Experimentally altering pre‐breeding sex steroids reduces extra‐pair paternity in female tree swallows
Bibliographic record
Abstract
Abstract Extra‐pair paternity commonly occurs in many socially monogamous animal species, yet the reasons why females mate with males outside the social pair bond remain poorly understood. Because sex steroids mediate aggressive and sexual behaviors that peak prior to egg laying in female birds, we tested whether they also influence the rate of extra‐pair paternity in nests of female tree swallows ( Tachycineta bicolor ). In one treatment, we experimentally elevated testosterone (T) using implants containing exogenous T, and in another treatment, we blocked the estrogenic and androgenic actions of T using implants containing 1,4,6‐androstatrien‐3,17‐dione in combination with flutamide ( ATD +F). Females with empty implants served as controls. Nests of females treated with T and those with ATD +F were less likely to contain extra‐pair offspring and had a lower proportion of extra‐pair offspring, compared to control females. Treating females with T also delayed clutch initiation dates and disrupted incubation behavior, as found in previous studies, but clutch sizes of T females did not differ from controls. Females treated with ATD +F tended to lay larger clutches than control and T‐treated females, which may be due to their clutch sizes not declining with later initiation dates as found in the T and control treatments; however, after controlling for brood size, ATD +F females produced nestlings that were lighter at day 16 than control females. Although the effect of T on extra‐pair paternity that we observed in tree swallows is consistent with previous studies in female birds, our results demonstrate that blocking the estrogenic and/or androgenic actions of T during pre‐breeding also lowers extra‐pair paternity. Overall, our study suggests that extra‐pair paternity in tree swallows is mediated by sex steroids of females.
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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".