The environment influences how an organism’s genotype determines its phenotype and how this phenotype affects its fitness. Here, to better understand this dual role of environment in the production and selection of phenotypic variation, we determined genotype–phenotype–fitness relationships for mutant strains of Saccharomyces cerevisiae in four environments. Specifically, we measured how promoter mutations of the metabolic gene TDH3 modified expression level and affected growth for four different carbon sources. In each environment, we observed a clear relationship between TDH3 expression level and fitness, but this relationship differed among environments. Mutations with similar effects on expression in different environments often had different effects on fitness and vice versa. Such environment-specific relationships between phenotype and fitness can shape the evolution of phenotypic plasticity. We also found that mutations disrupting binding sites for transcription factors had more variable effects on expression among environments than those disrupting the TATA box, which is part of the core promoter. However, mutations with the most environmentally variable effects on fitness were located in the TATA box, because of both the lack of plasticity of TATA box mutations and environment-specific fitness functions. This observation suggests that mutations affecting different molecular mechanisms contribute unequally to regulatory sequence evolution in changing environments.

环境会影响生物体的基因型如何决定其表型，以及该表型如何影响其适应性。在这里，为了更好地了解环境在表型变异的产生和选择中的双重作用，我们确定了四种环境中酿酒酵母突变菌株的基因型 - 表型 - 适应度关系。具体来说，我们测量了代谢基因 TDH3 的启动子突变如何改变四种不同碳源的表达水平并影响生长。在每种环境中，我们观察到 TDH3 表达水平与适应性之间存在明显的关系，但这种关系因环境而异。在不同环境中对表达具有相似影响的突变通常对适应性产生不同的影响，反之亦然。表型和适应性之间的这种环境特异性关系可以塑造表型可塑性的进化。我们还发现，破坏转录因子结合位点的突变比破坏 TATA 盒（核心启动子的一部分）的突变对环境中表达的可变影响更大。然而，由于 TATA 盒突变缺乏可塑性和环境特异性适应函数，因此对适应度影响最大的环境变量影响的突变位于 TATA 盒中。这一观察结果表明，在不断变化的环境中，影响不同分子机制的突变对调节序列进化的贡献不相等。