Seasonal divergence in reproductive timing on the verge of spring: comparing hypothalamic transcriptome of two seasonally sympatric North American songbird populations
Bibliographic record
Abstract
Every year as spring approaches and day length increases, many birds begin to reproduce, an annual expression of seasonal phenology that requires physiological preparation. In species distributed over a broad geographic range, populations that breed at higher latitudes are often migratory and delay reproduction until later in the year as compared to those breeding at lower latitudes. Dark-eyed Juncos serve as an excellent model for understanding the timing mechanisms regulating population-level variation in seasonal reproductive responses. We compared two seasonally sympatric dark-eyed junco populations in early spring. One migrates (Junco hyemalis hyemalis) and breeds in Alaska and Canada, while the other remains resident (Junco hyemalis carolinensis) and breeds in the Appalachian Mountains of Virginia USA. These populations exhibit different photoperiodic responses to the same environment with respect to activation of the HPG axis, leading to earlier gonadal recrudescence in the resident population. We caught co-wintering sympatric male migrant (n = 6) and resident (n = 7) juncos from the field in March and collected the hypothalamic tissues. We also collected blood samples to determine circulating testosterone and a wing feather to determine stable isotope ratios (δ2H) as estimate of breeding latitude. We found three differentially expressed genes, among which gonadotropin releasing hormone 1 (GnRH1) showed significantly higher expression in early breeding residents as compared to migrant juncos. The δ2H showed a positive linear correlation with testosterone levels and GnRH1 mRNA, providing strong evidence for latitudinal variation in breeding phenology. This study provides insight into the underlying neuroendocrine response giving rise to a population-level difference in the timing of reproduction observed in a seasonally sympatric (co-wintering) population of resident and migrant juncos.
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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 | 0.000 |
| 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".