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（socially monogamous）物种中，配偶外父权（extra-pair paternity）可通过允许携带优势表型的雄性独占交配机会，增强性间选择（inter-sexual selection）的作用强度。多项研究已发现雄性信号与配偶外交配行为间存在关联，但仍有大量研究未能解释配偶外交配成功率的变异。加深对生态制约因素在塑造行为过程中所起作用的认知，或有助于调和各项研究间的矛盾结论。我们以具有领域性的森莺科鸟类普通黄喉地莺（Geothlypis trichas）为研究对象，在空间维度下探究其配偶外交配行为。历时六年，我们记录了99只雄性个体共计158次繁殖尝试，最终得到369个鸟巢及520只采样雏鸟。该物种的领域空间分布差异显著：雄性个体的近邻数量介于0至10只之间，且存在3至39只邻近雏鸟可作为潜在的配偶外父权候选对象。配偶内与配偶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却随密度变化而改变。繁殖成功率的总方差在低密度环境下最高，且该方差主要由配偶内繁殖成功率的变异所解释；与之相反，在高密度环境中，配偶内与配偶外繁殖成功率均对繁殖成功方差产生显著贡献。羽色与配偶外交配行为间的关联同样随密度变化：在高密度环境下，羽色通过配偶外繁殖成功率受到强烈的性选择作用，但在低密度环境中未检测到相关选择。综上，塑造社会互动模式的生态因素，可通过促进或抑制交配偏好的表达，进而调控性选择的作用模式。