Data from: Cytonuclear incompatibility contributes to the early stages of speciation

Genetic incompatibility is a hallmark of speciation. Cytonuclear incompatibilities are proposed to be among the first genetic barriers to arise during speciation. Accordingly, reproductive isolation (RI) within species should be heavily influenced by interactions between the organelle and nuclear genomes. However, there are few clear examples of cytonuclear incompatibility within a species. Here, we show substantial postzygotic RI in first-generation hybrids between differentiated populations of an herbaceous plant (up to 92% reduction in fitness). RI was primarily due to germination and survival, with moderate RI for pollen viability. RI for survival was asymmetric and caused by cytonuclear incompatibility, with the strength of incompatibility linearly related to chloroplast genetic distance. This cytonuclear incompatibility may be the result of a rapidly evolving plastid genome. Substantial asymmetric RI was also found for germination, but was not associated with cytonuclear incompatibility, indicating endosperm or maternal-zygote incompatibilities. These results demonstrate that cytonuclear incompatibility contributes to RI within species, suggesting that initial rates of speciation could be influenced by rates of organelle evolution. However, other genetic incompatibilities are equally important, indicating that even at early stages, speciation can be a complex process involving multiple genes and incompatibilities.遗传不相容（genetic incompatibility）是物种形成的标志性特征。核质不相容（cytonuclear incompatibility）被认为是物种形成过程中最早出现的遗传障碍之一。据此，物种内的生殖隔离（reproductive isolation，RI）应在很大程度上受细胞器基因组与核基因组相互作用的影响。然而，物种内核质不相容的明确案例寥寥无几。本研究显示，一种草本植物不同分化种群间的第一代杂种存在显著的合子后生殖隔离（postzygotic reproductive isolation），其适合度降幅最高可达92%。该生殖隔离主要影响种子萌发与幼苗存活，对花粉活力仅造成中等程度的隔离效应。存活相关的生殖隔离呈不对称性，且由核质不相容所致，不相容的强度与叶绿体遗传距离呈线性相关。该核质不相容可能由快速进化的质体基因组所导致。种子萌发环节同样存在显著的不对称生殖隔离，但该隔离与核质不相容无关，提示其成因可能为胚乳（endosperm）或母本-合子不相容（maternal-zygote incompatibility）。上述结果表明，核质不相容可促成物种内的生殖隔离，这意味着物种形成的初始速率可能受细胞器基因组进化速率的影响。但其他类型的遗传不相容同样关键，这表明即便在物种形成的早期阶段，其过程也可涉及多个基因与多种不相容机制，是一个复杂的过程。