Characterization of the oxygen binding properties of hemoglobin from the ruby-throated hummingbird (Archilochus colubris)
Bibliographic record
Abstract
Weighing only between 2.5 and 4.8 g, the ruby-throated hummingbird (A. colubris) has one of the highest known mass-specific metabolic rates among birds. Despite this, there is a lack of available data on the oxygen binding properties of their hemoglobin (Hb). Here I measured the effect of allosteric effectors, pH and temperature on the O2-affinity (defined as the O2 partial pressure required for 50% Hb O2 saturation; P50) of ruby-throated hummingbird Hb, while also estimating their Hb buffering capacity. A comparison of Hb-O2 affinity (i.e. P50 values) between A. colubris and its sole congener, the black-chinned hummingbird (A. alexandri), revealed differences likely attributed to two β-chain amino acid substitutions. Under treatment conditions resembling the natural physiological state of hummingbird blood, A. colubris exhibited a similar Bohr effect (-0.401) and buffering capacity (4.88 mol H+ mol Hb4-1 pH-1) to those of other hummingbird species, though both variables were among the lowest values previously reported for birds. Nonetheless, the low buffering capacity is modelled to enhance the efficiency of their (relatively low) Bohr effect and may enable a high blood [Hb], which together with a relatively low blood O2 affinity is shown to markedly increase tissue O2 delivery. I also found that O2 binding of A. colubris Hb was thermally insensitive under natural physiological conditions. This thermal insensitivity could help ensure adequate O2 delivery both during and upon arising from torpor, while minimize heat loss at the lungs. These findings highlight the various O2 binding properties of A. colubris that together facilitate the efficient delivery of O2 to the tissues irrespective of temperature.
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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) | 0.000 | 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 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".