01453nas a2200121 4500008004100000245008400041210006900125520101100194100003201205700002001237700002101257856005301278 2014 eng d00aLateralization of Travelling Wave Response in the Hearing Organ of Bushcrickets0 aLateralization of Travelling Wave Response in the Hearing Organ 3 a

Travelling waves are the physical basis of frequency discrimination in many vertebrate and invertebrate taxa, including mammals, birds, and some insects. In bushcrickets (Tettigoniidae), the crista acustica is the hearing organ that has been shown to use sound-induced travelling waves. Up to now, data on mechanical characteristics of sound-induced travelling waves were only available along the longitudinal (proximal-distal) direction. In this study, we use laser Doppler vibrometry to investigate in-vivo radial (anterior-posterior) features of travelling waves in the tropical bushcricket Mecopoda elongata. Our results demonstrate that the maximum of sound-induced travelling wave amplitude response is always shifted towards the anterior part of the crista acustica. This lateralization of the travelling wave response induces a tilt in the motion of the crista acustica, which presumably optimizes sensory transduction by exerting a shear motion on the sensory cilia in this hearing organ.

1 aUdayashankar, Arun, Palghat1 aKössl, Manfred1 aNowotny, Manuela uhttps://dx.plos.org/10.1371/journal.pone.008609001910nas a2200181 4500008004100000245007300041210006900114520135500183653001001538653001101548653002901559653001101588653001301599100002001612700002101632700002001653856005501673 2014 eng d00aMechanical basis of otoacoustic emissions in tympanal hearing organs0 aMechanical basis of otoacoustic emissions in tympanal hearing or3 a

Tympanal hearing organs of insects emit dis- tortion–product otoacoustic emissions (DPOAes), which in mammals are used as indicator for nonlinear cochlear amplification, and which are highly vulnerable to manipu- lations interfering with the animal’s physiological state. Although in previous studies, evidence was provided for the involvement of auditory mechanoreceptors, the source of DPOAe generation and possible active mechanisms in tympanal organs remained unknown. Using laser Dop- pler vibrometry in the locust ear, we show that DPOAes mechanically emerge at the tympanum region where the auditory mechanoreceptors are attached. Those emission- coupled vibrations differed remarkably from tympanum waves evoked by external pure tones of the same frequency, in terms of wave propagation, energy distribution, and loca- tion of amplitude maxima. Selective inactivation of the auditory receptor cells by mechanical lesions did not affect the tympanum’s response to external pure tones, but abol- ished the emission’s displacement amplitude peak. These findings provide evidence that tympanal auditory recep- tors, comparable to the situation in mammals, comprise the required nonlinear response characteristics, which during two-tone stimulation lead to additional, highly localized deflections of the tympanum.

10aDPOAE10aInsect10alaser Doppler vibrometry10alocust10atympanum1 aMöckel, Doreen1 aNowotny, Manuela1 aKössl, Manfred uhttp://link.springer.com/10.1007/s00359-014-0914-202049nas a2200121 4500008004100000245009000041210006900131520160100200100003201801700002001833700002101853856005301874 2012 eng d00aTonotopically Arranged Traveling Waves in the Miniature Hearing Organ of Bushcrickets0 aTonotopically Arranged Traveling Waves in the Miniature Hearing 3 a

Place based frequency discrimination (tonotopy) is a fundamental property of the coiled mammalian cochlea. Sound vibrations mechanically conducted to the hearing organ manifest themselves into slow moving waves that travel along the length of the organ, also referred to as traveling waves. These traveling waves form the basis of the tonotopic frequency representation in the inner ear of mammals. However, so far, due to the secure housing of the inner ear, these waves only could be measured partially over small accessible regions of the inner ear in a living animal. Here, we demonstrate the existence of tonotopically ordered traveling waves covering most of the length of a miniature hearing organ in the leg of bushcrickets in vivo using laser Doppler vibrometery. The organ is only 1 mm long and its geometry allowed us to investigate almost the entire length with a wide range of stimuli (6 to 60 kHz). The tonotopic location of the traveling wave peak was exponentially related to stimulus frequency. The traveling wave propagated along the hearing organ from the distal (high frequency) to the proximal (low frequency) part of the leg, which is opposite to the propagation direction of incoming sound waves. In addition, we observed a non-linear compression of the velocity response to varying sound pressure levels. The waves are based on the delicate micromechanics of cellular structures different to those of mammals. Hence place based frequency discrimination by traveling waves is a physical phenomenon that presumably evolved in mammals and bushcrickets independently.

1 aUdayashankar, Arun, Palghat1 aKössl, Manfred1 aNowotny, Manuela uhttps://dx.plos.org/10.1371/journal.pone.003100802311nas a2200181 4500008004100000245006200041210006200103520174300165653002101908653001301929653001901942100002101961700003201982700001902014700002102033700002002054856005502074 2011 eng d00aSound Transduction in the Auditory System of Bushcrickets0 aSound Transduction in the Auditory System of Bushcrickets3 a

