DISSERTATION RESEARCH: Persistence of Monoecy in Deep Time: An Integrated Biological and Paleontological Approach

本计画结合古生物学与演化生物学，探讨性系统的演化。自然界中存在如此多的繁殖方法仍然很难解释。当代理论认为，有性生殖应该允许长期生存，因为遗传物质的传播和重组为生物种群提供了适应环境变化的能力。小型淡水甲壳类动物，还是？蛤蜊虾，？是研究性系统进化的理想选择，因为这一群体包含了由雄性和雌性组成的物种，雌性不再存在的物种已经完全被与雄性共存的自我繁殖的雌雄同体（具有使自己的卵子受精的能力）所取代，以及只有自我繁殖的雌雄同体的物种。利用不起眼的地方？蛤虾？作为一个研究群体，有可能通过甲壳（壳）形状分析技术来确定活种群和化石种群的性别。一旦性别被确定，我们就可以通过人口的性别比例来推断性系统。 这项研究的目的是从世界各地的化石库中收集化石数据，以便首次提供经验证据来测试有关地质时间尺度上性系统起源，持续时间和灭绝的既定理论。然后，我们可以解决普遍持有的信念，单性系统代表一个进化？死胡同这项研究的结果也将为未来的研究提供基础，利用化石记录对交配系统的进化进行变革性研究。

This project integrates paleontology and evolutionary biology to investigate the evolution of sexual systems. The existence of so many methods of reproduction in the natural world remains difficult to explain. Contemporary theories assume that sexual reproduction should allow long term survival as the dispersal and recombination of genetic material provides a population of organisms with the ability to adapt to environmental change. Small freshwater crustaceans, or ?clam shrimp,? are ideal for the study of sexual system evolution as the group contains species that comprise males and females, species where females no longer exist and have been completely replaced by self-fertilizing hermaphrodites (with the ability to fertilize their own eggs) coexisting with males, and species with only self-fertilizing hermaphrodites. Using the otherwise inconspicuous ?clam shrimp? as a study group, it is possible to identify sex via carapace (shell) shape analysis techniques in both living and fossil populations. Once sexes are identified, we can deduce sexual system via sex ratio of the population. This study aims to collect fossil data from worldwide repositories in order to provide, for the first time, empirical evidence to test established theories about the origination, duration and extinction of sexual systems over geologic timescales. We can then address the commonly held belief that unisexual systems represent an evolutionary ?dead end.? The results of this study will also provide a foundation for future research utilizing the fossil record to perform transformative studies into the evolution of mating systems.