Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada.
PLoS One. 2011;6(9):e25413. doi: 10.1371/journal.pone.0025413. Epub 2011 Sep 28.
Charles Darwin posited that secondary sexual characteristics result from competition to attract mates. In male songbirds, specialized vocalizations represent secondary sexual characteristics of particular importance because females prefer songs at specific frequencies, amplitudes, and duration. For birds living in human-dominated landscapes, historic selection for song characteristics that convey fitness may compete with novel selective pressures from anthropogenic noise. Here we show that black-capped chickadees (Poecile atricapillus) use shorter, higher-frequency songs when traffic noise is high, and longer, lower-frequency songs when noise abates. We suggest that chickadees balance opposing selective pressures by use low-frequency songs to preserve vocal characteristics of dominance that repel competitors and attract females, and high frequency songs to increase song transmission when their environment is noisy. The remarkable vocal flexibility exhibited by chickadees may be one reason that they thrive in urban environments, and such flexibility may also support subsequent genetic adaptation to an increasingly urbanized world.
查尔斯·达尔文(Charles Darwin)假设,第二性征是通过竞争来吸引配偶的结果。在雄性鸣禽中,专门的叫声代表着特别重要的第二性征,因为雌性更喜欢特定频率、幅度和持续时间的歌声。对于生活在人类主导的环境中的鸟类来说,历史上选择具有传达适应性的歌声特征可能与人为噪声带来的新的选择性压力相竞争。在这里,我们表明,当交通噪声较高时,黑头山雀(Poecile atricapillus)会使用较短、较高频率的歌声,而当噪声减弱时,它们会使用较长、较低频率的歌声。我们认为,山雀通过使用低频歌声来维持支配地位的叫声特征,从而平衡了相反的选择性压力,这种叫声特征可以排斥竞争者并吸引雌性,而高频歌声则可以在环境嘈杂时增加歌声的传播。山雀表现出的显著的声音灵活性可能是它们在城市环境中茁壮成长的原因之一,这种灵活性也可能支持它们随后对日益城市化的世界进行基因适应。