From the laboratory to the wild: salinity-based genetic differentiation of the European sea bass (Dicentrarchus labrax) using gene-associated and gene-independent microsatellite markers

Convincing evidence reporting adaptive variation for physiologically and/or ecologically important traits in marine taxa is often derived from studies comparing field and laboratory observations and based on candidate-gene markers, mainly allozymes, responding to habitat selection. Likewise, patterns of genetic differentiation between sea and lagoon populations of the euryhaline European sea bass (Dicentrarchus labrax) were shown to correlate with changes in allele frequencies recorded during experimental salinity challenges, suggesting potential role for local adaptation. However, there has been criticism of these past approaches, causing a need for further investigation. We reinvestigated this correlation in European sea bass using a set of 20 micro- and one minisatellite markers, some of which are associated with candidate genes. We used rigorous experimental settings to demonstrate that only one single gene-associated marker consistently reported significant genetic differentiation between fish raised in seawater compared to fish acclimated to freshwater (locus EIF3E; F (ST) = 0.060; p = 0.007, n = 268). A few other loci were shown to be false positive and did not respond to selection. Furthermore, a field study of sea-lagoon differentiation in wild European sea bass (n = 144) using the same loci reported marginally significant genetic differentiation at locus EIF3E (F (ST) = 0.0114, p = 0.068). This locus was identified as putatively under selection. Two other microsatellite loci associated with genes (DLA0070 and DLA0060, respectively) were found to significantly participate to sea-lagoon differentiation and deviate from neutral expectation. The evidence for sea-lagoon local adaptation in sea bass remains faint if not highly elusive.