A widespread Ponto-Caspian invader with a mistaken identity: integrative taxonomy elucidates the confusing taxonomy of<i>Trichogammarus trichiatus</i>(=<i>Echinogammarus</i>) (Crustacea: Amphipoda)
Bibliographic record
Abstract
Abstract Amphipods have diversified greatly in the Ponto-Caspian region. Although many of these species are prominent invaders their systematics remains unclear. Taking an integrative approach, we investigate the taxonomy of Trichogammarus trichiatus, a widespread invader in European inland waters. It was initially described from the north-eastern Black Sea coast as Chaetogammarus trichiatus by Martynov in 1932. A similar taxon, Chaetogammarus tenellus major, was described by Cărăușu from the western Black Sea in 1943 but later synonymized with C. trichiatus. Chaetogammarus trichiatus was itself shuffled between Chaetogammarus and the Atlanto-Mediterranean Echinogammarus, currently being assigned to Trichogammarus. Our analyses (six DNA markers, 60 measurements and scanning electron microscopic imaging) reveal that T. trichiatus and C. tenellus major are distinct species; the former is a Caucasian endemic, whereas the latter invaded Europe. Unexpectedly, T. trichiatus is an incipient species molecularly nested in Chaetogammarus ischnus, despite pronounced morphological and geographical differentiation. We also recover Chaetogammarus as polyphyletic, yet its member species are nested in the Ponto-Caspian radiation, thus distinct from Echinogammarus. Consequently, we reassign T. trichiatus to Chaetogammarus (Chaetogammarus trichiatus), synonymize Trichogammarus with Chaetogammarus and place C. tenellus major in the new genus Spirogammarus gen. nov. (Spirogammarus major comb. & stat. nov.). Chaetogammarus necessitates further systematic refinement.
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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 | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.002 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.000 | 0.002 |
| 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".