Crater lake cichlid evolved through hybridisation


A new study of cichlids which live in tiny lakes in the top of volcanoes in Cameroon, West Africa, has shown that one species evolved through hybridisation.

Cameroonian crater lake cichlid authority Dr Uli Schliewen of the Department of Ichthyology at Bavarian State Collection of Zoology in Munich, and his co-author B. Klee, studied the cichlids found in the Lake Barombi Mbo.

This small lake, which measures just 3 miles across, is one of a group of volcanic lakes in Cameroon, including Bermin and Ejagham, which were produced by massive eruptions millions of years ago.

Somehow, the lakes flooded and cichlids managed to get in, and have since evolved to produce species flocks of endemic cichlids that are found nowhere else on earth.

Schliewen and Klee say that the formation of these "megadiverse species flocks" of extremely closely related cichlids is explained by a combination of things, including natural selection, isolation and sexual selection.

However, some authors have also suggested that hybridisation may be responsible for some species arising. Initial hybrids could, they say, go on to form new forms that eventually evolve into distinct new species.

To test the theory Schliewen and Klee produced an evolutionary family tree, called a phylogeny, for the Barombi Mbo cichlids by analysing the mitochondrial and nuclear genes of the fish.

The results showed that the Barombi Mbo cichlid flock is monophyletic and that all 11 of the cichlid species in the lake had evolved from a single cichlid ancestor.

However, they also spotted a pattern in the phylogeny which they claim shows that secondary hybridisation had occured under sympatric conditions in Lake Barombi Mbo.

The results show that Pungu maclareni in fact formed thousands of years ago when two species crossed. The hybrid fish later evolved into a species in its own right. This is believed to be quite an unusual event in fish evolution.

Schliewen UK, Klee B (2004) - Reticulate sympatric speciation in Cameroonian crater lake cichlids. Front Zool. 2004 Oct 26; 1(1): 5.