The accumulation of methylamine counteracting solutes in elasmobranchs with differing levels of urea: a comparison of marine and freshwater species
Bibliographic record
Abstract
We compared levels of the major organic osmolytes in the muscle of elasmobranchs, including the methylamines trimethylamine oxide (TMAO), betaine and sarcosine as well as the beta-amino acids taurine and beta-alanine, and the activities of enzymes of methylamine synthesis (betaine and TMAO) in species with a wide range of urea contents. Four marine, a euryhaline in freshwater (Dasyatis sabina), and two freshwater species, one that accumulates urea (Himantura signifer) and one that does not (Potamotrygon motoro), were analyzed. Urea contents in muscle ranged from 229-352 micromol g-1 in marine species to 2.0 micromol g-1 in P. motoro. Marine elasmobranchs preferentially accumulate methylamines, possibly to counteract urea effects on macromolecules, whereas the freshwater species with lower urea levels accumulate the beta-amino acid taurine as the major non-urea osmolyte. A strong correlation (r2=0.84, P<0.001) with a slope of 0.40 was found between muscle urea content and the combined total methylamines plus total beta-amino acids, supporting the hypothesis that ;non-urea' osmolytes are specifically maintained at an approximately 2:1 ratio with urea in the muscle of elasmobranchs. All species examined had measurable synthetic capacity for betaine in the liver but only one species had detectable TMAO synthetic capacity. We propose a phylogenetic explanation for the distribution of TMAO synthesis in elasmobranchs and suggest that activation of liver betaine aldehyde dehydrogenase, relative to choline dehydrogenase, coincides with betaine accumulation in elasmobranchs. The latter relationship may be important in maintaining methylamine levels during periods of low dietary TMAO intake for species lacking TMAO synthesis.
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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".