Abstract

Based on an examination of λ_max values for photopigments extracted from a wide range of teleost fishes it was suggested over 20 years ago that these values are not evenly distributed throughout the wavelength range; rather, they tend to cluster around certain wavelength values. Although one can gain the impression that mammalian cone pigments may show a similar tendency to cluster around preferred values, the data available on such pigments have been too few and too variable to yield strong conviction. We have exploited the fact that many mammals are dichromatic, either as a species trait or as a polymorphic variant, to examine this issue. High frequency ERG flicker photometry was used to measure the spectra for the middle- to long-wavelength cones in more than 120 individual animals from 15 different species. The λ_max values for these cones range from ~511 to 562 nm. Analysis of the dervied λ_max values across all individuals provides strong evidence that the Amax values for the cone pigments of mammals occur at stepped intervals. The spacing is very similar to that suggested for fish pigments, the mean interval being 6.1 nm (SD = 1.0). This result provides the basis for speculations about the spectral positioning of other mammalian cones, including those of the human.

© 1985 Optical Society of America