Combining hybrid zone analysis with genomic data is a promising approach to understanding the genomic basis of adaptive divergence. It allows for the identification of genomic regions underlying barriers to gene flow. It also provides insights into spatial patterns of allele frequency change, informing about the interplay between environmental factors, dispersal and selection. However, when only a single hybrid zone is analysed, it is difficult to separate patterns generated by selection from those resulting from chance. Therefore, it is beneficial to look for repeatable patterns across replicate hybrid zones in the same system. We applied this approach to the marine snail Littorina saxatilis, which contains two ecotypes, adapted to wave-exposed rocks vs. high-predation boulder fields. The existence of numerous hybrid zones between ecotypes offered the opportunity to test for the repeatability of genomic architectures and spatial patterns of divergence. We sampled and phenotyped snails from seven replicate hybrid zones on the Swedish west coast and genotyped them for thousands of single nucleotide polymorphisms. Shell shape and size showed parallel clines across all zones. Many genomic regions showing steep clines and/or high differentiation were shared among hybrid zones, consistent with a common evolutionary history and extensive gene flow between zones, and supporting the importance of these regions for divergence. In particular, we found that several large putative inversions contribute to divergence in all locations. Additionally, we found evidence for consistent displacement of clines from the boulder–rock transition. Our results demonstrate patterns of spatial variation that would not be accessible without continuous spatial sampling, a large genomic data set and replicate hybrid zones.

中文翻译：

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使用复制混合区来了解适应性分歧的基因组基础

将混合区分析与基因组数据相结合是理解适应性分化的基因组基础的一种很有前途的方法。它允许识别基因流动障碍的基因组区域。它还提供了对等位基因频率变化空间模式的洞察，告知环境因素、扩散和选择之间的相互作用。然而，当仅分析单个混合区域时，很难将选择产生的模式与偶然产生的模式区分开来。因此，在同一系统中的复制混合区域中寻找可重复的模式是有益的。我们将这种方法应用于海洋蜗牛Littorina saxatilis，其中包含两种生态型，适用于波浪暴露的岩石与高捕食性巨石场。生态型之间存在许多混合区，为测试基因组结构的可重复性和分歧的空间模式提供了机会。我们从瑞典西海岸的七个复制杂交区对蜗牛进行了采样和表型分析，并对它们进行了数千个单核苷酸多态性的基因分型。贝壳形状和大小在所有区域都显示出平行倾斜。许多基因组区域显示出陡峭的倾斜和/或高度分化，在杂交区域之间共享，这与区域之间的共同进化历史和广泛的基因流动相一致，并支持这些区域对分歧的重要性。特别是，我们发现几个大的推定倒置导致所有位置的分歧。此外，我们发现了从巨石-岩石过渡中倾斜的一致位移的证据。我们的结果表明，如果没有连续的空间采样、大型基因组数据集和复制混合区，就无法获得空间变异模式。