Chereskin Emma, Connor Richard C, Friedman Whitney R, Jensen Frants H, Allen Simon J, Sørensen Pernille M, Krützen Michael, King Stephanie L
School of Biological Sciences, University of Bristol, Bristol BS8 1TQ, United Kingdom.
Biology Department, University of Massachusetts Dartmouth, North Dartmouth, MA 02747, USA; Department of Biological Sciences, Florida International University, 3000 NE 151st Street, North Miami, FL 33181, USA.
Curr Biol. 2022 Apr 11;32(7):1657-1663.e4. doi: 10.1016/j.cub.2022.02.019. Epub 2022 Mar 24.
Vocal interactions are intrinsic features of social groups and can play a pivotal role in social bonding. Dunbar's social bonding hypothesis posits that vocal exchanges evolved to "groom at a distance" when social groups became too large or complex for individuals to devote time to physical bonding activities. Tests of this hypothesis in non-human primates, however, suggest that vocal exchanges occur between more strongly bonded individuals that engage in higher grooming rates and thus do not provide evidence for replacement of physical bonding. Here, we combine data on social bond strength, whistle exchange frequency, and affiliative contact behavior rates to test this hypothesis in wild male Indo-Pacific bottlenose dolphins, who form multi-level alliances that cooperate over access to females. We show that, although whistle exchanges are more likely to occur within the core alliance, they occur more frequently between those males that share weaker social bonds, i.e., between core allies that spend less time together, while the opposite occurs for affiliative physical contact behavior. This suggests that vocal exchanges function as a low-cost mechanism for male dolphins that spend less time in close proximity and engage in fewer affiliative contact behaviors to reinforce and maintain their valuable alliance relationships. Our findings provide new evidence outside of the primate lineage that vocal exchanges serve a bonding function and reveal that, as the social bonding hypothesis originally suggested, vocal exchanges can function as a replacement of physical bonding activities for individuals to maintain their important social relationships.
声音互动是社会群体的内在特征，在社会联系中可发挥关键作用。邓巴的社会联系假说认为，当社会群体变得过于庞大或复杂，个体无法投入时间进行身体接触的联系活动时，声音交流就进化为“远距离梳理”。然而，在非人类灵长类动物中对这一假说的测试表明，声音交流发生在联系更为紧密、梳理频率更高的个体之间，因此没有为替代身体接触的联系提供证据。在此，我们结合社会联系强度、哨声交流频率和亲和接触行为率的数据，在野生雄性印度太平洋宽吻海豚中测试这一假说，这些海豚形成多层次联盟，在获取雌性方面进行合作。我们发现，虽然哨声交流更有可能在核心联盟内部发生，但它们在社会联系较弱的雄性之间发生得更频繁，即在一起时间较少的核心盟友之间，而亲和身体接触行为则相反。这表明，声音交流对近距离相处时间较少、亲和接触行为较少的雄性海豚来说，是一种低成本机制，用于加强和维持它们宝贵的联盟关系。我们的研究结果在灵长类动物谱系之外提供了新的证据，证明声音交流具有联系功能，并揭示出，正如社会联系假说最初所表明的那样，声音交流可以替代身体接触活动，让个体维持其重要的社会关系。
