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Madagascaran Toadlets (Scaphiophrynidae)

Madagascaran toadlets

(Scaphiophrynidae)

Class Amphibia

Order Anura

Family Scaphiophrynidae


Thumbnail description
Small to medium-size toad-like frogs with or without enlarged fingertips

Size
0.8–2.4 in (20–60 mm) in snout-vent length

Number of genera, species
2 genera; 9 species

Habitat
Semidesert, dry forest, rainforest, and mountain savanna

Conservation status
Not threatened

Distribution
Madagascar

Evolution and systematics

The systematics and phylogenetic relationships of the Scaphiophrynidae are of special interest because Scaphiophryne seems to represent a link between two major anuran lineages, the Ranoidea and Microhyloidea, indicating that the groups are closely related. Adult Scaphiophryne have typically microhylid features (e.g., dilated sacral diapophyses) in addition to sharing features of the Ranidae (e.g., possession of a complete shoulder girdle). The tadpoles of S. calcarata likewise represent a mosaic of characters of both families and intermediate features as well. Scaphiophryne therefore may represent an old lineage that has conserved a step in the evolution from the ranoid to the microhylid tadpole type and can be considered a "living fossil."

Reflecting the mosaic-like character distribution of Scaphiophryne, their classification in the anuran system was, and is, difficult. They were considered mostly a subfamily of Micro-hylidae, a subfamily of Ranidae, or a separate family. As of 2001, two genera are included in the Scaphiophrynidae: Scaphiophryne contains six nominal species and, in addition, several newly discovered but unnamed species, whereas Paradoxophyla includes only a single species. Unlike Scaphiophryne, however, Paradoxophyla has an incomplete shoulder girdle and typically microhylid tadpoles, with a median spiracle (breathing vent) and apparently without keratinized mouthparts. Further research is necessary to clarify its relationships with Scaphiophryne and other micro-hylids. No subfamilies are recognized.

Physical characteristics

Adult scaphiophrynids are 0.8–2.4 in (20–60 mm) in snoutvent length. The general body form of Scaphiophryne is somewhat toadlike. The legs are short, and well-developed metatarsal tubercles are present on the hind limbs. Some species (e.g., S. marmorata and S. gottlebei) have distinctly enlarged fingertips that may help them climb. The coloration varies widely, but some species are beautiful and have symmetrical markings on the back. The habitus of Paradoxophyla is different; at first glance, it resembles that of aquatic pipid frogs of the genus Hymenochirus.

Distribution

The family is endemic to Madagascar and inhabits most of the island at elevations from sea level to 6,600 ft (2,000 m),

although records are missing from far northern and northeastern Madagascar.

Habitat

Representatives of the Scaphiophrynidae occur in all climatic regions of Madagascar; S. calcarata, S. brevis, and S. gottlebei inhabit the hot and arid regions of the west and south. They are found in rocky formations, deciduous dry forest, open savanna, and even dry sand dunes close to the sea. Another group of species (e.g., S. madagascariensis) occurs in the cold, high montane savannas of central Madagascar below and above the tree line. Scaphiophryne marmorata and Paradoxophyla palmata inhabit primarily low and mid-elevation rain-forests of eastern Madagascar. Despite the different habitats of the adults, the larval habitat is similar in all species; tadpoles develop in stagnant and mostly temporary ponds and swamps.

Behavior

Scaphiophrynids are primarily nocturnal and terrestrial, spending the day buried in the ground under stones, fallen tree trunks, or other refuges. The species with expanded finger disks have some climbing abilities. The rainforestdwelling S. marmorata can be found in the leaf litter on the ground and climbing on mossy trees as well. Sometimes, it is even active during the day. Activity patterns in scaphiophrynids are highly seasonal. This is especially true for the species in arid regions and those in cold mountain habitats in which good climatic conditions for the development of tadpoles and juveniles are restricted to a short period of time. Most observations have been made at the beginning of the rainy season in December or January, when breeding takes place and activity is at its peak. After the rainy season the frogs in the arid habitats disappear for about six months and presumably estivate buried in the ground.

