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Title: Parasite-induced warning colouration
Author: Jones, R. S.
Awarding Body: University of Liverpool
Current Institution: University of Liverpool
Date of Award: 2016
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Parasites are ubiquitous in nature and are capable of exerting strong selection pressures on their hosts to enhance (or potentially reduce) transmission. Parasite manipulation of hosts can therefore drive evolution of various traits and phenotypes in the host to the benefit of the parasite. These adaptations can serve a number of purposes, working to enhance survival and reproduction of the parasite within its host. This thesis aims to elucidate the roles of various defences induced by the nematode Heterorhabditis bacteriophora and its symbiotic bacterium Photorhabdus luminescens in its obligate insect host, in which predation of the host is fatal for the parasitic colony. To do this I utilised both laboratory and field experiments to test a number of the defences with a variety of predators. To begin with I extended a previous study examining predation rates on uninfected and infected individuals by examining the effect of background on predation rates in the field. I found that prey that were conspicuous against their background received fewer attacks and were consumed less than those that were cryptic with respect to their background, enhancing survival for the parasitic colony within infected hosts. Following this I was then able to test a number of the defences utilising ground beetles, birds and mice as predators. In a laboratory setting I tested whether beetles could use any of the parasite-induced cues to avoid predation of infected waxworm hosts. I found infections were vulnerable early on (day 3 post-infection) in terms of chemical defence as beetles would consume this infection stage to a greater extent than either day 5 or 7 post-infection waxworms. However, beetles utilised the olfactory cue to avoid predation of infected hosts across all infection stages, protecting the parasite colony. Having seen an effect of the visual cue, and perhaps olfactory cue in the initial field experiment, I decided to test both these components in concert and singly in a laboratory environment with wild-caught great tits in Finland. There was not a clear benefit to multimodality in terms of attacks but there was in terms of consumption of infected waxworms at various stages of infection. Additionally, there was evidence that the olfactory cue overshadowed the visual cue in terms of attack at various stages of infection. Having examined the visual, chemical and olfactory cues, I then tested the role of bioluminescence in this nematode-bacterium system. Utilising house mice as predators I tested both the olfactory cue and bioluminescence cue with the same experimental design under differing light conditions, where the bioluminescence was and was not visible. Unlike in other predators tested, the olfactory cue did not elicit a strong avoidance response, resulting in only discriminatory behaviour towards later stage infections (day 7 post-infection). However, I found that bioluminescence was an effective cue at causing deterrence in house mice as mice spent less time near glowing than non-glowing prey. Overall, this thesis provides novel insights into the role of defences induced by a nematode-bacterium complex in protecting the infected host carcass against predation, which is fatal for the parasitic colony. Furthermore, the thesis provides ideas for future research to develop these findings further.
Supervisor: Speed, M. S. ; Fenton, A. Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral