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

轮虫是一种微小的(≤2毫米)无脊椎动物，在任何有液态水的地方都能找到。例如，它们栖息在浅海、湖泊、池塘、溪流、灌溉沟渠、沙漠中的短暂盆地、冰川上的融水坑以及土壤和植物上的薄水层。轮虫在生态系统中扮演着重要的角色，既是捕食者又是猎物，它们所含的营养物质在食物链上传递给昆虫和鱼类。科学家研究轮虫是为了更好地了解衰老、水产养殖、生态、发育和繁殖模式的演变。轮虫的一个令人着迷的特征是它们复杂的生命周期：一些轮回世代，而另一些轮虫主要通过克隆自己来繁殖。这项工作将使用基因分析和解剖学比较，依靠先进的显微成像来确定主要轮虫群体的进化史，并研究随着群体的进化，生命周期和繁殖模式是如何变化的。将考虑来自不同栖息地的许多物种，这项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，对在线数据库作出贡献，并将在一次全国会议上举行科学研讨会。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，以进行对这种多样化动物群体的研究。这个项目的目标是建立一个全面的轮虫系统学，重点放在Monogonta纲，这是该门中最特殊和多样化的谱系。这项研究将提供一个框架，以测试群体的多样化如何与不同生殖模式的起源相关。该项目有三个目标。(1)它将利用分子序列数据和形态建立轮虫的全面系统发育；形态研究将使用常规电子显微镜、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；将考虑至少100个物种的形态，代表近90%的科多样性。(2)利用系统发育和祖先状态重建的方法研究轮虫生殖特征的进化问题。具体地说，(A)母体提供营养(即母性繁殖)和内部孵化是如何从产卵物种进化而来的？(B)在单个动物中同时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)具有不同繁殖模式的物种产生的蛋壳在形态、化学和机械性能方面是否表现出相似之处，这些与生活史特征是否相关？以及(D)某些生活史阶段的较小规模是否进化了不止一次？(3)系统发育图还将用于识别单系群，提出轮虫的预测性分类，修改或产生属水平以上分类群的新诊断，以及产生种检索表。此外，由于轮虫是最多样化的支系(2000种)，也是更大的Gnathifera(约3575种，来自5个较高的分类群：毛下目、Gnathostomulida、Micrognathola、Rotifera、Acanthocephala)中唯一的裸体动物，轮虫是提供有关Gnathiferan进化的见解和帮助回答有关生殖多样性、颌类(例如Gnathifera)和寄生性(例如Acanthocephala)的问题的理想候选者。该奖项反映了NSF的法定使命，并已通过使用基金会的智力优势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.