DISSERTATION RESEARCH: A next-generation sequencing framework for understanding trait evolution across multiple scales in the Viburnum lentago clade

许多植物种类变化很大。即使在一个种群内，同一物种的植物在叶子形状或花朵颜色等特征上也可能彼此不同。然而，几乎所有关于性状进化的大规模研究都忽略了物种内部的这种变异，而是将单个值分配给每个物种。部分原因在于，我们对物种内部的变异与更长时间尺度上的进化分化之间的关系知之甚少。这个项目的重点是六种密切相关的灌木，原产于美国东部。目标是量化物种内部不同类型的变异，并将观察到的模式与这些物种在过去500万至2000万年间的进化联系起来。特别的重点将放在描述一组叶片特征（大小，形状，叶缘）的变化在单个植物内，在种群内，跨种群跨越生长条件的纬度梯度，和跨物种。这些数据将有助于更好地预测哪些性状最有可能进化，以及植物物种如何应对未来的气候变化。本项目采用新的新一代分子方法，对开花植物荚门中的Lentago谱系进行系统发育和系统地理数据分析。RAD（限制性内切位点相关DNA）标记将对每个物种超过30个个体进行测序，以创建一个跨越分化水平的高分辨率系统发育，将几百年前分化的种群与中新世的物种形成事件联系起来。这种系统发育框架将解决物种关系，确定进化分支内杂交的程度，并使研究人员能够重建每个物种的系统地理（种群水平）历史。由此产生的对共同祖先和迁徙历史的详细了解将为了解适应和基因流动如何在物种内部和物种之间产生和维持性状变异提供新的见解。该项目将提高对形态特征变异的起源的理解，变异类型如何在组织水平上转化，以及标志着生命之树更深分支的特征的出现。

Many plant species are extremely variable. Even within a population, plants of the same species can differ from one another in characteristics such as leaf shape or flower color. However, almost all broad-scale studies of trait evolution ignore such variation within species and instead assign a single value to each species. Partially for this we know little about how variation within species relates to evolutionary differentiation over longer timescales. This project focuses on six closely related species of shrubs that are native to the Eastern United States. The goal is to quantify different types of variation within species and to relate the observed patterns to how these species evolved over the past 5-20 million years. Special emphasis will be placed on describing variation in a set of leaf characteristics (size, shape, leaf margins) within individual plants, within populations, across populations spanning a latitudinal gradient in growing conditions, and across species. These data will allow a better prediction of which traits are most likely to evolve and how plant species might respond to future climate change. This project uses a new next-generation molecular method to generate phylogenetic and phylogeographic data for the Lentago lineage within the flowering plant clade Viburnum. RAD (Restriction site Associated DNA) markers will be sequenced for over 30 individuals per species to create a high-resolution phylogeny that spans across levels of divergence, linking populations that diverged only several hundred years ago to speciation events in the Miocene. This phylogenetic framework will resolve species relationships, determine the extent of hybridization within the clade, and enable the researchers to reconstruct the phylogeographic (population-level) history of each species. The resulting detailed understanding of common ancestry and migration history will provide new insight into how adaptation and gene flow generate and maintain trait variation within and among species. The project will improve understanding of the genesis of variation in morphological traits, of how types of variation translate across levels of organization, and of the emergence of the traits that mark deeper branches in the tree of life.