Sex chromosome turnover in African annual killifishes of the genus Nothobranchius
Bibliographic record
Abstract
Sex chromosomes of teleost fishes often have low levels of differentiation and undergo frequent turnovers. Annual Nothobranchius killifishes comprise representatives with male-heterogametic XY or X1X2Y sex chromosome systems, scattered across their phylogeny, nested within species lacking cytologically detectable sex chromosomes. They thus provide a suitable system to study sex chromosome evolution and turnover. Here, we combined molecular cytogenetics and genomic analyses to examine several multiple sex chromosome systems in Nothobranchius spp. and their outgroup Fundulosoma thierryi. We used fluorescence in situ hybridization with three sex chromosome-specific painting probes and bacterial artificial chromosomes (BAC) bearing eight orthologues of genes found to be repeatedly co-opted as master sex determining (MSD) genes in fishes. Our results suggest at least four independent origins of sex chromosomes in the genus Nothobranchius. The synteny block carrying amhr2 gene was shared by X1X2Y systems of N. brieni, N. guentheri and N. lourensi, but the autosomal additions and the overall neo-Y chromosome structure differed among these species. On the other hand, gdf6 gene was localized to neo-Y of F. thierryi. None of the mapped MSD gene candidates seems to determine sex in N. ditte. We further sequenced genomes of F. thierryi female and N. guentheri male by long-read platforms and performed analyses of male and female Pool-seq data and coverage to delimit their non-recombining regions, determine degree of their differentiation, and thus complement the cytogenetic data in assessing potential MSD genes. We found low level of sex chromosomes differentiation in F. thierryi. In N. guentheri, however, we identified two distinct evolutionary strata on neo-Y. The amhr2 gene resides in the younger stratum and has low allelic variation, which questions its role in sex determination.
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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 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| 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".