Biology Department, University of Massachusetts Dartmouth, North Dartmouth, MA 02747.
Department of Biological Sciences, Marine Sciences Program, Florida International University, North Miami, FL 33181.
Proc Natl Acad Sci U S A. 2022 Sep 6;119(36):e2121723119. doi: 10.1073/pnas.2121723119. Epub 2022 Aug 29.
Efforts to understand human social evolution rely largely on comparisons with nonhuman primates. However, a population of bottlenose dolphins in Shark Bay, Western Australia, combines a chimpanzee-like fission-fusion grouping pattern, mating system, and life history with the only nonhuman example of strategic multilevel male alliances. Unrelated male dolphins form three alliance levels, or "orders", in competition over females: both within-group alliances (i.e., first- and second-order) and between-group alliances (third-order), based on cooperation between two or more second-order alliances against other groups. Both sexes navigate an open society with a continuous mosaic of overlapping home ranges. Here, we use comprehensive association and consortship data to examine fine-scale alliance relationships among 121 adult males. This analysis reveals the largest nonhuman alliance network known, with highly differentiated relationships among individuals. Each male is connected, directly or indirectly, to every other male, including direct connections with adult males outside of their three-level alliance network. We further show that the duration with which males consort females is dependent upon being well connected with third-order allies, independently of the effect of their second-order alliance connections, i.e., alliances between groups increase access to a contested resource, thereby increasing reproductive success. Models of human social evolution traditionally link intergroup alliances to other divergent human traits, such as pair bonds, but our study reveals that intergroup male alliances can arise directly from a chimpanzee-like, promiscuous mating system without one-male units, pair bonds, or male parental care.
人类社会进化的研究主要依赖于与非人类灵长类动物的比较。然而，澳大利亚西部鲨鱼湾的一群宽吻海豚，结合了类似于黑猩猩的分裂-融合群体模式、交配系统和生活史，以及唯一的非人类的有策略的多层次雄性联盟的例子。不相关的雄性海豚在争夺雌性时形成了三个联盟级别，或“等级”：群体内联盟（即第一级和第二级）和群体间联盟（第三级），这是基于两个或更多第二级联盟之间的合作，对抗其他群体。雌雄两性都在一个开放的社会中导航，其特点是连续的重叠家园范围马赛克。在这里，我们使用全面的关联和伴侣关系数据来研究 121 名成年雄性之间的精细联盟关系。这项分析揭示了已知最大的非人类联盟网络，个体之间的关系高度分化。每个雄性与其他雄性直接或间接相连，包括与他们三级联盟网络之外的成年雄性的直接连接。我们进一步表明，雄性与雌性交配的持续时间取决于与第三级盟友的良好连接，而不依赖于他们的第二级联盟连接的影响，即群体之间的联盟增加了对有争议资源的获取，从而增加了繁殖成功率。人类社会进化的传统模式将群体间联盟与其他人类特有的特征联系起来，如配对关系，但我们的研究表明，群体间雄性联盟可以直接从类似于黑猩猩的、杂乱的交配系统中产生，而不需要一夫一妻制单位、配对关系或雄性亲代照顾。
