Kalan Ammie K, Boesch Christophe
Department of Primatology, Max Planck Institute for Evolutionary Anthropology, Leipzig, Germany.
Wild Chimpanzee Foundation, Leipzig, Germany.
PeerJ. 2018 Jun 28;6:e5079. doi: 10.7717/peerj.5079. eCollection 2018.
Loud calls are used by many species as long-distance signals for group defense, mate attraction, and inter- and intragroup spacing. Chimpanzee loud calls, or pant hoots, are used in a variety of contexts including group coordination and during male contests. Here, we observed an alpha male takeover in wild chimpanzees () during which the leaf clipping gesture re-emerged after disappearing for almost two years in this community. Leaf clipping only occurred in males and was observed almost exclusively prior to pant hoot vocalizations, as has been observed in other chimpanzee communities of the Taï forest in Côte d'Ivoire. Consequently, we hypothesized that leaf clipping may be important for male-male competition by affecting variation in the acoustic properties of male chimpanzee loud calls. We therefore investigated whether pant hoots preceded by leaf clipping differed acoustically from those without, while also testing the influence of social context on pant hoot variation, namely male dominance rank and hierarchy instability, i.e., before, during and after the alpha takeover. We found that pant hoots preceded by leaf clipping were longer, contained more call elements and drum beats, and lower fundamental and peak frequencies. Moreover, during the alpha takeover pant hoots were shorter, contained fewer drum beats and higher fundamental frequencies. Additionally, pant hoot and aggression rates were also highest during the alpha takeover with leaf clipping more likely to occur on days when pant hooting rates were high. Overall social rank had limited effects on pant hoot variation. We suggest that elevated arousal and aggression during the alpha takeover triggered the re-emergence of leaf clipping and the associated acoustic changes in pant hoots. Further research should focus on the potential mechanisms by which leaf clipping is connected to variation in pant hoots and cross-population comparisons of the behaviour.
许多物种会发出响亮的叫声作为远距离信号，用于群体防御、吸引配偶以及群体间和群体内的空间调节。黑猩猩的响亮叫声，即喘叫声，用于多种情境，包括群体协调和雄性争斗期间。在此，我们观察到野生黑猩猩群体中的一次首领更替，在此期间，剪叶手势在该群体中消失近两年后再次出现。剪叶行为仅出现在雄性身上，并且几乎只在喘叫发声之前被观察到，正如在科特迪瓦伊塔伊森林的其他黑猩猩群体中所观察到的那样。因此，我们推测剪叶行为可能通过影响雄性黑猩猩响亮叫声的声学特性变化，对雄性间的竞争具有重要意义。我们因此研究了有剪叶行为在前的喘叫声在声学上是否与没有剪叶行为的喘叫声不同，同时还测试了社会情境对喘叫变化的影响，即雄性优势等级和等级不稳定情况，也就是在首领更替之前、期间和之后。我们发现，有剪叶行为在前的喘叫声更长，包含更多的叫声元素和鼓点，且基频和峰值频率更低。此外，在首领更替期间，喘叫声更短，包含的鼓点更少，基频更高。此外，在首领更替期间，喘叫和攻击率也最高，在喘叫率高的日子里，剪叶行为更有可能发生。总体社会等级对喘叫变化的影响有限。我们认为，首领更替期间兴奋度和攻击性的提高引发了剪叶行为的再次出现以及喘叫声相关的声学变化。进一步的研究应聚焦于剪叶行为与喘叫声变化相关的潜在机制以及该行为的跨群体比较。
