Data from: Testing for biases in selection on avian reproductive traits and partitioning direct and indirect selection using quantitative genetic models

Key life history traits such as breeding time and clutch size are frequently both heritable and under directional selection, yet many studies fail to document micro-evolutionary responses. One general explanation is that selection estimates are biased by the omission of correlated traits that have causal effects on fitness, but few valid tests of this exist. Here we show, using a quantitative genetic framework and six decades of life-history data on two free-living populations of great tits Parus major, that selection estimates for egg-laying date and clutch size are relatively unbiased. Predicted responses to selection based on the Robertson-Price Identity were similar to those based on the multivariate breeder’s equation, indicating that unmeasured covarying traits were not missing from the analysis. Changing patterns of phenotypic selection on these traits (for laying date, linked to climate change) therefore reflect changing selection on breeding values, and genetic constraints appear not to limit their independent evolution. Quantitative genetic analysis of correlational data from pedigreed populations can be a valuable complement to experimental approaches to help identify whether apparent associations between traits and fitness are biased by missing traits, and to parse the roles of direct versus indirect selection across a range of environments.

诸如繁殖时间与窝卵数这类核心生活史性状，通常既具备可遗传性，又处于定向选择的作用之下，但诸多相关研究却未能观测到微观进化响应。对此的一种通用解释为，选择估计值会因遗漏了对适合度具有因果影响的相关性状而产生偏倚，然而能够有效验证这一解释的研究却寥寥无几。
本研究借助数量遗传框架，结合两个野生大山雀（Parus major）种群长达六十年的生活史数据，证实产卵日期与窝卵数的选择估计值相对无偏。基于罗伯逊-普莱斯恒等式（Robertson-Price Identity）预测的选择响应，与基于多元育种者方程所得结果高度一致，这表明分析中并未遗漏未被测量的共变性状。因此，针对这些性状的表型选择模式（其中产卵日期与气候变化密切相关）的变化，实则反映了育种值上选择压力的改变，且遗传约束似乎并未限制它们的独立进化。
对拥有谱系信息的种群的相关数据开展数量遗传分析，可作为实验方法的宝贵补充，有助于厘清性状与适合度间的表观关联是否因缺失性状而存在偏倚，并能解析不同环境下直接选择与间接选择的各自作用。