Bushcrickets (katydids) rely on only 20 to 120 sensory units located in their forelegs to sense sound. Situated in tiny hearing organs less than 1 mm long (40× shorter than the human cochlea), they cover a wide frequency range from 1 kHz up to ultrasounds, in tonotopic order. The underlying mechanisms of this miniaturized frequency-place map are unknown. Sensory dendrites in the hearing organ (crista acustica [CA]) are hypothesized to stretch, thereby driving mechanostransduction and frequency tuning. However, this has not been experimentally confirmed. Using optical coherence tomography (OCT) vibrometry, we measured the relative motion of structures within and adjacent to the CA of the bushcricket Mecopoda elongata. We found different modes of nanovibration in the CA that have not been previously described. The two tympana and the adjacent septum of the foreleg that enclose the CA were recorded simultaneously, revealing an antiphasic lever motion strikingly reminiscent of vertebrate middle ears. Over the entire length of the CA, we were able to separate and compare vibrations of the top (cap cells) and base (dorsal wall) of the sensory tissue. The tuning of these two structures, only 15 to 60 μm (micrometer) apart, differed systematically in sharpness and best frequency, revealing a tuned periodic deformation of the CA. The relative motion of the two structures, a potential drive of transduction, demonstrated sharper tuning than either of them. The micromechanical complexity indicates that the bushcricket ear invokes multiple degrees of freedom to achieve frequency separation with a limited number of sensory cells.

Bushcrickets (katydids) 仅依靠位于前腿的 20 到 120 个感觉单元来感知声音。它们位于不到 1 毫米长（比人类耳蜗短 40 倍）的微小听觉器官中，按音调顺序覆盖从 1 kHz 到超声波的广泛频率范围。这种小型化频率位置图的潜在机制尚不清楚。听觉器官中的感觉树突（crista acustica [CA]）被假设为拉伸，从而驱动机械转导和频率调谐。然而，这尚未得到实验证实。使用光学相干断层扫描 (OCT) 振动测量法，我们测量了丛林蟋蟀Mecopoda elongata的 CA 内和附近结构的相对运动. 我们在 CA 中发现了以前没有描述过的不同纳米振动模式。包围 CA 的两个鼓室和相邻的前腿中隔同时被记录，揭示了一种反相杠杆运动，让人联想到脊椎动物的中耳。在 CA 的整个长度上，我们能够分离和比较感觉组织顶部（帽细胞）和底部（背壁）的振动。这两种结构的调谐，仅相距 15 到 60 μm（微米），在锐度和最佳频率方面系统地不同，揭示了 CA 的调谐周期性变形。两种结构的相对运动，一种潜在的转导驱动，表现出比它们中任何一个都更敏锐的调谐。