Amphibians
Reed Frog
Hyperoliidae · also called sedge frog, bush frog
Africa has almost no true tree frogs. The little climbing frogs that grip the reeds above an African pond and fill the night with whistles and clicks are reed frogs — a separate family that evolved the tree-frog lifestyle on its own. Some of them are among the brightest frogs on the continent, and a few can change from female to male as adults.
Overview
Reed frogs are the family Hyperoliidae, around 230 species, almost all in sub-Saharan Africa with a handful in Madagascar and the Seychelles. They are small, slender, often vividly coloured frogs with sticky toe discs for climbing smooth stems, and they fill the ecological role that true tree frogs occupy elsewhere, through convergent evolution. All are insectivores that hunt at night among waterside vegetation.
Sitting out the day
A reed frog spends daylight perched in the open on a sunlit leaf, legs folded tight against the body, its back turned pale and reflective to bounce away heat and its skin chemistry shifted to resist drying. At night it darkens and becomes active. Juveniles of many species look so different from adults that they were once named as separate species.
Changing sex
In several Hyperolius reed frogs, individuals that matured and bred as females have later been found functioning as males — a genuine sequential sex change, which is common in fish but almost unknown in four-legged animals.
Breeding
Reed frogs lay their eggs on vegetation or mud just above the water, so hatching tadpoles drop in, away from egg predators. On warm nights after rain, males gather in dense choruses, each species with its own whistle or creak, audible from far off.
Status
Reed frogs as a family are Not Evaluated. Many are common and thrive in farm dams and gardens, but a number of forest and mountain species with small ranges in West Africa, Tanzania’s Eastern Arc, and Madagascar are threatened by deforestation, wetland drainage, and the chytrid fungus.
Reed Frog: common questions
Is a reed frog the same as a tree frog?
It fills the same niche but belongs to a different family. The true tree frogs of the Americas, Europe, Asia, and Australia are the family Hylidae. Africa has very few hylids, and the small climbing frogs that live among waterside vegetation there are instead the reed frogs, family Hyperoliidae, which evolved sticky toe pads, slender bodies, and a tree-frog lifestyle independently. So a reed frog is an African ecological equivalent of a tree frog rather than a close relative. The two groups look and behave similarly through convergent evolution, much as unrelated frogs on different continents have repeatedly become tree frogs.
Do reed frogs really change sex?
Some do, and it is one of the more remarkable findings in amphibian biology. In studies of several Hyperolius reed frogs kept and observed over time, a proportion of individuals that had developed ovaries and bred as females were later found to have functional testes and to court and mate as males, a true sequential sex change from female to male. This is common in fish but almost unheard of in tetrapods. It appears to be a natural part of these species' biology rather than a response to pollution, though the triggers and how widespread it is across the family are still being worked out.
How do reed frogs survive sitting in the sun all day?
By a combination of behaviour, colour, and skin chemistry. A reed frog spends the day perched in the open on top of a leaf or stem rather than hiding, which seems risky, but it folds its legs tightly under its body so only its back is exposed, and it turns that back pale and highly reflective to bounce away sunlight and heat. Its skin also becomes more resistant to water loss than that of most frogs, partly through a waxy secretion and pigment changes, so it can tolerate hours of sun and drying wind. At night it darkens, relaxes, and becomes active.
Why are reed frog choruses so loud?
The calling is competitive advertising. Male reed frogs gather at breeding pools and each tries to attract females and space out rivals with a species-specific call, and because a louder, more persistent, better-quality call wins more mates, selection pushes the calls to be as conspicuous as a small frog can manage. An inflatable vocal sac under the chin acts as a resonator, and many males calling together create a chorus that carries far and also swamps the ability of predators to home in on any one frog. Each species calls at its own pitch and rhythm so that females can pick out their own kind in the din.