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.008609002049nas 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/10.1063/1.3658131