Tanganyikan scale-eating cichlids studied

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The evolutionary history of Lake Tanganyika's scale-eating cichlids has been reconstructed by Austrian scientists.

Publishing their results in the latest issue of the journal Molecular Phylogenetics and Evolution, Stephan Koblmller, Bernd Egger, Christian Sturmbauer and Kristina Sefc examine the phylogenetic relationships of the Tanganyikan cichlid tribe Perissodini using a 1416-base pair DNA sequence of two mitochondrial genes (ND2 and partial control region) and from 612 AFLP (Amplified Fragment Length Polymorphism) markers.

The tribe Perissodini includes nine species, seven of which (Perissodus eccentricus, Perissodus microlepis, Plecodus elaviae, Plecodus multidentatus, Plecodus paradoxus, Plecodus straeleni and Xenochromis hecqui) are scale-eating species and the other two (Haplotaxodon microlepis and H. trifasciatus) feeding on zooplankton and small fish.

The results of the study confirm the placement of Haplotaxodon within the Perissodini, and also confirm the specific status of H. trifasciatus, a species described in 1999.

The authors also investigated the ages in which the Perissodini and lineages within the Perissodini evolved, and found that the Perissodini split off from its most recent ancestors 3.3"4.6 million years ago, making them ...one of the last tribes to emerge in the course of the primary Tanganyika radiation, which presumably took place right fter the establishment of a truly lacustrine environment....

Within the Perissodini, most of the radiation was found to have occurred 1.5"2 million years ago, with most species being older than 1 million years.

This rapid speciation also occurred at about the same time in many other Tanganyikan cichlid groups (e.g. Ectodini, Limnochromini, Bathybatini, and Lamprologini) and even in the platytelphusid crabs in the lake.

This suggests that the diversification of these groups were triggered by the same environmental factors, possibly a major drop in lake water level associated with increasing aridity in eastern Africa.

The authors also found that most of the Perissodini evolved in deep-water habitats, and that the group colonised the shallow habitat only recently.

For more information, see the paper: Koblmller, S, B Egger, C Sturmbauer and KM Sefc (2007) Evolutionary history of Lake Tanganyika s scale-eating cichlid fishes. Molecular Phylogenetics and Evolution 44, 1295"1305.