Independent or parallel evolution of similar traits is key to understanding the genetics and limitations of adaptation. Adaptation from the same genetic changes in different populations defines parallel evolution. Such genetic changes can derive from standing ancestral variation or de novo mutations and excludes instances of adaptive introgression. In this issue of Molecular Ecology, Walden et al.(2020) investigate the scale of parallel climate adaptation from standing genetic variation between two North American Arabidopsis lyrata lineages, each formed by a distinct evolutionary history during the last glacial cycle. By identifying adaptive variants correlated with three ecologically significant climatic gradients, they show that instead of the same genetic variants or even genes, parallel evolution is only observed at the level of biological processes. The evolution of independent adaptive variants to climate in two genetically close lineages is explained by their different post-glacial demographic histories. Separate glacial refugia and strong population bottlenecks were probably sufficient to change the landscape of shared allele frequencies, hindering the possibility of parallel evolution.

中文翻译：

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在第35个平行线以上对气候的并行适应。

相似性状的独立或平行进化是了解适应的遗传学和局限性的关键。来自不同种群的相同遗传变化的适应作用定义了平行进化。此类遗传变化可源自常规祖传变异或从头突变，并且不包括适应性渗入的情况。在本期《分子生态学》（Molecular Ecology）中，Walden等人（2020）从两个北美拟南芥lyrata世系之间的站立遗传变异研究了平行气候适应的规模，这两个世系由上一个冰川周期的独特进化史形成。通过识别与三个具有生态意义的气候梯度相关的适应性变体，他们表明，与相同的遗传变体甚至基因相比，平行进化仅在生物过程的水平上观察到。在两个遗传学上相近的世系中，气候的独立适应性变体的演化可以通过它们在冰川后的不同人口统计学历史来解释。单独的冰川避难所和强大的种群瓶颈可能足以改变共有等位基因频率的分布，从而阻碍了平行进化的可能性。