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

生命的多样性被组织成独立的实体，我们称之为物种。物种是很少或从不与其他种群杂交的种群。杂交的障碍在自然界中很重要，因为它们允许近亲谱系获得不同的性状。我的工作重点是了解物种之间屏障的原因和影响。我特别感兴趣的是那些出现了新障碍的情况，这些障碍大大减少或阻止了衍生种群与其祖先之间的杂交。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环境的能力产生重大影响外，无性恋还充当了生殖障碍。不同的无性克隆体在繁殖上彼此隔离，也与它们的性克隆体隔离。我在这里提出的研究旨在揭示不同无性克隆体生长的环境条件。他们是多面手吗，都能很好地忍受大致相同的条件？或者他们是专家，每个人都能容忍一小块环境蛋糕？我也对为什么两种策略——有性和无性——在自然界中持续存在感兴趣。有性种群，凭借其产生变异的能力，可能被预测能够胜过无性种群。另一方面，如果无性繁殖产生了一个非常成功的克隆，它可能会迅速传播（因为它不需要雄性，也不需要花粉传递），并胜过有性繁殖。也有可能是无性动物经历的基因流动障碍使它们能够更好地适应当地的环境条件。如果不断地面对来自更适合不同条件的种群的基因流动，有性种群可能处于不利地位。为了解决这些问题，我使用描述性方法和遗传标记来了解有性和无性种群的起源和繁殖动态，并辅以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.