Milk isotopic values demonstrate that nursing fur seal pups are a full trophic level higher than their mothers
Bibliographic record
Abstract
RATIONALE: In mammals including humans, mother-to-offspring transfer of nutrients has been the focus of several isotopic studies. Measurement of δ(13) C and δ(15) N values were mainly conducted on easily sampled tissues such as blood and hair that allow the calculation of apparent discrimination factors (∆(13) C and ∆(15) N) between offspring and maternal tissues. Quantifying real ∆(13) C and ∆(15) N values requires the measurement of the δ(13) C and δ(15) N values of milk, the exclusive food of newborns. Surprisingly, little isotopic information is available on milk and its biochemical components (lipids and proteins). METHODS: Paired blood and milk samples from 10 lactating females and their pups were collected from two otariid species, the Antarctic and subantarctic fur seals. Tissue δ(13) C and δ(15) N values were measured using continuous-flow isotope ratio mass spectrometry (CFIRMS) on maternal and offspring blood, and on whole milk, lipid-free milk and milk lipids, thus allowing the calculation and comparison of apparent (maternal blood to offspring blood) and real (lipid-free milk to offspring blood) ∆(13) C and ∆(15) N values. RESULTS: In both fur seal species, the apparent ∆(13) C values averaged ~0.0 ‰. Lipid-free milk was slightly (13) C-depleted compared with both maternal and pup blood and it was strongly (13) C-enriched (~6.3 ‰) compared with milk lipids. In contrast, the apparent and real ∆(15) N values averaged 1.2-1.4 and 2.6-3.0 ‰, respectively, the differences being explained by the ~1.5 ‰ lower milk δ(15) N values than those of maternal blood. CONCLUSIONS: In fur seals, the low apparent ∆(15) N translated into a higher real ∆(15) N value, amounting to a full trophic level, which is in agreement with the almost never verified hypothesis that (15) N differences between mothers and their offsprings should reflect one complete trophic level. The study highlights the need to measure milk isotopic values to disentangle the nutritional mother-to-offspring relationships.
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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 | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.001 |
| 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".