Human-driven translocations of species have diverse evolutionary consequences such as promoting hybridization between previously geographically isolated taxa. This is well illustrated by the solitary tunicate, Ciona robusta, native to the North East Pacific and introduced in the North East Atlantic. It is now co-occurring with its congener Ciona intestinalis in the English Channel, and C. roulei in the Mediterranean Sea. Despite their long allopatric divergence, first and second generation crosses showed a high hybridization success between the introduced and native taxa in the laboratory. However, previous genetic studies failed to provide evidence of recent hybridization between C. robusta and C. intestinalis in the wild. Using SNPs obtained from ddRAD-sequencing of 397 individuals from 26 populations, we further explored the genome-wide population structure of the native Ciona taxa. We first confirmed results documented in previous studies, notably (i) a chaotic genetic structure at regional scale, and (ii) a high genetic similarity between C. roulei and C. intestinalis, which is calling for further taxonomic investigation. More importantly, and unexpectedly, we also observed a genomic hotspot of long introgressed C. robusta tracts into C. intestinalis genomes at several locations of their contact zone. Both the genomic architecture of introgression, restricted to a 1.5 Mb region of chromosome 5, and its absence in allopatric populations suggest introgression is recent and occurred after the introduction of the non-native species. Overall, our study shows that anthropogenic hybridization can be effective in promoting introgression breakthroughs between species at a late stage of the speciation continuum.

中文翻译：

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两个海鞘之间的人为接触留下的渗入突破

人类驱动的物种易位具有不同的进化后果，例如促进以前地理上孤立的分类群之间的杂交。孤独的被囊动物Ciona robusta很好地说明了这一点，它原产于东北太平洋并被引入东北大西洋。它现在与英吉利海峡的同系物Ciona gutis和C . 地中海的肉饼。尽管它们的异域分歧很长，但第一代和第二代杂交在实验室中显示出引入和本地分类群之间的高度杂交成功。然而，以前的遗传研究未能提供最近C之间杂交的证据。罗布斯塔和C。野生肠杆菌。使用从 26 个种群的 397 个个体的 ddRAD 测序获得的 SNP，我们进一步探索了原生Ciona分类群的全基因组种群结构。我们首先确认了先前研究中记录的结果，特别是（i）区域范围内的混沌遗传结构，以及（ii）C之间的高度遗传相似性。柔莱和C . 肠道菌，这要求进一步的分类学调查。更重要的是，出乎意料的是，我们还观察到了长期渗入C的基因组热点。罗布斯塔大片进入C。肠杆菌基因组在其接触区的几个位置。基因渗入的基因组结构，仅限于 5 号染色体的 1.5 Mb 区域，以及在异域种群中的缺失表明基因渗入是最近的，并且发生在引入非本地物种之后。总体而言，我们的研究表明，人为杂交可有效促进物种形成连续体后期的物种间基因渗入突破。