Genomic sequences and genetic differentiation at associated tandem repeat markers in growth hormone, somatolactin and insulin-like growth factor-1 genes of the sea bass,Dicentrarchus labrax

Abstract

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 (F st > 0.06, p -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 (F st ≈ 0.05, p 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.