Data from: Environmental heterogeneity generates opposite gene-by-environment interactions for two fitness-related traits within a population

Theory predicts that environmental heterogeneity offers a potential solution to the maintenance of genetic variation within populations, but empirical evidence remains sparse. The livebearing fish Xiphophorus variatus exhibits polymorphism at a single locus, with different alleles resulting in up to five distinct melanistic “tailspot” patterns within populations. We investigated the effects of heterogeneity in two ubiquitous environmental variables (temperature and food availability) on two fitness-related traits (upper thermal limits and body condition) in two different tailspot types (wildtype and upper cut crescent). We found gene-by-environment (GxE) interactions between tailspot type and food level affecting upper thermal limits (UTL), as well as between tailspot type and thermal environment affecting body condition. Exploring mechanistic bases underlying these GxE patterns, we found no differences between tailspot types in hsp70 gene expression despite significant overall increases in expression under both thermal and food stress. Similarly, there was no difference in routine metabolic rates between the tailspot types. The reversal of relative performance of the two tailspot types under different environmental conditions revealed a mechanism by which environmental heterogeneity can balance polymorphism within populations through selection on different fitness-related traits.理论预测，环境异质性可为种群内遗传变异的维持提供潜在解决方案，但相关实证证据仍较为匮乏。胎生鱼类杂色剑尾鱼（Xiphophorus variatus）在单个基因座上表现出多态性，不同等位基因可使种群内出现多达五种不同的黑色素沉着"尾斑"表型。本研究针对两种尾斑类型（野生型与上新月切型），探究了两种普遍存在的环境变量（温度与食物可获得性）的异质性对两项适合度相关性状——最高热耐受极限（upper thermal limits, UTL）和身体状况——的影响。研究发现，尾斑类型与食物水平间的基因-环境互作（gene-by-environment, GxE）会影响最高热耐受极限，而尾斑类型与热环境间的GxE则会影响身体状况。为探究上述GxE模式背后的分子机制，我们发现，尽管在热胁迫与食物胁迫条件下，hsp70基因的表达量整体均显著上升，但两种尾斑类型间的hsp70基因表达并无差异。同样，两种尾斑类型的常规代谢速率也无显著差异。两种尾斑类型在不同环境条件下的相对表现发生逆转，这揭示了环境异质性可通过对不同适合度相关性状施加选择，从而维持种群内多态性的潜在机制。