Enigk Drew K, Thompson Melissa Emery, Machanda Zarin P, Wrangham Richard W, Muller Martin N
Department of Anthropology, University of New Mexico, Albuquerque, NM, USA.
Kibale Chimpanzee Project, Fort Portal, Uganda.
Behav Ecol Sociobiol. 2020 Jul;74(7). doi: 10.1007/s00265-020-02872-7. Epub 2020 Jun 22.
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.
群居哺乳动物通常生活在群体中，其中优势等级制度是获得配偶的重要决定因素。除了单独竞争外，雄性可能会组成两个或更多的联盟来攻击或恐吓对手。联盟的形成对青少年雄性可能特别有利，因为这有助于他们弥补身体和社交上的不成熟。然而，由于这些不足之处，青少年可能难以吸引到有效的联盟伙伴。在这里，我们研究了成熟雄性黑猩猩的行为，以测试联盟在较强或较弱个体中是否更频繁出现。我们的纵向研究跟踪了18只雄性（年龄在5至25岁之间），并在对乌干达基巴莱国家公园的卡尼亚瓦拉黑猩猩群落进行的12年观察中利用了1517个联盟。我们发现联盟形成的比率在整个成熟过程中有所增加，而且这种增加与攻击行为总体使用的增加无关。幼年黑猩猩几乎只与它们的母亲组成联盟，而青少年主要与同伴和成年雄性结成伙伴关系。当青少年和成年雄性相互组成联盟时，青少年比成年雄性更有可能加入成年雄性一方。最后，青少年与成年雄性在非攻击性的发声展示中比在攻击性联盟中更频繁地进行联合行为。综合来看，我们的结果表明，青少年雄性在很大程度上无法吸引到最强大的联盟伙伴，并且他们通过在竞争较小的情况下（即受到对手攻击的风险较低时）与成年雄性结成联盟来“尽力而为”。
