Data from: Subtle but ubiquitous selection on body size in a natural population of collared flycatchers over 33 years

Understanding the magnitude and long-term patterns of selection in natural populations is of importance, for example, when analyzing the evolutionary impact of climate change. We estimated univariate and multivariate directional, quadratic and correlational selection on four morphological traits (adult wing, tarsus and tail length, body mass) over a time period of 33 years (≈ 19 000 observations) in a nest-box breeding population of collared flycatchers (Ficedula albicollis). In general, selection was weak in both males and females over the years regardless of fitness measure (fledged young, recruits and survival) with only few cases with statistically significant selection. When data were analyzed in a multivariate context and as time series a number of patterns emerged; there was a consistent, but weak, selection for longer wings in both sexes, selection was stronger on females when the number of fledged young was used as a fitness measure, there were no indications of sexually antagonistic selection and we found a negative correlation between selection on tarsus and wing length in both sexes but using different fitness measures. Uni- and multivariate selection gradients were correlated only for wing length and mass. Multivariate selection gradient vectors were longer than corresponding vector of univariate gradients and had more constrained direction. Correlational selection had little importance. Overall, the fitness surface was more or less flat with few cases of significant curvature indicating that the adaptive peak with regard to body size in this species is broader than the phenotypic distribution, which has resulted in weak estimates of selection.

解析自然种群中选择作用的强度与长期模式，在分析气候变化的演化影响等场景中具有重要意义。本研究针对斑姬鹟（*Ficedula albicollis*）的巢箱繁殖种群开展了长达33年的观测研究（累计约19000次记录），对四项形态性状（成鸟翅长、跗跖长、尾长与体质量）估算了单变量与多变量方向选择、二次选择及相关选择。整体而言，多年来无论以繁殖幼鸟数、招募个体数还是存活率作为适合度指标，雌雄个体均表现出较弱的选择作用，仅少数案例存在统计学意义上的显著选择。当以多变量框架结合时间序列分析数据时，可观测到一系列模式：雌雄个体均存在持续但较弱的长翅选择；当以繁殖幼鸟数作为适合度指标时，雌性受到的选择作用更强；未发现性拮抗选择的迹象；此外，雌雄个体的跗跖长选择与翅长选择均呈负相关，但二者采用的适合度指标存在差异。单变量与多变量选择梯度仅在翅长与体质量性状间存在相关性。多变量选择梯度向量的模长大于对应的单变量梯度向量，且方向更趋受限。相关选择的整体作用微弱。总体而言，适合度曲面大致平坦，仅少数案例存在显著曲率，这表明该物种体型相关的自适应峰宽大于表型分布范围，进而导致选择强度的估算值偏低。