EVOTOXIS
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Evolving to xenobiotic induced stress |
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Research
Context and Issues
Anthropogenic stressors have influenced biodiversity at multiple scales, and xenobiotic contaminants remain a significant threat to the integrity of freshwater ecosystems. This fact is emphasized in the latest synthesis report from the European Environment Agency (SOER 2015), wherein more than half of all waterbodies surveyed received a classification of “less than good” with respect to their ecological status. Whilst catastrophic discharge events are an obvious threat to biodiversity, they are relatively rare. Conversely, chronic/repeated seasonal exposures at sub-lethal concentrations may pass unperceived, yet have significant long-term impacts. One such effect is the influence of pollutants on the evolutionary trajectories of species, a subject of growing concern in ecotoxicology and environmental risk management.Objectives
The project is planned around three interconnected objectives and analytical approaches, each designed to provide corroborating evidence into the nature of how populations have evolved following exposure to xenobiotic stressors. The ultimate goal is to integrate genomic and functional variation to test for selective/adaptive evolution. Specifically, the three principal objectives are to:
- use field- and lab-based methods to determine if xenobiotic stressors have exerted a selective effect on natural populations of Daphnia;
- use temporal and spatial structuring in RNA expression data to test for evidence of transcriptomic evolution in response to xenobiotic stress;
- evaluate if lines with a higher degree of plasticity in the expression of genes associated with the oxidative stress response are better primed for adaptation to xenobiotic contamination.
Methodology
As both an important prey item and a keystone species driving nutrient cycling in ponds and lakes, Daphnia are a critical component of freshwater ecosystems. Consequently, Daphnia have become important models in ecotoxicological risk assessment. They are also characterized by an interesting reproductive cycle alternating between clonal and sexual reproduction, providing an ideal model to explore the effects of chemical contaminants against a variety of genetic backgrounds. However, one of their most attractive properties is the production of resting eggs (ephippia) that may lay dormant for centuries in the sediment layer, yet be resuscitated when exposed to the proper stimuli. This provides an incredibly rare opportunity to study changes in molecular function in a deep historical context, to a time pre-dating the exposure of populations to anthropogenic chemical contaminants.
Using contemporary and resurrected populations of Daphnia from natural ponds and marshes in western France, an area of important agricultural production, this project will explore the effects that pesticide drift and runoff has had on the evolutionary history of this important species. Daphnia currently inhabiting sites located in protected areas will be compared with those from neighbouring waters impacted by the unintentional diffusion of agricultural chemicals, contrasting the effects of pesticide exposure on survival and reproduction in multiple independent lines. Additionally, high-throughput sequencing will be used to search for genomic signals of natural selection in wild populations, and to assay transcriptome-wide patterns of gene expression in response to exposure, both immediate and over multiple generations.
Expected Results
It is expected that this project will serve as a case study highlighting how an evolutionary perspective can be integrated into ecological risk assessment to better understand and manage the long-term effects of pollutants. Likewise, experiments are designed to make results useful beyond the immediate questions of interest to this remit. Though not essential to the immediate project objectives, results will allow for ancillary analyses of complex, functional genotype-phenotype associations, and help to better annotate the draft genome of an important model animal.
Partners
- INRA, Aquatic Ecology and Ecotoxicology experimental unit U3E, Rennes
- INRA GenoToul’s Genome & Transcriptome, platform, Toulouse
- University of Leuven, Belgique
- University of Turku, Finland
People involved
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BESNARD Anne-Laure, Technician Phone : +33 2 23 48 54 43 Email : anne-laure.besnard(at)inrae.fr |
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COLLINET Marc, Technician Phone : +33 2 23 48 55 29 Email : marc.collinet@inrae.fr |
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COUTELLEC Marie-Agnès, Scientist Phone : +33 2 23 48 52 48 Email : marie-agnes.coutellec@inrae.fr |
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MCCAIRNS Scott, Scientist Phone : +33 2 23 48 52 37 Email : scott.mccairns@inrae.fr |
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VASSAUX Danièle, Technician Phone : +33 2 23 48 56 69 Email : daniele.vassaux@inrae.fr |
Funding and Support
This project is funded by a “Young Researcher” grant (instrument JCJC) from the French National Research Agency (grant no: ANR-17-CE34-0004-01) under the Health-Environment “One Health” joint theme of the societal challenges comprising Work Programme 2017