Evolutionary divergence between sympatric species of southern African Hakes, Merluccius capensis and M. paradoxus. I. Electrophoretic analysis of proteins

Abstract

We estimated the amount of genetic divergence between two morphologically similar species of southern African hake, Merluccius capensis and M. paradoxus, with the electrophoretic analysis of proteins encoded by 31 loci. Nei's genetic distance between these taxa was 0·583 (±0·160) and is typical of evolutionary divergence between well differentiated congeneric species. We found no evidence of hybrid individuals. The mean heterozygosity over 13 samples of M. capensis was 0·055 and over 10 samples of M. paradoxus was 0·067. The present sympatric distributions of these fish are most likely the result of secondary contact after speciation in allopatry or the result of repeated dispersals of ancestral populations of other Atlantic Ocean hakes to southern Africa, rather than the result of sympatric speciation. There were significant excesses of rare alleles in both species as compared with that expected for neutral alleles in species at drift-mutation equilibrium. Average heterozygosities, however, were not appreciably reduced in comparison with other marine fish. Using genetic distance and the assumptions of the molecular clock, we estimate that the lineages leading to these species diverged from one another between 7 and 13 million years ago.