Social mammals often live in groups in which a dominance hierarchy is an important determinant of access to mates. In addition to competing individually, males may form coalitions of two or more to attack or intimidate rivals. Coalition formation could be particularly advantageous for adolescent males by helping them compensate for their physical and social immaturity. However, adolescents may struggle to attract effective coalition partners because of these inadequacies. Here, we examine the behavior of maturing male chimpanzees to test whether coalitions are more frequent among more or less powerful individuals. Our longitudinal study followed 18 males (ages 5 through 25 years) and utilized 1517 coalitions across 12 years of observation of the Kanyawara chimpanzee community in Kibale National Park, Uganda. We found that rates of coalition formation increased across maturation and that this increase was independent of a rise in the overall use of aggression. Juveniles formed coalitions almost exclusively with their mothers, while adolescents partnered primarily with peers and adult males. When adolescents and adult males formed coalitions with each other, the adolescents were more likely to join the adults than vice versa. Finally, adolescents engaged in joint behavior with adult males more often in non-aggressive vocal displays than in aggressive coalitions. Taken together, our results suggest that adolescent males are largely unable to attract the most powerful coalition partners and that they “make the best of a bad job” by joining adult males in less competitive situations, when the risk of receiving aggression from opponents is lower. Adolescent males are at a disadvantage in competing for powerful allies, because they have less strength to contribute to a cooperative dyad. Even when a variety of possible coalition partners are present, the partner choices of higher-ranking males likely limit the number of remaining individuals that are available and willing to form coalitions with adolescents. Accordingly, we found that males sorted with closely ranked coalition partners down the hierarchy, leaving adolescents to form coalitions with partners of similar rank to themselves rather than high-ranking adult males. There was no evidence for rank sorting in joint vocal displays, however. Additionally, adolescents participated in more than twice as many joint vocal displays as coalitions. These data suggest that joint vocal displays represent a viable alternative to coalitions for adolescents attempting to integrate themselves into the adult male social world.

中文翻译：

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竞争能力决定了野生雄性黑猩猩（Pan troglodytes schweinfurthii）成熟过程中的联盟参与和合作伙伴选择

社会性哺乳动物通常生活在群体中，在这些群体中，支配等级是获得配偶的重要决定因素。除了单独竞争外，雄性还可以组成两个或更多的联盟来攻击或恐吓对手。通过帮助他们弥补身体和社会上的不成熟，联盟的形成可能对青春期男性特别有利。然而，由于这些不足，青少年可能难以吸引有效的联盟伙伴。在这里，我们检查了成年雄性黑猩猩的行为，以测试联盟在或多或少强大的个体中是否更频繁。我们的纵向研究跟踪了 18 名男性（年龄 5 至 25 岁），并在乌干达基巴莱国家公园的 Kanyawara 黑猩猩社区的 12 年观察中利用了 1517 个联盟。我们发现联盟形成率随着成熟度的增加而增加，并且这种增加与整体使用侵略的增加无关。青少年几乎完全与他们的母亲结成联盟，而青少年主要与同龄人和成年男性合作。当青少年和成年男性相互结成联盟时，青少年更有可能加入成年人的行列，反之亦然。最后，与攻击性联盟相比，青少年与成年男性在非攻击性的声音展示中更频繁地进行联合行为。综上所述，我们的研究结果表明，青春期男性在很大程度上无法吸引最强大的联盟伙伴，并且他们通过在竞争较少的情况下加入成年男性来“充分利用糟糕的工作”，而此时受到对手攻击的风险较低. 青春期男性在争夺强大盟友方面处于劣势，因为他们没有足够的力量为合作的二人组做出贡献。即使存在各种可能的联盟伙伴，高级男性的伙伴选择也可能会限制剩余的可用并愿意与青少年结盟的人数。因此，我们发现男性与等级关系密切的联盟伙伴进行排序，使青少年与与自己相似级别的伙伴而不是高级成年男性形成联盟。然而，没有证据表明联合声乐展示中的等级排序。此外，青少年参加联合声乐表演的次数是联盟的两倍多。