Data from: Monogamy promotes altruistic sterility in insect societies

Monogamy is associated with sibling-directed altruism in multiple animal taxa, including insects, birds, and mammals. Inclusive-fitness theory readily explains this pattern by identifying high relatedness as a promoter of altruism. In keeping with this prediction, monogamy should promote the evolution of voluntary sterility in insect societies if sterile workers make for better helpers. However, a recent mathematical population-genetics analysis failed to identify a consistent effect of monogamy on voluntary worker sterility. Here, we revisit that analysis. First, we relax genetic assumptions, considering not only alleles of extreme effect—encoding either no sterility or complete sterility—but also alleles with intermediate effects on worker sterility. Second, we broaden the stability analysis—which focused on the invasibility of populations where either all workers are fully-sterile or all workers are fully-reproductive—to identify where intermediate pure or mixed evolutionarily-stable states may occur. Third, we consider a broader range of demographically-explicit ecological scenarios relevant to altruistic worker non-reproduction and to the evolution of eusociality more generally. We find that, in the absence of genetic constraints, monogamy always promotes altruistic worker sterility and may inhibit spiteful worker sterility. Our extended analysis demonstrates that an exact population-genetics approach strongly supports the prediction of inclusive-fitness theory that monogamy promotes sib-directed altruism in social insects.

单配偶制在包括昆虫、鸟类和哺乳动物在内的多个动物类群中，均与指向同胞的利他行为存在显著关联。广义适合度理论（Inclusive-fitness theory）可通过将高亲缘度界定为利他行为的促进因子，轻松阐释这一观测规律。依据该理论的预测，若不育职虫可作为更高效的协助者，单配偶制应当会促进昆虫社会中自愿不育性状的演化。然而，近期一项数学种群遗传学分析并未发现单配偶制对职虫自愿不育存在一致的影响效应。本研究重新审视了该分析：其一，我们放宽了遗传假设，不仅考量效应极端的等位基因——即编码完全可育或完全不育的等位基因——还纳入了对职虫不育具有中等效应的等位基因；其二，我们拓展了原有的稳定性分析——原分析仅关注种群中所有职虫均完全不育或均完全可育时的入侵性——以识别可能存在中等纯合或混合进化稳定状态的情境；其三，我们考虑了更广泛的、与利他性职虫不繁殖及更广泛意义上的真社会性（eusociality）演化相关的、明确人口统计学特征的生态场景。我们发现，在无遗传约束的条件下，单配偶制始终会促进利他性职虫不育，却可能抑制损他性职虫不育。本拓展分析证实，精确的种群遗传学方法能够有力支持广义适合度理论的预测：单配偶制会促进社会性昆虫中指向同胞的利他行为。