Ecological consequences of supernumerary arms in eastern Pacific sea stars
Bibliographic record
Abstract
Pentameric symmetry characterizes echinoderms and is most readily observed in sea stars. However, some pentamerous sea star individuals deviate from the normal 5-arm pattern, most likely as a result of errors in regeneration, but the frequency of these deviations and their ecological consequences for the individuals are poorly understood. Here, we report the extent of deviations from pentamery in multiple populations of co-occurring sea star species and tested 3 potential advantages of supernumerary arms—increased oral surface area, increased feeding, and faster righting response—in 1 species, the bat star Patiria miniata. Using underwater surveys and behavioural experiments at 16 sites in Barkley Sound, British Columbia, Canada, we found individuals with atypical arm numbers in 5 of 9 pentamerous sea star species. There were significant differences among sites and species, with site-specific mean percentages of atypical sea stars ranging from 0.8 to 14.6% and species-specific mean percentages ranging from 0 to 10%. Bat stars had the highest proportion of individuals with atypical numbers of arms, with site-specific frequencies ranging from 0 to 25%. The probability of feeding and righting speed were similar between bat stars with and without supernumerary arms, but bat stars with supernumerary arms had slightly larger oral surface areas for a given arm length, which could confer an advantage in adherence to the substrate. Although the advantages of supernumerary arms for bat stars appear to be negligible, the lack of any clear disadvantage suggests that selection against atypical variants might be weak, leading to limited selection on the accuracy of regeneration in this species.
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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 | 0.001 | 0.000 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.001 |
| 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".