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Published on: January 19, 2018
Effects of cell-bound microcystins on survival and feeding of Daphnia spp
T Rohrlack1, E Dittmann, T Börner
1Freshwater Biological Laboratory, University of Copenhagen, DK-3400 Hillerød, Denmark. TRohrlack@zi.ku.dk
Abstract:
The influence of cell-bound microcystins on the survival time and feeding rates of six Daphnia clones belonging to five common species was studied. To do this, the effects of the microcystin-producing Microcystis strain PCC7806 and its mutant, which has been genetically engineered to knock out microcystin synthesis, were compared. Additionally, the relationship between microcystin ingestion rate by the Daphnia clones and Daphnia survival time was analyzed. Microcystins ingested with Microcystis cells were poisonous to all Daphnia clones tested. The median survival time of the animals was closely correlated to their microcystin ingestion rate. It was therefore suggested that differences in survival among Daphnia clones were due to variations in microcystin intake rather than due to differences in susceptibility to the toxins. The correlation between median survival time and microcystin ingestion rate could be described by a reciprocal power function. Feeding experiments showed that, independent of the occurrence of microcystins, cells of wild-type PCC7806 and its mutant are able to inhibit the feeding activity of Daphnia. Both variants of PCC7806 were thus ingested at low rates. In summary, our findings strongly suggest that (i) sensitivity to the toxic effect of cell-bound microcystins is typical for Daphnia spp., (ii) Daphnia spp. and clones may have a comparable sensitivity to microcystins ingested with food particles, (iii) Daphnia spp. may be unable to distinguish between microcystin-producing and -lacking cells, and (iv) the strength of the toxic effect can be predicted from the microcystin ingestion rate of the animals.
Insights
Cell-bound microcystins harm all tested Daphnia clones, with survival directly linked to toxin ingestion rates. Daphnia cannot distinguish toxic from non-toxic cells, making ingestion rate the key factor in microcystin toxicity.
Area of Science:
- Aquatic toxicology
- Ecotoxicology
- Environmental science
Background:
- Microcystins are potent cyanobacterial toxins impacting aquatic ecosystems.
- Daphnia are crucial zooplankton in freshwater food webs, serving as indicators of water quality.
Purpose of the Study:
- To investigate the impact of cell-bound microcystins on Daphnia survival and feeding.
- To determine if Daphnia clone sensitivity varies and if ingestion rate predicts toxicity.
Main Methods:
- Comparing effects of microcystin-producing and non-producing Microcystis strains on Daphnia clones.
- Analyzing the correlation between microcystin ingestion rate and Daphnia survival time.
- Conducting feeding experiments to assess Daphnia feeding inhibition by Microcystis cells.
Main Results:
- Microcystins in Microcystis cells were toxic to all Daphnia clones tested.
- Daphnia median survival time strongly correlated with microcystin ingestion rate.
- Daphnia showed reduced feeding on both wild-type and mutant Microcystis, regardless of microcystin presence.
Conclusions:
- Daphnia species exhibit sensitivity to cell-bound microcystins.
- Daphnia ingestion rates, not differential susceptibility, primarily determine microcystin toxicity.
- Daphnia cannot differentiate between microcystin-producing and non-producing cells, impacting their survival.
