Of mammals and milk: how maternal stress affects nursing offspring
Bibliographic record
Abstract
Abstract A large body of research shows that maternal stress during an offspring’s early life can impact its phenotype in both the short and long term. In the Vertebrata, most research has been focused on maternal stress during the prenatal period. However, the postnatal period is particularly important in mammals because maternal milk provides a conduit by which maternal hormones secreted in response to stressors (glucocorticoids, GCs) can reach offspring. Moreover, lactation outlasts gestation in many species. Though GCs were first detected in milk over 40 years ago, few studies have explored how they affect nursing offspring, and no reviews have been written on how maternal stress affects nursing offspring in the natural world. We discuss the evolution of milk and highlight its importance in each of the three mammalian lineages: monotremes (subclass Monotremata), marsupials (infraclass Marsupialia), and eutherians (infraclass Placentalia). Most research on the effects of milk GCs on offspring has been focused on eutherians, but monotremes and marsupials rely on their mothers’ milk for a proportionally longer period of time, and so research on these taxa may yield more insight. We show that GCs are important for milk production, both during an individual nursing bout and over the entire lactation period, and review evidence of GCs moving from maternal blood to milk, and eventually to nursing offspring. We examine evidence from rodents and primates of associations between GC levels in lactating females (either blood or milk) and offspring behaviour and growth rates. We discuss ways that maternal stress may impact these offspring phenotypes outside of milk GCs, such as changes to: (1) milk output, (2) other milk constituents (e.g. macronutrients, growth factors, cytokines), and (3) maternal care behaviour. Critical to understanding the fitness impacts of elevated maternal GC levels during lactation is to place this within the context of the natural environment. Species‐specific traits and natural histories will help us to understand why such maternal stress produces different offspring phenotypes that equip them to cope with and succeed in the environment they are about to enter.
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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 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| 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".