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 the evolution of sex chromosomes, the causes and consequences of variation in the formation, degeneration, and turnover of sex chromosomes remain poorly understood. Comparative approaches in groups with sexual system variation can be valuable for understanding these questions. Plants are well-suited to such comparative studies, with many lineages containing relatively recent origins of dioecy and sex chromosomes as well as hermaphroditic close relatives. Rumex is a diverse genus of flowering plants harboring significant sexual system variation, including hermaphroditic and dioecious clades with XY sex chromosomes. Previous disagreement in the phylogenetic relationships among key species have rendered the history of sex chromosome evolution uncertain. Resolving this history is important to the development of Rumex as a system for the comparative study of sex chromosome evolution. Here, we leverage new transcriptome assemblies from 11 species representing the major clades in the genus, along with a whole-genome assembly generated for a pivotal hermaphroditic species, to further resolve the phylogeny and history of sex chromosome evolution in Rumex . Using phylogenomic approaches, we find evidence for two independent origins of sex chromosomes and introgression from unsampled taxa in the genus. Comparative genomics reveals massive chromosomal rearrangements in a dioecious species, with evidence for a complex origin of the sex chromosomes through multiple chromosomal fusions. However, we see no evidence of elevated rates of fusion on the sex chromosome in comparison with autosomes, providing no support for an adaptive hypothesis for the sex chromosome expansion. Overall, our results highlight the dynamic nature of sex chromosome systems in Rumex and illustrate the utility of the genus as a model for the comparative study of sex chromosome evolution.
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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 | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.002 | 0.001 |
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".