Evaluating effects of a multi-generation pollution on Caenorhabditis elegans' population
Résumé
The assessment of toxic effects at biologically and ecologically relevant scales is an important challenge in ecosystem protection. Indeed, in most time, stressors impact populations over longterm. The selection pressure exerted by a pollutant is known to amplify the phenomenon of natural selection and could lead to evolutionary changes across generations. It is therefore important to study the evolutionary response of a population submitted to a long term stress. Regarding this background, we assessed the evolution of two populations (control and exposed to 1.1 mM of the heavy radiotoxic metal, uranium) of the ubiquitous nematode Caenorhabditis elegans submitted to a long-term exposure to uranium. The experimentation was conducted over 16 generations and life history traits (growth, reproduction and survival) as well as dose-response evolution were assessed. These parameters were followed daily on individuals extracted from the populations and exposed to a range of concentration (from 0 to 1.2 mM U). Our experiment showed an increase of adverse effects as a function of uranium concentration. Indeed the NOEC for reproduction and growth traits were respectively of 0.5 mM U and 0.9 mM U. Moreover, reproduction and growth were respectively reduced by over 60% and 20% for individual exposed at 1.1 mM U. This reduction remained constant throughout the generations. We also pointed out the appearance of genetics differentiations on reproduction traits throughout the generations. This differentiation, observed from generation 3, showed us that the total egg-laying of the uranium population was significantly decreased compared with the control population. In contrast, no differentiations were highlighted on growth traits. Our results confirm the importance of studying environmental risks related to pollutant through multi-generational studies in order to capture effects that may appear after several generation of exposition.