Hymenopteran pollinators as agents of selection on flower colour in the New Zealand mountains: salient chromatic signals enhance flower discrimination

Flowering plants in New Zealand have often been described as having predominantly small white or pale flowers, possibly due to an absence of social insects as a major pollinating force. However, insect vision is considerably different to human perception, and these hypotheses need to be assessed considering insect perceptual capabilities. We collected spectral reflectance data from flowers of 23 native species in an alpine region of New Zealand at an altitude above 1500 m where 77% of flowers have been reported to possess small white or pale flowers. Our spectral analyses show that these flowers actually have very strong chromatic signals for hymenoptera colour vision. Indeed the spectral signals of these flowers most frequently have inflection points at about 400 and 500 nm, which closely match the region of best spectral discrimination by hymenopteran pollinators with a trichromatic visual system. When the flower spectra are plotted in a colour space designed for hymenoptera, the data reveals that most of the flower colours would be well detected against background foliage, and often reliably discriminated from the other flowers appearing in the same alpine environment. We thus demonstrate that New Zealand alpine flowers are actually well suited for visual detection and discrimination by biologically important hymenopteran pollinators.