Bridging the Gap Between Mammal and Insect Ears – A Comparative and Evolutionary View of Sound-Reception

Abstract

Insects must wonder why mammals have ears only in their head and why they evolved only one common principle of ear design—the cochlea. Ears independently evolved at least 19 times in different insect groups and therefore can be found in completely different body parts. The morphologies and functional characteristics of insect ears are as wildly diverse as the ecological niches they exploit. In both, insects and mammals, hearing organs are constrained by the same biophysical principles and their respective molecular processes for mechanotransduction are thought to share a common evolutionary origin. Due to this, comparative knowledge of hearing across animal phyla provides crucial insight into fundamental processes of auditory transduction, especially at the biomechanical and molecular level. This review will start by comparing hearing between insects and mammals in an evolutionary context. It will then discuss current findings about sound reception will help to bridge the gap between both research fields.

Auditory mechanics in the grig ( Cyphoderris monstrosa ): tympanal travelling waves and frequency discrimination as a precursor to inner ear tonotopy

“…The finding that the tympanal travelling waves and tonotopy resemble that of the tettigoniid CA evokes the following hypothesis of the mechanism by which the complex ear of the tettigoniids has evolved: natural resonant modalities of the tympanum form a simple tonotopic arrangement for high frequencies, which has been mechanically coupled to the DW over time to reduce the distance between tympanum displacement and the mechanosensory units, increasing hearing sensitivity. Later, the DW and CA have become more specialized for tonotopic reception, convergently evolving similar mechanics to the mammalian cochlea for enhanced frequency resolution [ 10 , 11 , 20 ]. Comparative investigations of ensiferan tympanal mechanics in a phylogenetic context could prove beneficial in refining this hypothesis.…”

“…The tympana act as pressure-difference receivers, converting airborne sound from multiple inputs into a single mechanical travelling wave in the inner ear, or crista acustica (CA), which lies above the anterior tracheal branch. The bushcricket CA has long been regarded as an analogous system to the mammalian cochlea [10,11,[18][19][20], separating incoming acoustic signals by their frequency information. However, in many ensiferans, acoustic communication among conspecifics is simply facilitated by a parallel between the frequency composition of the conspecific acoustic signals and the frequency response of the ear.…”

Variations in cochlea shape reveal different evolutionary adaptations in primates and rodents

“…Nonetheless, several anuran species are reportedly able to communicate in the ultrasound 9 , 10 . The mammalian fossil record shows that cochlea elongation and coiling evolved shortly after the three-ossicular chain evolved during the late Jurassic 11 . While this change in middle ear morphology was an important adaptive change, it alone would not have been enough to attain high-frequency hearing.…”

Ear pinnae in a neotropical katydid (Orthoptera: Tettigoniidae) function as ultrasound guides for bat detection

“…However, animals such as insects are too small to exploit diffractive effects of sound on their bodies to perceive minute differences in sound delays and intensities ( Michelsen and Larsen, 2008 ). As a result, vastly different species have convergently evolved separate mechanisms of hearing to fulfil similar functions ( Göpfert and Hennig, 2016 ; Köppl et al, 2014 ; Robert, 2005 ; Warren and Nowotny, 2021 ), including the detection of ultrasonic frequencies ( Strauß et al, 2014 ).…”