The molecular basis and evolution of host manipulation by nematomorph parasites

线虫，通常被称为马毛蠕虫，是三个完全寄生的动物门之一。线虫是无脊椎动物的寄生蠕虫，它们感染并操纵其最终节肢动物宿主（例如蟋蟀）的行为，使其跳入水中“自杀”。它们这样做是为了到达水生环境，这是它们完成生命周期所需要的。尽管对这种行为的观察相对普遍，但这种行为操纵在分子和遗传水平上的潜在机制仍未得到充分研究。因此，该项目的总体目标是调查涉及这种行为操纵的潜在分子机制，这种机制是如何进化的，以及英国和潜在的国际上线形生物的多样性，从而增加我们对这一研究不足领域的了解。本项目的初步目标包括：在实验室培养线虫的生命周期，同时保持最终宿主（蟋蟀）和副病原宿主（淡水蜗牛）的存量，并设计一种行为测定方法来分析实验操作。这个项目的方法论包括现场、实验室和计算组件。野外方面将包括从水生环境中收集自由生活的成虫、包囊或幼虫，或收集寄主（例如蟋蟀），将寄主放置在水中，等待蠕虫的出现。标本将从英国各地收集，可能会从美国和日本收集。在适用的情况下，通过显微镜或分子技术将所有标本鉴定到物种水平。基因组和遗传调查以及系统发育分析将用于调查英国线形动物的多样性，并在不同地点之间进行潜在的比较。实验室组成部分将包括在实验室建立和维持线虫的培养，以及它们的最终和副病原宿主的菌落。该系统将用于收集寄生虫的各个生命周期阶段的组织或分泌物，以及感染和未感染的宿主，这将使RNA，蛋白质和小RNA的提取和鉴定通过质谱或测序。分离的分泌物将用于昆虫宿主的行为分析，以调查每种分泌物改变宿主行为的能力。最后，本项目将使用生物信息学来研究哪些基因、蛋白质和小rna被表达及其表达水平。这些表达谱可以在蠕虫的生命周期阶段和宿主的感染状态之间进行比较。这将有助于研究这种行为操纵是如何进化的，例如，如果与宿主感染相关的特定基因、蛋白质或小RNA在线虫的整个生命周期中存在或表达，这可能意味着该基因、蛋白质或小RNA对线虫的功能至关重要，并且意外地产生了对线虫有益的特定行为效应，从而进化利用了这一点。相反，如果给定的基因、蛋白质或小RNA仅在与宿主感染相关的蠕虫阶段存在或表达，则可能意味着这种机制是在进入宿主后进化而来的，是一种重新进入水生环境以完成其生命周期的方法。

The Nematomorpha, commonly known as horsehair worms, comprise one of three fully parasitic animal phyla. Nematomorphs are parasitic worms of invertebrates, which infect and manipulate the behaviour of their definitive arthropod host (e.g. crickets) to 'commit suicide' by jumping into water. They do this to reach an aquatic environment, which they require to complete their life cycle. Although observations of this behaviour are relatively common, the underlying mechanism of this behavioural manipulation at a molecular and genetic level remains understudied. Therefore, the overall aims of this project are to investigate the underlying molecular mechanism involved in this behavioural manipulation, how this mechanism evolved, and the diversity of nematomorphs within the UK, and potentially internationally, thus increasing our knowledge of this understudied area.The initial objectives of this project involve; culturing the nematomorph life cycle in the laboratory whilst maintaining stocks of the definitive (cricket) and paratenic (freshwater snails) hosts, and designing a behavioural assay for analysis of experimental manipulation. The methodology for this project involves field, laboratory and computational components. Field aspects will involve collecting free-living adult worms, cysts or larvae from aquatic environments, or collecting the host (e.g. crickets), which would be placed in water for the emergence of worms. Specimens will be collected from various locations across the UK, with potential collection from the US and Japan. All specimens would be identified to species level, where applicable, via microscopy or molecular techniques. Genomic and genetic investigation, and phylogenetic analyses would be used to investigate the diversity of nematomorphs in the UK, with potential comparisons between locations. Laboratory components will involve establishing and maintaining a culture of nematomorphs, and colonies of their definitive and paratenic hosts in the laboratory. This system will be used for collection of tissue or secretions from the various life cycle stages of the parasite, and the infected and uninfected host, which will enable RNA, protein and small RNA extraction and identification via mass spectrometry or sequencing. Isolated secretions will be used in behavioural assays of the insect host to investigate the ability of each secretion to alter host behaviour. Finally, this project will use bioinformatics to investigate which genes, proteins, and small RNAs are expressed and the level of expression. These expression profiles can then be compared between the life cycle stages of the worm and infection status of the host. This will aid in investigating how this behavioural manipulation evolved, e.g. if a given gene, protein or small RNA associated with host infection is present or expressed throughout the nematomorph life cycle, it could imply said gene, protein or small RNA is essential for nematomorph functioning and accidently had the given behavioural effect, which being beneficial for the worm, evolved to exploit this. Conversely, if the given gene, protein or small RNA is only present or expressed during the stages of the worm associated with host infection, it could imply this mechanism evolved in response to being inside the host as a method to re-enter an aquatic environment to complete their life cycle.