BBC Earth (Asia) - - Special Feature -

Two species of tiny frogs, known as pumpkin toadlets, which live on the floor of Brazil’s At­lantic For­est, are un­able to hear their own (and each other’s) cries, it has been dis­cov­ered. This makes them the only two species known to have evolved in this way. The dis­cov­ery was made by a team of scientists from Brazil, Den­mark and the UK, led by Dr San­dra Goutte from Brazil’s Univer­si­dade Es­tad­ual de Camp­inas.

In or­der to find a mate, most frog species sig­nal their pres­ence to mem­bers of the op­po­site sex by calls, but mak­ing such calls con­sumes en­ergy and can at­tract preda­tors. The two species of pumpkin toadlet also make such calls, but lab­o­ra­tory test­ing at the Univer­sity of South­ern Den­mark sug­gested they are un­able to ac­tu­ally hear them, while anatom­i­cal stud­ies at Cam­bridge Univer­sity con­firmed that the part of the ear that would nor­mally de­tect the high fre­quen­cies in­volved is ves­ti­gial in the two species in­volved. In other words, like the hu­man tail­bone, it’s still there but no longer does any­thing.

Jakob Chris­tensen-Dals­gaard from the Univer­sity of South­ern Den­mark said: “We have never seen this be­fore: th­ese frogs make sounds that they can­not hear them­selves.”

Goutte added: “One would think that if a sig­nal is not per­ceived by its tar­get au­di­ence, it would be lost through evo­lu­tion.”

It’s thought that the calls have been re­tained be­cause the bright or­ange toadlets have re­place au­di­tory with vis­ual sig­nalling, and that the throat-swelling that pro­duces the call is now the way the toadlets at­tract a mate – with the re­sult­ing call now a mere by-prod­uct of this vis­ual sig­nal.

The pumpkin toadlets’ bright colours warn preda­tors of their tox­i­c­ity

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