Understanding the relative importance of short and long term evolutionary processes in species adaptation is central in evolutionary and ecological genetics because it helps understanding how and how fast species respond to environmental changes. In addition, intraspecific variability is of paramount importance for species adaptation to global changes. Atlantic salmon, Salmo salar, provides important ecosystem services but is a vulnerable species spanning its life cycle between the freshwater and the ocean ecosystems, two habitats particularly sensitive to human impacts and global changes. This species is renowned for its life history variability in particular for showing high variation in the age at maturity, especially for male individuals that can mature early before the seaward migration. This phenomenon called early male parr maturation (EMPM) is especially frequent in southernmost salmon populations pointing to an environmental effect on this reproductive behavioral trait. Previous studies had also showed that this phenotype may be under partial genetic control whose precise mechanism remains yet unknown. In the proposed research project GenEarly (Genetic determination of early male parr maturation in Atlantic salmon natural populations) we will combine behavioral ecology, quantitative genetics and population genomics approaches and use the state of the art in sequencing technology to shed new light on the genetic determinism and the genomic architecture of the EMPM phenotype in Atlantic salmon natural populations. The project will produce new understanding about genetic potentialities and constraints for reproductive behavior evolution in face of global changes with a particular focus on improving evolutionary trajectory predictability and conservation practices. Furthermore, scientific and technical qualities of the project will guaranty the successful start of the applicant career among one of the world leading research institute in biological sciences.