Does gene flow between species play a role in island adaptive radiations?

在岛屿上的“爆炸性”适应性辐射期间，物种的表型和生态适应的极快速度仍然是最耐人寻味的进化现象之一。岛屿种群的低遗传多样性可能会成为快速适应变化的障碍，因为自然选择需要遗传变异来进行选择。亲缘关系密切的物种的杂交和种间基因流动可能提供自然选择所需的遗传变异。尽管多个种间杂交已知，但几乎没有证据表明它可能在适应性进化中发挥作用。我们将使用夏威夷特有植物Schiedea属(石竹科)来推断种间基因流在适应性辐射中的作用。该属是最近植物中最令人印象深刻的适应性辐射之一，因为它进化了非常多样化的形态(从藤本植物到多年生草本植物和木本灌木丛)，并在短短数百万年内殖民了广泛的生态位。为了评估物种间的基因流在Schiedea的适应性辐射中的作用，我们将(I)估计有多大比例的基因显示出种间渐渗的证据，以及(Ii)测试正选择是否可能导致基因在几个物种之间的传播。一个积极选择的等位基因在几个物种中的传播应该会扭曲该基因的系统发育，使其与其他不受种间渐渗影响的基因的系统发育不相容。我们将估计裂片藻属系统发育发生扭曲的基因的比例，并测试这种扭曲是否可能是由于优势等位基因在几个物种中的传播造成的。

The extremely fast rate of phenotypic and ecological adaptation of species during 'explosive' adaptive radiations on islands remains one of the most intriguing evolutionary phenomena. Low genetic diversity of island populations may present an obstacle for fast adaptive changes, as natural selection needs genetic variation from which to select. Hybridisation of closely related species and interspecific gene flow may provide the genetic variation needed for natural selection. Although multiple cases of interspecific hybridisation are known, there is little evidence that it may play a role in adaptive evolution. We will use the Hawaiian endemic plant genus Schiedea (Caryophyllaceae) to infer the role of interspecific gene flow in adaptive radiation. This genus presents one of the most impressive recent adaptive radiations in plants, as it has evolved very diverse morphological forms (ranging from vines to perennial herbes and woody bushes) and colonised a wide range of ecological niches in just a few million years. To assess the role of gene flow between the species during adaptive radiation in Schiedea we will (i) estimate what proportion of genes show evidence for interspecific introgression, and (ii) test whether positive selection could have caused the spread of genes across several species. The spread of a positively selected allele across several species should distort the phylogeny of that gene, making it incompatible with the phylogenies of other genes not affected by interspecific introgression. We will estimate the proportion of genes with distorted phylogenies in genus Schiedea and will test whether the distortion could have been caused by the spread of advantageous alleles across several species.