Mantella expectata, the blue-legged mantella, is a small, brightly marked frog of the family Mantellidae, endemic to Isalo National Park and the area south of it in Madagascar. Like other mantellas, it carries alkaloid toxins in its skin, and its colours warn predators of that rather than simply decorating it. It shares its narrow range with another amphibian, the rainbow frog Scaphiophryne gottlebei, found in the same Isalo area.
Identification
Adults reach a snout-vent length of 20-30 mm. The back and top of the head are yellow, set off against blue legs, black flanks and black sides of the head, while the underside shows black marked with blue spots. The pattern is not perfectly fixed across the range. Some individuals have darker or greyer legs, and frogs from the northern part of the range tend to show a reddish lower back contrasting with the yellow upper back and crown. Males and females can be told apart in the field. Females run notably larger, and males carry a horseshoe-shaped blue spot on the lower jaw that females lack, alongside their own advertisement calls.
Habitat and range
The species is endemic to Madagascar, found in and south of Isalo National Park. Unlike forest-floor mantellas, it keeps to open, sun-exposed, temporary rocky streams and rocky canyons, and it is active by day rather than at night. That habitat is seasonal by nature, since the streams and canyon pools it depends on fill only part of the year, which shapes when and where the frog breeds.
Behaviour and breeding
Breeding runs from September to December, timed to the rains that flood the species’ canyon habitat. Rather than laying directly into water, females place eggs on canyon walls or under rocks, ahead of the seasonal flooding that will reach them; when the rains come and the site is inundated, the eggs complete their development in the resulting temporary pools. It is a short-lived species for a frog, with a typical maximum age of about three years in the wild.
Conservation
The facts box above carries the species’ current IUCN Red List category, Endangered. The main pressures are habitat loss and over-collection for the pet trade; its narrow, canyon-restricted range around Isalo leaves little room to absorb either.
Similar species
Within the genus, the yellow back, blue legs and black-and-blue-spotted underside of Mantella expectata are a fairly reliable combination, though individuals with darker, greyer legs or, in the north, a reddish lower back can look less typical at first glance. The clearer giveaway is habitat and range. This species keeps to sun-exposed rocky streams and canyons in and around Isalo National Park, a setting it shares with the unrelated rainbow frog, Scaphiophryne gottlebei, which is patterned in green and orange rather than yellow and blue and belongs to a different family entirely.