Molecular evidence for introgressive hybridization in New Zealand masked gulls
Bibliographic record
Abstract
We used mitochondrial DNA (mtDNA) gene sequences and nuclear microsatellite loci to investigate the extent and outcome of hybridization between the Black‐billed GullChroicocephalus bulleriand the Red‐billed GullChroicocephalus novaehollandiae scopulinusin New Zealand. Six of 26 sampled Black‐billed Gulls possessed mtDNA typical of Red‐billed Gulls, but allele frequencies at six polymorphic microsatellites provided little evidence of mixed ancestry expected in very recent hybrids. None of the Red‐billed Gulls sampled from different colonies possessed Black‐billed Gull mtDNA expected in the reciprocal cross, suggesting that hybridization in the two species typically occurs between female Red‐billed Gulls and Black‐billed Gull males. The lack of any hybrid signal in the nuclear loci indicates that there has been extensive backcrossing with Black‐billed Gulls, effectively diluting the Red‐billed Gull nuclear DNA contribution. Divergence of Red‐billed Gulls and Black‐billed Gulls occurred approximately 250 000 years ago, indicating that unsorted ancestral polymorphism is an unlikely alternative to hybridization. Comparing demographic models within an approximate Bayesian computation (ABC) framework, we confirm that the observed patterns cannot result from incomplete lineage sorting. Using an ABC random forest approach, we determined that the most likely model explaining the data is a recent introgression scenario, whereby unidirectional gene flow is re‐established following a period of strict isolation. The ability of Black‐billed and Red‐billed Gulls to successfully interbreed shows that despite significant differentiation (FST > 0.3), there has been insufficient time for the two species to develop complete reproductive isolation. The apparent one‐way transfer of Red‐billed Gull mtDNA into Black‐billed Gulls and extensive backcrossing argues against cytoplasmic–nuclear genome incompatibilities between the two species. We hypothesize that the specific mate recognition system cued on colours of soft parts normally functions to prevent hybridization, but that it can break down under demographic conditions where there is a shortage of available mates and a surplus of females in the Red‐billed Gull population. The high incidence of introgression in Black‐billed Gulls conflicts with field observations that interbreeding is extremely rare.
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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 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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".