Collaborative Research: Life cycle evolution in Rotifera: The influence of sexual reproduction on contemporary systematics of Monogononta

轮虫是微小的（≤2毫米）无脊椎动物，可以在任何有液态水的地方找到。例如，它们栖息在浅海、湖泊、池塘、溪流、灌溉沟渠、沙漠中短暂的盆地、冰川上的融水水坑以及土壤和植物上的薄层水。轮虫作为捕食者和猎物在生态系统中发挥着至关重要的作用，它们所含的营养物质通过食物链传递给昆虫和鱼类。科学家研究轮虫是为了更好地了解衰老、水产养殖、生态学、发育和生殖模式的进化。轮虫的一个迷人的特征是它们复杂的生命周期：有些世代交替，而另一些则主要通过克隆自己来繁殖。这项工作将使用遗传分析和解剖学的比较，依靠先进的显微成像来确定一个主要的轮虫群体的进化历史，并研究生命周期和繁殖模式如何随着群体的进化而变化。将考虑来自不同生境的许多物种，研究还将导致更好地描述鲜为人知的物种的生命周期。作为该项目的一部分，将举办教育讲习班和博物馆展览，为在线数据库提供资料，并在一次全国会议上举行一次科学专题讨论会。此外，一名博士后科学家，沿着研究生、本科生和高中生，将接受培训，对这种多样化的动物群体进行研究。该项目的目标是建立一个全面的轮虫系统发育，重点是单角轮虫纲，这是该门中最具物种多样性的谱系。这项研究将提供一个框架，以测试如何组的多样化是与不同的生殖模式的起源。该项目有三个目标。(1)它将使用分子序列数据和形态学产生一个全面的轮虫系统发育;形态学研究将利用传统的电子显微镜，聚焦离子束扫描电子显微镜，原子力显微镜和共聚焦激光扫描显微镜;至少100个物种的形态代表近90%的家庭多样性将被考虑。(2)它将使用生殖发生和祖先状态重建的方法来研究有关轮虫生殖特征进化的问题。特别是，（a）母亲如何提供营养（即，母养）和内部育雏进化产卵物种？(b)一只动物产生有丝分裂和减数分裂卵子的能力是如何从周期性单性生殖进化而来的？(c)不同繁殖方式的物种所产的蛋壳在形态、化学、机械性质上是否有相似之处，这些是否与生活史特征有关？以及（d）某些生命周期阶段的小尺寸是否进化了不止一次？(3)该系统还将用于识别单系类群，提出轮虫的预测分类，修订或产生属级以上分类单元的新诊断，并产生种检索表。此外，由于轮虫是最多样化的分支（2000种），也是更大的Gnathifera谱系中唯一的生殖分布组（来自五个更高分类群的约3575种：Chaetognatha，Gnathostomulida，Micrognathozoa，Rotifera，Dongocephala），轮虫是理想的候选者，可以提供对gnathifera进化的见解，并帮助回答有关生殖多样性进化的问题，颌骨（例如，Gnathifera）和寄生（例如，该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Rotifers are tiny (≤2 mm) invertebrate animals that can be found anywhere there is liquid water. For instance, they inhabit shallow sea water, lakes, ponds, streams, irrigation ditches, ephemeral basins in deserts, meltwater puddles on glaciers, and thin layers of water on soils and plants. Rotifers play vital roles in ecological systems as both predators and prey, and the nutrients they contain are passed up the food chain to insects and fish. Scientists study rotifers to better understand aging, aquaculture, ecology, development, and the evolution of reproductive modes. A fascinating feature of rotifers are their complex life cycles: some alternate generations, whereas others primarily reproduce by creating clones of themselves. This work will use genetic analyses and comparisons of anatomy that rely on advanced microscopic imaging to determine the evolutionary history of a major group of rotifers and examine how life cycles and reproductive mode changed as the group evolved. Many species from diverse habitats will be considered, and the research will also result in better characterization of the life cycles of species that are poorly known. As part of the project, educational workshops and museum displays will be produced, contributions will be made to online databases, and a scientific symposium will be held at a national meeting. Further, a postdoctoral scientist, along with graduate, undergraduate, and high school students, will be trained to conduct studies of this diverse animal group. The goal of this project is to build a comprehensive phylogeny of rotifers with a focus on the Class Monogononta, the most speciose and diverse lineage in the phylum. This research will provide a framework for testing how the diversification of the group is associated with the origins of different reproductive modes. The project has three aims. (1) It will produce a comprehensive phylogeny of rotifers using molecular sequence data and morphology; the morphological studies will utilize conventional electron microscopy, focused ion-beam scanning electron microscopy, atomic force microscopy, and confocal laser scanning microscopy; the morphology of at least 100 species representing nearly 90% of family diversity will be considered. (2) It will use the phylogeny and ancestral state reconstruction methods to investigate questions concerning the evolution of reproductive traits in rotifers. In particular, (a) how did the maternal provisioning of nutrients (i.e., matrotrophy) and internal brooding evolve from egg-laying species? (b) how did the ability to produce both mitotic and meiotic ova in a single animal evolve from cyclical parthenogenesis? (c) do eggshells produced by species with different reproductive modes show similarities in morphology, chemistry, and mechanical properties, and are these correlated with life history traits? And (d) has the small size of certain life cycle stages evolved more than once? (3) The phylogeny will also be used to identify monophyletic groups, present a predictive classification of rotifers, revise or produce new diagnoses for taxa above the genus level, and produce species keys. Additionally, because Rotifera is the most diverse clade (2000 species) and the only gonochoristic group within the larger lineage Gnathifera (~3575 species from five higher taxa: Chaetognatha, Gnathostomulida, Micrognathozoa, Rotifera, Acanthocephala), rotifers are ideal candidates to provide insights into gnathiferan evolution and help answer questions about the evolution of reproductive diversity, jaws (e.g., Gnathifera), and parasitism (e.g., Acanthocephala).This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.