Genetic basis of parallel local adaptation

生命进化的中心是新物种的起源。新物种的起源和现有物种的灭绝之间的平衡决定了目前的生物多样性水平。物种形成将微观进化与宏观进化联系起来，前者是由突变、遗传漂移和种群内自然选择引起的变化，后者是物种组合中随时间的变化。因此，如果我们要了解和管理生物多样性，物种形成是一个关键的研究过程。自达尔文以来，关于物种起源的研究已经有了很多，但仍有许多有待发现。这尤其适用于物种形成机制的遗传学。在这里，有许多新的机会，因为技术进步允许快速DNA测序和大规模确定基因类型，以及对这一过程的新见解。曾经，物种形成被认为需要一段时间的种群空间隔离，但现在有理论和经验研究表明，即使没有完全的地理隔离，适应当地环境也可能导致物种形成。这一过程的一个可能的例子是一种长春花属植物，Littorina saxatilis，它发现于欧洲各地的岩石海岸。在许多地区，存在两种密切接触的形式，一种适合于抵御波浪暴露，另一种适合抵抗螃蟹的捕食。这些形式仍然在它们的大多数基因组上交换基因，但我们之前已经证明，大约5%的基因组受到保护，不受基因交换的影响，可能是因为这些区域包含直接参与局部适应的基因。在本项目中，我们将在物种形成研究中提出两个普遍重要的问题：1.在Littorina物种形成的早期阶段，所涉及的基因组区域在欧洲不同地区是相同的，还是在地理上分离的区域中独立进化的形态？2.5%的分化区域是如何在基因组上分布的，是在几个大区块中还是在许多小片段中？此外，与该项目相关的一名博士生将测量不同外壳特征的选择，并询问这些外壳特征是否受到我们发现的正在选择的基因组区域的影响。我们将通过以各种方式扫描约克郡两种变种的基因组来解决这些问题，包括最近开发的高通量焦磷酸测序方法。然后，我们将在英国各地以及瑞典和西班牙的网站上测试候选基因和控制基因的差异。我们将在这些序列中开发标记，并结合学生进行的移植实验，对自然种群中的大样本进行基因分型，以测试标记之间以及标记与表型性状之间的关联。我们的数据将大大促进对Littorina系统和物种形成过程的理解，这是当地适应的结果。我们还将开发适用于其他物种形成模型系统的方法，并将在识别参与其他环境适应的基因方面具有价值，例如在保护生物学或农药耐药性管理方面。

At the centre of the evolution of life is the origin of new species. The balance between the origin of new species and the extinction of existing ones determines the current level of biological diversity. Speciation connects microevolution, changes due to mutation, genetic drift and natural selection within populations, to macroevolution, the variation through time in the mix of species. Therefore, speciation is a critical process to investigate if we are to understand and manage biological diversity. Much has been learned about the origin of species since Darwin but much remains to be found out. This applies particularly to the genetics of speciation mechanisms. Here, there are many new opportunities because of technical advances that allow rapid sequencing of DNA and large-scale determination of genotypes, as well as new insights into the process. At one time, speciation was thought to require a period of spatial separation of populations but now there are both theoretical and empirical studies suggesting that adaptation to local environments can lead towards speciation even without complete geographical isolation. One putative example of this process is a periwinkle, Littorina saxatilis, found on rocky shores around Europe. In many areas, two forms exist in close contact, one adapted to withstand wave exposure and the other to resist crab predation. These forms still exchange genes over most of their genomes but we have previously shown that about 5% of the genome is protected from gene exchange, presumably because these regions contain genes directly involved in local adaptation. In the present project, we will ask two questions of general importance in speciation research: 1. Are the genomic regions involved in the early stage of speciation seen in Littorina the same in different parts of Europe, or have the morphs evolved independently in geographically separated regions? 2. How is the 5% of differentiated regions distributed genomically, in a few large blocks or many small sections? In addition, a PhD student associated with the project will measure selection on different shell characters and ask whether these shell characters are influenced by the genomic regions that we find to be under selection. We will address these questions by initially scanning the genomes of the two morphs in Yorkshire in various ways, including a recently developed high-throughput pyrosequencing approach. We will then test divergence in candidate and control genes across the UK and also in Swedish and Spanish sites. We will develop markers in these sequences and genotype large samples from natural populations, in association with transplant experiments conducted by the student, to test for associations among markers and between markers and phenotypic traits. Our data will significantly advance understanding of the Littorina system and of the process of speciation as a consequence of local adaptation. We will also develop methods that will be applicable to other speciation model systems and will be valuable in identifying genes involved in adaptation in other circumstances, such as in conservation biology or the management of pesticide resistance.