Midas cichlids get a fat lip very quickly!

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It takes only a century for some cichlids to evolve fat lips, according to research published in a recent issue of the journal BMC Biology.

The paper by Kathryn Elmer and coauthors used genetic data to study the colonisation of Lake Apoyeque, a Nicaraguan crater lake that is only 1800 years old, by the Midas cichlid (Amphilophus cf. citrinellum).

The lake contains two forms of the cichlid – one with large, thick lips and another with thin lips (the normal form also found elsewhere), with the thick-lipped form constituting about a fifth of the population.

The authors applied gene coalescence analyses to 11 microsatellite loci and mitochondrial DNA sequences of the Lake Apoyeque cichlids, and their results suggested that the Midas cichlids in Lake Apoyeque originated via a single migration from neighbouring Lake Managua about 100 years ago. This implies that the fat-lipped form have evolved within this span of time.

By studying the morphology and ecology of the two forms, the authors have found a plausible reason for the two forms to evolve, since they appear to occupy different ecological niches.

The thick-lipped form has a thinner, more tapering head to enable it to eat insects and invertebrates from within rocky crevices, while the thin-lipped form has broader jaws with more teeth more suited to crushing molluscs (these dietary preferences are reflected by their gut contents).

Even though they appear so morphologically different, the authors found very little genetic difference between the two forms, suggesting that the two forms are populations in a very early stage of speciation (incipient species) and in the process of diverging due to disruptive selection and ecological diversification.

For more information, see the paper: Elmer, KR, TK Lehtonen, AF Kautt, C Harrod and A Meyer (2010) Rapid sympatric ecological differentiation of crater lake cichlid fishes within historic times. BMC Biology 8, 60. doi:10.1186/1741-7007-8-60.