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

许多植物物种都是极易变的。即使在一个种群内，同一物种的植物在叶形或花色等特征上也可能有所不同。然而，几乎所有关于性状进化的广泛研究都忽略了物种内的这种差异，而是为每个物种分配了一个单一的值。在一定程度上，我们对物种内的变异如何与更长时间尺度上的进化分化有关的了解甚少。这个项目主要关注六种关系密切的灌木，这些灌木原产于美国东部。其目标是量化物种内不同类型的变异，并将观察到的模式与这些物种在过去500-2000万年间的进化方式联系起来。将特别强调描述一组叶片特征(大小、形状、叶缘)在个体植物内、种群内、生长条件下跨越纬度梯度的种群之间和物种之间的变化。这些数据将使人们能够更好地预测哪些特征最有可能进化，以及植物物种可能如何应对未来的气候变化。该项目使用一种新的下一代分子方法来生成开花植物分支Viburnum中的Lentago血统的系统发育和系统地理数据。RAD(限制性内切酶相关DNA)标记将对每个物种30多个个体进行测序，以创建跨越不同水平的分歧的高分辨率系统发育图，将仅在几百年前分化的种群与中新世的物种形成事件联系起来。这一系统发育框架将解决物种关系，确定支系内杂交的程度，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理解将为适应和基因流动如何在物种内和物种之间产生和维持特征变异提供新的见解。该项目将提高对形态特征变异的起源、不同类型的变异如何在组织层次上转化以及标志着生命之树更深分支的特征的出现的理解。

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.