Evolution of NADH dehydrogenase subunit 2 in east African cichlid fish.

The complete sequence (1047 bp) of the mitochondrially encoded ND2 gene was obtained from 31 species of cichlid fishes to investigate the evolutionary history of the species flocks of the East African lakes. The observed pattern of nucleotide substitution in this sequence is typical of mitochondrial genes, showing a high transition bias and rapid mutational saturation, especially at codon positions where base frequencies are unequal. The base composition of the third position of codons is heterogeneous among species, suggesting frequent shifts in the pattern of substitution. Phylogenetic analysis of the sequences shows that the mtDNA variation in Lake Malawi cichlids is nested monophyletically within the range of variation shown by Tanganyikan cichlids. The closest Tanganyikan relatives of the Malawi flock are members of the tribe Tropheini. Classifications based on morphology are generally supported by the mtDNA data, with some significant exceptions in the Tropheini and Lamprologini. Because of an apparently rapid radiation of the Tanganyikan lineages, it is difficult to assess the basal topology of the Tanganyikan radiation at this time. Divergences among tribes are consistent with an intralacustrine radiation within the past 10 million years.