Chromaticity as a signal of ripeness in fruits taken by primates.

We have measured the reflectance spectra of many samples of fruit eaten by chimpanzees and three frugivorous monkey species. If the fruit are plotted in a colour space appropriate for catarrhine primates, several distinct ripening patterns are evident. The degree of ripeness of many species would be discernible by dichromatic primates, but for most fruit a trichromatic consumer would be at an advantage. However, by calculating which set of possible photopigments would maximise the chromatic distance between samples of each fruit species, we show that the spectral positions of the primate long- (L) and middle-wavelength (M) cone pigments are not optimised for this task.