The completion of genomic sequences of physiologically important genes frequently reveals
non-coding genetic elements such as tandem repeats (micro- and minisatellites) that are
often more polymorphic than nearby coding sequences. We obtained the complete genomic
sequences of three hormone genes in sea bass Dicentrarchus labrax: growth
hormone (dlGH), somatolactin (dlSL) and insulin-like
growth factor-1 (dlIGF-1), including 5′- and 3′-untranslated regions.
Mini- and microsatellites were discovered in both flanking and intron regions. Some were
partially conserved across Perciformes. To assess the usefulness and relevance of these
gene-associated markers for understanding population structure, an investigation was made
on genetic diversity and differentiation at four of them in (i) five wild
populations from the North Sea, the Bay of Biscay and the Western Mediterranean, and
(ii) two samples of hatchery-bred individuals from a
freshwater-acclimation experiment. Gene and allelic diversities were lower in cultured
individuals than in wild ones. Significant genetic differentiation was demonstrated
between Bay of Biscay + North Sea and Mediterranean populations
(Fst > 0.06, p < 0.001),
primarily due to dlGH-associated markers. Significant genetic
differentiation was also detected among the Atlantic and North Sea samples, but restricted
to the locus associated with dlSL. Significant genetic differentiation
was also found among experimental individuals before and after a salinity challenge
(Fst ≈ 0.05, p < 0.001), but was due
to dlSL and dlIGF-1 loci. Gene-associated markers proved
to be more efficient than formerly used anonymous microsatellite markers in providing a
clear picture of genetic differentiation.