Data from: Out-group threat promotes within-group affiliation in a cooperative fish

In social species, conflict with outsiders is predicted to affect within-group interactions, and thus influence group dynamics and the evolution and maintenance of sociality. While empirical evidence exists for a relationship between out-group conflict and intragroup behaviour in humans, experimental tests in other animals are rare. In a model fish system, we show that simulated out-group intrusions cause post-conflict increases in intragroup affiliation, but no changes in post-conflict intragroup aggression. Post-conflict affiliation was greater following intrusions by neighbouring compared to non-neighbouring individuals; neighbours represent greater threats to the dominance rank and breeding success of residents, and are visible in the aftermath of the intrusion. By providing strong evidence of a link between out-group conflict and post-conflict intragroup behaviour, and demonstrating that intragroup affiliation is affected by the nature of the out-group intrusion, our study shows the importance of considering post-conflict behaviour for our understanding of cooperation and social structure.

在社会性物种中，与外来者的冲突被推测会影响群体内部互动，进而影响群体动态以及社会性的演化与维持。尽管已有实证证据表明人类的外群体冲突（out-group conflict）与群体内行为（intragroup behaviour）之间存在关联，但针对其他动物的相关实验测试仍较为匮乏。在本研究采用的模式鱼类系统（model fish system）中，我们发现模拟外群体入侵（simulated out-group intrusions）会使得冲突后群体内亲和行为（intragroup affiliation）显著提升，但冲突后群体内攻击行为（intragroup aggression）并未发生显著变化。相较于非邻近个体入侵的情况，邻近个体（neighbouring individuals）入侵后的冲突后群体内亲和行为更为显著；这是因为邻近个体对定居群体的优势等级（dominance rank）与繁殖成功率（breeding success）构成更大威胁，且在入侵后的后续阶段中始终处于可观测状态。本研究通过为外群体冲突与冲突后群体内行为之间的关联提供坚实证据，并证实群体内亲和行为会受到外群体入侵性质的影响，揭示了在理解合作行为与社会结构（social structure）时，考量冲突后行为的重要性。