Data from: Inbreeding avoidance and female mate choice shape reproductive skew in capuchin monkeys (Cebus capucinus imitator)

Reproductive skew in multimale groups may be determined by the need for alpha males to offer reproductive opportunities as staying incentives to subordinate males (concessions), by the relative fighting ability of the alpha male (tug-of-war) or by how easily females can be monopolized (priority-of-access). These models have rarely been investigated in species with exceptionally long male tenures, such as white-faced capuchins, where female mate choice for novel unrelated males may be important in shaping reproductive skew. We investigated reproductive skew in white-faced capuchins at Sector Santa Rosa, Costa Rica, using 20 years of demographic, behavioural and genetic data. Infant survival and alpha male reproductive success were highest in small multimale groups, which suggests that the presence of subordinate males can be beneficial to the alpha male, in line with the concession model's assumptions. None of the skew models predicted the observed degree of reproductive sharing, and the probability of an alpha male producing offspring was not affected by his relatedness to subordinate males, whether he resided with older subordinate males, whether he was prime aged, the number of males or females in the group or the number of infants conceived within the same month. Instead, the alpha male's probability of producing offspring decreased when he was the sire of the mother, was weak and lacked a well-established position and had a longer tenure. Because our data best supported the inbreeding avoidance hypothesis and female choice for strong novel mates, these hypotheses should be taken into account in future skew models.

多雄性群体中的生殖偏倚（reproductive skew），可能由三类机制决定：一是雄性首领（alpha male）为向下属雄性提供留任激励而赋予其繁殖机会的让步模型（concessions），二是基于雄性首领相对战斗能力的拔河模型（tug-of-war），三是取决于雌性可被独占难易程度的优先准入模型（priority-of-access）。这类理论模型极少在雄性任期极长的物种中得到验证，比如白面卷尾猴（white-faced capuchins），该物种中雌性偏好选择陌生无亲缘关系雄性的行为，可能对生殖偏倚的形成具有关键影响。我们借助哥斯达黎加圣罗莎区（Sector Santa Rosa）白面卷尾猴种群长达20年的种群统计、行为学与遗传学数据，探究了该种群的生殖偏倚情况。研究发现，小型多雄性群体的幼崽存活率与雄性首领的繁殖成功率均为最高，这表明下属雄性的存在对雄性首领而言可能是有益的，这与让步模型的假设相符。现有各类偏倚模型均未准确预测观测到的生殖共享程度，且雄性首领繁育后代的概率，与其与下属雄性的亲缘关系、是否与年长下属雄性共处、是否处于壮年、群体内雄性/雌性数量，或是同月受孕幼崽数量均无关联。反之，当雄性首领是幼崽母亲的生父、体质较弱且未确立稳固地位，抑或任期更长时，其繁育后代的概率会出现下降。由于我们的数据最支持近交回避假说与雌性选择强势陌生雄性的假说，未来的生殖偏倚模型应将这两类假说纳入考量。