Department of Plant Sciences, University of Oxford, South Parks Road, Oxford, OX1 3RB, UK.
Department of Plant Sciences, University of Oxford, South Parks Road, Oxford, OX1 3RB, UK.
Curr Biol. 2019 Sep 23;29(18):3081-3086.e5. doi: 10.1016/j.cub.2019.07.059. Epub 2019 Sep 5.
One of the most long-standing and important mysteries in evolutionary biology is why biological diversity is so unevenly distributed across space and taxonomic lineages. Nowhere is this disparity more evident than in the multitude of rapid evolutionary radiations found on oceanic islands and mountain ranges across the globe [1-5]. The evolutionary processes driving these rapid diversification events remain unclear [6-8]. Recent genome-wide studies suggest that natural selection may be frequent during rapid evolutionary radiations, as inferred from work in cichlid fish [9], white-eye birds [10], new world lupins [11], and wild tomatoes [12]. However, whether frequent adaptive evolution is a general feature of rapid evolutionary radiations remains untested. Here we show that adaptive evolution is significantly more frequent in rapid evolutionary radiations compared to background levels in more slowly diversifying lineages. This result is consistent across a wide range of angiosperm lineages analyzed: 12 evolutionary radiations, which together comprise 1,377 described species, originating from some of the most biologically diverse systems on Earth. In addition, we find a significant negative correlation between population size and frequency of adaptive evolution in rapid evolutionary radiations. A possible explanation for this pattern is that more frequent adaptive evolution is at least partly driven by positive selection for advantageous mutations that compensate for the fixation of slightly deleterious mutations in smaller populations.
生物多样性在空间和分类群上的分布为何如此不均匀，这是进化生物学中最长期和最重要的奥秘之一。这种差异在全球海洋岛屿和山脉上发现的众多快速进化辐射中最为明显[1-5]。驱动这些快速多样化事件的进化过程仍不清楚[6-8]。最近的全基因组研究表明，自然选择在快速进化辐射中可能很频繁，这可以从慈鲷鱼[9]、白眼鸟[10]、新世界羽扇豆[11]和野生番茄[12]的研究中推断出来。然而，频繁的适应性进化是否是快速进化辐射的普遍特征仍未得到检验。在这里，我们表明适应性进化在快速进化辐射中比在进化较慢的谱系中的背景水平更为频繁。这一结果在分析的广泛的被子植物谱系中是一致的：12 个进化辐射，总共包括 1377 个已描述的物种，来自地球上一些生物多样性最丰富的系统。此外，我们发现快速进化辐射中种群大小和适应性进化频率之间存在显著的负相关。这种模式的一个可能解释是，更频繁的适应性进化至少部分是由有利突变的正选择驱动的，这些有利突变补偿了较小种群中轻微有害突变的固定。
