Dexamethasone treatment supports age‐related maturation of the stress response in altricial nestling birds
Bibliographic record
Abstract
In birds, the magnitude of the adrenocortical stress response can be down‐regulated during specific life‐history stages. Such modulation likely occurs when the effects of mounting robust corticosterone (Cort) elevations interfere with the normal progression of critical lifecycle activities (e.g. development, molt, migration, reproduction). The developmental hypothesis posits that altricial birds should display a ‘stress hyporesponsive period’ during the early post‐natal life stages, characterized by reduced adrenocortical stress responses compared to adult birds and a gradual age‐related increase. Such modulation would allow avoiding the potential deleterious effects that long‐term elevations of circulating Cort might exert on growth and development, when the physiological and behavioral abilities to cope with disturbance are limited. Two proximate hypotheses have been proposed to explain this age‐dependent pattern of Cort secretion. The ‘maturation hypothesis’ proposes a progressive age‐related growth, maturation and enhanced sensitivity to sensory input of the Hypothalamic‐Pituitary‐Adrenal (HPA) axis tissues, whereas the ‘negative feedback attenuation hypothesis’ proposes a gradual attenuation in the intensity of the negative feedback in the HPA axis. Here we tested these hypotheses by experimentally inducing negative feedback on the HPA axis via dexamethasone (DEX) treatment in nestling white storks Ciconia ciconia . Nestling age positively affected stress‐induced plasma Cort (STRESS‐Cort) levels during experimental handling and restraint, thus supporting the developmental hypothesis. DEX treatment significantly reduced STRESS‐Cort levels compared to saline (SAL) treatment, thus eliciting the expected negative feedback on the HPA axis. However, inter‐ and intra‐individual comparisons indicated no age effects on the intensity of the negative feedback exerted by DEX. Our results do not support the negative feedback attenuation hypothesis and suggest that progressive maturation of the HPA axis tissues is the proximate mechanism responsible for age‐related changes in the stress response during avian post‐natal development. We encourage further tests of the proposed proximate mechanisms during migration, breeding and molt.
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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 | 0.000 |
| 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 | 0.001 |
| Insufficient payload (model declined to judge) | 0.002 | 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".