The importance of gene flow in speciation of Heliconius

我建议使用现代高通量测序技术结合生态数据来解决物种形成研究中的一个主要问题：基因流动在物种形成中的重要性。物种形成是产生新物种生物多样性的基本途径。然而，基因流动在物种形成中的重要性以及选择在这一过程中的作用尚未得到很好的理解。基因流动可以对物种形成产生两种截然相反的影响：1)基因流动是物种形成的明显障碍，因为它往往会破坏共适应基因组合并使群体同质化。最近的理论论文将物种分化的过程概念化为基因流动海洋中的分化岛的四阶段模型。虽然很吸引人，但这种物种形成理论模型的经验支持仍然难以捉摸。在某些情况下，分类群之间的基因流动可能引发新物种的形成，这一过程被称为杂交物种形成。然而，很少有令人信服的杂交物种形成的例子，特别是在动物之间。我将研究基因流动对海螺物种形成的这两种影响。长期以来，新热带蝴蝶一直是研究物种形成的模型系统，因为存在代表整个物种形成连续体的分类群，从自由杂交的不同翅膀图案的种族，到偶尔在自然界杂交的同域物种，再到完全生殖隔离的物种。随着第一个Heliconius基因组序列的发表，Heliconius现在提供了适合全面研究物种形成中基因流动重要性的少数系统之一。拟研究的主要对象为三种Heliconius: H. elevatus、H. pardalinus和H. melpomene。我最近的工作已经证明了H. melpomene和H. elevatus物种之间的颜色模式基因的渗入。在遗传上，海拔猿人与帕达林猿人关系密切，但两者是截然不同的物种，分布在很大程度上重叠，并且已知在行为上存在差异。初步数据表明，直立猿人的基因组具有杂交起源，包括嵌入在直立猿人背景中的H. melpomene颜色模式基因。我将收集H. elevatus的全基因组序列数据，并对H. pardalinus和H. melpomene这两个假定的亲本种进行生态野外实验。这些结果数据将使我们能够检验关于基因流动在物种形成中的重要性和程度的假设。我有四个主要目标：1)我的分类群取样将允许对物种形成与基因流动的分歧岛假说进行实证检验。2)我将绘制H. elevatus和H. pardalinus物种形成早期阶段的遗传图谱。(3)实验设计将允许严格的测试，以确定海拔杉是否是杂交物种形成的结果。4)我将检验elevatus是由一个单一的还是由不同种族的H. melpomene的多个渗入事件形成的。物种形成是形成所有生态系统的基本进化过程，这项研究的发现将大大增加我们对新物种形成背后的基因组过程的理解。

I propose to use modern high-throughput sequencing technologies coupled with ecological data to address one of the major questions in speciation research: the importance of gene flow in speciation. Speciation is the fundamental route to the generation of new species biodiversity. However, the importance of gene flow in speciation, and the role of selection in this process are not well understood. Gene flow can have two diametrically opposite influences on speciation:1) Gene flow is an obvious hindrance to speciation as it will tend to break down co-adapted gene combinations and homogenize populations. Recent theoretical papers conceptualise the progress of species divergence in a four-phase model of islands of divergence amidst a sea of gene flow. While appealing, empirical support of this theoretical model of speciation remains elusive.2) In some cases gene flow between taxa could trigger the formation of new species in a process known as hybrid speciation. However, there are few convincing examples of hybrid speciation, particularly among animals.I will investigate these two effects of gene flow on speciation in Heliconius. Neotropical Heliconius butterflies have long been a model system for studying speciation owing to the the presence of taxa representing the entire speciation continuum from freely hybridizing races differing in wing patterning, through sympatric species that occasionally hybridize in nature, to fully reproductively isolated species. With the publication of the first Heliconius genome sequence, Heliconius now provides one of the few systems suited for comprehensively studying the importance of gene flow in speciation.The proposed research focuses on three Heliconius species: H. elevatus, H. pardalinus and H. melpomene. My recent work has demonstrated the introgression of colour pattern genes between the species H. melpomene and H. elevatus. H. elevatus is genetically very closely related to H. pardalinus, but the two are distinct species with largely overlapping distributions and known differences in behaviour. Preliminary data suggest that the genome of H. elevatus is of hybrid origin, comprising H. melpomene colour pattern genes embedded in a background of H. pardalinus. I will gather whole genome sequence data and carry out ecological field experiments on races of H. elevatus and its two putative parental species, H. pardalinus and H. melpomene. These resulting data will allow us to test hypotheses on the importance and extent of gene flow in speciation. I have four main objectives:1) My taxon sampling will allow empirical testing of the islands-of-divergence hypothesis of speciation with gene flow.2) I will genetically map traits responsible for the early stages of speciation in H. elevatus and H. pardalinus.3) The experimental design will allow rigorous testing of whether H. elevatus formed as a result of hybrid speciation.4) I will test whether H. elevatus was formed from a single or multiple introgression events from different races of H. melpomene.Speciation is a basic evolutionary process that shapes all ecosystems, and the findings of this research will add significantly to our understanding of the genomic processes underlying the formation of new species.