Metazoan adaptation to global change relies on selection of standing genetic variation. Determining the extent to which this variation exists in natural populations, particularly for responses to simultaneous stressors, is essential to make accurate predictions for persistence in future conditions. Here, we identified the genetic variation enabling the copepod Acartia tonsa to adapt to experimental ocean warming, acidification, and combined ocean warming and acidification (OWA) over 25 generations of continual selection. Replicate populations showed a consistent polygenic response to each condition, targeting an array of adaptive mechanisms including cellular homeostasis, development, and stress response. We used a genome-wide covariance approach to partition the allelic changes into three categories: selection, drift and replicate-specific selection, and laboratory adaptation responses. The majority of allele frequency change in warming (57%) and OWA (63%) was driven by shared selection pressures across replicates, but this effect was weaker under acidification alone (20%). OWA and warming shared 37% of their response to selection but OWA and acidification shared just 1%, indicating that warming is the dominant driver of selection in OWA. Despite the dominance of warming, the interaction with acidification was still critical as the OWA selection response was highly synergistic with 47% of the allelic selection response unique from either individual treatment. These results disentangle how genomic targets of selection differ between single and multiple stressors and demonstrate the complexity that nonadditive multiple stressors will contribute to predictions of adaptation to complex environmental shifts caused by global change.

中文翻译：

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实验进化揭示了海洋桡足类适应海洋变暖和酸化的协同基因组机制

后生动物对全球变化的适应依赖于对长期遗传变异的选择。确定这种变异在自然种群中存在的程度，特别是对同时应激源的反应，对于准确预测未来条件下的持久性至关重要。在这里，我们确定了使桡足类成为可能的遗传变异桃花心木适应实验性海洋变暖、酸化以及海洋变暖和酸化相结合 (OWA) 超过 25 代的连续选择。复制种群对每种情况都表现出一致的多基因反应，针对一系列适应性机制，包括细胞稳态、发育和应激反应。我们使用全基因组协方差方法将等位基因变化分为三类：选择、漂移和复制特定选择，以及实验室适应反应。变暖 (57%) 和 OWA (63%) 中的大部分等位基因频率变化是由复制之间共享的选择压力驱动的，但这种影响在仅酸化 (20%) 的情况下较弱。OWA 和变暖分享了他们对选择的 37% 的反应，但 OWA 和酸化只分享了 1%，表明变暖是 OWA 选择的主要驱动因素。尽管变暖占主导地位，但与酸化的相互作用仍然至关重要，因为 OWA 选择反应与 47% 的等位基因选择反应具有高度协同作用，这两种选择反应均来自任一单独处理。这些结果阐明了选择的基因组目标在单个和多个压力源之间有何不同，并证明了非加性多重压力源将有助于预测适应全球变化引起的复杂环境变化的复杂性。