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（一个多样化的农业上重要的群体）中谱系从异交向自交过渡的速率来实现。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变化，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显花植物中最常见的进化转变之一。尽管在这个问题上已经做了几十年的工作，但仍然不清楚是什么推动了自交的最初传播，并且解释这种模式的主要假设的测试也很少见。其中一个原因是，其他花的性状发生了一系列的快速变化，以响应自交，然后采取行动，掩盖传统的比较推理方法。此外，该项目还将培养研究生和本科生。在开花植物中，从异交到自交以及从二倍体到多倍体的转变是常见的，并且被认为是一致发生的。首先，多倍化可以作为一种过滤器，将新群体的建立限制在那些来自自交亲和祖先的群体。二是多倍化可以提供强有力的生殖保证，导致交配系统和倍性的联合转换。最后，在群体建立后，多倍化可以为自交的传播创造有利的环境。本研究通过建立一个交配系统和倍性数据库，并扩展一个多状态比较模型，估计了这三条途径在菊科植物中的转换速率。这些估计将被用来评估的相对重要性，在新多倍体自交传播的生殖保证。 该模型将显示为什么同时过渡到自交和多倍体是相对罕见的菊科和其他家庭与孢子体自交不亲和性（SI）。理论框架将扩展到解释为什么这样的SI系统可以生存与多倍体和岛屿殖民化的极端人口瓶颈。

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.