Intraspecific variation in the sensitivity of aquatic macrophytes to chemical contamination: the case of copper

Abstract : Intraspecific variability plays a pivotal role in short and long term responses of species to environmental fluctuations. This variability, expressed through different traits of individuals, can potentially influence species sensitivity to chemical contamination. This intraspecific variability is currently not taken into account in ecotoxicological risk assessment, whereas it can mislead its results. To examine this hypothesis, the importance of intraspecific variability in the response to copper (Cu) was quantified in controlled conditions for three aquatic macrophyte species, Lemna minor, Myriophyllum spicatum and Ceratophyllum demersum. Variations among genotypes of each of these 3 species were compared to interspecific variability. Results have highlighted a significant genotypic variability, whose importance depends on the species considered. Indeed, L. minor demonstrated a low variability, contrarily to M. spicatum whose variability in growth inhibition by Cu was higher than interspecific differences. In order to specify the extent and the mechanisms of genotypic variability in M. spicatum, other experiments involving measurements of life-history traits have been conducted on 7 genotypes exposed to Cu. Results showed that some genotypes were up to eightfold more sensitive to Cu than others (at concentrations ranging between 0.15 and 0.5 mg/L). These differences in sensitivity were partly explained by the traits measured, but physiological or transcriptomic endpoints may explain more precisely the source of these differences in sensitivity. Finally, 3 experiments with fluctuations in nutrient concentrations, light intensity and Cu pre-exposure have demonstrated that phenotypic plasticity plays an important role in L. minor sensitivity to Cu. Indeed, the weakening of individuals, as a result of unfavorable environmental conditions, can lead to a twofold increase in sensitivity to Cu. All these results demonstrated that intraspecific variability, whether it comes from genotypic variations or is linked to phenotypic plasticity, was in general lower than interspecific variability for the species and endpoints studied. However, its extent can vary depending on the species. It can therefore significantly influence aquatic macrophyte sensitivity to chemical contamination, and it would be relevant to account for it in ecotoxicological risk assessment.
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Eva Roubeau Dumont. Intraspecific variation in the sensitivity of aquatic macrophytes to chemical contamination: the case of copper. Ecotoxicology. Université Toulouse III Paul Sabatier (UT3 Paul Sabatier), 2018. English. ⟨tel-02059936⟩

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