Enzymatic flux capacities in hummingbird flight muscles: a “one size fits all” hypothesis
Bibliographic record
Abstract
Hummingbirds (family Trochilidae) are among the smallest endothermic vertebrates representing an extreme, among birds, in their physiological design. They are unique in their ability to sustain hovering flight, one of the most energetically demanding forms of locomotion. Given that hovering metabolic rate (HMR) in hummingbirds scales allometrically as M0.78(M is mass), we tested the hypothesis that variation in HMR may be correlated with variation in maximal enzyme activities (Vmaxvalues) of key enzymes in glucose and fatty acid oxidation pathways in the flight muscles of four species of hummingbirds ranging in body mass from 4 to 20 g. We also estimated metabolic flux rates from respirometric data obtained during hovering flight. The data are striking in the lack of correlation between Vmaxvalues and flux rates at most steps in energy metabolism, particularly at the hexokinase and carnitine palmitoyltransferase reactions. In the context of hierarchical regulation analysis, this finding suggests that metabolic regulation (resulting from variation in substrate, product, or allosteric regulator concentrations) dominates as the proximate explanation for the interspecific variation in flux. On the other hand, we found no evidence of hierarchical regulation of flux, which results from variation in Vmaxand is based on variation in enzyme concentration [E]. The evolutionary conservation of pathways of energy metabolism suggests that “one size fits all” among hummingbirds.
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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 | 0.001 | 0.003 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.002 | 0.000 |
| Science and technology studies | 0.001 | 0.002 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| 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".