Barnes, Megan
(2025)
The Ecological and Evolutionary Significance of Functional Variation in Mitochondria in the Three-spined Stickleback.
PhD thesis, University of Nottingham.
Abstract
Mitochondria are widely known as the ‘powerhouse of the cell’ due to their importance in energy metabolism, and the mitochondrial DNA (mtDNA) plays a central role as it encodes subunits of the oxidative phosphorylation pathway, responsible for the majority of this energy production when oxygen is available. Despite this fundamental role, the adaptive significance of mtDNA variation has often been overlooked. It is now well established that the mitogenome is not evolving neutrally as once assumed, with studies across numerous taxa identifying evidence of positive selection, or showing that mtDNA variation has functional consequences which can be associated with adaptation. However, pure mitochondrial effects have rarely been separated from nuclear genetic effects in natural study systems, mainly due to a lack of populations or species wherein variation in the mtDNA can be studied independent of potentially confounding variation in the nuclear genetic background. In this thesis, I focus on Atlantic three-spined stickleback (Gasterosteus aculeatus) on the Scottish island of North Uist, where, in migratory populations, two deeply diverged mitochondrial lineages segregate against a common nuclear genomic background. I show that the stickleback provides a valuable model to determine the adaptive significance of mtDNA variation. I first assessed the development of migratory stickleback, and examined the effect of anaesthetics on mitochondrial function. I then focused on variation between the two highly diverged mitochondrial lineages that likely diverged in allopatry on opposite sides of the Atlantic, but are now both widespread. Migratory populations were a mix of the two lineages, but resident populations in fresh water and saltwater lagoons were predominantly one lineage, suggesting differing adaptive potential. Using phylogenetic selection analyses, I found evidence that the mitogenomes of the Atlantic three-spined stickleback evolved under positive selection, so the mtDNA variation itself may be adaptive. Unlike previous work in natural populations, I was able to show that mtDNA variation had temperature-dependent consequences for mitochondrial respiration independent of the nuclear genetic background. By combining phylogeography, ecology, selection analyses and mitochondrial physiology, I show that mitochondrial variation makes an important contribution to the ecology and evolution of the Atlantic three-spined stickleback. To my knowledge, this research may be the first to explicitly link mtDNA variation to physiological mitochondrial differences and adaptive potential in natural populations, independent of the nuclear genome.
| Item Type: |
Thesis (University of Nottingham only)
(PhD)
|
| Supervisors: |
MacColl, Andrew
Chakrabarti, Lisa |
| Keywords: |
Mitochondria, mitochondrial DNA (mtDNA), Atlantic three-spined stickleback (Gasterosteus aculeatus) |
| Subjects: |
Q Science > QR Microbiology > QR100 Microbial ecology |
| Faculties/Schools: |
UK Campuses > Faculty of Medicine and Health Sciences > School of Life Sciences |
| Item ID: |
81567 |
| Depositing User: |
Barnes, Megan
|
| Date Deposited: |
31 Dec 2025 04:40 |
| Last Modified: |
31 Dec 2025 04:40 |
| URI: |
https://eprints.nottingham.ac.uk/id/eprint/81567 |
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