Drying of Lake Victoria did not stop evolution, says study

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Haplochromine cichlids from Lake Victoria underwent a drastic decline in population about 15,000"18,000 years ago, according to research published in a recent issue of the Proceedings of the National Academy of Sciences.

The study by Kathryn Elmer and coauthors studied the population genetics of the haplochromine cichlids of Lake Victoria based on nuclear genetic analysis (12 microsatellite loci from 400 haplochomines) of populations from Lake Kivu, Lake Victoria, and the connected and surrounding rivers and lakes.

The authors first examined the origin of the Lake Victorian cichlids, and found evidence that the Lake Kivu haplochromines acted as the source from which today s Lake Victoria basin haplochromines were colonised.

Using coalescent analysis, they dated this event to about 3.0"4.5 million years ago and then found evidence that the effective population size in lakes Victoria and Kivu has dropped to 3% (and in the region to less than 2%) of its previous size about 15,000"18,000 years ago.

This coincides with drastic climatic and geological changes in the late Pleistocene that resulted in a complete, or near complete, desiccation of the Lake Victoria basin between 15,000 and 18,000 years ago as suggested by paleolimnological data.

The origin and evolution of the enormously species-rich flock of haplochromine cichlid fishes of Lake Victoria has been debated among evolutionary biologists.

Some contend that the basin of Lake Victoria dried out completely approximately 15,000 to 18,000 years ago, and that the extant flock re-evolved since the basin refilled 15,000 years ago.

However, evidence from this study suggests that the Lake Victoria basin did not dry out completely, and surviving cichlids living in refugia within the basin recolonized the re-emerging lake.

For more information, see the paper: Elmer, KR, C Reggio, T Wirth, E Verheyen, W Salzburger and A Meyer (2009) Pleistocene desiccation in East Africa bottlenecked but did not extirpate the adaptive radiation of Lake Victoria haplochromine cichlid fishes. Proceedings of the National Academy of Sciences 106, pp. 13404"13409.