Evolution of a Novel Larval Body Plan - the Nemertean Pilidium Larva (Phylum Nemertea)

纤毛虫是一种令人着迷的浮游幼虫，发现于一组海洋线虫中。在这组蠕虫中，发育最大程度上是间接的。这意味着浮游幼虫和底栖成虫这两个生活史阶段的构造和功能完全不同。幼虫在幼虫体内形成，历时数周，然后在灾难性的变态过程中从幼虫中喷发出来，并迅速吞噬幼虫的身体。许多海洋无脊椎动物也有类似的间接发育。在其中许多阶段，发育被缩短或简化，导致直接发育，其中幼虫阶段，如果存在，与成虫相似。然而，在新月动物中，很明显，间接发展模式是从祖先的直接发展演变而来的。这个项目的目的是调查发育变化对纤毛虫幼虫的进化有什么贡献。一般的方法是比较有和没有棘突的线虫物种中同源胚胎细胞的命运和发育调控基因的表达。这一结果将阐明幼虫体内不同区域和成体羽毛内雏形的进化起源，并阐明如何在具有直接和间接发育的新月虫中建立身体平面的前后轴。该项目预计将对进化发育生物学的核心问题做出重大贡献，例如新的动物身体计划的起源。该项目为不同的本科生和研究生提供培训和研究机会，包括社区学院的学生，他们中的许多人来自代表性不足的群体。最后，该项目通过在海洋生物野外站维持一个分子实验室和先进的显微镜设施，扩大了其研究和教学能力，并为来自其他机构的来访科学家提供服务。

The pilidium is a fascinating planktonic larva found in one group of marine nemertean worms. In this group of worms the development is maximally-indirect. This means that the two life history stages, the planktonic larva and the benthic adult worm, are built and function entirely differently. The young worm forms inside the pilidium larva over the course of many weeks, then erupts from the larva during catastrophic metamorphosis, and promptly devours the larval body. Many marine invertebrate animals have similarly indirect development. In many of those the development has been abbreviated or simplified, giving rise to direct development, in which the larval stage, if present, resembles the adult. In nemerteans, however, it is clear, that indirect developmental mode evolved from ancestral direct development. This project aims to investigate what changes in development contributed to the evolution of the pilidium larva. The general approach is to compare fates of homologous embryonic cells and expression of developmental regulatory genes in nemertean species with and without the pilidium. The results will clarify the evolutionary origin of the different domains of the larval body and the adult rudiments inside the pilidium, and shed light on how the antero-posterior axes of the body plan is established in nemerteans with direct and indirect development. This project is expected to contribute significantly to central issues in evolutionary developmental biology, such as the origin of novel animal body plans. This project provides training and research opportunities for diverse undergraduate and graduate students, including community college students, many of which are from underrepresented groups. Finally, this project, by maintaining a molecular lab and advanced microscopy facility at a marine biological field station, expands its research and teaching capacity and serves visiting scientists from other institutions.