DISSERTATION RESEARCH: Effect of niche conservation versus niche evolution on diversification rate in the Neotropical plant genus Citharexylum (Verbenaceae)

据估计，新热带地区的种子植物种类比非洲、亚洲和大洋热带地区的总和还要多。最近对不同植物群的研究表明，尽管地理上分开，近亲物种往往占据相似的栖息地类型。这一观察结果导致了一种假设，即在许多种群中，分散是常见的，向新的、但合适的栖息地的迁移可以促进多样化。适应性也可以刺激植物群内部的辐射，尽管人们对这些看似罕见但重要的进化事件对生物多样性的贡献知之甚少。本文对新热带植物马鞭草属（Citharexylum，马鞭草科）的系统学进行了研究，并探讨了该属植物的传播和适应对物种多样化的相对贡献。了解生物在过去是如何分散和进化的研究，为预测这些相同的群体在未来可能如何分散和多样化提供了必要的历史背景。将培训一名研究生，向本科生介绍广泛的实验室和分析方法。这项研究还将通过在几个南美和中美洲国家建立合作来加强国际科研基础设施。该项目的目的是了解生物地理事件（迁移/定殖与适应）如何影响新热带植物谱系的多样化。本研究将阐明植物属（Citharexylum）的生物地理历史，这是一个起源于新热带多个生物群系的乔灌木谱系。将使用多个独立的位点推断出具有接近完整采样的cittharexylum的时间校准系统发育。系统发育推断将采用两层方法，使用高通量和传统测序方法来产生稳健的系统发育。然后，这个框架将用于测试关于该属的进化和生物地理学假设。统计分析将重建祖先的范围/气候生态位，并检测系统发育中多样化率变化的位置和幅度。此外，系统发育将使用化石校准的包括类群Lamiales的系统发育来确定时间，从而评估迁移和适应事件与新热带历史上已知的地质和气候事件。这项工作将有助于建立围绕多样化事件的时间和规模以及新世界生态位进化方向的知识基础。

The Neotropics are estimated to house more seed plant species than the African, Asian, and Oceanic tropics combined. Recent studies of diverse plant groups have noted that closely related species often occupy similar types of habitats despite being geographically separated. This observation led to the hypothesis that dispersal is common in many groups and that migration to new, but suitable habitats can spur diversification. Adaptations can also stimulate radiations within plant groups, though less is known about the contributions of these seemingly rare but important evolutionary events to biodiversity. This research will focus on the systematics of the Neotropical plant genus Citharexylum (Verbenaceae), and the relative contributions of dispersal and adaptation to species diversification in the group. Studies that provide an understanding of how organisms have dispersed and evolved in the past provide the necessary historical context to predict how these same groups are likely to disperse and diversify in the future. One graduate student will be trained and undergraduates will be introduced to a broad range of laboratory and analytical methods. The research will also enhance international scientific research infrastructure by establishing collaborations in several South and Central American countries. .The object of this project is to understand how biogeographic events (migration/colonization versus adaptation) influence diversification in Neotropical plant lineages. This study will elucidate the biogeographic history of the plant genus Citharexylum, a lineage of trees and shrubs that originated in and diversified into multiple biomes of the Neotropics. A time-calibrated phylogeny of Citharexylum with near-complete sampling will be inferred using multiple, independent loci. Phylogenetic inference will take a two-tiered approach using both high-throughput and traditional sequencing methods to produce a robust phylogeny. This framework will then be used to test evolutionary and biogeographic hypotheses about the genus. Statistical analyses will reconstruct ancestral ranges/climatic niches and detect the placement and magnitude of diversification rate shifts in the phylogeny. Additionally, the phylogeny will be dated using a fossil-calibrated phylogeny of the inclusive group Lamiales allowing assessment of migrations and adaptive events with known geologic and climatic events in the history of the Neotropics. This work will help build the foundation of knowledge surrounding the timing and magnitude of diversification events as well as the directionality of niche evolution in the New World.