Davies Nicholas G, Gardner Andy
London School of Hygiene and Tropical Medicine, London, UK.
School of Biology, University of St Andrews, St Andrews, UK.
R Soc Open Sci. 2018 May 9;5(5):172190. doi: 10.1098/rsos.172190. eCollection 2018 May.
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.
一夫一妻制与包括昆虫、鸟类和哺乳动物在内的多种动物类群中针对同胞的利他行为相关。广义适合度理论通过将高度的亲缘关系确定为利他行为的促进因素，很容易解释这种模式。与这一预测一致，如果不育的工蚁能成为更好的帮手，那么一夫一妻制应该会促进昆虫社会中自愿不育现象的进化。然而，最近一项数学种群遗传学分析未能确定一夫一妻制对工蚁自愿不育现象的一致影响。在此，我们重新审视该分析。首先，我们放宽遗传假设，不仅考虑编码无不育或完全不育的极端效应等位基因，还考虑对工蚁不育有中间效应的等位基因。其次，我们拓宽稳定性分析——该分析聚焦于所有工蚁完全不育或所有工蚁完全可育的种群的可入侵性——以确定可能出现中间纯合或混合进化稳定状态的情况。第三，我们考虑更广泛的与利他性工蚁不繁殖以及更普遍的真社会性进化相关的人口统计学明确的生态情景。我们发现，在没有遗传限制的情况下，一夫一妻制总是会促进利他性工蚁不育，并且可能抑制恶意的工蚁不育。我们的扩展分析表明，精确的种群遗传学方法有力地支持了广义适合度理论的预测，即一夫一妻制促进社会性昆虫中针对同胞的利他行为。
