Evolutionary divergence between sympatric species of southern African Hakes, Merluccius capensis and M. paradoxus. II. restriction enzyme analysis of mitochondrial DNA

Abstract

We used 11 restriction endonucleases to measure nucleotide sequence variation in mitochondrial DNA (mtDNA) within and between two species of hake from the coastal waters of South Africa. A total of 14 different composite genotypes were observed among 26 individuals of Merluccius capensis, but only 6 composite genotypes were observed for 24 individuals of M. paradoxus. A parsimony network connecting the composite genotypes for these species did not correspond with the geographies of either set of samples. In M. capensis, the restriction patterns of three enzymes (Ava I, Xba I, Xho I) and the network of composite genotypes indicate that an addition of about 400 nucleotides in length and a deletion of 200 nucleotides have occurred in pathways leading from the most common genotype. The amount of nucleotide site polymorphism for M. capensis was 0·022 and was significantly greater than the level of polymorphism in M. paradoxus, which was 0·009. These results suggest that M. paradoxus may have experienced a population bottleneck in the past. The amount of sequence divergence between these species was 11·6 per cent (±0·036) and is typical for well differentiated species. Using the assumptions of the molecular clock, this represents a divergence time of 5·8 (±1·8) million years.