Demographic expansion and subtle differentiation in the long-tailed hake Macruronus magellanicus: evidence from microsatellite data.

The impact of geographic heterogeneity and historical demographic factors on genetic diversity in the commercially exploited hake Macruronus magellanicus was examined applying microsatellite markers. A total of 450 fish from 6 different sites, collected in Atlantic Patagonia, were genotyped at 6 polymorphic loci. While analysis of variance-based methods (Fst-Rst) failed to detect differentiation, the exact test for genic differentiation and factorial correspondence analysis revealed subtle differences between coastal and continental shelf edge samples. Data suggest that M. magellanicus has been subjected to a demographic expansion 2.6 to 5 times its original size that occurred approximately 100,000 to 200,000 years ago. Another more recent expansion seems to have occurred a few generations ago. Implications of subtle structuring and demographic instability are discussed.