This project aims to restart a research career for the fellow, allowing her to be trained to up-to-date methods in experimental work, genomic tools and data-analysis, capitalizing on her former experience in evolutionary biology. This renewed experience in research is aiming to allow the fellow to move from a current full-time teaching position to research positions.The research context of the proposal is the interaction between selection levels, in connexion with the broader issue of the emergence of multicellularity. In multicellular organisms, selection can act at the higher level of the whole organism, but also at lower levels, like genes, nuclei, or cells, provided they are genetically heterogeneous. Intra organismal genetic heterogeneity does exist in any individual and may lead to genetic conflicts between selection levels. The best example is cancer, where genetic heterogeneity of some cells leads to the disruption of the whole organism. However, focusing on cheating cell lineages, like cancerous cells, may have lead to overlook that different levels of integration may also act in cooperation rather than generate genetic conflicts.Fungi, and among them ascomycetes, are ideal models to test for these issues of multilevel selection. Ascomycetes are indeed displaying a high potential for genetic heterogeneity and for nuclear selection, partly because of the dikaryotic phase in their life cycle. We intend to investigate if selection at the nuclear level is acting in cooperation, or conflict, with the organismal level.We will combine experimental approaches with genomic approaches, using next generation sequencing tools to resolve these issues. The host laboratory has a world-class expertise in these fields. This combination of approaches will be an important output to the mobility of the fellow, allowing her to interact with different groups of her laboratory of origin upon her re-establishment, and contributing to extend the european research network.