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Active amplification in insect ears: mechanics, models and molecules

Abstract

Active amplification in auditory systems is a unique and sophisticated mechanism that expends energy in amplifying the mechanical input to the auditory system, to increase its sensitivity and acuity. Although known for decades from vertebrates, active auditory amplification was only discovered in insects relatively recently. It was first discovered from two dipterans, mosquitoes and flies, who hear with their light and compliant antennae; only recently has it been observed in the stiffer and heavier tympanal ears of an orthopteran. The discovery of active amplification in two distinct insect lineages with independently evolved ears, suggests that the trait may be ancestral, and other insects may possess it as well. This opens up extensive research possibilities in the field of acoustic communication, not just in auditory biophysics, but also in behaviour and neurobiology. The scope of this review is to establish benchmarks for identifying the presence of active amplification in an auditory system and to review the evidence we currently have from different insect ears. I also review some of the models that have been posited to explain the mechanism, both from vertebrates and insects and then review the current mechanical, neurobiological and genetic evidence for each of these models.

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Abbreviations

BF:

Best frequency

CAP:

Compound action potentials

Iav:

Inactive

IHC:

Inner hair cell

JO:

Johnston’s organ

OHC:

Outer hair cell

Nan:

Nanchung

NompC:

No mechanoreceptor potential C

SRS:

Stimulus receiver structure

TilB:

Touch insensitive larvae B

TRP:

Transient receptor potential

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Acknowledgments

The author would like to acknowledge the support of the UK India Education and Research Initiative, a Biotechnology and Biological Sciences Research Council Grant and a Marie Curie fellowship. I would also like to gratefully acknowledge the Wissenschaftskolleg zu Berlin for a College for Life Sciences fellowship (2013/2014) during which this review was partly written. I would also like to thank the editors of this special issue for inviting me to write this review and for their patience while I did. I would also like to thank two anonymous referees whose comments and suggestions greatly improved this manuscript.

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Correspondence to Natasha Mhatre.

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Mhatre, N. Active amplification in insect ears: mechanics, models and molecules. J Comp Physiol A 201, 19–37 (2015). https://doi.org/10.1007/s00359-014-0969-0

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  • DOI: https://doi.org/10.1007/s00359-014-0969-0

Keywords

  • Acoustic communication
  • Active hearing
  • Insect hearing
  • Active auditory amplification
  • Active mechanosensation