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Chemical and natural stressors combined: from cryptic effects to population extinction.

ABSTRACT: In addition to natural stressors, populations are increasingly exposed to chemical pollutants released into the environment. We experimentally demonstrate the loss of resilience for Daphnia magna populations that are exposed to a combination of natural and chemical stressors even though effects on population size of a single stressor were cryptic, i.e. hard to detect statistically. Data on Daphnia population demography and along with model-based exploration of our predator-prey system revealed that direct trophic interactions changed the population size-structure and thereby increased population vulnerability to the toxicant which acts in a size selective manner. Moreover, population vulnerability to the toxicant increases with predator size and predation intensity whereas indirect trait-mediated interactions via predator kairomones may buffer chemical effects to a certain extent. Our study demonstrates that population size can be a poor endpoint for risk assessments of chemicals and that ignoring disturbance interactions can lead to severe underestimation of extinction risk.

SUBMITTER: Gergs A

PROVIDER: S-EPMC3687223 | biostudies-literature | 2013

REPOSITORIES: biostudies-literature

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Chemical and natural stressors combined: from cryptic effects to population extinction.

Gergs André A Zenker Armin A Grimm Volker V Preuss Thomas G TG

Scientific reports 20130101

In addition to natural stressors, populations are increasingly exposed to chemical pollutants released into the environment. We experimentally demonstrate the loss of resilience for Daphnia magna populations that are exposed to a combination of natural and chemical stressors even though effects on population size of a single stressor were cryptic, i.e. hard to detect statistically. Data on Daphnia population demography and along with model-based exploration of our predator-prey system revealed t ...[more]

PMID: 23783836

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Project description:The soil oligochaete Enchytraeus albidus is a standard test organism used in biological testing for Environmental Risk Assessment (ERA). Although effects are known at acute and chronic level, through survival, reproduction and avoidance behaviour endpoints, very little is known at the sub-cellular and molecular levels. In this study, the effects of soil properties (clay, organic matter and pH) and of the chemicals copper and phenmedipham were studied on gene expression in E. albidus during exposure periods of 2 days, 4 days and 3 weeks, using DNA microarrays based on a normalised cDNA library for this test species (Amorim et al., 2011) The main objectives of this study were: 1) to assess changes in gene expression of E. albidus over time, and 2) to identify molecular markers for natural and chemical exposures. Results showed a clear influence of exposure time in gene expression. Transcriptional responses to phenmedipham were seen at 2 days while the responses to copper and the different soils were more pronounced at 4 days of exposure. Some genes were differentially expressed in a stress specific manner and, in general, the responses were related with effects at energy metabolism and cell growth level. Fluorescently labelled cDNA, from enchytraeids exposed during 4 days and 3 weeks to control soil (LUFA 2.2) and to the different exposure conditions was synthesized for microarray analysis and hybridizations were performed. After scanning, spots were identified and ratios quantified using the QuantArray (Packard Biochip Technologies). Statistical analysis of the microarrays was performed using limmaGUI package (1.18.0) (Smyth, 2005) in the R (2.8.0) software environment (http://www.R-project.org/). After being submitted to local background subtraction, microarrays were normalized using global loess method. To statistically evaluate the differential gene expression between the different conditions, a gene-per-gene linear model (limma – linear model for microarray analysis) and empirical Bayes methods were applied. The results were then corrected for multiple testing using the Benjamini-Hochberg’s method (adjusted p<0.05 was considered significant) (Benjamini and Hochberg, 1995).

Project description:Microbial population responses to combined effects of chronic irradiation and other stressors (chemical contaminants, other sub-optimal conditions) are important for ecosystem functioning and bioremediation in radionuclide-contaminated areas. Quantitative mathematical modeling can improve our understanding of these phenomena. To identify general patterns of microbial responses to multiple stressors in radioactive environments, we analyzed three data sets on: (1) bacteria isolated from soil contaminated by nuclear waste at the Hanford site (USA); (2) fungi isolated from the Chernobyl nuclear-power plant (Ukraine) buildings after the accident; (3) yeast subjected to continuous ?-irradiation in the laboratory, where radiation dose rate and cell removal rate were independently varied. We applied generalized linear mixed-effects models to describe the first two data sets, whereas the third data set was amenable to mechanistic modeling using differential equations. Machine learning and information-theoretic approaches were used to select the best-supported formalism(s) among biologically-plausible alternatives. Our analysis suggests the following: (1) Both radionuclides and co-occurring chemical contaminants (e.g. NO2) are important for explaining microbial responses to radioactive contamination. (2) Radionuclides may produce non-monotonic dose responses: stimulation of microbial growth at low concentrations vs. inhibition at higher ones. (3) The extinction-defining critical radiation dose rate is dramatically lowered by additional stressors. (4) Reproduction suppression by radiation can be more important for determining the critical dose rate, than radiation-induced cell mortality. In conclusion, the modeling approaches used here on three diverse data sets provide insight into explaining and predicting multi-stressor effects on microbial communities: (1) the most severe effects (e.g. extinction) on microbial populations may occur when unfavorable environmental conditions (e.g. fluctuations of temperature and/or nutrient levels) coincide with radioactive contamination; (2) an organism's radioresistance and bioremediation efficiency in rich laboratory media may be insufficient to carry out radionuclide bioremediation in the field--robustness against multiple stressors is needed.

Dataset Information

Chemical and natural stressors combined: from cryptic effects to population extinction.

Publications

Chemical and natural stressors combined: from cryptic effects to population extinction.

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