Bibliographic record
Abstract
Sex is predicted to be a costly mode of reproduction associated with drawbacks such as a genetic transmission disadvantage, the destruction of favourable genetic associations, and the cost of finding mates. Despite this, most eukaryotic species reproduce sexually at least occasionally. In my thesis I use genomics and field work to explore the possible benefits and consequences of sexual reproduction. In Chapter 2, I analysed data from a mutation accumulation experiment using two highly asexual duckweed species. My analyses revealed some of the lowest known multicellular eukaryotic mutation rates, possibly a consequence of asexuality. In Chapter 3, I analysed patterns of linkage disequilibria (LD) in two population genomics datasets to explore the potential role of negative LD and synergistic epistasis among deleterious mutations in favouring sex. I found that patterns of genome-wide LD among deleterious mutations differed from those of neutral mutations, but that this was likely a by-product of complex demographic processes. Further analyses focusing specifically on deleterious mutations affecting genes in established genetic networks did suggest a signal of within-network negative LD, hinting at a possible role of negative epistasis in favoring the evolution of sex. In Chapter 4, I used exploratory population genomics analyses to examine signatures of selection and recombination in the facultatively sexual liverwort Marchantia polymorpha. My findings suggested that despite the likely limited dispersal of bryophyte sperm, M. polymorpha populations appear to engage in sexual reproduction at least occasionally. However, other analyses suggested that the M. polymorpha genome harbors a large fraction of deleterious genetic diversity, a possible hint of inefficient selection associated with predominantly asexual reproduction. Finally in Chapter 5, I attempted to experimentally compare the fitness of sexual and asexual offspring in M. polymorpha in a field experiment to broadly ask which mechanisms may favour the evolution of sex. However, my analyses suggested that almost all variation in fitness in my experiment was due to environmental heterogeneity, precluding any biologically meaningful comparisons of sexual and asexual offspring. Overall, my thesis contributes to our understanding of the consequences of sexual and asexual reproduction, particularly in species where both reproductive modes are employed.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.002 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".