Temporal genetic variation as revealed by a microsatellite analysis of European sardine ( Sardina pilchardus) archived samples

The Adriatic stock of European sardine ( Sardina pilchardus) has experienced large interannual demographic fluctuations over the last 30 years, with a severe decline beginning in 1991 and continuing until 1997. In the present study, six microsatellite loci were used on a time series collection of otoliths and scales from sampling locations of northern (Chioggia) and southern (Vieste) Adriatic Sea, with the aim to investigate the genetic effects of these stock biomass fluctuations. The northern samples showed significant reduction in observed heterozygosity ( H_O) and mean number of alleles ( N_a) that explain the genetic diversity variation, while the same parameters turned out to be more stable in the southern samples. In addition, we detected the presence of a genetic bottleneck and low effective population size ( N_e) values in several northern samples. Even if the northern and southern Adriatic sardine samples belong to the same genetic stock, the more pronounced decrease in genetic variability recorded in the northern sample led us to speculate that a more intensive fishing pressure and a more pronounced oceanographic isolation of this area could have accentuated the effects of the genetic bottleneck.