Data from: Individual dispersal decisions in a cooperative breeder: ecological constraints, the benefits of philopatry, and the social queue for dominance

1. Delayed dispersal is a key step in the evolution of familial animal societies and cooperative breeding. However, no consensus has been reached on the ecological and social circumstances driving delayed dispersal. 2. Here we test predictions from the ecological constraints and benefits of philopatry hypotheses as well as the recently-proposed dual benefits hypothesis to better understand the evolution of group-living and cooperative breeding. Furthermore, we consider how individual social circumstances within groups affect dispersal decisions. 3. We examine 11 years of life-history information on a wild population of cooperatively breeding southern pied babblers (Turdoides bicolor). We investigate the effects of ecological conditions, natal-group membership and individual social context on male and female dispersal delays, disperser survival and acquisition of dominance. 4. Female dispersal decisions are generally unconstrained by ecological or social circumstances. In contrast, males disperse in response to relaxed ecological constraints, decreases in nepotistic tolerance, or when low social rank in the queue for dominance decreases their likelihood of gaining a dominant breeding position. Early dispersal by end-of-queue males often leads to a head-of-queue subordinate position in a non-natal group, thereby increasing access to dominant breeding positions. However, males and females remaining in natal groups gain benefits of philopatry via increased survival and, for head-of-queue males, very high likelihood of acquisition of a breeding position. 5. Overall, predictions from the dual benefits hypothesis best describe these results, while some predictions from each of the ecological constraints and benefits of philopatry hypotheses were supported. The benefits of living and working together (collective action benefits) in large stable groups are of central importance in shaping dispersal delays in southern pied babbler societies. In addition, position in the subordinate social queue for dominance is key in determining access to reproduction, particularly for males. This research highlights the importance of considering the costs and benefits of individual social circumstances in dispersal decisions and illustrates how the dual benefits hypothesis offers new perspectives in understanding delayed dispersal.

1. 延迟扩散（delayed dispersal）是动物家族社会与合作繁殖演化进程中的关键环节。然而，学界尚未就驱动延迟扩散发生的生态与社会环境达成统一共识。
2. 本研究对生态限制假说、居留收益（benefits of philopatry）假说，以及新近提出的双重收益（dual benefits hypothesis）假说的相关预测进行检验，以期更深入地解析群居生活与合作繁殖的演化逻辑。此外，本研究还探讨了群体内部个体的社会处境对扩散决策的影响机制。
3. 我们以野生合作繁殖种群南方斑鸫鹛（Turdoides bicolor）为研究对象，梳理了该种群长达11年的生活史数据，并分析了生态条件、出生群体归属以及个体社会背景对雌雄个体扩散延迟时长、扩散者存活率以及统治地位获取情况的影响。
4. 雌性个体的扩散决策通常不受生态或社会条件的约束。与之相对，雄性仅在生态限制放松、亲族容忍度下降，或是在统治地位晋升队列中社会等级较低，导致其难以获得统治繁殖地位时，才会选择扩散。队列末尾的雄性提前扩散，往往能在非出生群体中成为队列首位的从属个体，进而提升其获得统治繁殖地位的概率。而留在出生群体中的雌雄个体，均可通过提高存活率获得居留收益；对于队列首位的雄性而言，更能获得极高的繁殖地位获取概率。
5. 总体而言，双重收益假说的预测最贴合本研究的结果，生态限制假说与居留收益假说的部分预测也得到了验证。在大型稳定群体中，群居协作所产生的集体行动收益，是塑造南方斑鸫鹛社会延迟扩散行为的核心因素。此外，从属个体在统治地位晋升队列中的位置，是决定其繁殖机会的关键因素，这一点在雄性个体中尤为突出。本研究强调了在探讨扩散决策时，需充分考量个体社会处境带来的成本与收益，并揭示了双重收益假说为理解延迟扩散机制提供了全新的研究视角。