Hybridisation and ecological opportunity together explain the rapid cichlid diversification in Lake Mweru

In this paper published in Nature Communications, we show that many new cichlid fish species evolved Lake Mweru, all of which evolved from hybrid origin. We show that in the nearby Lake Bangweulu, there are no new cichlid species and no evidence for hybridisation. This paper shows that the coincidence of ecological opportunity and hybridisation can explain species richness differences. Hybridisation can provide large genetic variation that facilitates the evolution of new species taking advantage of different ecological niches such as different food types or habitats.

This project was started by Ole Seehausen, Cyprian Katongo and Rike Stelkens plus others who set out for two East African Lakes that were thought to not harbour cichlid radiations despite presence of cichlids in the region and considerable lake sizes that would provide enough ecological opportunity for adaptive radiations [Read the Behind The Paper story]. With huge fishing efforts, measuring and classifying many hundred fishes (mostly by Ole) and performing extensive genomic data analyses (my part), we found that Lake Mweru cichlids have all evolved since a river capture event brought Zambezian and Congolese cichlid fishes together in Lake Mweru. These cichlids hybridised and diversified into over 40 species. Multiple radiations evolved from different combinations of ancestral lineages and these radiations complement each other beautifully. Nearby Lake Bangweulu got colonized by the same Zambezian lineages but not by the Congolese lineages. Here, no adaptive radiations occurred despite of all the ecological opportunities this lake provides.

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