Cichlid Study in Lakes Victoria and Malawi Highlights Adaptive Radiation

Study of Africa's Rift Valley Lakes shows cichlids quickly develop and form new species.

By David Alderton | July 9, 2012

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Coloration has been identified as being very significant, in terms of species diversification, as reflected here by the African cichlid called Pundamilia nyererei.

Why is it that some fish, such as the coelacanth, have remained essentially unchanged over the course of tens of millions of years, whereas others, such as the cichlids in Africa’s Rift Valley Lakes, undergo very rapid development, dividing and forming new species? A combined study carried out by the EAWAG Centre and the University of Bern in Switzerland has now provided some answers into this field.

It is clear that both external factors (such as climactic considerations and the diversity of habitat) can have an impact, as do species-specific traits (like behavior patterns and coloration of the fish themselves). What has not been investigated, however, is how these different factors interact together to create new species.

African Lakes
This latest study involved cichlids occurring in 46 lakes in Africa. Cichlids are ideal for this type of study because of the way that the group has undergone what is described as “adaptive radiation” or diversification in the larger African lakes. There are now more than 800 endemic species of cichlid found in Lake Victoria and Lake Malawi, which have developed from just a few founder species.

It has now been discovered that environmental factors combined with sexual selection are the two significant forces driving such change. Diversification is most likely to be observed in cichlid populations occurring in deeper lakes and in areas where there is high solar radiation. Interestingly, in contrast to the situation with land-based vertebrates, the size of the habitat is not apparently a significant factor.

In the case of species-specific considerations, it emerged that mate choice was highly significant, as revealed by clear distinction in coloration between males and females (sexual dichromatism) and adaptive radiation.

Impact of These Findings
As this combination of factors has now been identified, it increases the likelihood that cases of divergence can be predicted more easily in certain situations. Furthermore, this Swiss study means that it is also possible to predict adverse impacts on biodiversity, arising from human activity. If the water levels in a lake are lowered, for example, then it is likely that not only will the existing diversity amongst the species there decline, but the rate of species diversification in the future will fall off, as well.

Reference: Catherine E. Wagner, Luke J. Harmon, Ole Seehausen. Ecological opportunity and sexual selection together predict adaptive radiation. Nature, 2012; DOI: 10.1038/nature11144