Tests of Competing Hypotheses for the Maintenance of Sex and Parthenogenesis in Campeloma limum, a SE United States Snail

为什么生物会有性繁殖而不是无性繁殖，这是生物学中的突出问题之一。最近的模型表明，在无性生物相对于有性生物的传播率更高的情况下，无性生物可能会持续存在，原因有三：逃离寄生虫(红皇后假说)；针对有害突变的宽松选择；或无性恋者对边缘环境的局部适应。利用二倍体有性和无性的美国东南部淡水蜗牛，这项提案概述了这些假说的分子和实验现场测试。利用线粒体基因(细胞色素b)和核内含子(钙调素)的序列变异，我们将评估无性恋者是否比有性恋者有更高的分散率。我们还将通过现场实验来测试这三个模型的独特预测。由于植物病理学家、流行病学家和保护生物学家认识到寄主遗传多样性在疾病传播中起着重要作用，因此这项研究的结果对这些科学家来说将是相当重要的。这些结果也将引起进化生物学家的相当大的兴趣，因为这项研究将对有性和无性有机体的空间分布的生态和进化原因进行关键测试。

Why organisms reproduce sexually instead of asexually is one of the outstanding problems in biology. Recent models suggest that, under higher dispersal rates of asexuals relative to sexuals, asexual organisms may persist for three reasons: escape from parasites (Red Queen hypothesis); relaxed selection against deleterious mutations; or local adaptation of asexuals to marginal environments. Using diploid sexual and asexual Campeloma limum, a freshwater snail from the southeastern US, this proposal outlines molecular and experimental field tests of these hypotheses. Using sequence variation in a mitochondrial gene (cytochrome b) and a nuclear intron (calmodulin), we will assess whether asexuals have higher dispersal rates than sexuals. We will also test unique predictions of the three models by field experiments. Because plant pathologists, epidemiologists, and conservation biologists realize that host genetic diversity plays an important role in the spread of diseases, the results from this study will be of considerable to these scientists. These results will also be of considerable interest to evolutionary biologists, because the study will provide critical tests of ecological and evolutionary causes of the spatial distribution of sexual and asexual organisms.