The ‘Expansion-Contraction’ model of Pleistocene biogeography: rocky shores suffer a sea change?
Bibliographic record
Abstract
Approximately 20,000 years ago the last glacial maximum (LGM) radically altered the distributions of many Northern Hemisphere terrestrial organisms. Fewer studies describing the biogeographic responses of marine species to the LGM have been conducted, but existing genetic data from coastal marine species indicate that fewer taxa show clear signatures of post-LGM recolonization. We have assembled a mitochondrial DNA (mtDNA) data set for 14 co-distributed northeastern Pacific rocky-shore species from four phyla by combining new sequences from ten species with previously published sequences from eight species. Nuclear sequences from four species were retrieved from GenBank, plus we gathered new elongation factor 1-alpha sequences from the barnacle Balanus glandula. Results from demographic analyses of mtDNA for five (36%) species (Evasterias troschelii, Pisaster ochraceus, Littorina sitkana, L. scutulata, Xiphister mucosus) were consistent with large population expansions occurring near the LGM, a pattern expected if these species recently recolonized the region. However, seven (50%) species (Mytilus trossulus, M. californianus, B. glandula, S. cariosus, Patiria miniata, Katharina tunicata, X. atropurpureus) exhibited histories consistent with long-term stability in effective population size, a pattern indicative of regional persistence during the LGM. Two species of Nucella with significant mtDNA genetic structure showed spatially variable demographic histories. Multilocus analyses for five species were largely consistent with mtDNA: the majority of multilocus interpopulation divergence times significantly exceeded the LGM. Our results indicate that the LGM did not extirpate the majority of species in the northeastern Pacific; instead, regional persistence during the LGM appears a common biogeographic history for rocky-shore organisms in this region.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| 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 teacher head, 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".