Data from: Genetic basis of between-individual and within-individual variance of docility

Between-individual variation in phenotypes within a population is the basis of evolution. However, evolutionary and behavioural ecologists have mainly focused on estimating between-individual variance in mean trait and neglected variation in within-individual variance, or predictability of a trait. In fact, an important assumption of mixed-effects models used to estimate between-individual variance in mean traits is that within-individual residual variance (predictability) is identical across individuals. Individual heterogeneity in the predictability of behaviours is a potentially important effect but rarely estimated and accounted for. We used 11,389 measures of docility behaviour from 1,576 yellow-bellied marmots (Marmota flaviventris) to estimate between-individual variation in both mean docility and its predictability. We then implemented a double hierarchical animal model to decompose the variances of both mean trait and predictability into their environmental and genetic components. We found that individuals differed both in their docility and in their predictability of docility with a negative phenotypic covariance. We also found significant genetic variance for both mean docility and its predictability but no genetic covariance between the two. This analysis is one of the first to estimate the genetic basis of both mean trait and within-individual variance in a wild population. Our results indicate that equal within-individual variance should not be assumed. We demonstrate the evolutionary importance of the variation in the predictability of docility, and illustrate potential bias in models ignoring variation in predictability. We conclude that the variability in the predictability of a trait should not be ignored, and present a coherent approach for its quantification.

种群内个体间的表型变异是进化的基础。然而，进化生态学家与行为生态学家此前主要聚焦于估算平均性状的个体间方差，却忽视了个体内方差（即性状的可预测性）的变异。事实上，用于估算平均性状个体间方差的混合效应模型（mixed-effects models）有一项关键假设：个体间的个体内残差方差（residual variance，即可预测性）完全一致。行为可预测性的个体异质性是一项潜在的重要效应，但目前极少有研究对其开展估算与考量。
我们利用1576只黄腹旱獭（*Marmota flaviventris*）的11389条温顺性行为测量数据，同时估算了平均温顺性及其可预测性的个体间变异。随后我们采用双层次动物模型（double hierarchical animal model），将平均性状与可预测性的方差分解为环境组分与遗传组分。
研究结果显示，个体不仅在温顺性水平上存在差异，其温顺性的可预测性亦存在显著异质性，且二者呈负向表型协方差（phenotypic covariance）。我们还发现，平均温顺性及其可预测性均存在显著的遗传方差（genetic variance），但二者之间未检测到遗传协方差。
本研究是野生种群中同时估算平均性状与个体内方差遗传基础的首批研究之一。结果表明，不应默认个体内方差均一。我们证实了温顺性可预测性变异的进化重要性，并阐明了忽略可预测性变异的模型所存在的潜在偏倚。
综上，性状可预测性的变异不应被忽视，我们为此类变异的量化提供了一套严谨连贯的分析方法。