3.17 - Amplification and Feedback in Invertebrates

Abstract

Ears achieve their exquisite sensitivity by means of mechanical feedback: by pumping energy into sound-induced vibrations, motile mechanosensory cells amplify the mechanical input of the ear. While this amplificatory feedback has long been thought to be a unique characteristic of vertebrate auditory systems, recent studies have shown that sensitive hearing in invertebrates relies on mechanical feedback as well. Essential features of mechanical-feedback amplification have been documented for the ears of certain insects, including mosquitoes, Drosophila, locusts, and moths. In Drosophila, the source of the feedback has been traced to chordotonal sensory neurons, the insect counterpart of the vertebrate hair cells. Several mutations that abolish the feedback have been identified, and the molecular mechanisms that promote the mechanical feedback in insect auditory systems are beginning to be revealed. As insect chordotonal neurons and vertebrate hair cells appear to be evolutionarily related, the intriguing possibility exists that some of the molecular modules vertebrates and invertebrates employ to improve the sensitivity of hearing are evolutionarily conserved.