Data from: Disentangling plastic and genetic changes in body mass of Siberian jays

Spatial and temporal phenotypic differentiation in mean body size is of commonplace occurrence, but the underlying causes remain often unclear: both genetic differentiation in response to selection (or drift) and environmentally induced plasticity can create similar phenotypic patterns. Studying changes in body mass in Siberian jays (Perisoreus infaustus) over three decades, we discovered that mean body mass declined drastically (ca. 10%) over the first two decades, but increased markedly thereafter back to almost the initial level. Quantitative genetic analyses revealed that although body mass was heritable (h2 = 0.46), the pronounced temporal decrease in body mass was mainly a product of phenotypic plasticity. However, a concomitant and statistically significant decrease in predicted breeding values suggests a genetic component to this change. The subsequent increase in mean body mass was indicated to be entirely due to plasticity. Selection on body mass was estimated to be too weak to fully account for the observed genetic decline in body mass, but bias in selection differential estimates due to environmental covariance between body mass and fitness is possible. Hence, the observed body mass changes appear to be driven mainly by phenotypic plasticity. Although we were not able to identify the ecological driver of the observed plastic changes, the results highlight the utility of quantitative genetic approaches in disentangling genetic and phenotypic changes in natural populations.

平均体型的空间与时间表型分化（spatial and temporal phenotypic differentiation）虽属常见现象，但其潜在成因往往尚未明晰：针对选择（或遗传漂变）产生的遗传分化（genetic differentiation），以及环境诱导的表型可塑性（environmentally induced plasticity），均可催生相似的表型模式。本研究针对西伯利亚松鸦（Perisoreus infaustus）的体重变化展开了长达三十年的追踪，结果发现其平均体重在前二十年间大幅下降（约10%），随后又显著回升至接近初始水平。数量遗传分析（quantitative genetic analyses）结果显示，尽管体重具有可遗传性（狭义遗传力h²=0.46），但体重的显著时间下降主要源于表型可塑性。然而，预测育种值（predicted breeding values）同时出现了统计学上显著的下降，这表明该变化存在遗传组分。后续平均体重的回升则完全被归因于表型可塑性。对体重的选择强度估计过弱，无法完全解释观测到的体重遗传下降，但体重与适合度（fitness）之间的环境协方差（environmental covariance）可能导致选择差（selection differential）估计存在偏差。因此，观测到的体重变化似乎主要由表型可塑性驱动。尽管本研究未能明确引发此类可塑性变化的生态因子，但研究结果凸显了数量遗传方法在解析自然种群遗传与表型变化方面的应用价值。