Hybridisation played a large part in Malawi cichlid evolution

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Hybridisation has played a significant role in the early evolution of Lake Malawi's cichlids, according to a study published in a recent issue of the journal Molecular Biology and Evolution.

While hybridisation has been demonstrated to be an important process in the recent evolution of closely related species, there have been very few documented cases where it has played a part at the base of major radiations.

Martin Genner and George Turner reconstructed phylogenies of the haplochromine cichlids of Lake Malawi using mitochondrial and nuclear DNA to demonstrate that hybridisation took place early in the evolutionary history of the Lake Malawi cichlids.

The authors focused on three major lineages of Lake Malawi cichlids: the shallow-water rocky habitat "Mbuna" species, a group of dark-adapted "Deep-Benthic" species specialised for feeding in low-light conditions (dawn/dusk, under overhangs, and deep water) and a group of shallow water "Shallow-Benthic" soft-sediment feeders.  

Analysis of the mitochondrial DNA indicated a close relationship between the Mbuna and Deep-Benthic species, but an analysis of nuclear DNA showed that the Deep-Benthic cichlids were more closely related to the Shallow-Benthic cichlids, with which it shares similar head and body morphology.

Using computer models, the authors show that the similarity in mitochondrial DNA between the Mbuna and Deep-Benthic cichlids was due to hybridisation.

This supports the hypothesis that ancient hybridisation occurred within the Lake Malawi cichlid radiation, that the event occurred before the radiation of a species group adapted to low-light benthic habitats, and that this group went on to dominate the deep-water regions of Lake Malawi.

For more information, see the paper: Genner, MJ and GF Turner (2012) Ancient hybridisation and phenotypic novelty within Lake Malawi’s cichlid fish radiation. Molecular Biology and Evolution 29, pp. 195–206.

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