Dissertation Research: Mechanisms Defining Ecological Range Limits in a Plant Hybrid Zone

不同的物种通常在繁殖上彼此隔离。然而，在某些情况下，杂交区形成物种杂交受精并产生可存活的后代。本项目的重点是生理和传粉者的差异如何维持两个植物物种的不同海拔范围，从而维持物种差异，尽管有一些杂交。该研究系统包括在内华达山脉生长在不同海拔的两种牡丹野花。以往的实验表明，无论是传粉媒介的完全分离还是遗传屏障都不能阻止杂交，这表明环境因素的重要性。本实验将在三个海拔的普通园林中测量纯亲本和杂种的成活率和生长率。生理性状（光合速率和水分利用）将被测量，以确定它们是否负责决定纯亲本和杂交种的海拔范围。将研究传粉者，以确定杂交是否受到传粉者行为选择的限制。该项目将阐明不同物种和杂交种海拔范围形成的机制。它将有助于了解新物种的产生和维持，这是进化生物学的一个基本问题。它还将为保护受杂交威胁的稀有植物物种以及转基因作物与本地物种杂交的风险提供有用的信息。该项目每年将为一名研究生和几名本科生提供培训。

Different species are usually reproductively isolated from one another. However, in some cases hybrid zones form where species cross-fertilize and produce viable offspring. This project focuses on how physiological and pollinator differences maintain separate elevational ranges of two plant species, and thereby the species differences, despite some hybridization. The study system consists of two species of Penstemon wildflowers that grow at different elevations in the Sierra Nevada Mountains. Previous experiments indicated that neither complete separation of pollinators nor genetic barriers prevent hybridization, suggesting the importance of environmental factors. In the proposed experiment, survival and growth rate of pure parents and hybrids will be measured in common gardens at three elevations. Physiological traits (photosynthetic rate and water use) will be measured to determine whether they are responsible for determining the elevational ranges of pure parents and hybrids. Pollinators will be studied to determine whether hybridization is limited by behavioral choices of pollinators. This project will clarify mechanisms responsible for shaping elevational ranges of different species and hybrids. It will contribute to knowledge about the production and maintenance of new species, a fundamental issue in evolutionary biology. It will also provide useful information for conservation of rare plant species threatened by hybridization, and about risks of hybridization between genetically modified crops and native species. This project will provide training to one graduate student and several undergraduates per year of funding.