Cichlid fish visual systems: mechanisms of spectral tuning.

Hundreds of species of cichlid fishes have evolved in the Great Lakes of Africa. These colorful fishes are known for their ecological diversity. Here, we discuss the diversity of their visual systems. Cichlids have seven unique cone opsin genes, which produce visual pigments sensitive from the ultraviolet to the red end of the spectrum. Different species typically express three visual pigments to produce a trichromatic visual system. Because species differ in which sets of opsin genes they express, visual sensitivities can differ widely. In addition to the large visual pigment shifts from changing gene expression, cichlids can also more finely tune visual pigments through alterations in opsin amino acid sequence. Both of these tuning mechanisms likely play an important role in cichlid ecology and could contribute to the evolution of cichlid diversity through speciation.