Jonsson Thorin, Montealegre-Z Fernando, Soulsbury Carl D, Robson Brown Kate A, Robert Daniel
School of Life Sciences, Joseph Banks Laboratories, Green Lane, Lincoln LN6 7DL, UK School of Biological Sciences, University of Bristol, 24 Tyndall Avenue, Bristol BS8 1TQ, UK.
School of Life Sciences, Joseph Banks Laboratories, Green Lane, Lincoln LN6 7DL, UK
J R Soc Interface. 2016 Sep;13(122). doi: 10.1098/rsif.2016.0560.
The ear of the bush-cricket, Copiphora gorgonensis, consists of a system of paired eardrums (tympana) on each foreleg. In these insects, the ear is backed by an air-filled tube, the acoustic trachea (AT), which transfers sound from the prothoracic acoustic spiracle to the internal side of the eardrums. Both surfaces of the eardrums of this auditory system are exposed to sound, making it a directionally sensitive pressure difference receiver. A key feature of the AT is its capacity to reduce the velocity of sound propagation and alter the acoustic driving forces at the tympanum. The mechanism responsible for reduction in sound velocity in the AT remains elusive, yet it is deemed to depend on adiabatic or isothermal conditions. To investigate the biophysics of such multiple input ears, we used micro-scanning laser Doppler vibrometry and micro-computed X-ray tomography. We measured the velocity of sound propagation in the AT, the transmission gains across auditory frequencies and the time-resolved mechanical dynamics of the tympanal membranes in C. gorgonensis Tracheal sound transmission generates a gain of approximately 15 dB SPL, and a propagation velocity of ca 255 m s, an approximately 25% reduction from free field propagation. Modelling tracheal acoustic behaviour that accounts for thermal and viscous effects, we conclude that reduction in sound velocity within the AT can be explained, among others, by heat exchange between the sound wave and the tracheal walls.
戈氏突灶螽的耳朵由每只前腿上的一对鼓膜系统组成。在这些昆虫中，耳朵由一个充满空气的管道——声气管（AT）支撑，该管道将声音从前胸声气门传递到鼓膜内侧。这个听觉系统的鼓膜两面都暴露在声音中，使其成为一个方向敏感的压差接收器。声气管的一个关键特性是它能够降低声音传播速度并改变鼓膜处的声驱动力。声气管中声音速度降低的机制仍然难以捉摸，但被认为取决于绝热或等温条件。为了研究这种多输入耳朵的生物物理学，我们使用了微扫描激光多普勒振动测量法和微计算机X射线断层扫描技术。我们测量了戈氏突灶螽声气管中声音的传播速度、听觉频率范围内的传输增益以及鼓膜的时间分辨力学动态。气管声音传输产生约15 dB SPL的增益，传播速度约为255 m/s，比自由场传播速度降低了约25%。通过对考虑热效应和粘性效应的气管声学行为进行建模，我们得出结论，声气管内声音速度的降低，除其他因素外，可以通过声波与气管壁之间的热交换来解释。
