Understanding the drivers and dynamics of diversification is a central topic in evolutionary biology. Here, we investigated the dynamics of diversification in the cichlid fish Astatotilapia burtoni that diverged along a lake-stream environmental gradient. Whole-genome and morphometric analyses revealed that divergent selection was essential at the early stages of diversification, but that periods in allopatry were likely involved towards the completion of speciation. While morphological differentiation was continuous, genomic differentiation was not, as shown by two clearly separated categories of genomic differentiation. Reproductive isolation increased along a continuum of genomic divergence, with a 'grey zone' of speciation at ~0.1% net nucleotide divergence. The quantification of the extent of (non-)parallelism in nine lake-stream population pairs from four cichlid species by means of multivariate analyses revealed one parallel axis of genomic and morphological differentiation among seven lake-stream systems. Finally, we found that parallelism was higher when ancestral lake populations were more similar.

中文翻译：

---

非洲慈鲷鱼沿生态梯度的多样化动态和（非）平行进化

了解多样化的驱动因素和动态是进化生物学的一个中心话题。在这里，我们研究了沿着湖流环境梯度分化的慈鲷鱼的多样化动态。全基因组和形态计量分析表明，在多样化的早期阶段，不同的选择是必不可少的，但异域选择的时期可能涉及到物种形成的完成。虽然形态分化是连续的，但基因组分化不是，正如两个明显分开的基因组分化类别所示。生殖隔离沿着基因组差异的连续体增加，物种形成的“灰色区域”在约 0.1% 的净核苷酸差异处。通过多变量分析对来自四个慈鲷物种的九个湖流种群对（非）平行程度的量化揭示了七个湖流系统之间基因组和形态分化的一个平行轴。最后，我们发现祖先湖泊种群越相似，平行度越高。