Evolution and ecology of plant sexual systems

在历史进程中反复发生的进化转变是生物学家固有的兴趣所在。其中一种转变涉及到生物体繁殖方式的根本变化，仅在开花植物中就发生了至少100次：从雌雄同体进化到两性分离。在这一转变过程中，个体不能同时作为雌雄同体繁殖（即雌雄同体），而只能作为后代的母亲或父亲（即雌雄异株）。为什么个体要放弃自己的一种性别角色而成为专门的女性或男性呢？回到达尔文时代的生物学家已经思考过这个问题，但有两个关键问题仍然不清楚——这些问题可以通过结合现代分子遗传学和实验操作来解决，这是本文提出的研究的特点。首先，生态条件在向雌雄异株进化过渡中的重要性得到了广泛的认识，但却知之甚少。我将通过实验和对本地植物阔叶人马座（Sagittaria latifolia）的遗传分析，首次对环境条件对雌雄异株进化的关键步骤——雄性进化的影响进行实证研究。这个物种在具有雌雄异株和雌雄同体的种群中是不寻常的，使它成为一个理想的实验系统。第二，有证据表明雌雄异株谱系比雌雄同体谱系包含更少的物种，但其过程在很大程度上是未知的。利用在性系统中经历了快速多样化的世系，我们可以了解到结合性与分离性对多样性模式的影响。在加那利群岛辐射的紫堇似乎就是这样一个谱系，其中四分之一的物种具有二态繁殖系统。利用遗传和现场研究的紫堇，我将调查历史和当代的过程，塑造结合vs.分开的性别的演变。这里提出的方法组合将提供(a)对雌雄异株进化的新见解，以及(b)在高通量分子遗传学，高级实验设计和统计学方面为学生提供培训-在一系列生物学职业中高度寻求的技能。

Evolutionary transitions that occur repeatedly over the course of history are of inherent interest to biologists. One such transition involves a fundamental change in the way organisms reproduce and has occurred at least 100 times in the flowering plants alone: the evolution of separate sexes from hermaphroditism. During this transition, individuals cease being able to reproduce as both female and male parents (i.e., hermaphrodites) and instead act solely as mothers or fathers to their offspring (i.e., dioecy). Why should individuals give up one of their sex roles to become specialist females or males? Biologists going back to Darwin have thought about this question, but two key issues remain unclear - issues that can begin to be resolved using the combination of modern molecular genetics and experimental manipulations that characterizes the research proposed here. First, the importance of ecological conditions in evolutionary transitions to dioecy is widely recognized but poorly understood. I will provide the first empirical investigation of the effects of environmental conditions on a key step in the evolution of dioecy - the evolution of males - using experiments and genetic analysis of the native plant Sagittaria latifolia. This species is unusual in having both dioecious and hermaphroditic populations, making it an ideal experimental system. Second, there is evidence that dioecious lineages contain fewer species than hermaphrodite lineages, but the processes responsible are largely unknown. Much can be learned about the effect of combined vs. separate sexes on patterns of diversity using lineages that have undergone rapid diversification in their sexual systems. The Canary Islands radiation of Echium appears to be such a lineage, with one quarter of species having dimorphic breeding systems. Using genetic and field studies of Echium, I will investigate the historical and contemporary processes that shape the evolution of combined vs. separate sexes. The combination of approaches proposed here will provide (a) novel insights into the evolution of dioecy, and (b) training for students in high-throughput molecular genetics, and advanced experimental design and statistics - highly sought skills across a range of biological careers.