Visual system plasticity is differently mediated by cone opsin expression and chromophore composition in closely related cichlid species

Phenotypic plasticity allows organisms to rapidly adjust to environmental changes. Cichlid fish inhabit a wide range of light environments and show a large diversity in visual system properties, which makes them a good model system to address the role of phenotypic plasticity in visual adaptation. Cichlid retinal cone pigments consist of opsin proteins bound to Vitamin A₁ or A₂-derived chromophores. Plasticity in expression has been shown for cichlid opsin genes, but less is known about the contribution of cyp27c1, the enzyme that converts Vitamin A₁ into A_2,. Here, we studied both opsin and cyp27c1 expression patterns for three closely related cichlid species from different visual habitats in Lake Victoria, across different light treatments. We found differences in cyp27c1 as well as in opsin expression patterns between the three species. Experimental light treatments affected the developmental trajectory of cyp27c1 expression in one species and opsin expression in all three species. Within each species, we found large individual variation in cyp27c1 expression levels and no consistent association with opsin expression levels. These results indicate that visual system plasticity of even closely related species can be differentially mediated by opsin and cyp27c1 expression, possibly associated with species differences in visual niche.