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Rainforest insect hears like a human

Copiphora gorgonensis, a neotropical katydid from the National Natural Park Gorgona Island, Colombia. The species was used as the model organism to discover convergent evolution between the katydid and the mammalian ear.
[Image courtesy of Daniel Robert & Fernando Montealegre-Z]

The ear of the South American rainforest katydid sits on the insect's hind legs, and it's one of the smallest of all hearing organs. But in other ways, the katydid ear is remarkably similar to the mammalian ear, researchers have discovered.

Mammalian hearing involves three stages. First, airborne sound waves cause the eardrum to vibrate. Next, a trio of delicate ear bones in the middle ear amplifies these air-borne vibrations, producing more forceful vibrations that travel through the fluid of a structure in the inner ear called the cochlea. Finally, hair cells in the inner ear convert these traveling waves into electrical impulses that carry information to the brain.

Fernando Montealegre-Z of the University of Lincoln in the United Kingdom and colleagues now show that the hearing organ of the rainforest katydid uses a similar three-step process. The authors' key discovery is that the system includes a structure like the one in the mammalian middle ear, which also converts and amplifies vibrations. The fact that the two organisms separately evolved such similar hearing systems is remarkable because these animals are so distantly related.

The research appears in the 16 November issue of the journal Science.