Davison, Helen 
ORCID: 0000-0002-4302-5756
(2023)
Investigating the evolution and ecology of obscure bacterial symbioses found in invertebrates, ciliates and algae.
PhD thesis, University of Liverpool.
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Abstract
Bacterial symbioses form a fundamental part of the biology of most eukaryotic lifeforms, influencing their evolution, ecology, and behaviour. Their importance has been increasingly recognised in the last few decades, aided by advances in genomic and bioinformatic methods and analyses. As with most emerging fields, most of our knowledge comes from selected ‘model’ case studies, leaving the breadth of possible symbioses poorly explored. In this thesis I utilise a combination of bioinformatics, genomics, fieldwork, and microscopy to explore obscure symbioses across invertebrates, algae, and ciliates. First, I broaden the scope of available genomic and metabolic data available for rarer symbionts in invertebrates, a group that are often studied for their heritable symbionts. I argue that the group previously called Torix Rickettsia is distinct and diverse and should be regarded as a genus with at least three species, which I name ‘Candidatus Tisiphia’. I also report the first genome for the genus ‘Candidatus Megaira’, a widely recorded but poorly understood symbiont of microeukaryotes. I then explored the distribution of various symbiotic bacteria found in ciliates and algae, two host groups that are known to have strong links to symbiotic bacteria and the origins of symbioses but are rarely examined. I show the genus ‘Ca. Megaira’ appears as a deeply diverse, multi-species group of symbionts that is deserving of family status. I find ‘Ca. Megaira’ in both algae and ciliate species and infer that they have the potential to form protective symbioses. Likewise, I find diverse Parachlamydiales in algae and ciliates and propose three new species groups to aid taxonomic clarification of these bacteria. I provide potential microeukaryotic hosts for a group that are often divorced from host species when described and propose the possibility of nutritional and protective symbioses. Lastly, I develop a potential host-symbiont study system for future functional studies. Here, I demonstrate the existence of a likely heritable Ca. Tisiphia symbiont in the mosquito Anopheles plumbeus. It represents a potentially important system for onward application in manipulation of anopheline vector populations, which are currently restricted to a single symbiont. Finally, I synthesize these findings and argue future research should focus on the phenotypes of real-world symbioses discovered within this research.
| Item Type: | Thesis (PhD) |
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| Uncontrolled Keywords: | Anopheles, Bacterial endosymbionts, bioinformatics, Chlamydia, Evolution, Megaira, Phylogenomics, Rickettsia, Symbiosis |
| Divisions: | Faculty of Health and Life Sciences Faculty of Health and Life Sciences > Institute of Systems, Molecular and Integrative Biology |
| Depositing User: | Symplectic Admin |
| Date Deposited: | 14 Aug 2023 14:56 |
| Last Modified: | 14 Aug 2023 14:56 |
| DOI: | 10.17638/03170155 |
| Supervisors: |
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| URI: | https://livrepository.liverpool.ac.uk/id/eprint/3170155 |
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