The molecular basis and evolution of host manipulation by nematomorph parasites

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 level of expression of genes, proteins, and small RNAs are expressed will be investigated and compared between the life cycle stages of the worm and infection status of the host. 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.