Data from: Genetic composition of social groups influences male aggressive behaviour and fitness in natural genotypes of Drosophila melanogaster

Indirect genetic effects (IGEs) describe how an individual’s behaviour—which is influenced by his or her genotype—can affect the behaviours of interacting individuals. IGE research has focused on dyads. However, insights from social networks research, and other studies of group behaviour, suggest that dyadic interactions are affected by the behaviour of other individuals in the group. To extend IGE inferences to groups of three or more, IGEs must be considered from a group perspective. Here, I introduce the “focal interaction” approach to study IGEs in groups. I illustrate the utility of this approach by studying aggression among natural genotypes of Drosophila melanogaster. I chose two natural genotypes as “focal interactants”: the behavioural interaction between them was the “focal interaction.” One male from each focal interactant genotype was present in every group, and I varied the genotype of the third male—the “treatment male.” Genetic variation in the treatment male’s aggressive behaviour influenced the focal interaction, demonstrating that IGEs in groups are not a straightforward extension of IGEs measured in dyads. Further, the focal interaction influenced male mating success, illustrating the role of IGEs in behavioural evolution. These results represent the first manipulative evidence for IGEs at the group level.

间接遗传效应（Indirect Genetic Effects, IGEs）阐述了受个体自身基因型影响的行为，如何作用于与其发生互动的其他个体的行为。间接遗传效应的相关研究此前多聚焦于二元互动对。然而，社交网络研究与其他群体行为研究的结论表明，二元互动会受到群体内其他个体行为的影响。若要将间接遗传效应的推论拓展至包含三个及以上个体的群体，则需从群体视角出发对间接遗传效应进行研究。本文提出“焦点互动（focal interaction）”法以开展群体层面的间接遗传效应研究。本文以黑腹果蝇（Drosophila melanogaster）自然基因型个体间的攻击行为为例，阐明了该方法的实用性。本研究选取两种自然基因型作为“焦点互动个体（focal interactants）”，二者间的行为互动即为“焦点互动”。每个实验组中均包含来自两种焦点互动基因型的各一只雄性个体，并通过改变第三只雄性的基因型来设置处理组——该雄性即为“处理组雄性（treatment male）”。处理组雄性攻击行为的遗传变异会对焦点互动产生影响，这表明群体层面的间接遗传效应并非成对个体间接遗传效应的简单延伸。此外，焦点互动还会影响雄性的交配成功率，阐明了间接遗传效应在行为进化中的作用。本研究结果为群体层面的间接遗传效应提供了首个操控性实验证据。