Evolution of Spinal Nerve Number in Anuran Larvae
Bibliographic record
Abstract
We examined the number of segmental spinal nerves in 60 premetamorphic tadpoles, representing 43 species, 33 genera and 12 families of anurans. The number of spinal nerves shows a clear phylogenetic pattern, in which the primitive condition is variable, ranging from 23 to 29 pairs. Reduction of caudal spinal nerve number has occurred independently at least 7 times during anuran phylogeny. Reduction events have occurred among species within genera, among subfamilies within families, as well as at familial and higher taxonomic levels. In general, arachaeobatrachian larvae have significantly more spinal nerves than neobatrachian larvae. While 2 of the 7 reduction events have occurred within the Archaeobatrachia, both of these have occurred at low taxonomic levels. In the Neobatrachia, 3 of the 5 reductions have occurred at subfamilial or higher taxonomic levels. Overall, reduced spinal nerve number correlates with tadpole body size, but not with relative tail length or with developmental stage, at least within the range of stages we examined. There is a positive correlation between number of spinal nerves and minimum time from hatching to metamorphosis, at least within the Archaeobatrachia. Species with more pairs of nerves take longer to reach metamorphosis, possibly because they have more neural tissue to produce and to resorb. Spinal nerve number per se does not appear to be associated with larval microhabitat ecology or swimming behavior. Tadpoles exhibit greater variation in spinal nerve number than adult frogs. This greater variation is tolerated presumably because the tail is an expendable organ, which is lost at metamorphosis.
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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 | 0.002 | 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) | 0.001 | 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".