The ecophysiology of iron and vanadium accumulation by North Atlantic ascidians
Bibliographic record
Abstract
Some ascidians (Tunicata, Ascidiacea) accumulate high levels of iron and/or vanadium in their tissues, the latter being very unusual among animals. Previous work has investigated aspects of the vanadium accumulation by Phlebobranch ascidians, including the identification of the vanadocytes, the oxidation state of the vanadium and the pH in the vacuole in which it is held, and a proposed reduction mechanism for vanadium. The iron dynamics of these animals have received comparatively little attention. There is also a lack of data on the ecophysiological aspects of ascidian metal accumulation. This thesis examines the seasonal variation in vanadium and iron concentrations of two Phlebobranch ascidians, Ciona intestinalis and Ascidia callosa, which accumulate vanadium and iron, and a Stolidobranch ascidian, Halocynthia pyriformis, which accumulates iron only. Experiments examined whether these metal concentrations are responsive to increased food availability and dissolved vanadium concentration. -- An HPLC method was developed to simultaneously measure vanadium and iron in large numbers of biological samples. Using this method, a study of the metal concentrations of some tissues of C. intestinalis from Woods Hole, USA, found that the vanadium and iron concentrations in the hemocytes and other tissues was higher in March than in the fall or summer sampling periods, corresponding with high activity of a key enzyme of a proposed reductive pathway (G6PDH). A feeding experiment investigated whether food availability/particle concentration affects the vanadium and iron concentrations of C. intestinalis. While there were few differences in metal concentrations among high and low food groups, vanadium levels were maintained and iron levels rose compared to animals sampled fresh from Woods Hole. The former may be indicative of low vanadium loss rates and the latter of the importance of dietary sources of iron. -- This pattern was confirmed by a year long study of the vanadium and iron concentrations of tissues of two ascidians from Newfoundland, Canada. A. callosa, a high level vanadium accumulator, exhibited a peak in the vanadium and iron concentrations of the hemocytes and other tissues in spring prior to the spring plankton bloom. This corresponded with an increase in both the total number of circulating hemocytes and the proportion of cells containing reduced vanadium. H pyriformis, a non vanadium accumulator, exhibited a peak in the iron concentration of some tissues at the spring bloom. A vanadium enrichment experiment indicated that A. callosa can respond to increased environmental vanadium concentration. Vanadium concentration of the hemocytes and other tissues initially increased, followed by a marked decline, although remaining elevated above that of control animals. The vanadium exposed animals also displayed an increase in the total number of circulating hemocytes and the number of vanadocytes in all sampling periods. The vanadium levels used in this experiment did not cause an increase in the vanadium concentration of H. pyriformis.
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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 | 0.000 |
| 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) | 0.001 | 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".