Feeding ecology and diet

The food seems to consist mainly of insects, but few data are available.

Reproductive biology

Scaphiophrynids are primarily explosive breeders and reproduce after heavy and prolonged rains at the beginning of the rainy season (generally in December, January, or February). Males aggregate in or at the edge of temporary ponds and often form large choruses that produce a continuous loud noise that can be heard from long distances. Before they start calling, Scaphiophryne greatly inflate the extremely large vocal sac and the body as well. Sometimes calling males swimming at the water's surface are unable to dive when they are disturbed, because they cannot get rid of the air quickly. Amplexus is axillary. Females lay numerous small, pigmented eggs, which generally are deposited as a film on the surface of the water. The free-swimming and mainly filter-feeding tadpoles develop quickly to froglets if the water temperature is high.

Conservation status

Several Scaphiophryne species (e.g., S. gottlebei) seem to have a quite restricted distribution, but more research is necessary to assess their conservation status reliably.

Significance to humans

Some of the beautifully colored Scaphiophryne species are offered regularly in the pet trade.

Species accounts

List of Species

Web-foot frog
Mocquard's rain frog
Red rain frog

Web-foot frog

Paradoxophyla palmata

taxonomy

Microhyla palmata Guibé, 1974, Ambana, Chaînes Anosyennes, Madagascar.

other common names

None known.

physical characteristics

The snout-vent length is 0.8–1.0 in (20–24 mm); males are slightly smaller than females. This is a distinctive, small frog with a triangular body form, a pointed snout, small eyes, and fully webbed toes. The tympanum is indistinct, and the fingertips are not enlarged. The dorsum is brown, gray, or beige, with some small black spots. The venter is mostly white with distinct dark spots. Males have a dark vocal sac.

distribution

Rainforest in eastern Madagascar.

habitat

Known from pristine and degraded primary rainforest up to elevations of 3,300 ft (1,000 m).

behavior

From December to February, males call after dusk at the edge of puddles or larger ponds, mainly after heavy rains.

feeding ecology and diet

Nothing is known.

reproductive biology

The males' calls are rather loud trills reminiscent of crickets. Occasionally, males and couples in axillary amplexus swim on the surface of the water and dive quickly when disturbed. Females lay several hundred small pigmented eggs about 0.04 in (1 mm) in diameter surrounded by a gelatinous capsule. The gelatinous capsules and eggs emerge above the water surface. Embryonic development is rapid, and larvae hatch one day after egg deposition. The tadpoles are typical microhylid filter-feeding tadpoles and swim in open water.

conservation status

Because the range of this unique species covers most of the eastern rainforest belt, including several nature reserves, it may be considered as not threatened.

significance to humans

Apparently, this frog is unknown to most indigenous people.


Mocquard's rain frog

Scaphiophryne calcarata

taxonomy

Pseudohemisus calcaratus Mocquard, 1895, Madagascar.

other common names

None known.

physical characteristics

This is the smallest known Scaphiophryne; the snout-vent length is 0.8–1.1 in (20–27 mm) in males and 1.1–1.3 in (28–33 mm) in females. The dorsum is pale brown, gray, or green with or without darker symmetrical markings and a pale vertebral line. The flanks are dark brown, and the venter is white; the ventral surfaces of the thighs are red to violet. The throat is black in males and marbled brown and white in females. The tips of the fingers are not enlarged. The skin on the back is smooth or slightly granular. The tympanum is indistinct, and the webbing between the toes is poorly developed. The tadpoles have a sinistral spiracle and keratinized mouthparts, although the latter are poorly developed. On the other hand, they have unperforated nares, as is typical of microhylid larvae.

distribution

Distributed widely in western and southern Madagascar at elevations below 1,000 ft (300 m).

habitat

Grassland savanna, dry forest, and other arid habitats.

