Data from: Are there indirect fitness benefits of female extra-pair reproduction? Lifetime reproductive success of within-pair and extra-pair offspring

The forces driving extra-pair reproduction by socially monogamous females, and the resulting genetic polyandry, remain unclear. A testable prediction of the hypothesis that extra-pair reproduction partly reflects indirect selection on females is that extra-pair young (EPY) will be fitter than their within-pair young (WPY) maternal half-siblings. This prediction has not been comprehensively tested in a wild population, requiring data on the lifetime reproductive success (LRS) of maternal half-sib EPY and WPY. We used 17 years of genetic parentage data from song sparrows, Melospiza melodia, to compare the LRS of hatched EPY and WPY maternal half-siblings measured as their lifetime number of hatched offspring, recruited offspring and hatched grandoffspring. EPY hatchlings were not significantly fitter than WPY hatchlings for any of three measures of LRS. Furthermore, opposite to prediction, EPY hatchlings tended to have lower LRS than their maternal half-sibling WPY hatchlings on average. EPY also tended to be less likely to survive to hatch than their maternal half-sibling WPY. Taken together, these results fail to support one key hypothesis explaining the evolution of genetic polyandry by socially monogamous females and suggest there may be weak indirect selection against female extra-pair reproduction in song sparrows.

社会一夫一妻制雌性的配偶外繁殖驱动力及其引发的遗传一妻多夫现象，至今仍未得到明确阐释。针对“配偶外繁殖部分体现了对雌性的间接选择”这一假说，可检验的预测为：配偶外后代（extra-pair young, EPY）的适合度将高于其母系半同胞的配偶内后代（within-pair young, WPY）。该预测尚未在野生种群中得到全面验证，相关研究需获取母系半同胞的配偶外后代与配偶内后代的终生生殖成功（lifetime reproductive success, LRS）数据。本研究利用歌带鹀（Melospiza melodia）长达17年的遗传亲权数据，以孵化后代数、招募后代数及孵化孙辈数三项指标衡量终生生殖成功，对比了孵化出的母系半同胞配偶外后代与配偶内后代的终生生殖成功情况。在三项终生生殖成功指标中，配偶外孵化后代的适合度均未显著高于配偶内孵化后代。此外，与预测相悖的是，平均而言配偶外孵化后代的终生生殖成功往往低于其母系半同胞的配偶内孵化后代。配偶外孵化后代的孵化存活率也普遍低于其母系半同胞的配偶内后代。综合上述结果，本研究并不支持解释社会一夫一妻制雌性演化出遗传一妻多夫现象的核心假说之一，同时表明歌带鹀种群中可能存在针对雌性配偶外繁殖的弱间接选择压力。