Results from a meta-analysis investigating covariance between genetic and environmental (CovGE) effects in phenotypic results in published literature

Covariance can exist between the genetic and environmental influences on phenotype (CovGE) and can have an important role in ecological and evolutionary processes in nature and population responses to environmental change. CovGE is commonly called countergradient variation (CnGV; negative CovGE)or cogradient variation (CoGV; positive CovGE)and has been recognized in classic studies that have established several long-standing hypotheses about CnGV and CoGV. For instance, it is hypothesized that CnGV is more prevalent in nature than CoGV, that CnGV is more prevalent in fish, amphibian, and invertebrate taxa, across latitudinal or altitudinal environmental gradients, and more frequently occurs in metabolic compensation traits, including development, growth, feeding, metabolism, and activity, while CoGV is more commonly observed in morphological traits. The recent development of a standardized method to measure CovGE allows for the first rigorous quantitative exploration of these hypotheses. We use meta-analysis and apply the novel quantitative method to test whether the above hypotheses are supported in the literature. We found no differences in frequency of CnGV and CoGV, and no systematic patterns relative to taxa, environmental gradient, or trait type. However, our analyses suggest that CovGE may be as common as gene by environment (GxE) interactions. Given that CovGE is likely to have a strong impact on future outcomes for organisms experiencing environmental change, that significant CovGE occurred frequently, and the lack of systematic patterns in the occurrence of CovGE, we encourage a more widespread application of measuring CovGE.表型所受遗传影响与环境影响间可存在协方差（Covariance between genetic and environmental influences on phenotype，以下简称CovGE），其在自然界的生态与演化过程以及种群对环境变化的响应中均发挥着重要作用。CovGE通常被称为反梯度变异（Countergradient variation，简称CnGV，对应负协方差的CovGE）或同梯度变异（Cogradient variation，简称CoGV，对应正协方差的CovGE），这类变异已在多项经典研究中得到证实，这些研究确立了若干关于CnGV与CoGV的长期假说。例如，有假说认为CnGV在自然界中的出现频率高于CoGV，CnGV在鱼类、两栖类与无脊椎动物类群以及跨纬度或海拔的环境梯度中更为普遍，且更常出现在包括发育、生长、摄食、代谢与活动在内的代谢补偿性状中，而CoGV则更常见于形态性状。近期，一种用于量化CovGE的标准化方法得以开发，这使得学界首次能够对上述假说开展严谨的定量探索。本研究采用元分析（meta-analysis）方法，并运用这一全新的定量手段，在已发表文献中检验前述假说是否成立。研究结果显示，CnGV与CoGV的出现频率并无显著差异，且在类群、环境梯度或性状类型方面均未呈现系统性分布模式。不过，本研究的分析表明，CovGE的出现频率或许与基因-环境互作（gene by environment interaction，简称G×E）相当。鉴于CovGE可能对遭受环境变化的生物体的未来演化结局产生强烈影响，且显著的CovGE频繁出现，同时其出现并未呈现系统性模式，我们呼吁学界更广泛地推广CovGE测量方法的应用。