behavior

It seems nearly impossible to find this nocturnal species during the dry season. After the first heavy rains, however, large numbers of individuals walk around at night, and calling males and amplectant pairs gather in temporary, sun-exposed ponds and swamps.

feeding ecology and diet

One specimen had numerous large ants in its stomach.

reproductive biology

Males aggregate in large choruses and produce loud, noisy calls. A female was observed approaching a calling male. The male became very excited and strongly enhanced the repetition rate of his vocalizations before clasping the female. Breeding activity is explosive at the beginning of the rainy season and often is finished after a few nights. Each female lays several hundred small eggs about 0.04 in (1 mm) in diameter. The tadpoles are largely transparent, mostly swim in open water, and are mainly filter feeders, but they also feed on larger particles. The larval development is rapid, in a race against the desiccation of waters. After a few weeks, metamorphosis is completed, and tiny froglets, 0.2–0.3 in (5.5–7.5 mm) in snout-vent length, emerge.

conservation status

Being widely distributed and common in primary and secondary habitats, the species is not threatened.

significance to humans

At the beginning of the rainy season, S. calcarata occasionally may penetrate the huts of Madagascan people.


Red rain frog

Scaphiophryne gottlebei

taxonomy

Scaphiophryne gottlebei Busse and Böhme, 1992, Isalo, Vallée des Singes, Madagascar.

other common names

None known.

physical characteristics

The snout-vent length reaches 1.4 in (36 mm). This is a toadlet that is colored conspicuously with contrasting colors. Four pink or red symmetrically arranged patches surrounded by black and green are present on the dorsum. The flanks and legs are white with black bands on the legs. The venter is dark grayish violet. The tips of the fingers are distinctly enlarged. The skin on the back is smooth, and the tympanum is indistinct. The webbing between the toes and the inner metatarsal tubercle is well developed.

distribution

Known only from a small area of the Isalo massif in southwestern Madagascar.

habitat

Lives in eroded sandstone formations. In the Isalo massif, humid forests persist in canyons and on the slopes, although the climate is rather arid.

behavior

Found under stones during the day in the rainy season. It probably estivates during the dry season. The expanded terminal finger disks may indicate partial climbing habits. Disturbed specimens inflate themselves, probably as a strategy to protect against predators.

feeding ecology and diet

The diet in nature is unknown. In captivity the frog feeds on crickets and other insects.

reproductive biology

Nothing is known, but probably an explosive breeder at the beginning of the rainy season. Recently metamorphosed juveniles have been found at the edge of stagnant ponds.

conservation status

The species is not categorized by the IUCN and is not protected by CITES. However, because of the small known range, it may be considered potentially threatened.

significance to humans

This beautiful frog is offered regularly in the international pet trade.


Resources

Books

Glaw, Frank, and Miguel Vences. A Fieldguide to the Amphibians and Reptiles of Madagascar. 2nd ed. Köln: Vences & Glaw Verlag, 1994.

Periodicals

Blommers-Schlösser, R. M. A. "Observations on the Larval Development of Some Malagasy Frogs, with Notes on Their Ecology and Biology (Anura: Dyscophinae, Scaphiophryninae and Cophylinae)." Beaufortia 24, no. 309 (1975): 7–26.

Blommers-Schlösser, R. M. A., and C. P. Blanc. "Amphibiens (Première Partie)." Faune de Madagascar 75, no. 1 (1991): 1–379.

Busse, K., and W. Böhme. "Two Remarkable Frog Discoveries of the Genera Mantella (Ranidae: Mantellinae) and Scaphiophryne (Microhylidae: Scaphiophryninae) from the West Coast of Madagascar." Revue Française Aquariologie 19, no. 1–2 (1992): 57–64.

Wassersug, R. "The Pseudohemisus Tadpole: A Morphological Link Between Microhylid (Orton Type 2) and Ranoid (Orton Type 4) Larvae." Herpetologica 40, no. 2 (1984): 138–149.

Frank Glaw, PhD

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