Pseudogamy is a reproductive system in which females rely on the sperm of males to activate their oocytes, generally parasitizing males of other species, but do not use the sperm DNA. The nematode Mesorhabditis belari uses a specific form of pseudogamy, where females produce their own males as a source of sperm. Males develop from rare eggs with true fertilization, while females arise by gynogenesis. Males thus do not contribute their genome to the female offspring. Here, we explored the diversity of reproductive mode within the Mesorhabditis genus and addressed species barriers in pseudogamous species. To this end, we established a collection of over 60 Mesorhabditis strains from soil and rotting vegetal matter. We found that males from pseudogamous species displayed a reduced size of their body, male tail and sperm cells compared to males of sexual Mesorhabditis species, as expected for males that face little competition. Using rDNA sequences and crosses, we could define 11 auto-pseudogamous biological species, with closely related species pairs and a possible single origin of pseudogamy in the Mesorhabditis genus. Most crosses between males and females of different species did not even produce female progeny. This surprising species barrier in pseudogamous egg activation was pre or postcopulatory depending on the species pair. In the latter case, when hybrid embryos were produced, most arrested before the first embryonic cell division. Hybrid incompatibility between auto-pseudogamous species was due to defective interaction between sperm and oocyte as well as defective reconstitution of zygotic centrosomes. We established a collection of sexual and pseudo-sexual species which offer an ideal framework to explore the origin and consequences of transition to asexuality. Our results demonstrate that speciation occurs in the pseudogamous state. Whereas genomic conflicts are responsible for hybrid incompatibility in sexual species, we here reveal that centrosomes constitute key organelles in the establishment of species barrier.

中文翻译：

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线粒体线虫自假性物种的多样性和杂种不相容性。

假配偶是一种生殖系统，雌性依靠雄性精子激活卵母细胞，通常寄生其他物种的雄性卵，但不使用精子DNA。线虫belari线虫使用一种特定的伪配偶形式，雌性产生自己的雄性作为精子的来源。雄性由真正受精的稀有卵发育而来，雌性则由雌核发育而产生。因此，雄性对雌性后代没有贡献其基因组。在这里，我们探讨了中层皮炎属内生殖方式的多样性，并解决了假配偶物种中的种质障碍。为此，我们从土壤和腐烂的植物中建立了60多种中膜炎菌株。我们发现，来自一夫一妻制物种的雄性的体型减小了，雄性尾巴和精子细胞与有性中皮炎的雄性相比，男性面临的竞争很少。使用rDNA序列和杂交，我们可以定义11种自假生物物种，具有密切相关的物种对，并可能在中皮膜炎属中有单一配子起源。不同物种的雄性和雌性之间的大多数杂交甚至没有产生雌性后代。假配偶卵活化中这种令人惊讶的物种障碍是交配之前或交配后的，取决于物种对。在后一种情况下，当产生杂交胚胎时，大多数在第一次胚胎细胞分裂之前就被捕了。自身假性物种之间的杂合不相容性是由于精子与卵母细胞之间相互作用的缺陷以及合子中心体的重组缺陷。我们建立了一个性和伪性物种的集合，它们提供了一个理想的框架来探索无性恋的起源和后果。我们的结果表明物种形成于一夫一妻制状态。尽管基因组冲突是性物种中杂种不相容的原因，但我们在这里揭示了中心体是建立物种屏障的关键细胞器。