No signature of selection on the C-terminal region of glucose transporter 2 with the evolution of avian nectarivory
Bibliographic record
Abstract
Abstract Background Flying birds, especially those that hover, need to meet high energetic demands. Birds that meet this demand through nectarivory face the added challenges of maintaining homeostasis in the face of spikes in blood sugar associated with nectar meals, as well as transporting that sugar to energetically demanding tissues. Nectarivory has evolved many times in birds and we hypothesized that the challenges of this dietary strategy would exert selective pressure on key aspects of metabolic physiology. Specifically, we hypothesized we would find convergent or parallel amino acid substitutions among different nectarivorous lineages in a protein important to sensing, regulating, and transporting glucose, glucose transporter 2 (GLUT2). Methods Genetic sequences for GLUT2 were obtained from ten pairs of nectarivorous and non-nectarivorous sister taxa. We performed PCR amplification of the intracellular C-terminal domain of GLUT2 and adjacent protein domains due to the role of this region in determination of transport rate, substrate specificity and glucosensing. Results Our findings have ruled out the C-terminal regulatory region of GLUT2 as a target for selection by sugar-rich diet among avian nectarivores, though selection among hummingbirds, the oldest avian nectarivores, cannot be discounted. Conclusion Our results indicate future studies should examine down-stream targets of GLUT2-mediated glucosensing and insulin secretion, such as insulin receptors and their targets, as potential sites of selection by nectarivory in birds.
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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 | 0.000 |
| Research integrity | 0.001 | 0.001 |
| 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".