Data from: Better than fish on land? Hearing across metamorphosis in salamanders

Early tetrapods faced an auditory challenge from the impedance mismatch between air and tissue in the transition from aquatic to terrestrial lifestyles during the Early Carboniferous (350 Ma). Consequently, tetrapods may have been deaf to airborne sounds for up to 100 Myr until tympanic middle ears evolved during the Triassic. The middle ear morphology of recent urodeles is similar to that of early 'lepospondyl' microsaur tetrapods, and experimental studies on their hearing capabilities are therefore useful to understand the evolutionary and functional drivers behind the shift from aquatic to aerial hearing in early tetrapods. Here, we combine imaging techniques with neurophysiological measurements to resolve how the change from aquatic larvae to terrestrial adult affects the ear morphology and sensory capabilities of salamanders. We show that air-induced pressure detection enhances underwater hearing sensitivity of salamanders at frequencies above 120 Hz, and that both terrestrial adults and fully aquatic juvenile salamanders can detect airborne sound. Collectively, these findings suggest that early atympanic tetrapods may have been pre-equipped to aerial hearing and are able to hear airborne sound better than fish on land. When selected for, this rudimentary hearing could have led to the evolution of tympanic middle ears.早石炭世（350 Ma，即距今3.5亿年）时期，早期四足类（tetrapods）在从水生向陆生生活方式转变的过程中，面临着空气与机体组织间的声学阻抗失配所引发的听觉挑战。因此，在三叠纪演化出鼓膜中耳之前的长达1亿年（100 Myr）的时间里，早期四足类或许无法感知空气传播的声音。现生有尾两栖类（urodeles）的中耳形态与早期鳞椎类（lepospondyl）微蜥类（microsaur）四足类相似，因此针对其听觉能力开展的实验研究，有助于阐明早期四足类从水生听觉向空气传播听觉转变背后的演化与功能驱动机制。本研究结合成像技术与神经生理学测量手段，解析了从水生幼体到陆生成体的转变如何影响蝾螈的中耳形态与感官功能。研究结果显示，在120赫兹以上的频率区间内，空气诱导的压力感知可提升蝾螈的水下听觉灵敏度；同时，陆生成体与完全水生的幼体蝾螈均能检测到空气传播的声音。综合以上发现，本研究暗示：早期无鼓膜（atympanic）四足类可能已经具备了空气传播听觉的预适应能力，且在陆地上的空气传声感知能力优于鱼类。若经过定向选择，这种初步的听觉能力可推动鼓膜中耳的演化。