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、灌溉渠、沙漠中的短暂盆地、冰川上的融水水坑以及土壤和植物上的薄层水中。轮虫在生态系统中扮演着至关重要的角色，既是捕食者又是猎物，它们所含的营养物质通过食物链向上传递给昆虫和鱼类。科学家研究轮虫是为了更好地了解它们的衰老、水产养殖、生态、发育和生殖模式的进化。轮虫的一个令人着迷的特点是它们复杂的生命周期：一些轮虫交替繁殖，而另一些轮虫主要通过克隆自己来繁殖。这项工作将利用遗传分析和解剖学比较，依靠先进的显微成像来确定一个主要轮虫群体的进化史，并研究生命周期和生殖模式是如何随着群体的进化而变化的。将考虑来自不同栖息地的许多物种，并且该研究还将更好地表征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，将对在线数据库作出贡献，并将在全国会议上举行一次科学专题讨论会。此外，一名博士后科学家以及研究生、本科生和高中生将接受培训，对这一多样化的动物群体进行研究。本项目的目标是建立一个全面的轮虫系统发育，重点关注单胞纲，这是该门中物种最多、种类最多的分支。这项研究将为测试群体的多样化如何与不同生殖模式的起源相关联提供一个框架。该项目有三个目标。(1)利用分子序列数据和形态学得出轮虫的综合系统发育；形态学研究将利用传统电子显微镜、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；将考虑代表近90%科多样性的至少100个物种的形态。(2)利用系统发育和祖先状态重建方法探讨轮虫生殖性状的进化问题。特别是(a)母性提供营养（即营养不良）和内部孵化是如何从产卵物种进化而来的？(b)在单一动物中产生有丝分裂和减数分裂卵子的能力是如何从周期性孤雌生殖进化而来的？(c)不同繁殖方式的物种所产的蛋壳在形态、化学和力学性质上是否有相似之处？这些是否与生命史特征有关？(d)某些生命周期阶段的小尺寸是否进化了不止一次？(3)系统发育还可用于轮虫单系类群的鉴定、轮虫属的预测分类、轮虫属以上分类群的修正或新诊断以及种键的生成。此外，由于轮虫纲是最多样化的分支（2000种），也是大谱系Gnathifera（来自五个高级分类群：Chaetognatha、Gnathostomulida、Micrognathozoa、Rotifera、Acanthocephala）中唯一的gonchchoristic类群，轮虫是了解Gnathifera进化和帮助回答生殖多样性、颌（例如Gnathifera）和寄生（例如Acanthocephala）进化的理想候选。该奖项反映了美国国家科学基金会的法定使命，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.