Doctoral Dissertation Research: Multi-Scale Analysis of Gene Flow in the Emergent Aquatic Macrophyte Hymenocallis coronaria

水运动是许多水生植物种子传播的主要媒介，在整个旱地流域是单向的。基于陆地环境的基因流动模型，种子传播往往是多向的，可能不足以代表水生植物的基因流动模式。然而，很少有研究调查单向水流对水生植物遗传变异模式的影响，并且这些研究报告了相互矛盾的结果。此外，种群内部和种群之间的基因流动很少在流环境中进行研究，并且关于这些过程如何在不同的分析尺度上发挥作用的许多问题仍然存在。这个博士论文研究改进项目将使用分子技术来检查冠状膜藻（浅滩蜘蛛百合）的基因流动，这是一种水生植物，出现在从阿拉巴马州到南卡罗来纳州的山前溪流的浅滩栖息地，但在其分布范围的几个流域中却没有。该项目的第一个广泛目标是研究单向流对冠膜绦虫种群内和种群间遗传结构和基因流动的影响。具体来说，核DNA和叶绿体DNA标记的组合将用于(1)确定遗传变异性是否在种群内部和种群之间逐渐增加，(2)检查溪流环境中花粉流与种子流的影响，以及(3)测试三种基因流模型中哪一种最能代表种群之间的基因流模式。第二个广泛的目标是研究生境特征和土地利用历史对种群分布、遗传结构和基因流动的影响，以及这些因素如何反过来影响水生大型植物的微观进化过程。与分子技术相结合，将测量水流流量、水温、浊度、溶解氧、河道沉积物深度、浅滩岩性以及浅滩岩石单元的走向和倾角，以确定(1)哪些因素与冠膜虫种群的缺失有关，这些因素位于物种范围的中间；(2)从无人居住的流域中排除种群是史前起源还是最近人类相关干扰的结果；(3)随着土地利用的持续变化，孤立流域中的种群是否面临更大的灭绝风险。冠膜藻是一种罕见的植物，在美国东南部的分布范围相对有限。这种植物被阿拉巴马州和乔治亚州列为受威胁或濒危物种。它被南卡罗来纳州列为濒危物种；并受到《濒危物种法》的保护。由于水库蓄水，有文献记载的种群灭绝已经发生，而且种群继续受到水资源进一步开发的威胁。除了提供水生环境中基因流动的信息外，本研究还将进一步了解这种相对罕见的物种对其生存范围内环境条件变化的反应。研究结果还将为资源管理者制定政策提供参考，这些政策不仅会影响这种特定的国家级濒危植物资源，还可能影响整个地区受同一套干扰影响的其他水生植物。作为博士论文研究改进奖，该奖项还将提供支持，使有前途的学生建立一个强大的独立研究生涯。

Water movement, which is the primary seed dispersal agent for many aquatic plants, is unidirectional throughout an upland drainage basin. Models of gene flow based on terrestrial environments, where seed dispersal is often multidirectional, are likely inadequate for representing patterns of gene flow in aquatic plants. Few studies have investigated the influence of unidirectional stream flow on patterns of genetic variation in aquatic plants, however, and these studies have reported contradictory results. Furthermore, gene flow both within and among populations has rarely been examined in stream environments, and many questions remain concerning how these processes function at different scales of analysis. This Doctoral Dissertation Research Improvement project will use molecular techniques to examine gene flow in Hymenocallis coronaria (shoals spider lily), an aquatic plant that occurs in shoal habitats in piedmont streams from Alabama to South Carolina but is absent from several watersheds in the middle of its range. The project's first broad objective is to examine the effects of unidirectional stream flow on genetic structure and gene flow within and among populations of Hymenocallis coronaria. Specifically, a combination of nuclear DNA and chloroplast DNA markers will be used to (1) determine whether genetic variability increases progressively downstream both within and among populations, (2) examine the influence of pollen flow vs. seed flow in stream environments, and (3) test which of three gene flow models best represents the patterns of gene flow among populations. The second broad objective is to examine the effects of habitat characteristics and land-use history on population distribution, genetic structure, and gene flow, and how these factors, in turn, affect microevolutionary processes in an aquatic macrophyte. In concert with molecular techniques, stream discharge, water temperature, turbidity, dissolved oxygen, sediment depth in the channel, shoals lithology, and strike and dip of the shoals rock units will be measured to determine (1) which factors are associated with the absence of Hymenocallis coronaria populations from the middle of the species range, (2) whether the exclusion of populations from the uninhabited drainage basins is of prehistoric origin or result from more recent human-related disturbance, and (3) whether populations in isolated drainages are at a greater risk for extinction with ongoing land-use changes.Hymenocallis coronaria is a rare plant that has a relatively restricted range in the southeastern United States. The plant is protected as a threatened or endangered species by the states of Alabama and Georgia. It is listed as imperiled by the state of South Carolina; and protection has been sought under the Endangered Species Act. Documented population extinctions have occurred due to reservoir impoundment, and populations continue to be threatened by further water resource development. In addition to providing information about gene flow in aquatic environments, this research will further basic understanding of the response of this relatively rare species to changing environmental conditions within its range. The results also will inform resource managers as they formulate policy that affects not only this particular state-level endangered botanical resource but potentially other aquatic plants throughout the region affected by the same set of disturbances. As a Doctoral Dissertation Research Improvement award, this award also will provide support to enable a promising student to establish a strong independent research career.