BACH, LIS

ABSTRACT Capitella capitata, formerly regarded as a single opportunistic, cosmopolitan polychaete species, characteristically present in dense populations in highly disturbed environments, has subsequently been shown to consist of a closely related complex of an unknown number of sibling species. Previous studies in our laboratory have shown response differences between Capitella species when exposed to fluoranthene (Flu), a 4-ringed PAH. Of the two species addressed in this study, Capitella sp. I was found to be physiologically better adapted (i.e., more tolerant) to Flu- contaminated sediments compared to the sibling species Capitella sp. S. In the present study an investigation was performed to examine whether differences in tolerance between the two Capitella species are due to differences in activity of biotransformation, measured as the amount of Flu-metabolites produced. We found that Capitella sp. I took up more Flu from the sediment than sp. S, but that sp. I was also much more effective at biotransforming this PAH, while the net amounts of parent Flu accumulated by the two species were similar. The ability to biotransform was reflected in accumulation patterns of Flu in the two species, as Capitella sp. I primarily accumulated Flu metabolites in the cytosol and sp. S mainly accumulated untransformed Flu in the membrane fraction. Due to moderate biotransformation ability in sp. S and the fact that Flu needs biotransformation to become genotoxic, Flu exposure was not associated with increased DNA damage in the cells of the sensitive species (i.e., sp. S) measured by the comet assay. As DNA damage (and implementation of the comet assay) often is used as a biomarker of exposure to and effects of PAH, the usefulness of this assay and DNA damage as a environmental biomarker must be questioned on the basis of the results achieved in this study and the fact that DNA damage is tightly coupled to biotransformation ability. Furthermore, since the two species showed such remarkable differences in response to Flu exposure, differences in general condition (measured as energy reserves), between the two species were examined, to test whether organisms under stress measurably alter the composition of stored energy. Capitella sp. I and sp. S were exposed to different concentrations of Flu-contaminated sediments and analysed for protein-, glycogen- and lipid content. There was no evidence for a more pronounced effect of Flu exposure in Capitella sp. S compared to sp. I by any of the parameters measured. Capitella sp. I did however show a decrease in lipid content, probably as a result of higher energy demand for biotransformation. When unexposed, the two species showed significant differences in the amount of protein, glycogen, and lipid, as Capitella sp. I contained more lipids and less protein than sp. S. Overall, this study demonstrated that tolerance to PAHs (such as Flu) is greatly affected by the ability to biotransform, as many of the intracellular and extracellular events are influenced by the hydrophilicity/lipophilicity of the toxicants. Furthermore, it is clear that other aspects of PAH toxicity may be more relevant than DNA damage for predicting tolerance differences between species. Also, that two so closely related species can show such contradictory relationships between biochemical responses and earlier observed life table responses demonstrates that biomarkers, such as DNA damage and energy storage depletion, cannot be used as simple predictors of whole organism responses to toxicants. However, the dissimilarity in the responses to Flu exposure between the two species open up for some very interesting prospective research areas such as: differences in the induction of biotransformation genes, membrane effects caused by Flu exposure and differences in ability to utilize organic rich food sources.ABSTRACT Capitella capitata, formerly regarded as a single opportunistic, cosmopolitan polychaete species, characteristically present in dense populations in highly disturbed environments, has subsequently been shown to consist of a closely related complex of an unknown number of sibling species. Previous studies in our laboratory have shown response differences between Capitella species when exposed to fluoranthene (Flu), a 4-ringed PAH. Of the two species addressed in this study, Capitella sp. I was found to be physiologically better adapted (i.e., more tolerant) to Flu- contaminated sediments compared to the sibling species Capitella sp. S. In the present study an investigation was performed to examine whether differences in tolerance between the two Capitella species are due to differences in activity of biotransformation, measured as the amount of Flu-metabolites produced. We found that Capitella sp. I took up more Flu from the sediment than sp. S, but that sp. I was also much more effective at biotransforming this PAH, while the net amounts of parent Flu accumulated by the two species were similar. The ability to biotransform was reflected in accumulation patterns of Flu in the two species, as Capitella sp. I primarily accumulated Flu metabolites in the cytosol and sp. S mainly accumulated untransformed Flu in the membrane fraction. Due to moderate biotransformation ability in sp. S and the fact that Flu needs biotransformation to become genotoxic, Flu exposure was not associated with increased DNA damage in the cells of the sensitive species (i.e., sp. S) measured by the comet assay. As DNA damage (and implementation of the comet assay) often is used as a biomarker of exposure to and effects of PAH, the usefulness of this assay and DNA damage as a environmental biomarker must be questioned on the basis of the results achieved in this study and the fact that DNA damage is tightly coupled to biotransformation ability. Furthermore, since the two species showed such remarkable differences in response to Flu exposure, differences in general condition (measured as energy reserves), between the two species were examined, to test whether organisms under stress measurably alter the composition of stored energy. Capitella sp. I and sp. S were exposed to different concentrations of Flu-contaminated sediments and analysed for protein-, glycogen- and lipid content. There was no evidence for a more pronounced effect of Flu exposure in Capitella sp. S compared to sp. I by any of the parameters measured. Capitella sp. I did however show a decrease in lipid content, probably as a result of higher energy demand for biotransformation. When unexposed, the two species showed significant differences in the amount of protein, glycogen, and lipid, as Capitella sp. I contained more lipids and less protein than sp. S. Overall, this study demonstrated that tolerance to PAHs (such as Flu) is greatly affected by the ability to biotransform, as many of the intracellular and extracellular events are influenced by the hydrophilicity/lipophilicity of the toxicants. Furthermore, it is clear that other aspects of PAH toxicity may be more relevant than DNA damage for predicting tolerance differences between species. Also, that two so closely related species can show such contradictory relationships between biochemical responses and earlier observed life table responses demonstrates that biomarkers, such as DNA damage and energy storage depletion, cannot be used as simple predictors of whole organism responses to toxicants. However, the dissimilarity in the responses to Flu exposure between the two species open up for some very interesting prospective research areas such as: differences in the induction of biotransformation genes, membrane effects caused by Flu exposure and differences in ability to utilize organic rich food sources

TOLERANCE DIFFERENCES BETWEEN SIBLINGS OF THE POLYCHAETE SPECIES COMPLEX CAPITELLA CAPITATA TO THE PAH, FLUORANTHENE

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