RECENT, ALLOPATRIC, HOMOPLOID HYBRID SPECIATION: THE ORIGIN OF SENECIO SQUALIDUS (ASTERACEAE) IN THE BRITISH ISLES FROM A HYBRID ZONE ON MOUNT ETNA, SICILY
Bibliographic record
Abstract
Homoploid hybrid speciation occurs through stabilization of a hybrid segregate (or segregates) isolated by premating and/or postmating barriers from parent taxa. Theory predicts that ecological and spatial isolation are of critical importance during homoploid hybrid speciation, and all confirmed homoploid hybrid species are ecologically isolated from their parents. Until recently, such species have been identified long after they originated, and consequently it has not been possible to determine the relative importance of spatial and ecological isolation during their origin. Here we present evidence for the recent origin (within the past 300 years) of a new homoploid hybrid species, Senecio squalidus (Asteraceae), in the British Isles, following long-distance dispersal of hybrid material from a hybrid zone between S. aethnensis and S. chrysanthemifolius on Mount Etna, Sicily, Italy. Historical records show that such hybrid material from Sicily was introduced to the Oxford Botanic Garden in Britain in the early part of the 18th century and that S. squalidus began to spread from there after approximately 90 years. A survey of randomly amplified polymorphic DNA/intersimple sequence repeats (RAPD/ISSR) marker variation demonstrated that S. squalidus is a diploid hybrid derivative of S. aethnensis and S. chrysanthemifolius that grow at high and low altitudes, respectively, on Mount Etna and that form a hybrid zone at intermediate altitudes. Senecio squalidus contained 11 of 13 RAPD/ISSR markers that were recorded at high frequency in S. chrysanthemifolius but were absent or occurred at low frequency in S. aethnensis, and 10 of 13 markers for which the reverse was true. Bayesian admixture analysis showed that all individuals of S. squalidus surveyed were of mixed ancestry with relatively high mean proportions of ancestry derived from both S. chrysanthemifolius and S. aethnensis (0.644 and 0.356, respectively). We argue that long-distance isolation of hybrid material from its parents on Mount Etna would have helped favor the origin and establishment of S. squalidus in the British Isles, regardless of whether the initial hybrid material introduced to Britain was preadapted to local conditions.
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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".