The relationship between lens transmission and opsin gene expression in cichlids from Lake Malawi

The lens plays an important role in regulating the wavelengths of light that reach the retina. However, the evolutionary relationship between lens transmission and retinal sensitivity remains cloudy at best. We examined the relationship between lens transmission and opsin gene expression in a group of rapidly radiating cichlids from East Africa. Lens transmission was bimodal, either cutting off around 360 or 400 nm, and appeared to be quite labile evolutionarily. We found a strong correlation between lens transmission and SWS1 (UV) opsin gene expression, suggesting that UV transmitting lenses are adaptive in cichlids. Species which expressed high levels of SWS2B (violet) opsin varied in their lens transmission while most species that expressed high levels of SWS2A (blue) opsin had UV blocking lenses. In no instance did lens transmission appear to limit retinal sensitivity. Finally, the strong correlation that we observe between SWS1 expression and lens transmission suggests that these two traits might be coupled genetically.