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Title: Investigating the relationship between gut microbiota and animal behaviour
Author: Heys, Chloe Elizabeth
ISNI:       0000 0004 7658 9237
Awarding Body: University of Liverpool
Current Institution: University of Liverpool
Date of Award: 2018
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An individual's gut microbiota is increasingly recognised as having a key role in many host behaviours. In insects, the environment largely determines the host gut microbiota, with the majority ingested through the diet. In this thesis, I examine a series of host-gut microbiota relationships within three species of Drosophila with varied ecologies. Initially, I analyse the current methods used to eliminate the gut microbiota in Drosophila melanogaster, key to studying host-microbiota relationships and providing a foundation for this thesis. I then use this information to assess the role of the gut microbiota as an honest signal in age-based mate choice in Drosophila pseduoobscura. Finally, I examine the role the gut microbiota plays in specialisation in Drosophila sechellia, through adaptation to its toxic host plant, Morinda citrifolia. To attribute a specific behaviour to the gut microbiota, it must first be removed. However, removal can have serious physiological side effects on the host organism, and the most effective and least detrimental method of doing this is widely debated. I analyse commonly used methods of removing the gut microbiota in Drosophila melanogaster and find the addition of lowdose streptomycin to the dietary media is more effective and has fewer physiological effects than other methods such as egg dechorionation or rearing on a sterile diet. Female Drosophila pseudoobscura are known to discriminate between males based on age. This may occur through the alteration of the cuticular hydrocarbon (CHC) profile of males, which can alter due to a varied gut microbiota caused by a varied diet. I determine that the gut microbiota influences female preference for older males and is a key component of attractiveness to females. I examine the role of the gut microbiota in Drosophila sechellia, in adaptation to its toxic host plant, Morinda citrifolia, and characterise the gut microbiota of this Drosophilid species for the first time. Rearing flies on M. citrifolia, a standard laboratory diet, and an additional salak (Salacca zalacca) fruit that lacks the toxic compounds present in M. citrifolia, I find that flies reared on a laboratory diet have a significantly reduced weight. However, there is no impact on development time or subsequent mating behaviours when compared to individuals reared on the wild, M. citrifolia diet. Finally, by creating experimental evolution lines of D. melanogaster supplemented with D. sechellia gut microbiota, I disentangle the role of pH in shaping the gut microbiota from the co-evolution of the gut microbiota within D. sechellia. D. melanogaster are highly averse to the scent of octanoic acid, the main toxic constituent within M. citrifolia, whereas D. sechellia are highly attracted. After ten generations D. melanogaster show significantly less aversity to octanoic acid. I determine that Lactobacillus plantarum acts as a detoxifying agent by metabolising octanoic acid, therefore suggesting this bacterium has been fundamental to the ecological transition and specialisation of D. sechellia. Taken together, the chapters of this thesis further uncover the role of hostmicrobiota interactions in important ecological and evolutionary processes within Drosophila, from elucidating a principle method in gut microbiota research, to underlying mate choice mechanisms and finally to dietary specialisation.
Supervisor: Darby, Alistair ; Lewis, Zenobia Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral