Genetic differentiation within the European sea bass (D. labrax) as revealed by RAPD-PCR assays

Abstract

We have used RAPD-PCR assays to identity DNA polymorphisms in the European sea bass (Dicentrarchus labrax). We studied samples from eight Mediterranean localities and one Atlantic sample from Portugal. A sample from a congeneric species (D. punctatus) was included for comparison. The study included 107 RAPD markers and 260 individuals. Within-population RAPD variation was high, but between-population genetic differentiation was quite low. Mediterranean populations clustered along a northwest-southeast transect. This distribution may be related to past marine regressions, which have shaped the distribution of other fish species in the region. The pattern of genetic differentiation based on RAPD markers was compared to the patterns of genetic differentiation based on allozyme data on the same populations. Data were also compared to a microsatellite survey on the same species. Merits and limits of the three techniques in detecting genetic differentiation are discussed. Through a comparison with a previous study in which hatchery samples were repeatedly subjected to acclimation to freshwater, it was possible to detect an ecological component to the pattern of RAPD differentiation in wild samples. We identified a subset of RAPD bands that differed significantly in frequency between marine and lagoon samples. These same bands changed in frequency in the experimental samples after freshwater acclimation, with the acclimated samples resembling samples from lagoons. We suggest that markers are associated with genomic regions involved in tolerance for varying salinity levels and that the acclimation experiments reflected the differential survival of genotypes naturally occurring in lagoons.