Lyth, Sophie
(2024)
The ecology of a sex ratio distorting meiotic driver.
PhD thesis, University of Liverpool.
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Abstract
Subverting the laws of fair Mendelian inheritance, selfish genetic elements (SGEs) bias their own transmission into subsequent generations, often at the cost to the rest of the genome. These systems are common in nature and can spread rapidly to fixation due to their transmission advantage. In this thesis, I examine a particular type of SGE, X chromosome meiotic drive (XCMD), in Drosophila subobscura. XCMD manipulates gamete production in males, where selfish X chromosomes kill Y-bearing sperm during spermatogenesis, resulting in the production of only daughters. Despite the transmission advantage of these X chromosomes, many XCMD systems in nature remain at low and stable frequencies, and do not rapidly spread to fixation as expected. Indeed, the XCMD system in D. subobscura has remained at a frequency of approximately 20% in North Africa for at least 50 years. The factors that are strong enough to counteract the transmission advantage of the selfish X chromosome, however, remain poorly understood. In this thesis, I examine factors that could prevent the XCMD system in D. subobscura from rapidly spreading to fixation. I first examine the effect of extreme temperatures on individuals that carry XCMD, to investigate if this is a stabilising force of drive. There has previously been evidence of a relationship between XCMD and temperature, as many species that carry XCMD show a latitudinal cline in drive frequency. Thus, varying temperatures may prevent XCMD from spreading, but here I find extreme temperatures were not a stabilising force. I then characterise the first strong suppressor of XCMD in D. subobscura. Suppression of drive rescues Y-bearing sperm, allowing SR carrying males to produce sons. Here, I show that this suppressor is capable of restoring normal sex ratios, rather than a 100% female bias progeny that drive causes. The remaining chapters of this thesis go on to investigate the nature of the drive suppressor. In spite of the predicted selection pressure for this suppressor to spread, drive remains at intermediate frequencies and suppression against it remains rare. Motivated by this observation, I search for fitness costs that are associated with carrying this suppressor in chapters 4 and 5 as an explanation as to why it has not become fixed within populations that harbour drive. My final chapter will then investigate the strength of the suppressor to see if it is capable of restoring normal 50:50 sex ratios to populations. Using an experimental evolution approach, I investigate whether suppression against XCMD can rescue laboratory populations from extinction as a result of the presence of meiotic drive.
| Item Type: | Thesis (PhD) |
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| Additional Information: | Permanent email address: sophie_lyth@hotmail.co.uk |
| Divisions: | Faculty of Health and Life Sciences Faculty of Health and Life Sciences > Institute of Infection, Veterinary and Ecological Sciences Faculty of Health and Life Sciences > Institute of Systems, Molecular and Integrative Biology Faculty of Health and Life Sciences > Institute of Systems, Molecular and Integrative Biology > School of Life Sciences |
| Depositing User: | Symplectic Admin |
| Date Deposited: | 18 Sep 2024 12:56 |
| Last Modified: | 08 Feb 2025 03:03 |
| DOI: | 10.17638/03182068 |
| Supervisors: |
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| URI: | https://livrepository.liverpool.ac.uk/id/eprint/3182068 |
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