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

这个项目的目标是评估驱动开花植物自花受精能力进化的潜在机制。这一目标将通过测量芥菜家族从异交到自交的速度来实现，芥菜家族是一个多样化的、在农业上重要的群体。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广泛变化，这通常被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，向自花授粉的转变是开花植物最常见的进化转变之一，这是令人惊讶的。尽管在这个问题上做了几十年的研究，但我们仍然不清楚是什么推动了自交的最初传播，对解释这种模式的主要假说的测试也很少见。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，然后使传统的比较推理方法变得模糊。此外，该项目还将对研究生和本科生进行培训。在开花植物中，从异交到自交和从二倍体到多倍体的转变很常见，被认为是同时发生的。自交和多倍体之间的联系可以通过三种不相互排斥的途径发生。首先，多倍化可以起到过滤器的作用，将新种群的建立限制在那些源自自交亲和祖先的种群。其次，多倍化可以提供强大的生殖保障，导致交配系统和倍性的联合过渡。最后，多倍化可以在种群建立后为自交的传播创造良好的环境。本研究通过建立十字花科植物交配系统和倍性数据数据库，并扩展多态比较模型，估计了十字花科植物这三条途径的过渡率。这些估计将被用来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十字花科和其他具有孢子体自交不亲和性(SI)的家族中，同时向自交和多倍体的转变相对较少。理论框架将被扩展，以解释为什么这种SI系统能够经受住与多倍体和岛屿殖民相关的极端种群瓶颈。

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.