Data from: Spatial distribution of nests constrains the strength of sexual selection in a warbler

In socially monogamous species, extra-pair paternity may increase the strength of inter-sexual selection by allowing males with preferred phenotypes to monopolize matings. Several studies have found relationships between male signals and extra-pair mating, but many others fail to explain variation in extra-pair mating success. A greater appreciation for the role that ecological contingencies play in structuring behavioral processes may help to reconcile contradictory results. We studied extra-pair mating in a spatial context in the common yellowthroat (Geothlypis trichas), a territorial wood warbler. Over the course of six years, we observed 158 breeding attempts by 99 males, resulting in a total of 369 nests and 520 sampled nestlings. The spatial distribution of territories varied greatly, with males having between 0 and 10 close neighbors and between 3 and 39 neighboring nestlings close enough to represent extra-pair siring opportunities. Both within-pair and extra-pair reproductive success increased with breeding density, but the opportunity for sexual selection and strength of selection varied with density. Total variance in reproductive success was highest at low density and was mostly explained by variation in within-pair success. In contrast, at high density, both within-pair and extra-pair success contributed substantially to variance in reproductive success. The relationships between plumage and extra-pair mating also varied by density; plumage was under strong sexual selection via extra-pair mating success at high density but no selection was detected at low density. Thus, ecological factors that structure social interactions can drive patterns of sexual selection by facilitating or constraining the expression of mating preferences.

在社会一夫一妻制物种中，婚外父权（extra-pair paternity）可通过让携带偏好表型的雄性独占交配权，增强性间选择（inter-sexual selection）的强度。已有多项研究发现雄性信号与婚外交配（extra-pair mating）行为存在关联，但其余大量研究却未能阐释婚外交配成功率的变异规律。若能更深入地理解生态偶然性在构建行为过程中的作用，或可有助于调和这些相悖的研究结论。本研究以具领域性的林莺——普通黄喉地莺（Geothlypis trichas）为研究对象，在空间情境下探究其婚外交配行为。历经六年的野外调查，我们记录了99只雄性的158次繁殖尝试，共计获得369个鸟巢以及520只取样雏鸟。其领域的空间分布差异显著：雄性个体的近邻数量介于0至10只之间，且存在3至39只足够邻近的雏鸟，可作为雄性获得婚外父权的潜在对象。婚内与婚外繁殖成功率均随繁殖密度升高而提升，但性选择机会与选择强度则随密度发生变化。繁殖成功率的总变异在低繁殖密度下达到峰值，且该变异主要由婚内繁殖成功率的差异所解释。与之相反，在高繁殖密度下，婚内与婚外繁殖成功率均对繁殖成功率的变异产生了显著贡献。羽色与婚外交配行为的关联同样随繁殖密度发生变化：在高繁殖密度下，羽色通过婚外交配成功率受到强烈的性选择作用，而在低繁殖密度下则未检测到选择效应。由此可见，构建社会互动模式的生态因子，可通过促进或约束交配偏好的表达，进而塑造性选择的格局。