Squeakers and cricket frogs
(Arthroleptidae)
Class: Amphibia
Order: Anura
Family: Arthroleptidae
Thumbnail description
Mostly small, inconspicuous brown frogs
Size
The frogs are generally less than 1 in (25 mm) long, although some, like the East African species Arthroleptis tanneri, may exceed 2.4 in (60 mm)
Number of genera, species
8 genera; 77 species
Habitat
Forest
Conservation status
Not threatened
Distribution
Sub-Saharan Africa
Evolution and systematics
No fossils are known from this terrestrial family. There is an ongoing debate concerning the relationships of this group. The consensus appears to be that it is not a subsection of the Ranidae, and should retain its status as a discrete family. Two subfamilies are recognized—the Arthroleptinae and the Astylosterninae—although an alternative classification regards each as a distinct family. The characteristics of the Arthroleptinae include a typical hourglass pattern on the back, and the presence of an elongated third finger in males. The characteristics of the Astylosterninae include bent fingers with projecting bony tips.
Physical characteristics
These are smooth-skinned terrestrial frogs. A longitudinal middorsal fine skin ridge is characteristic of the Arthroleptinae. Webbing is absent between the toes. Some species have enlarged disks on the fingers and toes. The frogs are mostly less than 1 in (25 mm) long, although some, like the East African species A. tanneri, may exceed 2.4 in (60 mm). The limbs and body are gracile in most species, although some of the burrowing species are robust and have robust limbs and flattened tubercles on the heel. A characteristic arthroleptine pattern is a dark hourglass or series of diamond-shaped markings along the dorsal midline. The background color varies greatly within a species, and can range from red to olive. Adult males in the Arthroleptinae have extremely long third fingers. In some species the finger may reach 40% of the body length. The astylosternines are mostly large frogs associated with fast-flowing streams in forests. The subfamily is distinguished on small differences in anatomy; most have curved sharp terminal phalanges that protrude through the skin of the finger tip.
Distribution
The family is found throughout tropical Africa from sea level to 9,800 ft (3,000 m) in forest or wooded savanna. The ranges are decreasing as the African rainforest is being destroyed.
Habitat
The frogs are known from the moist tropics, where they are found in leaf litter. The arthroleptines are inhabitants of natural forests, but will live in any dense vegetation. Many astylosternines are associated with rapidly flowing torrents on forested slopes. There are no free-swimming larvae in Arthroleptinae, whereas large, well-muscled astylosternine larvae develop in fast-flowing streams.
Behavior
The adults are active throughout the year, with peaks of feeding and breeding after rain. They emerge only after dark in more open habitats, but can be found active in the shaded forest during the day. In areas where there is a distinct dry season they estivate. Males engage in combat with other males during the breeding season, in an effort to hold a breeding territory.
Feeding ecology and diet
The leaf litter frogs eat minute insects and other arthropods like small spiders, as well as other frogs. The larger, more robust species will eat anything that moves, providing it can be forced into the mouth. The terrestrial frogs move through the leaf litter taking small moving arthropods. The river dwellers feed along the edge of the water.
Reproductive biology
Arthroleptines are terrestrial breeders with direct development. Large, yolky eggs are laid in a hollow nest on the ground and develop into small adults without a free-swimming tadpole stage. Astylosternines deposit eggs in quiet backwaters of streams; they develop into torrent-adapted tadpoles. There are peaks of calling after rain, and most egg clutches are laid during the start to middle of the rainy season. In moist forests near rivers, breeding takes place over an extended period. Male arthroleptines call from concealed sites in leaf litter, although some species like the common squeaker sometimes call in the open from ground level. Astylosternine males call from the shallow edges of rivers. The eggs of arthroleptines are laid in small clutches under dead leaves. In these moist surroundings they hatch rapidly into juveniles, passing through a tadpole stage in the egg. There is no direct parental care, although the males of some species attract more than one female into the breeding territory, effectively placing the eggs from previous females within his care. Little is known of astylosternine breeding, but the hairy frog, Trichobatrachus robustus, remains underwater near the eggs, apparently to protect them from predators.
Conservation status
This is an endemic African family. Squeakers are common, and it is not unusual to see two or three along every step of a forest path or along the bank of a river. As the African forests are being logged, the available habitat is contracting, and the populations of all the forest amphibians are becoming smaller.
Significance to humans
The small arthroleptines are not of direct importance to humans; they are not eaten and they are not toxic. The larger astylosternines, such as the hairy frog, are a prized food of local people.
Species accounts
Common squeakerTanner's litter frog
Bush squeaker
Ugandan squeaker
Crowned forest frog
Hairy frog
Resources
Books:Channing, Alan. Amphibians of Central and Southern Africa. Ithaca, NY: Comstock Publishing Associates, 2001.
Passmore, Neville, and Vincent Carruthers. South African Frogs: A Complete Guide. Revised edition. Halfway House, South Africa: Southern Book Publishers and Johannesburg: Witwatersrand University Press, 1995.
Rödel, Mark-Oliver. Herpetofauna of West Africa. Vol. 1, Amphibians of the West African Savanna. Frankfurt: Chimaira, 2000.
[Article by: Alan Channing, PhD]
