Ecology shapes epistasis in a genotype-phenotype-fitness map for stick insect colour

Genetic interactions such as epistasis are widespread in nature and can shape evolutionary dynamics. Epistasis occurs due to non-linearity in biological systems, which can arise via cellular processes that convert genotype to phenotype and via selective processes that connect phenotype to fitness. Few studies in nature have connected genotype to phenotype to fitness for multiple potentially interacting genetic variants. Thus, the causes of epistasis in the wild remain poorly understood. Here, we show that epistasis for fitness is an emergent and predictable property of non-linear selective processes. We do so by measuring the genetic basis of cryptic colouration and survival in a field experiment with stick insects. We find that colouration exhibits a largely additive genetic basis, but with some effects of epistasis that enhance differentiation between colour morphs. In terms of fitness, different combinations of loci affecting colouration confer high survival in one host-plant treatme...上位性（epistasis）这类遗传互作在自然界中广泛存在，并可塑造进化动力学过程。上位性源于生物系统的非线性特性，这类非线性可通过将基因型转化为表型的细胞过程，以及将表型与适合度（fitness）相联结的选择过程产生。目前鲜有研究能在自然情境下，针对多个潜在存在互作的遗传变异，构建完整的基因型-表型-适合度关联链条。因此，野生群体中上位性的成因仍有待深入解析。本研究证实，针对适合度的上位性是非线性选择过程的一种涌现且可预测的特性。我们通过开展竹节虫野外实验，测定了隐蔽体色与存活能力的遗传基础，以此验证了上述结论。研究发现，体色的遗传基础整体以加性效应为主，但同时存在部分上位性效应，可强化不同体色形态间的分化。就适合度而言，影响体色的基因座的不同组合，在某一寄主植物处理组中可赋予较高的存活能力……