Data from: The genetic relatedness in groups of joint-nesting Taiwan Yuhinas: low genetic relatedness with preferences for male kin

The relative importance of direct and indirect fitness and, thus, the role of kinship in the evolution of social behavior is much debated. Studying the genetic relatedness of interacting individuals is crucial to improving our understanding of these issues. Here, we used a seven-year data set to study the genetic structure of the Taiwan yuhina (Yuhina brunneciceps), a joint-nesting passerine. Ten microsatellite loci were used to investigate the pair-wised relatedness among yuhina breeding group members. We found that the average genetic relatedness between same-sex group members was very low (0.069 for male dyads and 0.016 for female dyads). There was also a low ratio of closely-related kin (r>0.25) in the cooperative breeding groups of yuhinas (21.59% and 9.68% for male and female dyads, respectively). However, the relatedness of male dyads within breeding groups was significantly higher than female dyads. Our results suggest that yuhina cooperation is maintained primarily by direct fitness benefits to individuals; however, kin selection might play a role in partner choice for male yuhinas. Our study also highlights an important, but often neglected, question: Why do animals form non-kin groups, if kin are available? We use biological market theory to propose an explanation for group formation of unrelated Taiwan yuhinas.

直接适合度（direct fitness）与间接适合度（indirect fitness）的相对重要性，以及亲缘关系在社会行为演化中的作用，长期以来学界对此颇具争议。探究互动个体间的遗传亲缘关系，对于深化我们对这些议题的理解至关重要。本研究依托七年数据集，对联合营巢的雀形目鸟类台湾纹胸鹛（Yuhina brunneciceps）的遗传结构展开分析。我们选取10个微卫星位点（microsatellite loci），对该鸟类繁殖群成员间的成对亲缘关系进行探究。研究发现，同性群内成员的平均遗传亲缘度极低：雄性成对个体的亲缘度为0.069，雌性成对个体为0.016。该鹛的合作繁殖群中，亲缘关系紧密（亲缘系数r>0.25）的个体占比同样较低：雄性成对个体占比为21.59%，雌性成对个体占比为9.68%。但繁殖群内雄性成对个体的亲缘度显著高于雌性成对个体。本研究结果表明，台湾纹胸鹛的合作行为主要依靠个体获得的直接适合度收益得以维持；不过，亲缘选择或许在雄性个体的配偶选择中发挥一定作用。本研究同时提出了一个重要却常被忽视的问题：若存在可及的亲缘个体，动物为何会选择形成非亲缘群？我们借助生物学市场理论（biological market theory），为台湾纹胸鹛的非亲缘群形成机制提供一种解释。