Is there evidence for the Bruce effect in white-faced capuchins?
Bibliographic record
Abstract
Infanticide by males is an extreme form of sexual conflict that can increase male reproductive success at a cost to female reproductive success. Females have evolved a variety of strategies to reduce the occurrence and the cost of infanticide, including the termination of pregnancy after nontraumatic exposure to nonsire males, known as the Bruce effect. A recent model proposed that the Bruce effect will evolve in populations if the risk of infanticide is high and alpha male replacements occur routinely but infrequently relative to gestation length. We tested this model using 38 years of demographic data from a population of wild white-faced capuchins, Cebus imitator , in Sector Santa Rosa of the Área de Conservación Guanacaste, Costa Rica. We found that this population has a high rate of infanticide associated with alpha male replacements that occur every 2.9 years on average. Applying this model to our population leads to the prediction that capuchins should exhibit the Bruce effect, as the associated reproductive costs would be lower than the expected costs of future infanticide. However, we did not find evidence of any type of male-mediated prenatal loss in this species: female birth rates after alpha male replacements were not lower compared to stable periods. Possible explanations include that white-faced capuchins do not respond to extreme events with reproductive inhibition, or that other female strategies such as allonursing better mitigate the costs of infanticide. Finally, the evolution of female reproductive strategies may not be labile enough that it can be predicted from population-specific social and demographic patterns without regard to phylogenetic constraints. More studies are needed to understand the conditions that determine the occurrence and evolution of the Bruce effect in wild mammalian populations. • The Bruce effect is a female strategy to reduce the costs of infanticide. • It will evolve in species with high infanticide and infrequent alpha male replacements. • White-faced capuchins are predicted to exhibit the Bruce effect. • Birth rates after alpha male replacements suggest no evidence for the Bruce effect. • Costs and benefits of different female strategies are likely to differ across species.
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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 | 0.001 |
| 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".