Beyond speciation genes: Is post-zygotic isolation maintaining species insympatry?

新物种如何出现并持续存在被认为是“神秘中的神秘”（达尔文，1859）。虽然我们已经走了很长的路来揭示多样化的一些秘密，但同域性中的物种形成现象仍然令人困惑。哈姆雷特是一组密切相关的珊瑚礁鱼类，是研究这一现象的绝佳系统，因为它们最近的多样化，18种不同物种中有多达9种共同出现在同一个珊瑚礁上。哈姆雷特种之间最显著的差异在于它们的颜色模式，这在通过基于视觉的选择性交配的生殖隔离中起着核心作用。然而，成功的产卵事件之间的哈姆雷特物种可以发生在自然种群。这些罕见的杂交种是可行的，而它们在野外或实验室中的适应性在很大程度上仍然未知。然而，不同的哈姆雷特物种坚持共域没有受精障碍和不完全的配偶选择，后合子生殖障碍必须存在。这种障碍可以由（表观）遗传不相容性驱动，导致异常的表观遗传沉默或过表达，转座因子的重新激活和基因组不稳定性，这些都是紧密相连的。即使在低流行率下，这些机制也会导致杂交适合度降低，因此对维持不同物种至关重要。我将解决这一现象与三个相互关联的目标，旨在（一）评估杂交种的相对健身，（二）表征哈姆雷特物种之间的功能分化（DNA甲基化和基因表达），（三）确定后合子障碍维持不同的物种在同域。哈姆雷特是一个强大的模型来研究这些目标，不仅因为他们的生态进化历史和可用的基因组资源，但也因为他们的交配策略。作为同时雌雄同体，小村交替性别角色在一个产卵事件。这使我们能够在解决合子后障碍时描绘性别的影响，这很重要，因为卵子和精子是RNA和DNA甲基化遗传的非常不同的载体。两者合计，该项目将提供无与伦比的洞察杂交不相容性，并探讨高基因流下的海洋物种形成的合子后障碍。

How new species emerge and persist is considered “that mystery of mysteries” (Darwin 1859). While we have come a long way to uncover some of the secrets of diversification, the phenomenon of speciation in sympatry remains puzzling. The hamlets, a group of closely related coral reef fishes, are an excellent system to study this phenomenon, because of their recent diversification with as many as 9 out of 18 different species co-occurring on the same reef. The most notable difference between hamlet species lies in their color pattern, which plays a central role in reproductive isolation via visual based assortative mating. Yet, successful spawning events between hamlet species can occur in natural populations. These rare hybrids are viable, while their fitness in the wild or the laboratory remains largely unknown. However, for distinct hamlet species to persist in sympatry with no fertilization barriers and incomplete mate choice, post-zygotic reproductive barriers must exist. Such barriers can be driven by (epi)genetic incompatibilities resulting in aberrant epigenetic silencing or overexpression, the reactivation of transposable elements and genome instability, which are tightly interlinked. Even at low prevalence, these mechanisms would result in decreased hybrid fitness and thus be critical to maintaining distinct species. I will address this phenomenon with three interlinked objectives aiming at (I) assessing the relative fitness of hybrids, (II) characterizing the functional differentiation (DNA methylation and gene expression) between hamlet species, and (III) identifying post-zygotic barriers maintaining distinct species in sympatry. Hamlets are a powerful model to investigate these objectives not only because of their eco-evolutionary history and the genomic resources available, but also because of their mating strategy. As simultaneous hermaphrodites, hamlets alternate sex roles during one spawning event. This allows us to delineate the effect of sex when addressing post-zygotic barriers, which is important as egg and sperm are very different vectors for the inheritance of RNA and DNA methylation. Taken together, this project will provide unparalleled insights into hybrid incompatibilities and explore the post-zygotic barriers underlying marine speciation under high gene flow.