The ecophysiology of iron and vanadium accumulation by North Atlantic ascidians
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 oxid...
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| Format: | Thesis |
| Language: | English |
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Memorial University of Newfoundland
2009
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| Online Access: | https://research.library.mun.ca/8983/ https://research.library.mun.ca/8983/1/Stacey_JoyE.pdf |
| Summary: | 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 ... |
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