Population-specific variations of the genetic architecture of sex determination in wild European sea bass Dicentrarchus labrax L.

Among the different sex determination modalities exhibited by fish species, polygenic sex determination (PSD) may show variations in terms of genetic and environmental components between populations exposed/adapted to different environments. European sea bass (Dicentrarchus labrax) is an interesting model, combining both a PSD system and a genetic subdivision into an Atlantic and a Mediterranean lineage, with genetic substructures within the Mediterranean Sea. We produced experimental progeny crosses (N = 927) from broodstock sampled in four wild populations (North Atlantic, NAT; Western Mediterranean, WEM; North-Eastern Mediterranean, NEM; South-Eastern Mediterranean, SEM). There were less females than males in the progeny, both in the global dataset (32.5%) and within each paternal group (from 25.1% for NEM to 39.0% for WEM), with significant variation among populations, dams and sires. Sex, body weight (BW) and body length (BL) showed moderate heritability (0.52 ± 0.17, 0.46 ± 0.17, 0.34 ± 0.15, respectively). Sex was genetically correlated with BW and BL (rA sex/BW = 0.69 ± 0.12, rA sex/BL = 0.66 ± 0.13). The wGWAS performed both on the global dataset and within each paternal group revealed a different genetic architecture of sex determination between Atlantic and Mediterranean populations (9 QTLs found in NAT, 7 in WEM, 5 in NEM and 4 in SEM, with a cumulated variance explained of 27.04%, 21.87%, 15.89% and 12.10%, respectively) with a more similar genetic architecture among geographically close populations compared to geographically distant populations, consistent with the hypothesis of a population-specific evolution of polygenic sex determination systems in different environments.