European green crabs (<i>Carcinus maenas</i>) in the northeastern Pacific: genetic evidence for high population connectivity and current‐mediated expansion from a single introduced source population
Bibliographic record
Abstract
Abstract Aim The European green crab ( Carcinus maenas ) expanded dramatically after its introduction to the west coast of North America, spreading over 1000 km in < 10 years. We use samples of Carcinus maenas collected over time and space to investigate the genetic patterns underlying the species’ initial establishment and spread, and discuss our findings in the context of the species’ life history characteristics and demography. Location The central west coast of North America, encompassing California, Oregon, and Washington (USA) and British Columbia (Canada). Methods We collected 1040 total samples from 21 sites representing the major episodes of population establishment and expansion along the west coast of North America. Microsatellite markers were used to assess genetic diversity and structure at different time points in the species’ spread, to investigate connectivity between embayments and to estimate both short‐term effective population sizes and the number of original founders. Assignment testing was performed to determine the likely source of the introduction. Results Carcinus maenas in western North America likely derived from a single introduction of a small number of founders to San Francisco Bay, CA from the east coast of North America. Throughout its western North American range, the species experiences periodic migration between embayments, resulting in a minor loss of genetic diversity in more recently established populations versus the populations in the area of initial establishment. Main conclusions Low genetic diversity has not precluded the ability of C. maenas to successfully establish and spread on the west coast of North America. An efficient oceanographic transport mechanism combined with highly conducive life history traits are likely the major drivers of C. maenas spread. Evidence for a single introduction underscores the potential utility of early detection and eradication of high‐risk invasive 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 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 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".