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

点击翻译按钮获取中文摘要

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.