The role of light environment in the evolution of color vision genes in butterflies and moths

Opsins, combined with a chromophore, are the primary light-sensing molecules in animals and are crucial for color vision. Throughout animal evolution duplications and losses of opsin proteins are common, but it is unclear what is driving these gains and losses. Light availability has been implicated and dim environments are often associated with low opsin diversity and loss. Correlations between high opsin diversity and bright environments, however, are tenuous. To test if increased light availability is associated with opsin diversification, we examined diel-niche and opsins from transcriptomes of 175 butterflies and moths (Lepidoptera). At least 14 independent opsin duplications are associated with bright environments. We estimated rates of opsin evolution and found that opsins from diurnal taxa evolve faster — at least 13 amino acids were identified with higher dN/dS rates. Modeling the 3D protein structure and analyzing the spatial distribution of these amino acids revealed that a subset was close enough to the photopigment retinal to change the spectral sensitivity of the opsin. These results demonstrate that high light availability increases opsin diversity and evolution rate and potentially affects spectral tuning in Lepidoptera.