The gut microbiome of the wild great tit (Parus major): drivers and fitness consequences

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Somers, Shane Edmond
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University College Cork
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The gut microbiome plays a vital role in its host’s ecology. Clinical studies have shown gut microbes increase host health and fitness by providing digestive and immune functions, as well as aiding development. Natural variation in the microbiome is widely believed to affect host fitness in the wild but we are lacking experimental studies to test this. The microbiome varies with both host and environmental factors but most studies to date have focussed on individual factors and not adequately addressed the multiple overlapping and hierarchical drivers of microbiome variation working at environmental, host and microbial scales. This thesis investigates the role of the gut microbiota in host fitness, and how this is affected by and varies across contexts. Additionally, we address sources of variation in the gut microbiota at a host and environmental level, accounting for host ecology and drivers at different scales. We find that the host’s weight is correlated with microbiome diversity during development but that the direction of this relationship is context dependent. This shows that the microbiome interacts with the environment to determine host fitness and is important because it helps explain the contradictory findings linking diversity to weight. We also show that the interaction between the host, its microbiome and environment change with developmental stage. Specifically, we found that the microbiome of developed individuals is remarkably resilient to environmental perturbation, while developing individuals are much more sensitive, with important implications for future experiments. We developed a novel method for experimentally perturbing the microbiome that will allow microbiome researchers to begin testing hypotheses linking the microbiome to host ecology and evolution in natural settings. Finally, we show that welfare measures, such as environmental enrichment may interact with the gut microbiota to impact on host health and behaviour. In summary, I show that variation in the microbiome is linked to host ecology and that this variation is linked to host fitness.
Microbiome , Fitness , Microbiota , Gut microbiome , Great tit , Ornithology , Wild microbiome
Somers, S. E. 2023. The gut microbiome of the wild great tit (Parus major): drivers and fitness consequences. PhD Thesis, University College Cork.