Low genetic differentiation among morphologically distinct Labeobarbus species (Teleostei: Cyprinidae) in the Lake Victoria and Albertine basins, Uganda: Insights from mitochondrial DNA

Labeobarbus altianalis and L. bynni bynni are hexaploid cyprinid fishes in the genus Labeobarbus. In the Great Lakes region of Africa, these two large-bodied barbs exhibit considerable morphological variations. Their intraspecific classification, currently based on geographical distribution and morphological variation, is of limited application due to the overlapping nature of the water systems. Patterns of genetic variation in the Albertine and Victoria drainage basins in Uganda were assessed using mitochondrial sequences of the control region (470 basepairs) and the cytochrome b gene (627 basepairs). At the control region 36 distinct haplotypes were observed in a total of 177 individuals. Relatively low overall nucleotide diversity (π = 0.010) was observed. Hierarchical analysis of the molecular variance revealed significant differentiation between populations in the total sample (F_ST = 0.172, p < 0.001), among populations within each basin (F_SC = 0.047, p < 0.001), but no significant subdivision among basins (F_CT = 0.131, p > 0.05). Phylogenetic analysis of the control region haplotypes resulted in a star-shaped phylogeny, with no clusters that reflect current taxonomic designation, morphotypes or basins. Phylogenetic analysis of cytochrome b gene sequences resulted in a tree topology similar to that observed for the control region. Thus the morphological characteristics separating the two species are intraspecific variation and the whole sample probably belongs to the same species.