Evolutionary Dynamics Underlying Species Diversification

生物多样性在许多不同的尺度上都很明显，从种群中个体之间的差异到不同物种和其他分类类群之间的差异。进化生物学的一个主要目标是了解这些不同水平的变异之间的联系。所有的分类差异最终都可以追溯到种群中个体之间的遗传差异。然而，目前还不清楚这种遗传变异是如何导致不同表型随着时间的推移而演变的。例如，是什么导致种群分化并形成新物种，是什么限制了进化可能走的道路？回答这些问题一直很困难，因为导致物种差异的基因往往定义不清，也因为自然选择和遗传漂移等过程导致这些基因的特定版本或等位基因固定的细节尚不清楚。分子和进化遗传学的最新进展使首次以完全整合的方式解决这些问题成为可能。特别是，控制物种间表型差异的基因现在可以在从单个家系到种群和物种的一系列尺度上进行分离和研究。对于相距几个碱基到几百万个碱基的DNA序列，可以很容易地确定这些基因及其周围的变异。通过测量这种遗传变异如何分布在不同的地理范围和分离时期，可以估计基因从一个地方流动到另一个地方的速度，以及自然选择或随机波动(遗传漂移)对进化变化的影响程度。此外，可以通过将这些方法并行应用于几个基因来研究遗传交互作用。通过整合所有这些信息，可以构建和评估从个体到物种层面的模型，为理解多样性的演变提供一个连贯的框架。采用这种综合方法需要一个具有几个特征的生物系统。它应该具有发达的分子遗传学，在物种内和物种之间表现出遗传上易于处理的多样性，便于实地研究，并允许研究多个基因之间的相互作用。目前满足所有这些要求的为数不多的系统之一是金鱼草(骁龙)的花色变化。我们建议利用这一系统在时间、空间和遗传尺度上研究多样性的演化。这将涉及到围绕三个关键的花色基因的变异，这三个基因被认为是物种间差异的重要因素。在最小的时间尺度上，我们将在物种相遇和杂交的区域确定基因从一代到下一代的流动模式。这将允许在田间测量不同基因组合的适合度(即后代数量)。在中等尺度上，我们将调查一系列遗传标记的波动，以给出对基因流动和自然选择强度的长期估计。在最大的时间尺度上，我们将比较几个物种中每个基因的DNA序列和功能的差异。这应该会揭示出不同的等位基因是如何出现的，以及它们传播的速度有多快。将为每个分析尺度开发适当的理论和模型。然后，这些将被整合在一起，形成一个从个体到物种层面的全面框架。除了更深入地了解生物多样性的起源，该项目还将为几名年轻的研究人员提供多学科培训，并促进对进化和发育生物学的更全面的理解。

Biological diversity is evident at many different scales, from variation between individuals in a population to the distinctions between different species and other taxonomic groupings. A major aim of evolutionary biology is to understand the connections between these different levels of variation. All taxonomic distinctions ultimately trace back to genetic differences between individuals in populations. However, it is unclear how such genetic variation has led to the evolution of diverse phenotypes over time. What, for example, causes populations to diverge and form new species and what constrains the paths that evolution may take? Answering such questions has been difficult because the genes underlying species differences are often poorly defined and because the details by which processes like natural selection and genetic drift have led to fixation of particular versions or alleles of these genes remain unclear. Recent advances in molecular and evolutionary genetics make it possible to address these issues in a fully integrated way for the first time. In particular, genes controlling phenotypic differences between species can now be isolated and studied at a whole series of scales, from individual pedigrees to populations and species. The variation in and around these genes can be readily determined for DNA sequences that are few bases to millions of bases apart. By measuring how such genetic variation is distributed over different geographical ranges and periods of separation, estimates can be obtained for the rates at which genes flow from place to place, and the extent to which natural selection or random fluctuations (genetic drift) influence evolutionary change. Moreover, genetic interactions can be studied by applying these methods to several genes in parallel. By integrating all of this information, models from the individual to species level may be constructed and evaluated, providing a coherent framework for understanding the evolution of diversity. Taking such an integrated approach requires a biological system with several features. It should have well developed molecular genetics, exhibit genetically tractable diversity within and between species, be convenient for field studies and allow interactions between multiple genes to be studied. One of the few systems that currently meets all of these requirements is flower colour variation in Antirrhinum (snapdragon). We propose to exploit this system to study the evolution of diversity at a range of temporal, spatial and genetic scales. This will involve characterising variation around three key flower colour genes that are known to be important for inter-specific differences. At the smallest temporal scale, we will determine the pattern of gene flow from one generation to the next in a region where species meet and hybridise. This will allow the fitness (i.e. the number of offspring) of different gene combinations to be measured in the field. Over the medium scale, we will survey fluctuations in a range of genetic markers to give longer term estimates of gene flow and the intensity of natural selection. At the largest temporal scale, we will compare variation in DNA sequence and function of each gene in several species. This should throw light on how distinct alleles arose and how quickly they spread. Appropriate theories and models will be developed for each scale of analysis. These will then be integrated to arrive at an overall framework that spans variation from the individual to species level. In addition to providing a deeper understanding of the origins of biodiversity, the project will provide multidisciplinary training for several young researchers and promote a more integrated understanding of evolutionary and developmental biology.