Convergent Evolution Between Insect and Mammalian Audition

Science  16 Nov 2012:
Vol. 338, Issue 6109, pp. 968-971
DOI: 10.1126/science.1225271

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How to Hear

In mammalian ears, a chain of biophysical events allows for the translation of airborne acoustic energy into mechanical vibrations that can be detected by mechanosensory cells in the cochlear. Mammalian ears have been considered largely unique in this transformation because it is the delicate, mammalian-specific, bones of the middle ear that facilitate this transmission, known as impedence conversion. In most other vertebrates the bones that make up the middle ear function as part of the lower jaw, limiting the potential for vertebrate convergence in this process. However, Montealegre-Z. et al. (p. 968, see the Perspective by Hoy) show that the rainforest katydid, an insect with ears on its hind legs, have converged on a similar three step impedence conversion process using a unique tympanum-lever organ. This convergence, across millions of years of evolutionary distance, shows the flexibility of morphology to adapt to biophysical challenges.


In mammals, hearing is dependent on three canonical processing stages: (i) an eardrum collecting sound, (ii) a middle ear impedance converter, and (iii) a cochlear frequency analyzer. Here, we show that some insects, such as rainforest katydids, possess equivalent biophysical mechanisms for auditory processing. Although katydid ears are among the smallest in all organisms, these ears perform the crucial stage of air-to-liquid impedance conversion and signal amplification, with the use of a distinct tympanal lever system. Further along the chain of hearing, spectral sound analysis is achieved through dispersive wave propagation across a fluid substrate, as in the mammalian cochlea. Thus, two phylogenetically remote organisms, katydids and mammals, have evolved a series of convergent solutions to common biophysical problems, despite their reliance on very different morphological substrates.

  • Present address: School of Life Sciences, Riseholme Campus, University of Lincoln, Lincoln, LN2 2LG, UK.

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