DISSERTATION RESEARCH: Empirical, theoretical, and comparative tests of major hypotheses for the recurrent evolution of self-fertilization

该项目的目标是评估驱动开花植物自我受精能力进化的潜在机制。这一目标将通过测量芥菜科谱系从异交到自交受精的速率来实现，芥菜科是一个多样化和农业上重要的群体。开花植物在花的大小、形状和颜色上表现出令人难以置信的多样性，这通常归因于开花植物和传粉者的共同进化。考虑到异花授粉在进化中的潜在重要作用，令人惊讶的是，向自花受精的转变是开花植物中最常见的进化转变之一。尽管在这个问题上已经研究了几十年，但我们仍然不清楚是什么推动了自恋的最初传播，对解释这种模式的主要假设的测试也很少。其中一个原因是，其他花卉性状的一系列快速变化是对自交的反应，这使得传统的比较推断方法变得模糊。此外，该项目还将培养研究生和本科生。在开花植物中，从异交到自交和从二倍体到多倍体的转变是常见的，并且被认为是协同发生的。自交和多倍体之间的关联可以通过三种不相互排斥的途径发生。首先，多倍体化可以起到过滤器的作用，将新种群的建立限制在那些来自自相容祖先的种群中。其次，多倍体化可以提供强大的生殖保障，使交配制度和倍性共同过渡。最后，在种群建立后，多倍体化可以为自交的传播创造有利的环境。本研究通过构建杂交系统和倍性数据数据库，并扩展多态比较模型，估算了这三种途径在芸苔科植物中的转换速率。这些估计将用于评估生殖保证在新多倍体自交传播中的相对重要性。该模型将说明为什么在芸苔科和其他具有孢子体自交不亲和（SI）的科中，同时向自交和多倍体过渡的情况相对较少。理论框架将被扩展到解释为什么这样的SI系统可以在与多倍体和岛屿殖民化相关的极端人口瓶颈中生存下来。

The goal of this project is to evaluate the underlying mechanisms that drive the evolution of the ability for flowering plants to self-fertilize. This goal will be accomplished by measuring the rate at which lineages transition from outcrossing to self-fertilizing in the mustard family, a diverse and agriculturally important group. Flowering plants display an incredible breadth of variation in flower size, shape, and color that is generally attributed to the co-evolution of flowering plants and pollinators. Considering the potentially important role of cross-pollination in evolution, it is surprising that the shift to self-fertilization is one of the most common evolutionary transitions in flowering plants. Despite decades of work on this subject, it is still not clear what drives the initial spread of selfing and tests of the leading hypotheses explaining this pattern are rare. One reason for this is that a series of rapid changes in other floral traits occur in response to selfing, which then act to obscure traditional methods of comparative inference. Additionally, the project will result in the training of graduate and undergraduate students.In flowering plants, shifts from outcrossing to selfing and from diploidy to polyploidy are common and are thought to occur in concert An association between selfing and polyploidy can occur through three non-mutually exclusive pathways. First, polyploidization could act as a filter, limiting the founding of new populations to those that originate from a self-compatible progenitor. Second, polyploidization could provide strong reproductive assurance resulting in the joint transition of mating system and ploidy. Finally, polyploidization could create a favorable environment for the spread of selfing after the population is established. This research estimates the transition rates of these three pathways in the Brassicaceae by assembling a database of mating system and ploidy data and extending a multi-state comparative model. These estimates will be used to evaluate the relative importance of reproductive assurance in the spread of selfing in neopolyploids. The model will show why simultaneous transitions to selfing and polyploidy are relatively rare in Brassicaceae and other families with sporophytic self-incompatibility (SI). The theoretical framework will be extended to explain why such SI systems can survive extreme population bottlenecks associated with polyploidy and island colonization.