Fun frog facts

By Rupert Wilkey

Frogs have evolved a wide variety of ways of increasing the chances that their vulnerable eggs and tadpoles survive to maturity. To date, 29 such reproductive modes have been described, including adults carrying young on their backs and laying eggs in burrows. Recently the University of Estadual Paulista in Brazil and the University of Vienna in Austria have described yet another reproductive mode -- the bubble nest -- a phenomenon more usual in fish.

After heavy rain, the university researchers came across an aggregation of hundreds of the Brazilian frog Chiasmocleis leucosticta in a temporary pool in a forest clearing. Pairs were seen to float immobile on the water surface, the male on the back of the female. Unlike other male frogs who have to hang on to their mates for dear life, males of this species are "glued" in place by an adhesive substance which allows them to let go with their legs.

The male fertilizes the 200 or so eggs laid by the female. These eggs stick together by means of a viscous mucus and float to the surface. The adults then set about constructing a bubble nest for the eggs by repeatedly taking lungfuls of air, diving under the clutch and releasing the air through their nostrils. These bubbles are then trapped in the mucus. The male will sometimes continue adding bubbles to the nest after the pair have gone their separate ways. Sometimes the pair have trouble splitting because of the "glue." It is thought that the bubbles suspend the eggs in an oxygen rich layer.

Chiromantis constructs a foam nest for the eggs in vegetation overhanging ponds and streams. When the tadpoles hatch, they drop into the water below to complete their development.

Heleioporus lays her eggs underground in a burrow. When the rains come, they emerge and metamorphose into froglets in the temporary pool.

The Midwife Toad, Pipa pipa, places her eggs on her back where they embed and are protected until hatching by a new layer of the mother's skin that grows over them.