Phylogenomics resolves key relationships in <i>Rumex</i> and uncovers a dynamic history of independently evolving sex chromosomes
Bibliographic record
Abstract
Abstract Sex chromosomes have evolved independently many times across eukaryotes. Despite a considerable body of literature on sex chromosome evolution, the causes and consequences of variation in their formation, degeneration, and turnover remain poorly understood. Chromosomal rearrangements are thought to play an important role in these processes by promoting or extending the suppression of recombination on sex chromosomes. Sex chromosome variation may also contribute to barriers to gene flow, limiting introgression among species. Comparative approaches in groups with sexual system variation can be valuable for understanding these questions. Rumex is a diverse genus of flowering plants harboring significant sexual system and karyotypic variation, including hermaphroditic and dioecious clades with XY (and XYY) sex chromosomes. Previous disagreement in the phylogenetic relationships among key species has rendered the history of sex chromosome evolution uncertain. Resolving this history is important for investigating the interplay of chromosomal rearrangements, introgression, and sex chromosome evolution in the genus. Here, we use new transcriptome assemblies from 11 species representing major clades in the genus, along with a whole-genome assembly generated for a key hermaphroditic species. Using phylogenomic approaches, we find evidence for the independent evolution of sex chromosomes across two major clades, and introgression from unsampled lineages likely predating the formation of sex chromosomes in the genus. Comparative genomic approaches revealed high rates of chromosomal rearrangement, especially in dioecious species, with evidence for a complex origin of the sex chromosomes through multiple chromosomal fusions. However, we found no evidence of elevated rates of fusion on the sex chromosomes in comparison with autosomes, providing no support for an adaptive hypothesis of sex chromosome expansion due to sexually antagonistic selection. Overall, our results highlight a complex history of karyotypic evolution in Rumex, raising questions about the role that chromosomal rearrangements might play in the evolution of large heteromorphic sex chromosomes.
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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 | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.000 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 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".