The acoustic adaptation hypothesis (AAH) states that signals should evolve towards an optimal transmission of the intended information from senders to intended receivers given the environmental constraints of the medium that they traverse. To date, most AAH studies have focused on the effect of stratified vegetation on signal propagation. These studies, based on the AAH, predict that acoustic signals should experience less attenuation and degradation where habitats are less acoustically complex. Here, we explored this effect by including an environmental noise dimension to test some AAH predictions in two clades of widespread amphibians (Bufonidae and Ranidae) that actively use acoustic signals for communication. By using data from 106 species in these clades, we focused on the characterization of the differences in dominant frequency (DF) and frequency contour (i.e., frequency modulation [FM] and harmonic performances) of mating calls and compared them between species that inhabit flowing-water or still-water environments. After including temperature, body size, habitat type and phylogenetic relationships, we found that DF differences among species were explained mostly by body size and habitat structure. We also showed that species living in lentic habitats tend to have advertisement calls characterized by well-defined FM and harmonics. Likewise, our results suggest that flowing-water habitats can constrain the evolutionary trajectories of the frequency-contour traits of advertisement calls in these anurans. Our results may support AAH predictions in frogs that vocalize in noisy habitats because flowing-water environments often produce persistent ambient noise. For instance, these anurans tend to generate vocalizations with less well-defined FM and harmonic traits. These findings may help us understand how noise in the environment can influence natural selection as it shapes acoustic signals in affected species.

中文翻译：

---

噪声限制了流水蛙叫声频率轮廓的演变：两个进化枝的比较分析

声学适应假设 (AAH) 指出，考虑到信号所经过的介质的环境限制，信号应该朝着从发送者到预期接收者的预期信息的最佳传输方向发展。迄今为止，大多数 AAH 研究都集中在分层植被对信号传播的影响上。这些基于 AAH 的研究预测，在栖息地的声学复杂性较低的地方，声学信号应该经历较少的衰减和退化。在这里，我们通过包括环境噪声维度来测试一些 AAH 预测在两个广泛使用的两栖动物进化枝（蟾蜍科和蛙科）中积极使用声学信号进行通信来探索这种影响。通过使用这些进化枝中 106 个物种的数据，我们专注于表征交配呼叫的主频率 (DF) 和频率轮廓（即频率调制 [FM] 和谐波性能）的差异，并在居住在流水或静水环境中的物种之间进行比较。在包括温度、体型、栖息地类型和系统发育关系后，我们发现物种间的 DF 差异主要由体型和栖息地结构来解释。我们还表明，生活在 lentic 栖息地的物种往往具有以明确定义的 FM 和谐波为特征的广告呼叫。同样，我们的结果表明，流水栖息地可以限制这些无尾目中广告呼叫的频率轮廓特征的进化轨迹。我们的结果可能支持在嘈杂栖息地发声的青蛙的 AAH 预测，因为流水环境通常会产生持续的环境噪音。例如，这些无尾猿倾向于产生具有不太明确的 FM 和谐波特征的发声。这些发现可能有助于我们了解环境中的噪音如何影响自然选择，因为它会影响受影响物种的声学信号。