Variation in anonymous and EST-microsatellites suggests adaptive population divergence in turbot

We studied the variation at 30 anonymous and 30 expressed sequence tag (EST)-associated microsatellites in 4 natural populations of turbot Scophthalmus maximus living in habitats with different salinity and temperature conditions. We identified putative divergent selection effects on 3 genes: the fibroblast growth factor receptor, the beta microglobuline, and the trap alpha gene for translocon associate protein. The markers closely linked to these genes showed significant deviations from the neutral expectations using 2 different statistical methods in several pairwise population comparisons involving samples from salty and brackish environments. Our results confirmed the weak genetic structure among populations from the northeast Atlantic and the low but significant genetic differentiation of turbot from the Baltic Sea. These results suggest that populations from the Baltic-Atlantic transition area could be accumulating adaptive polymorphisms in the face of high gene flow.