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根本途径。然而，基因流在物种形成中的重要性以及选择在这一过程中的作用还没有被很好地理解。基因流动对物种形成有两个截然相反的影响：1)基因流动是物种形成的明显障碍，因为它会破坏共同适应的基因组合，使种群同质化。最近的理论论文在一个四阶段模型中概念化了物种分化的进展，该模型是在基因流动的海洋中的分歧岛的四阶段模型。2)在某些情况下，分类群之间的基因流动可能会在一个被称为杂交物种形成的过程中触发新物种的形成。然而，杂交物种形成的令人信服的例子很少，特别是在动物中。我将研究基因流动对赫利柯乌斯物种形成的这两个影响。新热带螺旋藻蝴蝶长期以来一直是研究物种形成的模式系统，因为分类群的存在代表了从自由杂交的不同翼型的小种到偶尔在自然界中杂交的共域物种，到完全繁殖的孤立物种的整个物种形成连续体。随着第一个赫利柯乌斯基因组序列的公布，赫利柯乌斯现在提供了少数几个适合于全面研究物种中基因流重要性的系统之一。拟议的研究集中在三个赫利柯斯物种：H.levatus、H.pardalinus和H.Melpomene。我最近的工作证明了颜色模式基因在物种H.Melpomene和H.levatus之间的导入。白纹伊蚊在遗传上与细纹夜蛾有非常密切的亲缘关系，但两者是不同的物种，分布有很大重叠，行为也有已知的差异。初步数据表明，华支睾吸虫的基因组为杂交种，其基因组中含有镶嵌在华支睾吸虫背景中的梅尔波烯色型基因。我将收集全基因组序列数据，并对H.levatus及其两个可能的亲本物种H.pardalinus和H.Melpomene进行生态田间实验。这些由此产生的数据将使我们能够测试关于物种形成中基因流动的重要性和程度的假设。我有四个主要目标：1)我的分类样本将允许对物种形成与基因流动的分歧岛假说进行经验检验。2)我将从基因上定位导致H.levatus和H.pardalinus物种形成早期阶段的性状。3)实验设计将允许严格测试H.levatus是否是由杂交物种形成的。4)我将测试H.levatus是由来自不同小种的单个或多个导入事件形成的。专门化是塑造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.