Mitochondrial phylogeny of the endemic mouthbrooding lineages of cichlid fishes from Lake Tanganyika in eastern Africa |
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Authors: | Sturmbauer C; Meyer A |
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Institution: | Department of Ecology and Evolution, State University of New York, Stony Brook 11794-5245. |
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Abstract: | Of the three cichlid species flocks in eastern Africa, Lake Tanganyika
harbors the oldest species assemblage, which is also the most diverse
morphologically and behaviorally. For 12 species (20 individuals) of 12
genera of the tribe Ectodini, 852 bp from two segments (cytochrome b and
control 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. Comparisons
of sequence divergences revealed that the single Tanganyikan tribe Ectodini
appears to be approximately five times older than the whole Lake Malawi
cichlid species flock, suggesting that the radiation of the Tanganyikan
mouthbrooding lineages took place long before the species flocks of Lakes
Malawi and Victoria evolved. Seven of nine surveyed tribes of Tanganyikan
cichlids appear to be approximately equally divergent, and this seems to
corroborate the hypothesis of a rapid simultaneous formation of lineages at
an early stage in the history of the Lake Tanganyika species flock. The
close genetic relationship between the endemic Tropheus lineage and a
nonendemic "Haplochromine," Astatotilapia burtoni, indicates that members
of the tribe Tropheini may be the sister group of the cichlid flocks of
Lakes Malawi and Victoria. The phylogenetic analyses demonstrate the
monophyly of the Ectodini and identify the Cyprichromini as their sister
group among the Tanganyikan cichlids. Within the tribe Ectodini the
molecular data suggest both a branching pattern different than that
previously proposed and a subdivision of the Ectodini into four clades,
instead of the two originally described. The previously postulated model of
morphological transformations believed to be responsible for the
drastically different types of ecological specialization found among the
Ectodini might therefore be in need of reinterpretation. Characters
immediately related to foraging and nutrition seem to be particularly prone
to homoplasy, even among members of a single lineage of cichlid fishes.
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