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.

理论研究表明，环境异质性为维持种群内的遗传变异提供了潜在路径，但相关实证证据仍较为匮乏。胎生鱼类杂色剑尾鱼（Xiphophorus variatus）在单基因座上存在多态性，不同等位基因可在种群中形成多达五种独特的黑化尾斑表型。本研究针对两种尾斑类型（野生型与上新月形），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——高温耐受极限（upper thermal limits, UTL）与身体状况的影响。研究发现，尾斑类型与食物水平间存在影响高温耐受极限的基因-环境互作（gene-by-environment, G×E），同时尾斑类型与温度环境间也存在影响身体状况的G×E互作。为探究上述G×E互作模式的分子机制，本研究检测了尾斑类型间的热休克蛋白70（hsp70）基因表达差异：尽管在温度胁迫与食物胁迫下，整体基因表达量均显著上升，但不同尾斑类型间的表达量并无显著差异。类似地，不同尾斑类型的常规代谢速率也未见显著差异。两种尾斑类型在不同环境条件下的相对表现发生反转，这揭示了环境异质性可通过对不同适合度相关性状的选择，维持种群内多态性的潜在机制。