Movie file for Breaking the succession rule: the costs and benefits of an alpha-status take-over by an immigrant rhesus macaque on Cayo Santiago

Explaining intraspecific variation in reproductive tactics hinges on measuring associated costs and benefits. Yet, this is difficult if alternative (purportedly less optimal) tactics remain unobserved. We describe a rare alpha-position take-over by an immigrant male rhesus macaque in a population where males typically gain rank via succession. Unusually, male aggressiveness after the take-over correlated with rank and mating success. The new alpha achieved the highest mating and reproductive success. Nevertheless, he sired only 4 infants due to high extra-group paternity (59.3%). The costs of his immigration tactic were high: after the mating season ended, unable to deter coalitionary attacks by resident males, he was overthrown. The following year he had the highest relative annual weight loss and levels of immune activation among males in the group. Succession-based rank-acquisition in large, provisioned groups of macaques thus appears to be actively maintained by resident males, who impose high costs on challengers.

阐释物种内繁殖策略的差异性，关键在于衡量与之相关的成本与收益。然而，若替代（所谓较低优化的）策略未被观察到，则这一过程变得尤为困难。本文描述了一次罕见的移民雄性猕猴在通常通过继位获得等级的种群中的alpha地位接管事件。值得注意的是，接管后的雄性攻击性与其等级和交配成功率相关。新alpha实现了最高的交配和繁殖成功率。尽管如此，由于其高群外父系比例（59.3%），他仅育有4个后代。其移民策略的成本高昂：在交配季节结束后，他无法阻止居住雄性的联盟攻击，最终被推翻。次年，他在群体中雄性中相对年体重损失和免疫激活水平最高。因此，在大型的、有供给的猕猴群体中，基于继位的等级获取似乎被居住雄性积极维持，他们向挑战者施加了高昂的成本。