Dissertation Research: The Roles of Edaphic Shifts and Long-Distance Dispersal in the Evolution of the American Desert Genus Tiquilia (Boraginaceae)

德克萨斯大学的Robert Jansen博士和Michael Moore先生获得了一笔资助，用于研究不同植物物种对土壤的不同耐受性如何影响植物的进化。植物生物学家早就知道，不同土壤类型之间的界限常常促进新物种的进化。然而，他们很少研究土壤耐受性的这种变化对相关植物物种整个群体的进化史的重要性。Jansen和Moore将通过评估Tiquilia属进化过程中土壤耐受性变化的影响来具体解决这个更大规模的进化问题。Tiquilia的27种小型沙漠灌木非常适合这项研究，因为尽管它们生长在北美和南美气候相似的沙漠中，但它们在土壤偏好方面存在显著差异。提基利亚的个别物种生长在三种基质制度之一：深砂，石膏，或石膏和石灰石。为了确定该属底物转移的进化模式，将收集提奎里亚所有物种的几个基因的DNA序列。这些序列将被用来建立一个详细描述这些物种之间关系的进化树。然后，这棵树将被用作推断该属土壤偏好历史的基础。该项目是第一批评估基质变化对整个植物群进化史影响的研究之一。考虑到土壤类型在决定植物物种地理分布方面排名第二，仅次于气候，令人惊讶的是，只有少数研究解决了近亲植物物种的进化历史和土壤偏好之间的关系。因此，这项研究有望大大提高我们对植物群进化中未被重视和潜在重要影响的理解。

A grant has been awarded to Dr. Robert Jansen and Mr. Michael Moore at the University of Texas to study how the differing soil tolerances of individual plant species have influenced plant evolution. Plant biologists have long known that boundaries between different soil types often promote the evolution of new species. However, they have rarely examined the importance of such shifts in soil tolerance on the evolutionary history of whole groups of related plant species. Jansen and Moore will specifically address this larger scale evolutionary question by assessing the influence of shifting soil tolerances during the evolution of the genus Tiquilia. The 27 species of small desert shrubs in Tiquilia are ideally suited for this study because they differ remarkably in soil preference despite occurring in the climatically similar deserts of North and South America. Individual species of Tiquilia grow in one of three substrate regimes: deep sand, gypsum, or both gypsum and limestone. To determine the evolutionary pattern of substrate shifts in this genus, DNA sequences of several genes will be collected for all species of Tiquilia. These sequences will be utilized to develop an evolutionary tree detailing the relationships among these species. This tree will then be used as a basis to infer the history of soil preference in the genus. This project represents one of the first studies to assess the significance of substrate shifts in patterning the evolutionary history of an entire plant group. Considering that soil type ranks second behind climate in determining the geographic distribution of plant species, it is surprising that only a handful of studies have addressed the relationship between evolutionary history and soil preference among closely related plant species. This study therefore promises to advance substantially our understanding of an underappreciated and potentially important influence on the evolution of plant groups.