New Insight into the Demography History, Evolution, and Phylogeography of Horseshoe Crabs with Special Emphasis on American Species
Bibliographic record
Abstract
Xiphosurids (Merostomata, Xiphosura) are a group of chelicerates with a rich and complex evolutionary history that is constantly being updated through new discoveries. In this study, we re-estimated the divergence time of the extant horseshoe crab species with new fossil calibration points and addressed the inter- and intraspecific relationships of the American horseshoe crab through a phylogeographic perspective. In order to achieve our objectives, three datasets were compiled from fragments of different lengths of the COI gene that include sequences from 154 individuals, representing the Mexican populations. In addition to these, the datasets also included previously published sequences corresponding to individuals from different US populations and Asian horseshoe crab species. Firstly, we estimated the divergence times of extant horseshoe crab species by Bayesian methods using multiple fossil calibration points. Subsequently, we investigated the phylogeographic relationships and demographic history of Limulus polyphemus in the Americas utilizing various datasets. The time of divergence of the two Asian species clades was estimated to be approximately 127 million years ago (Ma). Phylogeographic relationships between the Asian and American species are linked through a minimum of 86 mutational steps. In America, phylogeographic relationships reflect differentiation between US and Mexican populations of L. polyphemus. We detect signs of demographic expansion for the Mexican population during the last 75,000 years, as well as an absence of phylogeographic structuring. The evolutionary history of horseshoe crabs is older than previously believed; however, the current distribution and demographic changes have probably been influenced by environmental events of the recent past, such as the glacial–interglacial periods that occurred during the Pleistocene.
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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 | 0.001 |
| 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 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".