Research article

Adaptive sequence evolution in a color gene involved in the formation of the characteristic egg-dummies of male haplochromine cichlid fishes

Walter Salzburger^{* 1,2,3} , Ingo Braasch^{* 1,4} and Axel Meyer¹

¹Lehrstuhl für Zoologie und Evolutionsbiologie, Department of Biology, University Konstanz, 78457 Konstanz, Germany

²Department of Ecology and Evolution, University of Lausanne, 1015 Lausanne, Switzerland

³Zoologisches Institut der Universität Basel, Evolutionsbiologie, Universität Basel, 4051 Basel, Switzerland

⁴Physiological Chemistry I, University of Würzburg, 97074 Würzburg, Germany

author email corresponding author email* Contributed equally

BMC Biology 2007, 5:51doi:10.1186/1741-7007-5-51

Published:	15 November 2007

Abstract

Background

The exceptionally diverse species flocks of cichlid fishes in East Africa are prime examples of parallel adaptive radiations. About 80% of East Africa's more than 1 800 endemic cichlid species, and all species of the flocks of Lakes Victoria and Malawi, belong to a particularly rapidly evolving lineage, the haplochromines. One characteristic feature of the haplochromines is their possession of egg-dummies on the males' anal fins. These egg-spots mimic real eggs and play an important role in the mating system of these maternal mouthbrooding fish.

Results

Here, we show that the egg-spots of haplochromines are made up of yellow pigment cells, xanthophores, and that a gene coding for a type III receptor tyrosine kinase, colony-stimulating factor 1 receptor a (csf1ra), is expressed in egg-spot tissue. Molecular evolutionary analyses reveal that the extracellular ligand-binding and receptor-interacting domain of csf1ra underwent adaptive sequence evolution in the ancestral lineage of the haplochromines, coinciding with the emergence of egg-dummies. We also find that csf1ra is expressed in the egg-dummies of a distantly related cichlid species, the ectodine cichlid Ophthalmotilapia ventralis, in which markings with similar functions evolved on the pelvic fin in convergence to those of the haplochromines.

Conclusion

We conclude that modifications of existing signal transduction mechanisms might have evolved in the haplochromine lineage in association with the origination of anal fin egg-dummies. That positive selection has acted during the evolution of a color gene that seems to be involved in the morphogenesis of a sexually selected trait, the egg-dummies, highlights the importance of further investigations of the comparative genomic basis of the phenotypic diversification of cichlid fishes.