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指出，尽管地理上相互隔开，但密切相关的物种往往占据着相似类型的栖息地。这一观察结果导致了一种假设，即扩散在许多种群中很常见，迁徙到新的但合适的栖息地可以刺激多样性。适应也可以刺激植物群体内的辐射，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。本研究将集中于新热带植物(马鞭草科)的系统学研究，以及种群内扩散和适应对物种多样性的相对贡献。了解生物体在过去是如何分散和进化的研究，为预测这些相同的种群在未来可能如何分散和多样化提供了必要的历史背景。将对一名研究生进行培训，并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洲和中美洲国家建立合作来加强国际科学研究基础设施。本项目的目的是了解生物地理事件(迁徙/殖民与适应)如何影响新热带植物谱系的多样性。这项研究将阐明蜡梅属植物的生物地理史，这是一种乔木和灌木的谱系，起源于新热带地区，并多样化为多种生物群。利用多个独立的基因座，可以推断出近乎完全采样的时间校准的花椒的系统发育。系统发育推断将采取两层方法，同时使用高通量和传统测序方法，以产生强大的系统发育图。然后，这个框架将被用来测试关于该属的进化和生物地理假说。统计分析将重建祖先范围/气候生态位，并检测多样化比率变化在系统发育中的位置和大小。此外，还将使用经化石校准的拉米亚目种群的系统发展史来确定系统发展的日期，以便根据新热带地区历史上已知的地质和气候事件来评估迁徙和适应事件。这项工作将有助于建立围绕多样化活动的时机和规模以及新世界利基演变的方向性的知识基础。

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.