Molecular and Behavioural Mechanisms of Host Manipulation by Nematomorph Parasites

Abstract

Nematomorphs are parasitic worms of arthropods and are one of the most understudied animal phyla. Their life cycle spans aquatic and terrestrial environments including a free-living aquatic adult stage and an obligate parasitic juvenile stage in terrestrial arthropods. To return to an aquatic environment to reproduce, the mature worms manipulate the behaviour of their terrestrial host to seek out and enter water, a behaviour not normally observed in the host. This is an example of the extended phenotype of the parasite, with parasitic genes having a phenotypic effect on the host. The exact mechanism of this behavioural manipulation, at both a behavioural and molecular level, is unknown. Previous hypotheses include an attraction to water, attraction to polarised light, and the induction of erratic behaviour, though a combination of these behaviours could be involved. Previous investigations into this manipulation have been predominantly behavioural. Understanding this manipulation, both behaviourally and molecularly, will improve our knowledge of host-parasite interactions with potential applications for conservation and pest control. This thesis aimed to investigate the behavioural and molecular mechanisms of host behavioural manipulation by nematomorphs. In Chapter 2, the nematomorph life cycle was initiated from a wild collected UK species (Gordius aquaticus) and previously domesticated US species (Paragordius varius). Chapter 3 focuses on the water attraction hypothesis via dehydration through investigating the behaviour and proteome of house crickets, Acheta domesticus, which were either dehydrated or infected with the nematomorph Paragordius varius. Chapter 4 focuses on the erratic behaviour hypothesis and characterises the abnormal behaviours of Paragordius varius infected crickets in comparison to uninfected controls. Chapter 4 also explores the role of parasite secretions in manipulating host behaviour via injections of naïve crickets and identification of manipulating molecules (proteins and small RNAs) in the secretions of immature and mature P. varius and host haemolymph. Chapter 3 and 4 also explore other physiological effects on the host as a result of nematomorph infection. Overall, this thesis contributes to our understanding of host-parasite interactions, specifically host behavioural manipulation, with novel insights into the underlying molecular mechanisms involved.  

Date of Award	20 May 2026
Original language	English
Awarding Institution	University of Bath
Supervisor	Vicky Hunt (Supervisor), Daniel Henk (Supervisor) & Lauren Hughes (Supervisor)