Classification and phylogenetic relationships of African tilapiine fishes inferred from mitochondrial DNA sequences

African cichlid fishes are composed of two major lineages, the haplochromin es and the tilapiines. Whereas the phylogenetic relationships of the haploc hromines have been studied extensively, primarily because of their spectacu lar adaptive radiations in the Great Lakes of East Africa, little is known about the relationships among the tilapiine species, despite the fact that they have become an important component of African, indeed world, aquacultu re. To remedy this situation, molecular phylogenetic analysis of tilapiine fishes was undertaken. A segment of mitochondrial DNA encompassing the term inal part of the tRNA(Pro) gene and the most variable part of the control r egion was amplified by the polymerase chain reaction with DNA samples isola ted from 42 tilapiine species, and the amplification products were subjecte d to heteroduplex analysis and sequencing. Phylogenetic trees based on 68 s equences revealed the existence of 11 sequence groups and 11 single-sequenc e branches. The groups, designated Ti1 through Ti11, were distinguished by specific combinations of diagnostic substitutions, formation of monophyleti c clusters, and separation by genetic distances in excess of 0.04. Although the relationships among the groups could not be resolved, the sequences se parated Oreochromis and Sarotherodon from Tilapia, as defined by Trewavas. The Oreochromis sequences clustered with the Sarotherodon sequences and thu s supported the hypothesis that the mouthbrooding behavior of the tilapiine fishes evolved only once from the substrate-spawning behavior. Since on ph ylogenetic trees the O. alcalicus (sub)species were always separated from O . amphimelas by other Oreochromis species, it was concluded that the adapta tion to life in water with a high salt concentration and high pH values evo lved independently at least twice in the tilapiine fishes. The tilapiines d iverged from the haplochromines more than 8 million years ago; most of the intragroup divergences among the tilapiines took place an estimated 1.1 to 6 million years ago. (C) 2001 Academic Press.