The shrimp that likes it dirty
Lay summary by Mijke van der Zee
Most hypersaline ecosystems have a fairly simple food chain, and the biodiversity of invertebrates is low. The most common invertebrates in these environments are the species of the brine shrimp, Artemia. These organisms show a high tolerance to extremely variable salinities, temperatures and oxygen concentrations. In the genus Artemia, there are several sibling species, two of them originating in the New World (the Americas), the other 4 in the Old World (Europe, Africa, Asia). Many ecotoxicological studies use brine shrimp as an experimental organism, but the researchers often forget to take into account the biodiversity of the genus Artemia. The species or strains of different origins are not properly identified or not mentioned at all, or sometimes the commercially obtained cysts are reported as A. salina (Old World origin), whereas it is more likely they are from the species A. franciscana (AF, New World origin). Anthropogenic activities such as pet trade and saltwork operations have spread A. franciscana throughout the Old World, where it has become an invasive pest and out-competes and eradicates the native species. The mechanisms of this eradication are still poorly understood. This research aimed to study the potential role played by the pesticide chlorpyrifos in the competition mechanism leading to the establishment of the invasive A. franciscana and the disappearance of native populations of A. parthenogenetica (PD). The effects of the pesticide on both species were tested at different stages of their life cycles and at different concentrations ranging from 0.1, 1.0 and 5.0 μg/l, a clean brine control group and a 5μg/l acetone control group. Several traits were examined: temporal parameters, quantitative (fecundity) parameters, type of reproduction, and percentage of viable/non-viable nauplii and cysts. Furthermore, the cholinesterase (ChE) activity at different developmental stages was analyzed.
For AF it was found that concentrations of 5 μg/l caused significant higher mortality, and for PD this concentration reached 100% mortality after 7 days. Most of the reproductive parameters measured in both species were not affected by exposure to chlorpyfiros. In both species the fecundity parameters were significantly affected, and in PD there was also a significant effect in the temporal parameters. Population growth rate was substantially reduced in both species compared to the control group, with PD being more sensitive to exposure to chlorpyfiros. Fertility also significantly declined in both species after treatment with the toxicant. Overall, both species were affected by exposure to chlorpyfiros, but AF survived better and its fecundity remained higher than the fecundity of PD individuals. This gives AF a better chance in survival and leading to establishment as invasive species.
The ChE activity in AF adult females was significantly lower at 1 and 5 μg/l, and in males the activity decreased in all concentrations tested. For PD there was a significant decrease in ChE activity at all tested concentrations. This, again speaks of the higher resistance of AF before the toxicant, and confirms the relevance of ChE as a biomarker of exposure in invertebrates.
For further information
Read the Aquatic Toxicology original research article which this summary is based on ‘Aquatic pollution may favor the success of the invasive species A. franciscana?’ (April 2015).
Visit the profile of the research ambassador, Mijke van der Zee, who wrote this summary.
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