Pattern, Process and the Evolution of Sexual Dimorphism in Three-Spine Stickleback Fish Gasterosteus Aculeatus from Vancouver Island, British Columbia
Bibliographic record
Abstract
Males and females of a species often differ from one another in phenotype—a phenomenon known as sexual dimorphism. Sexual dimorphism is most often attributed to sexual selection. However, sexual dimorphism also derives from natural selection when resource competition generates disruptive selection favoring specialization on different resources, resulting in niche partitioning and the evolution of dimorphism in traits related to competition. Sexual dimorphism may be an important route to increased individual fitness (i.e., more resources, more survival). For example, ecologically driven divergent selection between sexes may derive from differences in their environments, resulting in the evolution of dimorphism in traits related to habitat use and resource competition. Such differences between sexes should reduce intersexual competition. First, an existing dataset was used to quantify the existence of sexual dimorphism in 32 populations of Three-spine Stickleback fish, comprised of 16 paired lake-stream populations. We tested for shared and unique aspects of dimorphism within and across lake-stream pairs and asked whether variation in dimorphism could be explained by variation in the environment. We found a significant effect of sex, showing that dimorphism exists in the lake-stream pairs, implying that female sticklebacks are repeatably different from males. Next, using Three-spine Stickleback, we ran a 5-week enclosure experiment with 119 cages containing either same-sex or opposite-sex pairs, using body condition and survival to measure dimorphism's effects on competition. We found that male-male pairs ended with better body conditions than female- female and male-female pairs. Individually, males also had slightly better survival rates than females. This suggests that our evidence is mixed and that natural selection may be driven by patterns of sexual selection in the evolution of sexual dimorphism.
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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 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 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".