Data from: Experimental evidence that brighter males sire more young in tree swallows

Across taxa, extra-pair mating is widespread among socially monogamous species, but few studies have identified male ornamental traits associated with extra-pair mating success, and even fewer studies have experimentally manipulated male traits to determine whether they are related directly to paternity. As a consequence, there is little experimental evidence to support the widespread hypothesis that females choose more ornamented males as extra-pair mates. Here, we conducted an experimental study of the relationship between male plumage colour and fertilization success in tree swallows (Tachycineta bicolor), which have one of the highest levels of extra-pair mating in birds. In this study, we experimentally dulled the bright blue plumage on the back of males (with nontoxic ink markers) early in the breeding season prior to most mating. Compared with control males, dulled males sired fewer extra-pair young, and, as a result, fewer young overall. Among untreated males, brighter blue males also sired more extra-pair young, and in paired comparisons, extra-pair sires had brighter blue plumage than the within-pair male they cuckolded. These results, together with previous work on tree swallows, suggest that extra-pair mating behaviour is driven by benefits to both males and females.

在各类生物类群中，配偶外交配在社会一夫一妻制物种中广泛存在，但目前鲜有研究鉴定出与配偶外交配成功率相关的雄性装饰性状，且通过实验操纵雄性性状以明确其是否直接影响父权的研究更是寥寥无几。因此，支持“雌性会选择装饰性更强的雄性作为配偶外交配对象”这一主流假说的实验证据极为匮乏。本研究以鸟类中配偶外交配水平最高的物种之一——树燕（Tachycineta bicolor）为研究对象，开展了一项探究雄性羽色与受精成功率之间关联的实验研究。本研究于繁殖季早期、多数交配行为发生前，使用无毒记号笔对雄性个体背部的亮蓝色羽色进行了实验性褪暗处理。与对照组雄性相比，经褪暗处理的雄性所育配偶外子代数量更少，整体子代总数亦随之降低。在未接受处理的雄性个体中，羽色更鲜亮的雄性同样能产生更多配偶外子代；在配对比较分析中，配偶外父本的亮蓝色羽色显著亮于其所背叛的原配雄性。结合此前针对树燕的相关研究，本研究结果表明，配偶外交配行为的演化是由雄性与雌性双方均可获得的收益所驱动的。