Mitochondrial phylogeny of the endemic mouthbrooding lineages of cichlid fishes from Lake Tanganyika in eastern Africa

Of the three cichlid species flocks in eastern Africa, Lake Tanganyikaharbors the oldest species assemblage, which is also the most diversemorphologically and behaviorally. For 12 species (20 individuals) of 12genera of the tribe Ectodini, 852 bp from two segments (cytochrome b andcontrol region) of the mitochondrial genome were sequenced. In addition,orthologous sequences were obtained from eight species (11 individuals)representing other mouthbrooding lineages from Lake Tanganyika. Comparisonsof sequence divergences revealed that the single Tanganyikan tribe Ectodiniappears to be approximately five times older than the whole Lake Malawicichlid species flock, suggesting that the radiation of the Tanganyikanmouthbrooding lineages took place long before the species flocks of LakesMalawi and Victoria evolved. Seven of nine surveyed tribes of Tanganyikancichlids appear to be approximately equally divergent, and this seems tocorroborate the hypothesis of a rapid simultaneous formation of lineages atan early stage in the history of the Lake Tanganyika species flock. Theclose genetic relationship between the endemic Tropheus lineage and anonendemic "Haplochromine," Astatotilapia burtoni, indicates that membersof the tribe Tropheini may be the sister group of the cichlid flocks ofLakes Malawi and Victoria. The phylogenetic analyses demonstrate themonophyly of the Ectodini and identify the Cyprichromini as their sistergroup among the Tanganyikan cichlids. Within the tribe Ectodini themolecular data suggest both a branching pattern different than thatpreviously proposed and a subdivision of the Ectodini into four clades,instead of the two originally described. The previously postulated model ofmorphological transformations believed to be responsible for thedrastically different types of ecological specialization found among theEctodini might therefore be in need of reinterpretation. Charactersimmediately related to foraging and nutrition seem to be particularly proneto homoplasy, even among members of a single lineage of cichlid fishes.