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）理应主要受细胞器与核基因组间互作的影响。然而，目前物种内核质不相容的明确案例寥寥无几。
本研究在一种草本植物不同分化种群的第一代杂交后代中，检测到显著的合子后生殖隔离，其适合度降幅最高可达92%。该生殖隔离主要体现在种子萌发与幼苗存活阶段，花粉活力仅表现出中等程度的生殖隔离效应。与存活相关的生殖隔离呈不对称性，且由核质不相容导致，其不相容强度与叶绿体遗传距离呈线性相关。这种核质不相容可能由进化速率较快的质体基因组所引发。
研究还在种子萌发阶段发现了显著的不对称生殖隔离，但该现象与核质不相容无关，提示其成因可能为胚乳不相容或母本-合子不相容。上述结果表明，核质不相容可推动物种内生殖隔离的形成，这意味着物种形成的初始速率可能受细胞器进化速率的影响。但其他类型的遗传不相容同样发挥着重要作用，这表明即便在物种形成早期，其过程也可能极为复杂，涉及多个基因与多种不相容机制。