Dissertation Research: Competition and Genotypic Diversity in Poeciliopsis

在鱼属Poeciliopsis （Poeciliidae）中，所有的雌性无性系都共存于墨西哥沙漠溪流中，雄性和雌性都是密切相关的有性繁殖物种。过去的研究已经证实，在食物资源和栖息地空间的利用上，遗传上固定的差异有助于有性和无性系的共存。本研究由两部分组成。(1)在人工养殖中进行两个无性系和一个有性系内部和之间的竞争实验，以测试遗传变异群体是否表现出相对于单克隆群体更低的种内竞争。这项研究的结果将揭示有性生殖的生态优势。(2)实地研究将量化两个无性系和有性系的自然密度和相对频率。这些收集的结果将显示上述三种系在密度和相对频率范围内的相对繁殖成功率。这种生态学研究对于提高对自然种群遗传变异的成本和收益的认识是必要的。然而，本研究也有潜在的应用价值。基因一致的种群可以在受控制的环境中生长得很好，比如肥沃和浇水充足的农田，但在不受控制的环境中不太可能表现得同样好。水产养殖者和自然资源保护主义者都面临着在不受控制的环境中维持种群的问题，因此需要了解维持这些种群的遗传变异的生态效益。

In the fish genus Poeciliopsis (Poeciliidae) all female clones coexist in Mexican desert streams with males and females of closely related sexually reproducing species. Past work has confirmed that genetically fixed differences in the use of food resources and habitat space contribute to the coexistence of sexual and asexual lines. The proposed study consists of two parts. (1) Competition experiments within and between two clonal lines and a sexual line will be conducted in artificial streams to test whether genetically variable populations show lowered intraspecific competition relative to monoclonal populations. Results from this study will shed light on the ecological advantage of sexual reproduction. (2) Field studies will quantify natural densities and relative frequencies of the two clonal lines and the sexual line. Results from these collections will show the relative reproductive success of the above three lines in a range of densities and relative frequencies. Such ecological studies are necessary for increasing knowledge of the costs and benefits of genetic variability in natural populations. However, this study also has potential applied value as well. Genetically uniform populations can grow well in controlled environments, such as well fertilized and well watered agricultural fields, but are unlikely to perform as well in uncontrolled environments. Both aquaculturists and conservationists are confronted with maintaining populations in uncontrolled environments, and therefore need to understand the ecological benefits of maintaining genetic variation in these populations.