Place based frequency representation, called tonotopy,is a typical property of hearing organs for the discrimination of different frequencies. Due to its coiled structure and secure housing, it is difficult access the mammalian cochlea. Hence, our knowledge about in vivo inner-ear mechanics is restricted to small regions. In this study, we present in vivo measurements that focus on the easily accessible, uncoiled auditory organs in bushcrickets, which are located in their foreleg tibiae. Sound enters the body via an opening at the lateral side of the thorax and passes through a horn-shaped acoustic trachea before reaching the high frequency hearing organ called crista acustica. In addition to the acoustic trachea as structure that transmits incoming sound towards the hearing organ, bushcrickets also possess two tympana, specialized plate-like structures, on the anterior and posterior side of each tibia. They provide a secondary path of excitation for the sensory receptors at low frequencies. We investigated the mechanics of the crista acustica in the tropical bushcricket Mecopoda elongata. The frequency-dependent motion of the crista acustica was captured using a laser-Doppler-vibrometer system. Using pure tone stimulation of the crista acustica, we could elicit traveling waves along the length of the hearing organ that move from the distal high frequency to the proximal low frequency region. In addition, distinct maxima in the velocity response of the crista acustica could be measured at ̃7 and ̃17 kHz. The travelling-wave-based tonotopy provides the basis for mechanical frequency discrimination along the crista acustica and opens up new possibility to investigate traveling wave mechanics in vivo.

10aLDV-measurements10atonotopy10atraveling wave1 aNowotny, Manuela1 aUdayashankar, Arun, Palghat1 aWeber, Melanie1 aHummel, Jennifer1 aKössl, Manfred uhttp://aip.scitation.org/doi/abs/10.1063/1.365813100620nas a2200181 4500008004100000245009100041210006900132653002300201653001900224653001200243653002700255100002100282700002100303700001900324700002000343700002000363856005500383 2010 eng d00aAcoustic-induced motion of the bushcricket (Mecopoda elongata, Tettigoniidae) tympanum0 aAcousticinduced motion of the bushcricket Mecopoda elongata Tett10aAcoustic resonance10ainsect hearing10atrachea10aVibration measurements1 aNowotny, Manuela1 aHummel, Jennifer1 aWeber, Melanie1 aMöckel, Doreen1 aKössl, Manfred uhttp://link.springer.com/10.1007/s00359-010-0577-602072nas a2200205 4500008004100000245008700041210006900128520133100197653001601528653002001544653002201564653001901586653002901605653001801634100002101652700002101673700002001694700002101714856013101735 2014 eng d00aProcessing of simple and complex acoustic signals in a tonotopically organized ear0 aProcessing of simple and complex acoustic signals in a tonotopic3 a

Processing of complex signals in the hearing organ remains poorly understood. This paper aims to contribute to this topic by presenting investigations on the mechanical and neuronal response of the hearing organ of the tropical bushcricket species Mecopoda elongata to simple pure tone signals as well as to the conspecific song as a complex acoustic signal. The high-frequency hearing organ of bushcrickets, the crista acustica (CA), is tonotopically tuned to frequencies between about 4 and 70 kHz. Laser Doppler vibrometer measurements revealed a strong and dominant low-frequency-induced motion of the CA when stimulated with either pure tone or complex stimuli. Consequently, the high-frequency distal area of the CA is more strongly deflected by low-frequency-induced waves than by high-frequency-induced waves. This low-frequency dominance will have strong effects on the processing of complex signals. Therefore, we additionally studied the neuronal response of the CA to native and frequency-manipulated chirps. Again, we found a dominant influence of low-frequency components within the conspecific song, indicating that the mechanical vibration pattern highly determines the neuronal response of the sensory cells. Thus, we conclude that the encoding of communication signals is modulated by ear mechanics.

10abushcricket10acrista acustica10aElectrophysiology10ainsect hearing10alaser Doppler vibrometry10aTettigoniidae1 aHummel, Jennifer1 aWolf, Konstantin1 aKössl, Manfred1 aNowotny, Manuela uhttps://royalsocietypublishing.org/doi/10.1098/rspb.2014.1872https://royalsocietypublishing.org/doi/pdf/10.1098/rspb.2014.187201893nas a2200181 4500008004100000022001300041245010200054210006900156260001600225300001800241490000700259520129300266100002101559700002101580700002301601700002101624856006601645 2016 eng d a0960982200aAuditory fovea in the ear of a duetting katydid shows male-specific adaptation to the female call0 aAuditory fovea in the ear of a duetting katydid shows malespecif cJan-12-2016 aR1222 - R12230 v263 a

Convergent evolution has led to surprising functional and mechanistic similarities between the vertebrate cochlea and some katydid ears 1 ;  2. Here we report on an ‘auditory fovea’ (Figure 1A) in the duetting katydid Ancylecha fenestrata (Tettigoniidae). The auditory fovea is a specialized inner-ear region with a disproportionate number of receptor cells tuned to a narrow frequency range, and has been described in the cochlea of some vertebrates, such as bats and mole rats 3 ;  4. In tonotopically organized ears, the location in the hearing organ of the optimal neuronal response to a tone changes gradually with the frequency of the stimulation tone. However, in the ears of A. fenestrata, the sensory cells in the auditory fovea are tuned to the dominant frequency of the female call; this area of the hearing organ is extensively expanded in males to provide an overrepresentation of this behaviorally important auditory input. Vertebrates developed an auditory fovea for improved prey or predator detection. In A. fenestrata, however, the foveal region facilitates acoustic pair finding, and the sexual dimorphism of sound-producing and hearing organs reflects the asymmetry in the mutual communication system between the sexes ( Figures 1B, S1).

1 aScherberich, Jan1 aHummel, Jennifer1 aSchöneich, Stefan1 aNowotny, Manuela uhttp://linkinghub.elsevier.com/retrieve/pii/S0960982216312611