Adaptation to local climatic conditions is commonly found within species, but whether it involves the same intraspecific genomic variants is unknown. We studied this question in North American Arabidopsis lyrata, whose current distribution is shaped by post-glacial range expansion from two refugia, resulting in two distinct genetic clusters covering comparable climatic gradients. Using pooled whole-genome sequence data of 41 outcrossing populations, we identified loci associated with three niche-determining climatic variables in the two clusters and compared these outliers. Little evidence was found for parallelism in climate adaptation for single nucleotide polymorphisms (SNPs) and for genes with an accumulation of outlier SNPs. Significantly increased selection coefficients supported them as candidates of climate adaptation. However, the fraction of gene ontology (GO) terms shared between clusters was higher compared to outlier SNPs and outlier genes, suggesting that selection acts on similar pathways but not necessarily the same genes. Enriched GO terms involved responses to abiotic and biotic stress, circadian rhythm and development, with flower development and reproduction being among the most frequently detected. In line with GO enrichment, regulators of flowering time were detected as outlier genes. Our results suggest that while adaptation to environmental gradients on the genomic level are lineage-specific in A. lyrata, similar biological processes seem to be involved. Differential loss of standing genetic variation, probably driven by genetic drift, can in part account for the lack of parallel evolution on the genomic level.

中文翻译：

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对气候的谱系特异性适应涉及北美拟南芥的开花时间。

对当地气候条件的适应通常在物种中发现，但它是否涉及相同的种内基因组变异尚不清楚。我们在北美拟南芥中研究了这个问题，其目前的分布是由两个避难所的冰川后范围扩张形成的，导致两个不同的遗传簇覆盖相当的气候梯度。使用 41 个异交种群的汇总全基因组序列数据，我们确定了与两个集群中三个决定生态位的气候变量相关的基因座，并比较了这些异常值。对于单核苷酸多态性 (SNP) 和具有异常 SNP 积累的基因，几乎没有发现气候适应平行性的证据。显着增加的选择系数支持它们作为气候适应的候选者。然而，与离群 SNP 和离群基因相比，集群之间共享的基因本体 (GO) 术语的比例更高，这表明选择作用于相似的途径但不一定是相同的基因。丰富的 GO 术语涉及对非生物和生物胁迫、昼夜节律和发育的反应，其中花发育和繁殖是最常检测到的。与 GO 富集一致，开花时间的调节因子被检测为异常基因。我们的研究结果表明，虽然在基因组水平上对环境梯度的适应在 A. lyrata 中具有谱系特异性，但似乎涉及类似的生物学过程。可能由遗传漂移驱动的常设遗传变异的差异损失可以部分解释基因组水平上缺乏平行进化。