Allozyme and microsatellite loci provide discordant estimates of population differentiation in the endangered dusky grouper (Epinephelus marginatus) within the Mediterranean Sea

The dusky grouper, Epinephelus marginatus, inhabits coastal reefs in the Me diterranean Sea and Atlantic Ocean. A decline in the abundance of this long -lived protogynous hermaphrodite has led to its listing as an endangered sp ecies in the Mediterranean, and heightened management concerns regarding it s genetic variability and population substructure. To address these concern s, we analysed genetic variation at seven microsatellite and 28 allozyme lo ci in dusky groupers sampled from seven areas (for microsatellites) and thr ee areas (for allozymes) in the west-central Mediterranean. Levels of genet ic variability were higher for microsatellites than for allozymes (mean H-E = 0.78 and 0.07, respectively), but similar to those observed in other mar ine fishes with comparable markers. Both microsatellites and allozymes reve aled significant genetic differentiation among all areas analysed with each class of marker, but the magnitude of differentiation revealed by allozyme s over three locales (F-ST = 0.214) was greater than that detected with mic rosatellites over seven areas, or over the three areas shared with the allo zyme analysis (F-ST = 0.018 and -0, respectively). A large proportion of th e allozyme differentiation was due to a single locus (ADA*) possibly influe nced by selection, but allozyme differentiation over the three areas was st ill highly significant (F-ST = 0.06, P < 0.0001), and the 95% confidence in tervals for allozyme and microsatellite FST did not overlap when this locus was excluded. There was no evidence of isolation by distance with either c lass of markers. Our results lead us to conclude that dusky groupers are no t panmictic in the Mediterranean Sea and suggest that they should be manage d on a local basis. However, more work is needed to elucidate genetic relat ionships among populations.