Developmental Evolution of Facultative Parasitism: Mechanisms Underlying Body Plan Remodeling in the Sea Anemone Edwardsiella

寄生虫的数量超过了自由生活的物种，可能是4比1，它们在自然生态系统中发挥着重要作用。寄生虫可能直接危害人类或人类赖以生存的物种，也可能通过控制有害物种的数量间接帮助人类。根据寄生虫的丰度和多样性，很明显，寄生虫在过去的许多场合都是从自由生活的祖先进化而来的。然而，人们对从自由生活物种到寄生物种的显著转变知之甚少，这主要是因为大多数已经被描述为寄生的进化转变发生在数千万或数亿年前。本研究通过利用一种处于成为寄生虫早期阶段的新模式物种来解决寄生的起源。作为一个成年海葵，Edwardsiella lineata的外表和行为都像一个典型的自由生活的海葵。然而，它的幼虫可以侵入栉水母记忆虫的身体，在那里发育成一条小蠕虫，通过从宿主的肠道中窃取部分消化的食物为生。有趣的是，在没有合适的寄主的情况下，海葵的幼虫可以直接发育成成虫。这种灵活性允许直接比较从幼虫到寄生虫的发育途径和从幼虫到自由生活的海葵的发育途径。分子和基因组技术将用于研究控制发育的基因，研究这些基因的功能在寄生虫发育过程中是如何改变的。除了这项研究解决的基本科学问题外，还将产生显著的更广泛的影响。鉴于寄主物种记忆藻是一种贪婪的捕食者，对商业上重要的鱼类，而爱德华氏菌有控制记忆藻种群的潜力，更多的寄生虫发展的知识将为其作为生物防治剂的可能使用提供信息。此外，这种寄主-寄生虫系统很容易在课堂环境中进行研究，作为研究的结果，将开发实验室练习，使新英格兰沿岸的高中和大学生物教师能够轻松、廉价地将寄生的活体演示纳入他们的教学计划。

Parasites outnumber free-living species, perhaps 4 to 1, and they play important roles in natural ecosystems. Parasites may directly harm humans or those species that humans depend on, or they may indirectly help humanity by controlling the abundance of pest species.Based on the abundance and diversity of parasites, it is clear that parasites evolved from free-living ancestors on many occasions in the past. However, the remarkable transition from free-living species to parasitic species is very poorly understood, mainly because most of the evolutionary transitions to parasitism that have been characterized occurred tens or hundreds of millions of years ago. This research addresses the origin of parasitism by utilizing a new model species that is in the early stages of becoming a parasite. As an adult, the lined sea anemone, Edwardsiella lineata looks and acts like a typical free-living sea anemone. However, its larva can invade the body of the comb jelly Mnemiopsis, where it develops into a small worm and makes its living by stealing partially digested food from the host's gut. Interestingly, in the absence of a suitable host, the anemone's larva can develop directly into an adult. This flexibility permits a direct comparison between the developmental pathway that leads from a larva to a parasitic worm and the developmental pathway that leads from a larva to a free-living sea anemone. Molecular and genomic techniques will be used to study the genes that control development, asking how the functions of these genes are altered during parasite development. Aside from the fundamental scientific questions addressed by this research, there will be notable Broader Impacts. Given that the host species Mnemiopsis is a voracious predator on commercially important fishes, and Edwardsiella has the potential to control Mnemiopsis populations, greater knowledge of the parasite's development will inform its possible use as a biological control agent. Furthermore, this host-parasite system is easy to study in the classroom setting, and, as an outgrowth of the research, laboratory exercises will be developed that will allow high school and college biology instructors located along the New England coast to easily and inexpensively incorporate living demonstrations of parasitism into their lesson plans.