Personality (i.e., among-individual variation in average behavior) often covaries with fitness, but how such personality–fitness relationships come about is poorly understood. Here, we explore potential mechanisms by which two female personality traits (female–female aggression and female nest defense as manifested by hissing behavior) were linked with annual reproductive success in a population of great tits (Parus major), a socially monogamous species with biparental care. We hypothesized that personality-related differences in reproductive success result from variation in reproductive decision (lay date, brood size) and/or parental provisioning rates. Relative support for these mechanisms was evaluated using path analysis on data collected in two successive years. We reveal that larger broods were provisioned at a higher rate by both parents and that female, but not male, provisioning rate was involved in the trade-off between offspring number (brood size) and fledgling mass. Among-individual variation in female aggression, via its association with female provisioning rate, was negatively linked to fledgling mass (i.e., indirect effect), yet only in one of the study years. Male provisioning rate did not influence these relationships. In contrast, among-individual variation in hissing behavior was directly and negatively linked with fledgling mass in both years, via an underlying mechanism that remains to be identified (i.e., direct effect). Together, our findings emphasize that personality–fitness relationships may come about via different mechanisms across personality traits and/or years, thereby illustrating additional complexity in how selection might act on and maintain among-individual variation in behavioral phenotypes in the wild.

中文翻译：

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将女性个性与生殖成功联系起来的途径是特质和年份特定的

人格（即，平均行为的个体差异）通常与适应性相关，但是人们对这种人格-健康关系如何产生的了解却很少。在这里，我们探讨了在两个女的个性特征（女女的侵略和表现由嘶嘶行为女巢防御）在大山雀的人口（每年繁殖成功链接的潜在机制大山雀），具有双亲照顾的一夫一妻制物种。我们假设生殖成功中与人格相关的差异是由生殖决策（产蛋日期，育雏量）和/或父母提供率的变化引起的。通过对连续两年收集的数据进行路径分析，评估了对这些机制的相对支持。我们发现，父母双方都以较高的比率提供较大的亲鱼，而雌性而不是男性的提供率与后代数量（亲鱼大小）和雏鸡质量之间的权衡有关。女性侵略的个体差异（通过其与女性供应率的关联）与羽翼未丰的质量（即间接影响）负相关，但仅在研究年份之一。男性供应率不影响这些关系。相比之下，在这两年中，嘶嘶行为的个体差异与刚起步的质量有直接和负面的联系，这是有待发现的潜在机制（即直接影响）。总之，我们的研究结果强调，人格与健康之间的关系可能通过人格特征和/或年限的不同机制产生，从而说明了选择如何在野外行为表型上起作用并维持其个体差异的额外复杂性。