Abstract Within socially monogamous breeding systems, levels of extra-pair paternity can vary not only between species, populations, and individuals, but also across time. Uncovering how different extrinsic conditions (ecological, demographic, and social) influence this behavior will help shed light on the factors driving its evolution. Here, we simultaneously address multiple socio-ecological conditions potentially influencing female infidelity in a natural population of the cooperatively breeding Seychelles warbler, Acrocephalus sechellensis. Our contained study population has been monitored for more than 25 years, enabling us to capture variation in socio-ecological conditions between individuals and across time and to accurately assign parentage. We test hypotheses predicting the influence of territory quality, breeding density and synchrony, group size and composition (number and sex of subordinates), and inbreeding avoidance on female infidelity. We find that a larger group size promotes the likelihood of extra-pair paternity in offspring from both dominant and subordinate females, but this paternity is almost always gained by dominant males from outside the group (not by subordinate males within the group). Higher relatedness between a mother and the dominant male in her group also results in more extra-pair paternity—but only for subordinate females—and this does not prevent inbreeding occurring in this population. Our findings highlight the role of social conditions favoring infidelity and contribute toward understanding the evolution of this enigmatic behavior.

中文翻译：

---

塞舌尔莺的社会生态条件和女性不忠

摘要 在社会一夫一妻制的育种系统中，配对外亲子关系的水平不仅在物种、种群和个体之间存在差异，而且还随着时间的推移而变化。揭示不同的外部条件（生态、人口和社会）如何影响这种行为将有助于揭示驱动其进化的因素。在这里，我们同时解决了可能影响合作繁殖的塞舌尔莺（Acrocephalus sechellensis）自然种群中女性不忠的多种社会生态条件。我们对所包含的研究人群进行了超过 25 年的监测，使我们能够捕捉个体之间和不同时间段的社会生态条件的变化，并准确地确定亲子关系。我们测试了预测领地质量、繁殖密度和同步性、群体规模和组成（下属的数量和性别）以及避免近亲繁殖对女性不忠影响的假设。我们发现，较大的群体规模会增加占主导地位的雌性和从属雌性的后代中产生额外配对父子关系的可能性，但这种父子关系几乎总是由来自群体外部的占主导地位的雄性获得（而不是由群体内的从属雄性获得）。母亲和群体中占主导地位的雄性之间的较高亲缘关系也会导致更多的额外父子关系——但仅限于从属雌性——但这并不能阻止该群体中近亲繁殖的发生。我们的研究结果强调了有利于不忠的社会条件的作用，并有助于理解这种神秘行为的演变。