Comparative population genetics of flatfish reveal a common structuring oceanic front

Identification of the genetic patterning of marine species is crucial for conservation management. Using landscape genetic analysis, we have identified common gene flow barriers in three co-occurring demersal fish that share various life-history traits: turbot (Scophthalmus maximus ), brill (S. rhombus) and sole (Solea solea). By applying neutral loci, we were able to identify several subgroups across the Northeast Atlantic Ocean, although the level of differentiation varies among these species. While the integration of gene-linked markers showed that selection may overcome the homogenizing effect of gene flow, landscape genetic analysis indicated that the level of explained adaptive genetic variation differs among the oceanographic basins of the North Sea and Baltic Sea.
According to our results, genetic differentiation in flatfish depends on two aspects: (i) the synergy between oceanographic fronts and species-specific spawning behavior, together with (ii) the different selection pressures within each basin that lead to relatively stronger local adaption. We conclude that in order to define biologically relevant population units and understand the connectivity between populations, multi-species comparison and investigation of environmental, spatial and life-history traits interactions highly important.