Zhang Fang, Chen Pan, Chen Zhuqing, Zhao Juan
College of Life Sciences, Anhui Normal University, Wuhu 241000, Anhui, China, 241000.
Curr Zool. 2015 Dec;61(6):996-1003. doi: 10.1093/czoolo/61.6.996. Epub 2015 Dec 1.
The ultrasonic communication in Concave-eared torrent frogs is believed to be an adaptation to avoid masking by the intense low-frequency noise of the rushing stream in their habitat. The acoustic adaptation hypothesis for ultrasonic origin predicts that some organisms subjecting to persistent acoustic interference from broadband, low-frequency environmental noise, might shift their signal frequency upward into frequency bands with lower noise energy. In other words, low-frequency environmental noise might cause upward shifts of species' vocalization frequencies making their signals more conspicuous. Presently, it is unclear whether male adjust their signal features in response to a change in the ambient noise level. We tested the prediction of the acoustic adaptation hypothesis by recording the vocalizations of male inhabiting two streams with different background noise levels in Huangshan in central China and comparing their call features including the fundamental frequency (F0). Results showed that the spectrotemporal characteristics of the vocal signals of males in the two habitats were indifferent, except the duration of the call harmonic segments and three parameters related to the call fundamental frequency (F0). In terms of the F0, the pooled and individual frog data showed that frogs inhabiting the noisier habitat tended to emit calls having higher F0. The higher F0 increases the signal-to-noise ratio, thus benefiting the detection of vocalization. Thus, similar to several anuran species, concave-eared torrent frogs also display noise-dependent adjustment of vocal pitch in their vocalizations for making them more audible.
凹耳湍蛙的超声通讯被认为是一种适应性特征，以避免被其栖息地湍急溪流中强烈的低频噪声所掩盖。超声起源的声学适应假说预测，一些受到宽带低频环境噪声持续声学干扰的生物，可能会将其信号频率向上转移到噪声能量较低的频段。换句话说，低频环境噪声可能会导致物种发声频率向上偏移，使其信号更易被察觉。目前，尚不清楚雄性凹耳湍蛙是否会根据环境噪声水平的变化来调整其信号特征。我们通过记录中国中部黄山地区两条背景噪声水平不同的溪流中雄性凹耳湍蛙的叫声，并比较它们包括基频（F0）在内的叫声特征，来检验声学适应假说的预测。结果表明，除了叫声谐波段的持续时间以及与叫声基频（F0）相关的三个参数外，两个栖息地雄性凹耳湍蛙的发声信号的频谱时间特征并无差异。就F0而言，汇总的和单个青蛙的数据都表明，生活在噪声较大栖息地的青蛙往往发出F0较高的叫声。较高的F0提高了信噪比，从而有利于发声的检测。因此，与几种无尾目物种类似 , 凹耳湍蛙在发声时也表现出对嗓音音调的噪声依赖性调节，以使它们的声音更易被听到。
