Griffin, Joanne 
ORCID: 0000-0002-6401-7544
(2019)
Investigating the Biology of Host Shifts of Heritable Microbes.
PhD thesis, University of Liverpool.
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Abstract
Arthropods are commonly infected with chronic bacterial infections that are passed from mother to offspring, typically transovarially. Obligate mutualists provide arthropod hosts with nutrients, facultative mutualists protect hosts against natural enemies, and reproductive parasites alter the host’s offspring sex ratio. These phenotypes ensure future transmission events of the endosymbiont. Heritable microbe frequencies vary across host populations. Some species, for example Wolbachia, are predicted to be in over 50% of all arthropod species and do not appear to have any focussed taxonomic affiliations whereas Cardinium is present in 7% of species, with spiders and mites a pronounced incidence hotspot. The incidence of heritable microbes in nature is in part a product of their capacity to host shift. The success of the host shift depends on host compatibility (ability to receive and transmit a novel endosymbiont without the bacteria causing excess pathology or eliciting the host’s immune response). Compatibility evolves independently of the novel endosymbiont and a key determinant of the bacteria’s success is the phylogenetic distance of the novel host from the ancestral host. However, the extent to which host compatibility is an evolvable trait is unknown. In this thesis, I address key factors affecting host compatibility to novel endosymbiont infection. I assess the speed of evolution of host compatibility in the melanogaster subgroup of drosophilids, to novel endosymbiont, Spiroplasma poulsonii and find closely related species do differ in compatibility, as predicted by the phylogenetic clade model of compatibility. I serendipitously observed a phenotype switch in the bacterium in laboratory culture and compile preliminary evidence to form a better representation of the endosymbiont’s behaviour. Within this system, I also investigate the role of gut microbiota in determining host compatibility and find that gut microbiota and Spiroplasma do not interact to influence host life history traits. The thesis then examines interactions of a very different heritable microbe, Arsenophonus nasoniae. A. nasoniae relies on mixed modes of transmission to spread throughout host populations and is highly infectious. I observe that A. nasoniae presents an immune challenge to both adult female and diapausing larvae of its native host, Nasonia vitripennis. The bacterium presents fitness costs to novel host, Nasonia giraulti, reducing fecundity and upregulating immune genes. Further, I present a novel mechanism of symbiont control through oxidative stress and iron sequestration. These findings have important implications for host shift biology of heritable microbes and highlight the importance of including life history traits in evaluations of host-symbiont dynamics.
| Item Type: | Thesis (PhD) |
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| Divisions: | Faculty of Health and Life Sciences > Faculty of Health and Life Sciences |
| Depositing User: | Symplectic Admin |
| Date Deposited: | 13 Aug 2020 13:12 |
| Last Modified: | 19 Jan 2023 00:12 |
| DOI: | 10.17638/03066624 |
| Supervisors: |
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| URI: | https://livrepository.liverpool.ac.uk/id/eprint/3066624 |
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