Data from: Increased extra-pair paternity in broods of aging males and enhanced recruitment of extra-pair young in a migratory bird

Despite keen interest in extra-pair mating in birds, its adaptive significance remains unresolved. Here, we use a multi-year dataset to test whether traits of a female's social mate influence her propensity to produce extra-pair offspring in a population of house wrens, and whether producing extra-pair young has consequences for a female's fitness through effects on offspring survival. Females were most likely to produce extra-pair offspring when paired with old males and when paired with males on poor-quality territories, although this latter effect was marginally non-significant. Among offspring, the cutaneous immunity of within-pair young decreased as the age of their sires increased, but cutaneous immunity of extra-pair young was not affected by the age of their extra-pair sires or by the age of the males rearing them. Extra-pair offspring were more likely than within-pair offspring to return as breeding adults to the local population, with extra-pair sons being more likely to return as a breeder for multiple years. Our findings support the hypothesis that females produce extra-pair offspring to enhance their inclusive fitness beyond what they are capable of given the male with which they are socially paired.

尽管学界对鸟类配偶外交配（extra-pair mating）已有浓厚研究兴趣，但其适应性意义至今仍未明确。本研究依托多年期数据集，在家鹪鹩（house wrens）种群中开展两项检验：一是雌性的社会配偶的性状是否会影响其产生配偶外后代（extra-pair offspring）的倾向；二是产生配偶外幼崽是否会通过影响后代存活，进而对雌性的进化适合度产生影响。雌性与年老雄性配对，或是与占据低质量领地的雄性配对时，更易产生配偶外后代；不过后一种效应仅接近显著水平，未达到统计学显著性阈值。在后代中，同配偶幼崽（within-pair young）的皮肤免疫功能随其生父的年龄增长而下降，但配偶外幼崽的皮肤免疫功能既不受其配偶外生父年龄的影响，也不受抚养它们的雄性年龄的影响。配偶外后代作为繁殖成体回迁至本地种群的概率高于同配偶后代，其中配偶外雄性后代连续多年回迁参与繁殖的概率更高。本研究结果支持如下假说：雌性通过产生配偶外后代，可提升自身的广义适合度（inclusive fitness），超越其与社会配偶配对时所能达到的适合度水平。