Wade Michael J, Goodnight Charles J
Department of Biology, Indiana University, Bloomington, Indiana 47405, USA.
Evolution. 2006 Apr;60(4):643-59.
We report the findings of our theoretical investigation of the effect of random genetic drift on the covariance of identity-by-descent (ibd) of nuclear and cytoplasmic genes. The covariance in ibd measures of the degree to which cyto-nuclear gene combinations are heritable, that is, transmitted together from parents to offspring. We show how the mating system affects the covariance of ibd, a potentially important aspect of host-pathogen or host-symbiont coevolution. The magnitude of this covariance influences the degree to which the evolution of apparently neutral cytoplasmic genes, often used in molecular phylogenetics, might be influenced by selection acting on unlinked nuclear genes. To the extent that cyto-nuclear gene combinations are inherited together, genomic conflict is mitigated and intergenomic transfer it facilitated, because genes in both organelle and nuclear genomes share the same evolutionary fate. The covariance of ibd also affects the rate at which cyto-nuclear epistatic variance is converted to additive variance necessary for a response to selection. We find that conversion is biased in species with separate sexes, so that the increment of additive variance added to the nuclear genome exceeds that added to the cytoplasmic genome. As a result, the host might have an adaptive advantage in a coevolutionary arms race with vertically (maternally) transmitted pathogens. Similarly, the nuclear genome could be a source of compensatory mutations for its organellar genomes, as occurs in cytoplasmic male sterility in some plant species. We also discuss the possibility that adaptive cytoplasmic elements, such as favorable mitochondrial mutations or endosymbionts (e.g., Wolbachia), have the potential to release heritable nuclear variation as they sweep through a host population, supporting the view that cytoplasmic introgression plays an important role in adaptation and speciation.
我们报告了关于随机遗传漂变对核基因与细胞质基因的血缘同一性（ibd）协方差影响的理论研究结果。ibd协方差衡量了细胞核 - 细胞质基因组合的可遗传程度，即从亲代传递到子代的共同程度。我们展示了交配系统如何影响ibd协方差，这是宿主 - 病原体或宿主 - 共生体协同进化中一个潜在的重要方面。这种协方差的大小影响了在分子系统发育学中常用的看似中性的细胞质基因进化可能受到作用于非连锁核基因的选择影响的程度。在细胞核 - 细胞质基因组合一起遗传的程度上，基因组冲突得到缓解，基因组间的转移得到促进，因为细胞器基因组和核基因组中的基因共享相同的进化命运。ibd协方差还影响细胞核 - 细胞质上位性方差转化为对选择作出反应所需的加性方差的速率。我们发现，在具有两性分离的物种中，这种转化存在偏差，使得添加到核基因组的加性方差增量超过添加到细胞质基因组的增量。因此，宿主在与垂直（母系）传播的病原体的协同进化军备竞赛中可能具有适应性优势。同样，核基因组可能是其细胞器基因组补偿性突变的来源，就像一些植物物种中的细胞质雄性不育现象那样。我们还讨论了适应性细胞质元件，如有利的线粒体突变或内共生体（如沃尔巴克氏体），在席卷宿主种群时有可能释放可遗传的核变异的可能性，这支持了细胞质渗入在适应和物种形成中起重要作用的观点。
