Meeting Abstract
Mammalian vision begins with retinal photopigments composed of a chromophore and an opsin protein. Most mammals possess a short wavelength-sensitive opsin 1 (SWS1) pigment that is primarily sensitive to either ultraviolet or violet light, leading to variation in color perception across species. Despite knowledge of both ultraviolet- and violet-sensitive SWS1 classes in mammals for 25 years, the adaptive significance of this variation has not been subjected to hypothesis testing. We gathered data on SWS1 for 402 mammal species, providing novel SWS1 sequences for 97 species. Utilizing an ancestral sequence reconstruction method, we estimate that the ancestral mammal possessed an ultraviolet SWS1 pigment and violet-sensitive pigments evolved at least 12 times in mammalian history. We also observed that ultraviolet pigments, previously considered to be a rarity, appear to be very common in mammals. We then used phylogenetic comparative methods to test the hypotheses that the evolution of violet-sensitive SWS1 is associated with increased light exposure, extended longevity, and longer eye length. We discovered that diurnal mammals and species with longer eyes are more likely to have violet-sensitive than UV-sensitive pigments. We hypothesize that as mammals evolved larger body sizes, they evolved longer eyes, which limited transmittance of ultraviolet light to the retina due to an increase in Rayleigh scattering, and as mammals began to invade diurnal temporal niches, they evolved lenses with low UV-transmittance to reduce chromatic aberration and/or photo-oxidative damage.
