Human‐mediated transport creates secondary contacts between genetically differentiated lineages, bringing new opportunities for gene exchange. When similar introductions occur in different places, they provide informally replicated experiments for studying hybridisation. We here examined 4,279 Mytilus mussels, sampled in Europe and genotyped with 77 ancestry‐informative markers. We identified a type of introduced mussels, called “dock mussels,” associated with port habitats and displaying a particular genetic signal of admixture between M. edulis and the Mediterranean lineage of M. galloprovincialis. These mussels exhibit similarities in their ancestry compositions, regardless of the local native genetic backgrounds and the distance separating colonised ports. We observed fine‐scale genetic shifts at the port entrance, at scales below natural dispersal distance. Such sharp clines do not fit with migration‐selection tension zone models, and instead suggest habitat choice and early‐stage adaptation to the port environment, possibly coupled with connectivity barriers. Variations in the spread and admixture patterns of dock mussels seem to be influenced by the local native genetic backgrounds encountered. We next examined departures from the average admixture rate at different loci, and compared human‐mediated admixture events, to naturally admixed populations and experimental crosses. When the same M. galloprovincialis background was involved, positive correlations in the departures of loci across locations were found; but when different backgrounds were involved, no or negative correlations were observed. While some observed positive correlations might be best explained by a shared history and saltatory colonisation, others are likely produced by parallel selective events. Altogether, genome‐wide effect of admixture seems repeatable and more dependent on genetic background than environmental context. Our results pave the way towards further genomic analyses of admixture, and monitoring of the spread of dock mussels both at large and at fine spacial scales.

中文翻译：

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复制的人为杂交揭示了海洋贻贝的平行混合模式。


人类介导的运输在遗传分化的谱系之间创造了二次接触，为基因交换带来了新的机会。当类似的介绍发生在不同的地方时，他们会提供非正式的重复实验来研究杂交。我们在这里检查了 4,279 只贻贝，这些贻贝在欧洲取样，并使用 77 个祖先信息标记进行了基因分型。我们发现了一种引入的贻贝类型，称为“码头贻贝”，与港口栖息地相关，并显示出M. edulis和地中海谱系M. galloprovincialis之间混合的特殊遗传信号。无论当地的原生遗传背景和殖民港口之间的距离如何，这些贻贝在祖先组成上都表现出相似性。我们在港口入口处观察到了精细尺度的遗传转变，其尺度低于自然扩散距离。这种尖锐的斜坡不符合迁移选择紧张区模型，而是表明栖息地选择和对港口环境的早期适应，可能还伴有连通性障碍。码头贻贝的传播和混合模式的变化似乎受到当地遗传背景的影响。接下来，我们检查了不同位点的平均混合率的偏差，并将人类介导的混合事件与自然混合群体和实验杂交进行比较。当涉及相同的M. galloprovincialis背景时，发现不同位置的基因座偏离呈正相关；但当涉及不同背景时，没有观察到相关性或负相关性。 虽然一些观察到的正相关性可能可以通过共同的历史和跳跃性殖民来最好地解释，但其他的可能是由平行的选择性事件产生的。总而言之，混合物的全基因组效应似乎是可重复的，并且更依赖于遗传背景而不是环境背景。我们的结果为进一步进行混合物基因组分析以及在大尺度和精细空间尺度上监测码头贻贝的传播铺平了道路。