Data from: Testing for beneficial reversal of dominance during salinity shifts in the invasive copepod Eurytemora affinis, and implications for the maintenance of genetic variation

Maintenance of genetic variation at loci under selection has profound implications for adaptation under environmental change. In temporally and spatially varying habitats, non-neutral polymorphism could be maintained by heterozygote advantage across environments (marginal overdominance), which could be greatly increased by beneficial reversal of dominance across conditions. We tested for reversal of dominance and marginal overdominance in salinity tolerance in the salt-to-freshwater invading copepod Eurytemora affinis. We compared survival of F1 offspring generated by crossing saline and freshwater inbred lines (between-salinity F1 crosses) relative to within-salinity F1 crosses, across three salinities. We found evidence for both beneficial reversal of dominance and marginal overdominance in salinity tolerance. In support of reversal of dominance, survival of between-salinity F1 crosses was not different from that of freshwater F1 crosses under freshwater conditions and saltwater F1 crosses under saltwater conditions. In support of marginal overdominance, between-salinity F1 crosses exhibited significantly higher survival across salinities relative to both freshwater and saltwater F1 crosses. Our study provides a rare empirical example of complete beneficial reversal of dominance associated with environmental change. This mechanism might be crucial for maintaining genetic variation in salinity tolerance in E. affinis populations, allowing rapid adaptation to salinity changes during habitat invasions.

在选择压力作用下的基因座维持遗传变异，这一过程对环境变化条件下的适应性演化具有深远意义。在时空异质性生境中，环境间的杂合子优势（heterozygote advantage，即边缘超显性marginal overdominance）可维持非中性多态性（non-neutral polymorphism）；而不同条件下显性效应的有益反转（beneficial reversal of dominance）可进一步大幅增强这一维持效应。本研究以盐-淡水入侵性桡足类Eurytemora affinis为研究对象，针对其盐度耐受性相关的显性反转与边缘超显性现象开展了检验。我们设置了三类盐度梯度，分别比较了盐度近交系与淡水近交系杂交获得的F1后代（跨盐度杂交F1代，between-salinity F1 crosses），与同盐度近交系杂交获得的F1后代（同盐度杂交F1代，within-salinity F1 crosses）的存活率。实验结果表明，盐度耐受性相关的有益显性反转与边缘超显性现象均存在显著证据。针对显性反转现象的验证结果显示：在淡水环境下，跨盐度杂交F1代的存活率与淡水同盐度杂交F1代无显著差异；在海水环境下，其存活率则与海水同盐度杂交F1代无显著差异。针对边缘超显性现象的验证结果显示：在所有盐度梯度下，跨盐度杂交F1代的存活率均显著高于淡水同盐度杂交F1代与海水同盐度杂交F1代。本研究为环境变化相关的完全有益显性反转现象提供了罕见的实证案例。该机制可能在Eurytemora affinis种群的盐度耐受性遗传变异维持过程中发挥关键作用，使其在生境入侵过程中可快速适应盐度变化。