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.跨各类群而言，社会单配制物种的婚外配（extra-pair mating）现象普遍存在，但现有研究极少能明确与婚外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验证其是否直接影响父权关系的研究更是屈指可数。正因如此，目前鲜有实验证据能支撑这一广为流传的假说：雌性会选择装饰程度更高的雄性作为婚外配对象。本研究以鸟类中婚外配比例最高的物种之一——树燕（Tachycineta bicolor）为研究对象，开展了雄性羽色与受精成功率之间关联的实验探究。本研究于繁殖季早期、多数交配行为发生前，采用无毒记号笔对雄性个体背部的鲜亮蓝色羽色进行了黯淡处理。与对照组雄性相比，经羽色黯淡处理的雄性所抚育的婚外子代数量更少，整体子代总数亦随之降低。在未接受处理的雄性个体中，羽色更鲜亮的蓝色个体所抚育的婚外子代数量同样更多；配对比较结果显示，婚外父本的蓝色羽色亮度显著高于其所在配对中的婚内配偶雄性。结合此前针对树燕的相关研究成果，本研究结果表明，婚外配行为的演化驱动力来源于雌雄双方均可获得的适应性收益。