Barnard-Kubow Karen B, So Nina, Galloway Laura F
Department of Biology, University of Virginia, Charlottesville, Virginia, 22904.
Current Address: Doctoral Program in Neurobiology and Behavior, Columbia University, New York, NY, 10027.
Evolution. 2016 Dec;70(12):2752-2766. doi: 10.1111/evo.13075. Epub 2016 Oct 18.
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.
遗传不亲和性是物种形成的一个标志。细胞核质不亲和性被认为是物种形成过程中最早出现的遗传障碍之一。因此，物种内的生殖隔离（RI）应该受到细胞器基因组与核基因组之间相互作用的严重影响。然而，在一个物种内几乎没有细胞核质不亲和性的明确例子。在这里，我们展示了一种草本植物不同分化种群之间第一代杂交种中显著的合子后生殖隔离（高达92%的适合度降低）。生殖隔离主要归因于萌发和存活，花粉活力的生殖隔离程度适中。存活的生殖隔离是不对称的，由细胞核质不亲和性导致，不亲和性的强度与叶绿体遗传距离呈线性相关。这种细胞核质不亲和性可能是叶绿体基因组快速进化的结果。在萌发方面也发现了显著的不对称生殖隔离，但与细胞核质不亲和性无关，表明存在胚乳或母本 - 合子不亲和性。这些结果表明细胞核质不亲和性对物种内的生殖隔离有贡献，这表明物种形成的初始速率可能受到细胞器进化速率的影响。然而，其他遗传不亲和性同样重要，这表明即使在早期阶段，物种形成也可能是一个涉及多个基因和不亲和性的复杂过程。
