Testing the gravity hypothesis of sexual size dimorphism: are small males faster climbers?
Bibliographic record
Abstract
Summary Moya‐Laraño et al. (2002 ; Evolution 56, 420–425) showed that female‐biased sexual size dimorphism is more pronounced in tree‐dwelling spider species than in species inhabiting lower‐lying substrates. They proposed the Gravity Hypothesis for sexual size dimorphism: small size should be advantageous for males in habitats where successful mate searching requires climbing, because mass‐specific power and hence the speed of climbing against gravity, must decrease with increasing size. Their biomechanical model is based on a false premise, that the cross‐sectional area of a muscle determines its power output. In fact, muscle power is proportional to muscle volume, and hence mass‐specific power should be independent of size. We therefore predict, contrary to the Gravity Hypothesis, that climbing speed should be independent of body size. We tested these contrasting predictions using adult male Western black widow spiders Latrodectus hesperus, a species in which males span a broad range of sizes. In accordance with our prediction, and contrary to the Gravity Hypothesis, we found no relationship between vertical climbing speed and any of a series of size measures, whereas on a horizontal surface, speed was positively related to size. Our results, as well as the error we exposed in the biomechanical model underlying the Gravity Hypothesis, indicate that selection for vertical climbing speed in males cannot account for patterns of sexual size dimorphism in spiders.
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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 | 0.002 | 0.008 |
| 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 | 0.001 |
| Scholarly communication | 0.000 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.003 | 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".