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Genetic determination of early male parr maturation in Atlantic salmon natural populations

Final Report Summary - GENEARLY (Genetic determination of early male parr maturation in Atlantic salmon natural populations)

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. Intraspecific variability is of paramount importance for species adaptation to global changes. Atlantic salmon, Salmo salar, is renowned for its life history variability. In particular male can mature early and reproduce before the seaward migration. Previous studies had also showed that this phenotype may be under partial genetic control whose precise mechanism remains yet unknown. The research project GenEarly combines experimental 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 alternative reproductive tactics in Atlantic salmon natural populations.
Field experiment was conducted to identify environmental and / or genetic factors related to early male maturation. We apply a mixed experimental design including controlled crosses and rearing of offspring in a semi-natural channel allowing applying the environmental threshold model, a statistical framework derived from the field quantitative genetic, in a realistic ecological setting. Results showed strong genetic effect on early male maturation threshold whose genetic architecture is further investigated using a genomics perspective by genotyping a high number of genetic markers scattered across the genome, including microsatellites and insertion-deletions in addition to single nucleotide polymorphisms (SNP) genotyped using a Genotyping By Sequencing (GBS) approach. The high density of genetic markers analyzed have been localized in the salmon genome and used to detect candidate markers linked to early male maturation within the mapping population obtained by controlled crosses and among samples from natural populations. In addition, sequencing of the transcriptome (RNAseq) have been implemented to identify functional polymorphisms within expressed genes potentially involved in early male maturation. All identified candidate genetic markers have been used to developed a SNP genotyping array that is now used to complement the genotypic data in order to implement a QTL analysis on the mapping population and a genomic scan on natural population integrating both neutral and functional polymorphisms. This integrative project should 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.
Meanwhile, effective training for new skills related to fish biology, a new scientific field for the Fellow, and application of Next Generation Sequencing (NGS) technologies has help to the efficient integration of the Fellow within its Research Institute where it had been granted a tenured position as a permanent researcher. Implementation of the GenEarly research project has been an effective mean for the Fellow to consolidate his career development and to offer a practical experience in project management. Finally, GenEarly implementation in collaboration with technical, administrative and scientific staff at the host Research Unit has guaranty the successful integration of the Fellow among one of the world leading research institute in biological sciences.