Species introductions promote secondary contacts between taxa with long histories of allopatric divergence. Anthropogenic contact zones thus offer valuable contrasts to speciation studies in natural systems where past spatial isolations may have been brief or intermittent. Investigations of anthropogenic hybridization are rare for marine animals, which have high fecundity and high dispersal ability, characteristics that contrast to most terrestrial animals. Genomic studies indicate that gene flow can still occur after millions of years of divergence, as illustrated by invasive mussels and tunicates. In this context, we highlight three issues: (i) the effects of high propagule pressure and demographic asymmetries on introgression directionality, (ii) the role of hybridization in preventing introduced species spread, and (iii) the importance of postzygotic barriers in maintaining reproductive isolation. Anthropogenic contact zones offer evolutionary biologists unprecedented large scale hybridization experiments. In addition to breaking the highly effective reproductive isolating barrier of spatial segregation, they allow researchers to explore unusual demographic contexts with strong asymmetries. The outcomes are diverse, from introgression swamping to strong barriers to gene flow, and lead to local containment or widespread invasion. These outcomes should not be neglected in management policies of marine invasive species.

This article is part of the theme issue ‘Towards the completion of speciation: the evolution of reproductive isolation beyond the first barriers’.

物种引入促进了具有长期异域分化历史的分类群之间的二次接触。因此，人为接触区与自然系统中过去的空间隔离可能是短暂或间歇性的物种形成研究形成了有价值的对比。海洋动物的人为杂交研究很少，其繁殖力强，传播能力强，与大多数陆生动物不同。基因组研究表明，经过数百万年的分化，基因流动仍然可以发生，如侵入性贻贝和被囊类动物所示。在这种情况下，我们强调三个问题：（i）高繁殖压力和人口不对称对渗入方向的影响，（ii）杂交在防止引入物种传播中的作用，(iii) 合子后屏障在维持生殖隔离方面的重要性。人为接触区为进化生物学家提供了前所未有的大规模杂交实验。除了打破空间隔离的高效生殖隔离障碍外，它们还允许研究人员探索具有强烈不对称性的异常人口背景。结果是多种多样的，从基因渗入淹没到基因流动的强大障碍，并导致局部遏制或广泛入侵。在海洋入侵物种的管理政策中不应忽视这些结果。除了打破空间隔离的高效生殖隔离障碍外，它们还允许研究人员探索具有强烈不对称性的异常人口背景。结果是多种多样的，从基因渗入淹没到基因流动的强大障碍，并导致局部遏制或广泛入侵。在海洋入侵物种的管理政策中不应忽视这些结果。除了打破空间隔离的高效生殖隔离障碍外，它们还允许研究人员探索具有强烈不对称性的异常人口背景。结果是多种多样的，从基因渗入淹没到基因流动的强大障碍，并导致局部遏制或广泛入侵。在海洋入侵物种的管理政策中不应忽视这些结果。

这篇文章是主题问题“走向物种形成的完成：超越第一道障碍的生殖隔离的进化”的一部分。