Abstract Many studies investigated variation in the frequency of extrapair paternity (EPP) among individuals. However, our understanding of within-individual variation in EPP remains limited. Here, we comprehensively investigate variation in EPP at the within-individual level in a population of blue tits (Cyanistes caeruleus). Our study is based on parentage data comprising >10 000 genotyped offspring across 11 breeding seasons. First, we examined the repeatability of the occurrence of EPP, the number of extrapair offspring, the number of extrapair partners, and the occurrence of paternity loss using data from males and females that bred in multiple years. Second, we tested whether within-individual changes in EPP between breeding seasons relate to between-year changes in the local social environment. Repeatabilities were generally low but significant for the occurrence and number of extrapair young in females and for whether a male sired extrapair young or not. We found no evidence that the presence of the former social partner or changes in the proportion of familiar individuals or in phenotypic traits of the neighbors influenced changes in levels of EPP in females. However, in adult males, a decrease in the average body size of male neighbors was associated with higher extrapair siring success. If confirmed, this result suggests that the competitive ability of a male relative to its neighbors influences his extrapair mating success. We suggest that alternative hypotheses, including the idea that within-individual changes in EPP are due to “chance events” rather than changes in an individual’s social breeding environment, deserve more consideration.

中文翻译：

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对蓝山雀 (Cyanistes caeruleus) 的配对外亲子关系的个体内变异分析显示，重复性较低，且邻近变化的影响较小


摘要 许多研究调查了个体之间的配对外亲子关系 (EPP) 频率的差异。然而，我们对 EPP 个体内部差异的理解仍然有限。在这里，我们全面研究了蓝山雀 (Cyanistes caeruleus) 种群个体内 EPP 的变异。我们的研究基于包括 11 个繁殖季节超过 10 000 个基因分型后代的亲缘数据。首先，我们使用多年繁殖的雄​​性和雌性的数据检查了 EPP 发生的重复性、外对后代的数量、外对伴侣的数量以及亲子关系丧失的发生率。其次，我们测试了繁殖季节之间 EPP 的个体内部变化是否与当地社会环境的年份变化有关。重复性一般较低，但对于雌性中外对幼体的出现和数量以及雄性是否生育外对幼体而言具有重要意义。我们没有发现任何证据表明前社会伴侣的存在或熟悉个体比例的变化或邻居表型特征的变化会影响女性 EPP 水平的变化。然而，在成年雄性中，雄性邻居平均体型的减小与较高的配对成功率相关。如果得到证实，这一结果表明，雄性相对于其邻居的竞争能力会影响其外配对的成功率。我们建议其他假设值得更多考虑，包括个体内部 EPP 变化是由于“偶然事件”而不是个体社会繁殖环境的变化这一观点。