Visual ecology of true lemurs suggests a cathemeral origin for the primate cone opsin polymorphism

In contrast to the majority of primates, which exhibit dedicated diurnality or nocturnality, all species of Eulemur are cathemeral. Color vision, in particular, is strongly affected by the spectral composition and intensity of ambient light, and the impact of activity period on the evolution of primate color vision is actively debated. We studied three groups of wild brown lemurs (Eulemur fulvus) in Ankarafantsika National Park, Madagascar over a one-year span. We also used non-invasive fecal DNA collection and analysis to study the opsin genes underlying the color vision of 24 individuals. We quantify the color and brightness of dietary fruits and modeled the chromaticity and discriminability of food objects to different visual phenotypes under daylight, twilight, and moonlight conditions. We found that E. fulvus possesses routine dichromacy, unlike its congener E. flavifrons, for which polymorphic trichromacy has been reported. Our models suggest that dichromacy is well-suited to the ...