Thesis: Anthropogenic pressures on ecosystems, such as pollution by radioactive substances, can affect the survival and maintenance of populations. Faced with these stressors, individuals can respond rapidly through phenotypic plasticity and in the longer term, populations can adapt. However, these responses are accompanied by costs. Considering these mechanisms is important to estimate the consequences of stressors on the evolution of populations and their long-term maintenance. In this context, the aim of this project is to experimentally study the evolution of Caenorhabditis elegans populations exposed to gamma ionizing radiation (IR) and to evaluate the associated costs. For this purpose, measurements of several life history traits were performed on C. elegans populations exposed to IR (0 – 1.4 and 50 mGy.h-1) for 20 generations. Different experimental designs were also performed to establish the underlying causes of the observed trait changes and to highlight costs related to these changes. Briefly, the results showed that IR has deleterious impacts on reproduction, survival and population growth, especially at 50 mGy.h-1. In addition, we observed an adaptation of populations to IR accompanied by costs and selection of reproduction by outcrossing. These results show that an anthropogenic pressure such as IR can modify the evolutionary trajectory of a population, questioning the long-term survival of these organisms and highlight the need for such an approach in the context of an ecological risk assessment