Department of Biology, Duke University, Durham, North Carolina.
Mol Ecol. 2019 Apr;28(7):1709-1729. doi: 10.1111/mec.14945. Epub 2019 Apr 13.
Gene flow is thought to impede genetic divergence and speciation by homogenizing genomes. Recent theory and research suggest that sufficiently strong divergent selection can overpower gene flow, leading to loci that are highly differentiated compared to others. However, there are also alternative explanations for this pattern. Independent evidence that loci in highly differentiated regions are under divergent selection would allow these explanations to be distinguished, but such evidence is scarce. Here, we present multiple lines of evidence that many of the highly divergent SNPs in a pair of sister morning glory species, Ipomoea cordatotriloba and I. lacunosa, are the result of divergent selection in the face of gene flow. We analysed a SNP data set across the genome to assess the amount of gene flow, resistance to introgression and patterns of selection on loci resistant to introgression. We show that differentiation between the two species is much lower in sympatry than in allopatry, consistent with interspecific gene flow in sympatry. Gene flow appears to be substantially greater from I. lacunosa to I. cordatotriloba than in the reverse direction, resulting in sympatric and allopatric I. cordatotriloba being substantially more different than sympatric and allopatric I. lacunosa. Many SNPs highly differentiated in allopatry have experienced divergent selection, and, despite gene flow in sympatry, resist homogenization in sympatry. Finally, five out of eight floral and inflorescence characteristics measured exhibit asymmetric convergence in sympatry. Consistent with the pattern of gene flow, I. cordatotriloba traits become much more like those of I. lacunosa than the reverse. Our investigation reveals the complex interplay between selection and gene flow that can occur during the early stages of speciation.
基因流被认为通过同质化基因组来阻碍遗传分歧和物种形成。最近的理论和研究表明，足够强大的分歧选择可以克服基因流，导致与其他基因座相比高度分化的基因座。然而，对于这种模式也有替代解释。有充分的证据表明，高度分化区域的基因座受到分歧选择的影响，这将允许区分这些解释，但这种证据很少。在这里，我们提出了多种证据表明，在一对姐妹喇叭花物种（Ipomoea cordatotriloba 和 I. lacunosa）中，许多高度分化的 SNP 是面对基因流时分歧选择的结果。我们分析了整个基因组的 SNP 数据集，以评估基因流的数量、抗渗入能力和对抗渗入的基因座的选择模式。我们表明，在同域中两种物种之间的分化比在异域中要低得多，这与同域中的种间基因流一致。基因流似乎从 I. lacunosa 到 I. cordatotriloba 要比在相反方向上大得多，导致同域和异域的 I. cordatotriloba 比同域和异域的 I. lacunosa 更不同。许多在异域中高度分化的 SNP 经历了分歧选择，尽管在同域中存在基因流，但在同域中仍能抵抗同质化。最后，在所测量的八个花和花序特征中有五个表现出同域的不对称趋同。与基因流模式一致，I. cordatotriloba 的特征变得更像 I. lacunosa 的特征，而不是相反。我们的调查揭示了在物种形成的早期阶段选择和基因流之间复杂的相互作用。
