Discrimination of signal carotenoid content using multidimensional chromatic information

Red, orange and yellow carotenoid-based ornaments, which are widely used as sexual signals in many birds, fish and reptiles, are known to exhibit multidimensional chromatic variation as a result of both the concentration and relative proportions of different constituent carotenoids with differing spectral properties. This is thought to reflect intrinsic variation in signaller quality, making it a useful basis for female choice. However, whether females are able to discriminate relevant variation in carotenoid concentration and/or composition independently of each other, and of other phenotypic or behaviour traits, and if so, how this mediates their choice, is poorly understood. Here, female three-spined sticklebacks (Gasterosteus aculeatus) were presented with computer-animated courting males that varied exclusively in the appearance of their carotenoid-based colouration; specifically, each male’s signal provided a perceptual match for carotenoid colouration expressed by live males with...