Adaptive Evolution of M3 Lysin—A Candidate Gamete Recognition Protein in the Mytilus edulis Species Complex
Bibliographic record
Abstract
Marine invertebrate gamete recognition proteins (GRPs) are classic examples of rapid adaptive evolution of reproductive proteins, and hybridizing Mytilus blue mussels allow us to study the evolution of GRPs during speciation following secondary contact. Even with frequent hybridization, positive selection drives divergence of M7 lysin, one of the three Mytilus egg vitelline envelope (VE) lysins. Mytilus trossulus and M. edulis form a broad hybrid zone in the Canadian Maritimes and eastern Maine, isolated by strong (but partial) gamete incompatibility. M7 lysin, however, is an unlikely GRP controlling this gametic incompativility, as earlier studies showed either weak or no positive selection and extensive introgression between the two species. We used reverse transcriptase-polymerase chain reaction and cloned several alleles of M3 lysin, a potent VE lysin encoded by a nonhomologous gene whose evolution has not been studied. McDonald-Kreitman and HKA tests reveal strong positive selection, which PAML branch-site models detect in 19.7% of the codons. Protein structure predictions show that replacements map exclusively to one face of the carbohydrate recognition domain (CRD) of this C-type lectin, with codons under positive selection localizing to CRD regions known to control ligand specificity. Polymorphism/divergence analyses show that selective sweep has purged M. edulis but not M. trossulus of polymorphism, and unique to M3 is an absence of fixed substitutions and broad haplotype sharing between M. edulis and Mediterranean M. galloprovincialis. Taken together, these results suggest that different lysins serve as GRPs in different Mytilus hybrid zones, with M3 likely co-opted to play this role in the western Atlantic.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 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) | 0.000 | 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 teacher head, 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".