Palm fruit colours are linked to the broad-scale distribution and diversification of primate colour vision systems

A long-standing hypothesis in ecology and evolution is that trichromatic
colour vision (the ability to distinguish red from green) in frugivorous
primates has evolved as an adaptation to detect conspicuous (reddish)
fruits. This could provide a competitive advantage over dichromatic
frugivores which cannot distinguish reddish colours from a background of
green foliage. Here, we test whether the origin, distribution and
diversity of trichromatic primates is positively associated with the
availability of conspicuous palm fruits, i.e. keystone fruit resources for
tropical frugivores. We combine global data of colour vision, distribution
and phylogenetic data for more than 400 primate species with fruit colour
data for more than 1700 palm species, and reveal that species richness of
trichromatic primates increases with the proportion of palm species that
have conspicuous fruits, especially in subtropical African forests. By
contrast, species richness of trichromats in Asia and the Americas is not
positively associated with conspicuous palm fruit colours.
Macroevolutionary analyses further indicate rapid and synchronous
radiations of trichromats and conspicuous palms on the African mainland
starting 10 Ma. These results suggest that the distribution and
diversification of African trichromatic primates is strongly linked to the
relative availability of conspicuous (versus non-conspicuous) palm fruits,
and that interactions between primates and palms are related to the
coevolutionary dynamics of primate colour vision systems and palm fruit
colours.