Research on the genetics of invasive species often focuses on patterns of genetic diversity and population structure within the introduced range. However, a growing body of literature is demonstrating the need to study how native genotypes affect both ecological and evolutionary mechanisms within the introduced range. Here, we used genotyping‐by‐sequencing to study both native and introduced ranges of the amphiatlantic marine invertebrate Ciona intestinalis. A previous study using microsatellites analysed samples collected along the Swedish west coast and showed the presence of genetically distinct lineages in deep and shallow waters. Using 1,653 single nucleotide polymorphisms (SNPs) from newly collected samples (285 individuals), we first confirmed the presence of this depth‐defined genomic divergence along the Swedish coast. We then used approximate Bayesian computation to infer the historical relationship among sites from the North Sea, the English Channel and the northwest Atlantic and found evidence of ancestral divergence between individuals from deep waters off Sweden and individuals from the English Channel. This divergence was followed by a secondary contact that led to a genetic admixture between the ancestral populations (i.e., deep Sweden and English Channel), which originated the genotypes found in shallow Sweden. We then revealed that the colonization of C. intestinalis in the northwest Atlantic was as a result of an admixture between shallow Sweden and the English Channel genotypes across the introduced range. Our results showed the presence of both past and recent genetic admixture events that together may have promoted the successful colonizations of C. intestinalis. Our study suggests that secondary contacts potentially reshape the evolutionary trajectories of invasive species through the promotion of intraspecific hybridization and by altering both colonization patterns and their ecological effects in the introduced range.

中文翻译：

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次生接触和遗传混合物形成了两栖表层底栖无脊椎动物的定殖。

对入侵物种的遗传学研究通常侧重于引入范围内的遗传多样性模式和种群结构。然而，越来越多的文献表明有必要研究本地基因型如何影响引入范围内的生态和进化机制。在这里，我们使用测序基因分型来研究两栖大西洋海洋无脊椎动物海鞘的本地和引入范围。之前的一项使用微卫星的研究分析了沿瑞典西海岸收集的样本，结果表明深水和浅水区域存在遗传上不同的谱系。利用新收集的样本（285 个个体）中的 1,653 个单核苷酸多态性 (SNP)，我们首先确认了瑞典海岸沿线存在这种深度定义的基因组分歧。然后，我们使用近似贝叶斯计算来推断北海、英吉利海峡和西北大西洋遗址之间的历史关系，并发现来自瑞典深水区的个体和来自英吉利海峡的个体之间祖先分歧的证据。这种分歧之后是二次接触，导致祖先群体（即瑞典深海和英吉利海峡）之间的基因混合，从而起源于瑞典浅海发现的基因型。然后我们发现，肠棒状杆菌在西北大西洋的定殖是瑞典浅海区和英吉利海峡基因型在引入范围内混合的结果。我们的结果表明过去和最近的基因混合事件的存在可能共同促进了肠弯曲杆菌的成功定殖。我们的研究表明，二次接触可能通过促进种内杂交并改变引入范围内的殖民模式及其生态效应来重塑入侵物种的进化轨迹。