The origin, spread and consequences of asexual polyploidy in the sunflower family

生命的多样性被组织成我们认为是物种的独立实体。物种是很少或从不与其他群体杂交的群体。杂交的障碍在自然界中很重要，因为它们允许密切相关的谱系获得不同的性状。我的工作重点是了解物种之间障碍的原因和影响。我特别感兴趣的是那些出现新障碍的情况，这些障碍大大减少或阻止了衍生种群及其祖先之间的杂交。我研究的植物群是向日葵家族的成员，其中一些种群已经从有性繁殖转变为无性繁殖。当这种转变发生时，除了对种群产生遗传变异和适应不断变化的条件的能力产生巨大影响外，无性恋还成为生殖障碍。不同的无性克隆在生殖上彼此隔离，也与它们的有性克隆隔离。我在这里提出的研究旨在揭示不同无性克隆生长的环境条件。他们是不是都能很好地忍受大致相同的条件的多面手？或者他们是专家，每个人都能忍受一小块环境蛋糕？我也很感兴趣的是，为什么性和无性这两种策略在自然界中持续存在。有性繁殖的种群，凭借其产生变异的能力，可能被预测能够胜过无性繁殖的种群。另一方面，如果无性繁殖产生了一个非常成功的克隆，它可能能够迅速传播（因为它不需要雄性，也不需要花粉转移），并胜过有性繁殖。也有可能无性恋者经历的基因流动障碍使他们能够更好地适应当地的环境条件。如果一个有性繁殖的种群不断地面临来自更适合不同条件的种群的基因流动，那么这个种群就可能处于不利地位。为了解决这些问题，我使用描述性的方法和遗传标记来了解性和无性种群的起源和生殖动态，我补充这些实验来测试不同种群在一系列田间和温室条件下的适应性。

The diversity of life is organized into separate entities that we recognize as species. Species are groups of populations that rarely or never interbreed with other such groups. Barriers to interbreeding are important in nature because they allow closely related lineages to acquire distinct traits. My work focuses on understanding the causes and effects of barriers between species. In particular I am interested in those cases where new barriers have arisen that greatly reduce or prevent interbreeding between a derivative population and its progenitor. The plant groups that I study are members of the sunflower family in which some populations have switched from sexual to asexual reproduction. When this switch occurs, in addition to having dramatic consequences on a population's ability to generate genetic variation and adapt to changing conditions, asexuality serves as a reproductive barrier. Different asexual clones are reproductively isolated from one another, as well as being isolated from their sexual counterparts. The research that I propose here aims to uncover the environmental conditions under which different asexual clones can grow. Are they generalists that all tolerate roughly the same conditions equally well? Or are they specialists, each able to tolerate a small slice of the environmental pie? I am also interested in why two strategies, sexual and asexual, persist in nature. Sexual populations, with their ability to generate variation, might be predicted to be able to outcompete asexuals. On the other hand, if asexuality produces a highly successful clone, it may be able to spread quickly (because it won't require males, or pollen transfer) and outcompete sexuals. It is also possible that the barrier to gene flow experienced by asexuals allows them to better match local environmental conditions. A sexual population may be at a disadvantage if constantly faced with gene flow from populations better suited to different conditions. In order to address these questions, I use descriptive approaches and genetic markers to understand the origin and reproductive dynamics of sexual and asexual populations, and I supplement these with experiments to test the fitness of different populations under a range of field and greenhouse conditions.