Directional hearing in insects with internally coupled ears

Abstract

Compared to all other hearing animals, insects are the smallest ones, both in absolute terms and in relation to the wavelength of most biologically relevant sounds. The ears of insects can be located at almost any possible body part, such as wings, legs, mouthparts, thorax or abdomen. The interaural distances are generally so small that cues for directional hearing such as interaural time and intensity differences (IITs and IIDs) are also incredibly small, so that the small body size should be a strong constraint for directional hearing. Yet, when tested in behavioral essays for the precision of sound source localization, some species demonstrate hyperacuity in directional hearing and can track a sound source deviating from the midline by only [Formula: see text]-[Formula: see text]. They can do so by using internally coupled ears, where sound pressure can act on both sides of a tympanic membrane. Here we describe their varying anatomy and mode of operation for some insect groups, with a special focus on crickets, exhibiting probably one of the most sophisticated of all internally coupled ears in the animal kingdom.

Evidence of the impact of noise pollution on biodiversity: a systematic map

“…In particular, amphibians communicate extensively using sounds (i.e. chorus frogs) [107], insects demonstrate hyperacuity in directional hearing [108], reptiles (in particular snakes) and spiders can feel vibrations [109][110][111][112].…”

Animals and ICE: meaning, origin, and diversity

“…There is indeed a pressure-gradient microphone in each leg and the distance between the two tympana in each leg is very small (~0.1 mm), justifying the notion of (discretized) gradient, but Autrum does not indicate any relation between the two “ears” located in the left and right leg respectively, which are cm apart. It is now known (Römer and Schmidt 2016) that ears of crickets and bush-crickets receive indirect input from the spiracle in the contralateral leg, quite similar to the key element of ICE as it occurs in vertebrates. As Autrum correctly pointed out, there is just a single directional microphone in the leg, so to speak of the U47 type.…”

“…In both groups, the tympana are formed in connection with the tracheal system in the foreleg tibia, and the sensory cells are probably modified chordotonal organs present in the leg before the evolution of tympana. The two tympana are coupled through the tracheal system (Römer and Schmidt 2016). In the acridid grasshoppers, tympanic ears form from thoracic air sacs that communicate across the midline, also producing a coupled-ear system.…”

Lung-to-ear sound transmission does not improve directional hearing in green treefrogs (Hyla cinerea)

“…The lungs can influence the magnitude of the tympanum's directionality, with these effects being more pronounced at frequencies near the resonance frequency of the lungs (Jørgensen, 1991;; see also reviews in Christensen-Dalsgaard, 2005, 2011. While internally coupled ears also play functional roles in directional hearing in some other vertebrates, such as lizards and crocodilians (Bierman et al, 2014;Carr and Christensen-Dalsgaard, 2016;Christensen-Dalsgaard and Manley, 2008;Christensen-Dalsgaard et al, 2011), and in some invertebrates, such as crickets and katydids (Römer, 2015;Römer and Schmidt, 2016), the frog's lung-to-ear sound transmission pathway appears to be unique among vertebrates, and its precise contribution to directional hearing remains uncertain (Bee and Christensen-Dalsgaard, 2016). At present, each tympanum's directional response is thought to result from the interaction of sound impinging directly on its external surface and sound that indirectly reaches its internal surface from the other tympanum via the internal coupling and from the lungs via the glottis.…”