A molecular phylogeny of the Lake Tanganyika cichlid lineage Cyprichromini has given scientists a new perspective on how the fish evolved.
Brandstatter, Salzburger and Sturmbauer, who are well-known for their previous molecular phylogenetic works on the cichlids, examined the mitochondrial genes of a number of Cyprichromis species - a form of pelagic maternal-mouthbrooding cichlid endemic to Lake Tanganyika.
Their findings, which are due to be published in the journal Molecular Phylogenetics and Evolution in February 2005 show that the group has progressively adapted itself towards a pelagic life.
The molecular biologists studied three mitochondrial gene segments and used a variety of computational phylogenetic techniques to produce evolutionary family trees that show how the species are related to each other.
The trees produced by each of three different tree-building methods subdivided the Cyprichromini into four distinct lineages: one holding Paracyprichromis species; one holding Cyprichromis zonatus; one holding the Cyprichromis microlepidotus group and another holding Cyprichromis pavo and Cyprichromis leptosoma.
The team says that their findings support the recent redescription of Cyprichromis zonatus as a fish that doesn't fit in as well with the others in the Cyprichromini lineage.
The team also made some interesting comments on the evolution of the group:
"Concerning ecology and mating behavior, a clear evolutionary trend towards progressive adaptation to the pelagic zone emerges during the evolution of the Cyprichromini.
"The linearized tree analysis further shows that the four lineages have split almost contemporaneously. The mean Kimura-2-parameter distance among the four lineages emerging from the primary radiation of the Cyprichromini amounts to 7.21% and is in close agreement to that previously found for the primary radiation of the tribe Tropheini (7.01%), a lineage of rock-dwelling cichlids endemic to Lake Tanganyika.
"To date, the influence of lake level fluctuations as promoters of diversification has been demonstrated only for rock-dwelling cichlids. Based on the agreeement in temporary patterns of diversification, we suggest that Pleistocene lake level changes have left a similar genetic imprint in a group of cichlid fishes that progressively colonized the open water during their radiation."
For more information see the paper: Brandsttter A, Salzburger W, Sturmbauer C (2005) - Mitochondrial phylogeny of the Cyprichromini, a lineage of open-water cichlid fishes endemic to Lake Tanganyika, East Africa. Mol Phylogenet Evol. 2005 Feb; 34(2): 382-91