Data from: Position-dependent hearing in three species of bushcrickets (Tettigoniidae, Orthoptera)

A primary task of auditory systems is the localization of sound sources in space. Sound source localization in azimuth is usually based on temporal or intensity differences of sounds between the bilaterally arranged ears. In mammals, localization in elevation is possible by transfer functions at the ear, especially the pinnae. Although insects are able to locate sound sources, little attention is given to the mechanisms of acoustic orientation to elevated positions. Here we comparatively analyse the peripheral hearing thresholds of three species of bushcrickets in respect to sound source positions in space. The hearing thresholds across frequencies depend on the location of a sound source in the three-dimensional hearing space in front of the animal. Thresholds differ for different azimuthal positions and for different positions in elevation. This position-dependent frequency tuning is species specific. Largest differences in thresholds between positions are found in Ancylecha fenestrata. Correspondingly, A. fenestrata has a rather complex ear morphology including cuticular folds covering the anterior tympanal membrane. The position-dependent tuning might contribute to sound source localization in the habitats. Acoustic orientation might be a selective factor for the evolution of morphological structures at the bushcricket ear and, speculatively, even for frequency fractioning in the ear.

听觉系统的核心任务之一是对空间内的声源进行定位。方位角方向的声源定位通常基于双侧排布双耳间的声音时域差与强度差。在哺乳动物中，可通过耳部（尤其是耳廓）的传递函数实现仰角方向的声源定位。尽管昆虫具备声源定位能力，但针对仰角方位的声学定向机制却鲜有关注。本研究针对3种螽斯（bushcrickets）的外周听阈展开对比分析，以探究其对空间内声源位置的响应特性。受试动物前方的三维听觉空间中，声源位置会影响跨频率听阈：不同方位角位置与不同仰角位置对应的听阈均存在差异。这种依赖于声源位置的频率调谐具有物种特异性。在窗饰螽（Ancylecha fenestrata）中，不同声源位置间的听阈差异最为显著；相应地，该物种拥有较为复杂的耳部形态，包含覆盖前鼓膜（tympanal membrane）的表皮褶皱。这种位置依赖性的频率调谐或有助于该类群在自然生境中实现声源定位。声学定向或许是螽斯耳部形态结构演化的选择因子之一，甚至可推测其对耳部的频率分化亦存在选择作用。