogMAP: 1263

Distribution

H. marmoratus is a wide-ranging inhabitant of the savannas of sub-Saharan Africa, from Senegal in the west, to Ethiopia and Somalia in the east, and southward to Angola, eastern Namibia (Caprivi), Botswana, Zimbabwe and Mozambique (Poynton and Broadley 1985a).

In the atlas region the species is distributed from Derdepoort (2426DA) in the far western corner of Limpopo Province, eastward across the dry northern and central parts of the province into the lowveld, and south through eastern Mpumalanga and central and eastern Swaziland to northern KwaZulu-Natal, reaching Mfolozi (2831BD) and Ntambanana district (2831DB) in the south. In 1999, it was recorded in Gauteng Province in a borrow pit at Burkea Park near Pretoria, but this outlying record may represent an accidental translocation.

A morphologically similar species, H. guineensis broadleyi, apparently reaches the southern limits of its range north of the Soutpansberg in Limpopo Province, where it is known from two historical records. This species can be distinguished from H. marmoratus by differences in its advertisement call (see species account for H. g. broadleyi).

The atlas data for H. marmoratus are reliable but incomplete.

Habitat

This species thrives in semi-arid environments and is well-adapted to breeding in shallow, temporary water bodies. In the atlas region it inhabits a variety of bushveld vegetation types in the Savanna Biome.

Breeding habitat includes pans, waterholes or artificial impoundments, as well as the isolated pools that form in riverbeds as water levels drop. The substrate usually consists of fine mud or clay, but burrows have been observed in coarser sandy sediments too.

In West Africa, H. marmoratus is found mainly in savanna habitats but also occurs in forest, and tadpoles have been encountered in a wide range of water bodies, except major rivers (Rödel 2000).

Life history

These burrowing frogs spend the dry season in a torpid state, underground. They begin to call as soon as the first spring rains have soaked the ground, sometimes even before standing water has accumulated at the breeding site. At this time they construct extensive, shallow, tortuous tunnels, in low muddy areas that are likely to fill with subsequent rains, or close to the edges of pools that have already formed. The tunnels form conspicuous low ridges on the surface, often intersect, and sometimes terminate in larger, rounded chambers. Males usually leave the tunnels and call from the surface, but in the absence of ground cover they may call from within the tunnels or chambers (pers. obs). Food includes ants, termites and earthworms (Rödel 2000; Channing 2001).

Choruses at Hans Merensky Nature Reserve typically comprise groups of 5–8 males that participate in discrete bouts of calling, alternating with periods of silence (pers. obs.). One male usually initiates calling, followed by the other members of the group. Calling males may be as little as 30 cm apart.

Amplexus is inguinal. Once in amplexus, the female selects a suitable oviposition site and disappears beneath the surface, male in tow, to excavate a nest. Nests may be constructed in low-lying areas that are subsequently flooded after rain (Kaminsky et al. 1999), or in more elevated positions away from the water’s edge. For example, nests have been found 15 cm to 8 m from the water’s edge in South Africa (pers. obs.; Jacobsen 1989), while in Comoé National Park in Ivory Coast, nests have been found up to 100 m from the nearest pool (Rödel 2000).

A chamber is constructed in which a spherical mass of 88–242 eggs are laid (Rödel 2000). Sterile jelly capsules are laid on top of the fertile eggs and the entire mass is bound together by a fibrous substance that prevents the egg mass from being flattened by the female, who sits on top of the mass until the eggs hatch. After hatching, the developing tadpoles cling to the body of their mother, who actively defends them against intruders (Rödel et al. 1995).

In dry weather, development is arrested and the tadpoles can remain in the chambers for as long as two months in anticipation of the next rains (Kaminsky et al. 1999). If rising water floods the nest, the tadpoles leave it (at any stage of development) and enter the water to feed. If the nest is not flooded, the female provides an escape route from the nest to the water by constructing a surface slide down which the tadpoles wriggle to the water (Rödel et al. 1995; Kaminsky et al. 1999). If this is not possible, the female may carry her tadpoles to the water while they adhere to her body.

Since the tadpoles of H. marmoratus often begin their development before the breeding site contains water, they have an advantage over tadpoles of species that lay their eggs only after heavy rain in that, once the site is flooded, Hemisus tadpoles take less time to reach metamorphosis and are exposed to predators for a shorter period of time. These adaptations are advantageous in an environment where rainfall is unpredictable and highly variable.

Conservation

The species does not appear to be at risk, as much of its habitat is used for game and cattle farming and is relatively undisturbed. It occurs in a number of provincial nature reserves and national parks.

Current distribution map

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