Environmental variation experienced by a species across space and time can promote the maintenance of genetic diversity that may be adaptive in future global change conditions. Selection experiments have shown that purple sea urchin, Strongylocentrotus purpuratus, populations have adaptive genetic variation for surviving pH conditions at the "edge" (pH 7.5) of conditions experienced in nature. However, little is known about whether populations have genetic variation for surviving low-pH events beyond those currently experienced in nature or how variation in pH conditions affects organismal and genetic responses. Here, we quantified survival, growth, and allele frequency shifts in experimentally selected developing purple sea urchin larvae in static and variable conditions at three pH levels: pH 8.1 (control), pH 7.5 (edge-of-range), and pH 7.0 (extreme). Variable treatments recovered body size relative to static treatments, but resulted in higher mortality, suggesting a potential tradeoff between survival and growth under pH stress. However, within each pH level, allele frequency changes were overlapping between static and variable conditions, suggesting a shared genetic basis underlying survival to mean pH regardless of variability. In contrast, genetic responses to pH 7.5 (edge) versus pH 7.0 (extreme) conditions were distinct, indicating a unique genetic basis of survival. In addition, loci under selection were more likely to be in exonic regions than regulatory, indicating that selection targeted protein-coding variation. Loci under selection in variable pH 7.5 conditions, more similar to conditions periodically experienced in nature, performed functions related to lipid biosynthesis and metabolism, while loci under selection in static pH 7.0 conditions performed functions related to transmembrane and mitochondrial processes. While these results are promising in that purple sea urchin populations possess genetic variation for surviving extreme pH conditions not currently experienced in nature, they caution that increased acidification does not result in a linear response but elicits unique physiological stresses and survival mechanisms.

中文翻译：

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紫海胆幼虫对极端和可变 pH 条件的独特基因组和表型响应

一个物种跨越空间和时间经历的环境变化可以促进遗传多样性的维持，这种多样性可能在未来的全球变化条件下具有适应性。选择实验表明，紫海胆（Strongylocentrotus purpuratus）种群具有适应性遗传变异，可在自然界经历的条件的“边缘”（pH 7.5）下生存。然而，人们对种群是否具有在当前自然界经历的低 pH 值事件之外幸存的遗传变异或 pH 值条件的变化如何影响生物体和遗传反应知之甚少。在这里，我们量化了在三个 pH 水平的静态和可变条件下实验选择的发育中的紫海胆幼虫的存活、生长和等位基因频率变化：pH 8.1（对照）、pH 7.5（范围边缘）、和 pH 值 7.0（极端）。相对于静态处理，可变处理恢复了体型，但导致更高的死亡率，这表明在 pH 压力下生存和生长之间存在潜在的权衡。然而，在每个 pH 水平内，等位基因频率变化在静态和可变条件之间重叠，这表明无论变异性如何，均值 pH 的存活率是一个共同的遗传基础。相比之下，对 pH 7.5（边缘）和 pH 7.0（极端）条件的遗传反应是不同的，表明生存的独特遗传基础。此外，选择下的基因座更可能位于外显子区域而不是调节区，表明选择针对蛋白质编码变异。在可变 pH 7.5 条件下选择的位点，更类似于自然界中周期性经历的条件，执行与脂质生物合成和代谢相关的功能，而在静态 pH 7.0 条件下选择的位点执行与跨膜和线粒体过程相关的功能。虽然这些结果很有希望，因为紫海胆种群具有遗传变异，可以在目前自然界中没有经历过的极端 pH 条件下生存，但他们警告说，酸化增加​​不会导致线性反应，但会引发独特的生理压力和生存机制。