Ashworth Laboratories, Institute of Evolutionary Biology, University of Edinburgh, Edinburgh, UK.
Ashworth Laboratories, Edinburgh Genomics, Edinburgh, UK.
Mol Ecol. 2018 Mar;27(5):1214-1228. doi: 10.1111/mec.14426. Epub 2017 Dec 9.
Within the plant kingdom, many genera contain sister lineages with contrasting outcrossing and inbreeding mating systems that are known to hybridize. The evolutionary fate of these sister lineages is likely to be influenced by the extent to which they exchange genes. We measured gene flow between outcrossing Geum rivale and selfing Geum urbanum, sister species that hybridize in contemporary populations. We generated and used a draft genome of G. urbanum to develop dd-RAD data scorable in both species. Coalescent analysis of RAD data from allopatric populations indicated that the species diverged 2-3 Mya, and that historical gene flow between them was extremely low (1 migrant every 25 generations). Comparison of genetic divergence between species in sympatry and allopatry, together with an analysis of allele frequencies in potential parental and hybrid populations, provided no evidence of contemporary introgression in sympatric populations. Cluster- and species-specific marker analyses revealed that, apart from four early-generation hybrids, individuals in sympatric populations fell into two genetically distinct groups that corresponded exactly to their morphological species classification with maximum individual admixture estimates of only 1-3%. However, we did observe joint segregation of four putatively introgressed SNPs across two scaffolds in the G. urbanum population that was associated with significant morphological variation, interpreted as tentative evidence for rare, recent interspecific gene flow. Overall, our results indicate that despite the presence of hybrids in contemporary populations, genetic exchange between G. rivale and G. urbanum has been extremely limited throughout their evolutionary history.
在植物界中，许多属包含具有相反异交和自交交配系统的姐妹谱系，这些系统已知会杂交。这些姐妹谱系的进化命运很可能受到它们交换基因的程度的影响。我们测量了异交的 Geum rivale 和自交的 Geum urbanum 之间的基因流动，这是在当代种群中杂交的姐妹种。我们生成并使用了 G. urbanum 的草图基因组来开发可在两个物种中评分的 dd-RAD 数据。来自异域种群的 RAD 数据的合并分析表明，这些物种在 2-3 Mya 前分化，并且它们之间的历史基因流动非常低（每 25 代有 1 个移民）。同域和异域种群中物种间遗传分化的比较，以及潜在亲本和杂交种群中等位基因频率的分析，都没有提供同域种群中当代渐渗的证据。聚类和物种特异性标记分析表明，除了四个早期世代的杂种外，同域种群中的个体分为两个遗传上明显不同的群体，这与它们的形态物种分类完全对应，最大个体混合估计值仅为 1-3%。然而，我们确实观察到四个假定渐渗的 SNP 在 G. urbanum 种群中跨越两个支架的联合分离，这与显著的形态变异有关，被解释为罕见的、近期种间基因流动的初步证据。总体而言，我们的结果表明，尽管当代种群中存在杂种，但 G. rivale 和 G. urbanum 之间的遗传交换在其进化历史中一直非常有限。
