The importance of direct fitness for helpers in advanced insect societies

长期以来，自私个体之间合作和利他行为的进化一直困扰着生物学家。汉密尔顿的包容性健康理论解释说，当帮助者帮助一个有繁殖能力的亲属时，他们可以获得间接的健康利益，并通过他们的帮助增加其后代的数量。此外，群居哺乳动物和鸟类中的帮助者可以通过接管巢穴或领地中的繁殖位置，或通过提高照顾后代的技能，从而直接获得健康，这对自己的后代也有好处。但是，这种直接的健康益处在蚂蚁等先进的社会群体中也很重要吗？工人们的行为表明他们是。许多蚁族的工蚁都能从未受精卵中产生雄性，但通常不会在蚁后在场的情况下这样做。然而，蚁后死后，工蜂建立了社会和繁殖等级秩序，只有排名靠前的工蜂才会产卵。此外，在社会上占主导地位的工蚁会避免昂贵的任务，比如觅食和保卫蚁群。这表明，员工的目标是保留直接健身的选择，但自私是否有回报从未被量化。在这个项目中，我们将通过首次估计野生群居昆虫种群的工蜂直接适应度来填补我们对社会性的理解中的这一重要空白。为此，我们将通过野外普查和雄性母性的遗传分析来确定Temnothorax crassispinus蚁群中工蚁繁殖的丰度。此外，我们将通过控制繁殖实验和测量精子数量和生存能力来确定工蜂和蜂后生育的雄性是否在适应性状上存在差异。最后，通过操纵群体组成，我们将研究工人的自私是否对群体的凝聚力和生产力有代价。该项目建立在对粗松毛虫进行广泛试点研究的基础上。该研究从目前关于包容性适合度和亲缘选择价值的热烈讨论中获得了额外的现实，并将使我们对高级群居昆虫的群居性维持有更全面的了解。

The evolution of cooperation and altruistic behavior among selfish individuals has long puzzled biologists. Hamilton s theory of inclusive fitness explains that helpers can gain indirect fitness benefits when they assist a breeding relative and through their help increase the number of its offspring. In addition, helpers in group-living mammals and birds can gain direct fitness through taking over the breeding position in the nest or territory or through improving their brood care skills, which later benefits their own offspring. But are such direct fitness benefits also important in advanced eusocial societies, such as ants? The behavior of workers suggests that they are. Workers of many ant species can produce males from unfertilized eggs, but usually refrain from doing so in the presence of the queen. After the death of the queen, however, workers establish social and reproductive rank orders and only the top-ranking workers lay eggs. Furthermore, socially dominant workers refrain from costly tasks, such as foraging and colony defense. This suggests that workers aim to retain the option of obtaining direct fitness, but whether selfishness pays off has never been quantified. In this project we will fill this important gap in our understanding of eusociality by for the first time estimating worker direct fitness in a wild social insect population. To do so we will determine the abundance of worker reproduction in colonies of Temnothorax crassispinus ants by censuses in the field and by genetic analyses of the maternity of males. In addition, we will determine whether worker-and queen-produced males differ in fitness traits through controlled breeding experiments and measuring sperm quantity and viability. Finally, through manipulation of colony composition we will examine whether worker selfishness has a cost for colony cohesiveness and productivity. The project builds on extensive pilot studies in T. crassispinus. It receives additional actuality from the ongoing heated discussion about the value of inclusive fitness and kin selection and will lead to a more complete understanding of the maintenance of eusociality in advanced social insects.