Signal lengthening is not a strategy for animals to mitigate noise interference

Many species of animals rely on acoustic communication for critical life activities. The efficacy of acoustic communication, however, can be seriously hindered by ambient noise. Although it has been widely reported that signallers modify the structure of their acoustic signals in noise, whether such signal modulations contribute to reducing noise interference is often unclear. Signal duration is a perceptually important parameter that can directly affect signal detection. Here, we address whether signal lengthening is an adaptive strategy for improving acoustic communication in noise, combing results from a meta-analysis, a noise playback experiment, and numerical simulations. The meta-analysis showed that animals from arthropods to mammals showed a mixed pattern of signal duration modifications in response to noise, covering all three possibilities of an increase, a decrease, and no change. The noise playback experiment revealed that noise-induced signal duration modulation was characterized by strong inter-individual variations and correlated positively with signal amplitude, challenging the functional role of signal lengthening in reducing noise interference. Lastly, numerical simulations suggest that experimentally observed signal duration increases in noise disappear when the effect size is considered. We conclude that signal lengthening is not a strategy for animals to mitigate noise interference, despite its wide occurrence.

诸多动物物种依靠声学通信完成关键生命活动。然而，环境噪声会严重阻碍声学通信的效能。尽管已有大量研究报道信号发送者会在噪声环境下调整其声学信号的结构，但这类信号调制是否有助于降低噪声干扰，目前仍尚不明确。信号时长是一项具有感知重要性的参数，可直接影响信号的探测效果。本研究通过整合荟萃分析（meta-analysis）、噪声回放实验与数值模拟的结果，探讨信号时长延长是否为提升噪声环境下声学通信效率的适应性策略。荟萃分析结果显示，从节肢动物到哺乳类的各类动物在应对噪声时，其信号时长的调制模式存在多样性，涵盖延长、缩短及无变化三种情况。噪声回放实验结果表明，噪声诱导的信号时长调制具有显著的个体间差异，且与信号振幅呈正相关，这对信号时长延长在降低噪声干扰中的功能作用提出了挑战。最后，数值模拟结果显示，若纳入效应量分析，实验中观测到的噪声环境下信号时长延长现象便不复存在。综上，尽管信号时长延长现象广泛存在，但它并非动物用以减轻噪声干扰的适应性策略。