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

这个项目结合古生物学和进化生物学来研究性系统的进化。自然界中为什么存在如此多的繁殖方法仍然很难解释。当代理论认为，有性繁殖应该允许长期生存，因为遗传物质的扩散和重组为有机体提供了适应环境变化的能力。小型淡水甲壳动物，或？文蛤虾，？是研究有性系统进化的理想物种，因为该种群包含由雄性和雌性组成的物种，雌性不再存在并完全被与雄性共存的自交性两性(具有使自己的卵受精的能力)所取代的物种，以及只有自交两性的物种。用其他不起眼的？蛤仔虾？作为一个研究小组，在活的和化石的种群中，通过甲壳形状分析技术来鉴定性别是可能的。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别制度。这项研究的目的是从世界各地的储存库中收集化石数据，以便首次提供经验证据，以检验关于性系统在地质时间尺度上的起源、持续时间和灭绝的既定理论。然后，我们就可以解决普遍持有的观点，即单性恋系统代表着进化的死胡同。这项研究的结果还将为未来利用化石记录对交配系统的进化进行变革性研究提供基础。

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.