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

得克萨斯大学的罗伯特·詹森博士和迈克尔·摩尔先生获得了一项拨款，用于研究单个植物物种对不同土壤的耐受性如何影响植物进化。植物生物学家早就知道，不同土壤类型之间的边界往往会促进新物种的进化。然而，他们很少研究土壤耐受性的这种变化对整个相关植物种群进化史的重要性。Jansen和Moore将通过评估在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范围的进化问题。Tiquilia的27种小型沙漠灌木非常适合进行这项研究，因为它们的土壤偏好明显不同，尽管它们生活在气候相似的北美和南美沙漠。Tiquilia的个别物种生长在三种底物中的一种：深沙、石膏或石膏和石灰岩。为了确定该属底物转移的进化模式，将收集所有种的Tiquilia的几个基因的DNA序列。这些序列将被用来开发一棵进化树，详细描述这些物种之间的关系。然后，这棵树将被用作推断该属土壤偏好历史的基础。这个项目代表了第一批评估底物变化在构建整个植物群的进化历史中的意义的研究之一。考虑到土壤类型在决定植物物种地理分布方面仅次于气候，令人惊讶的是，只有少数研究探讨了进化历史与密切相关植物物种之间的土壤偏好之间的关系。因此，这项研究有望极大地促进我们对植物群进化的一种未被认识的、潜在的重要影响的理解。

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.