Jurene E. Kemp & Allan G. Ellis
Flower colour is thought to primarily act as an attractant to pollinators. However, if flowers become more conspicuous to pollinators, they may also become more apparent to herbivores. Plants thus face an evolutionary conflict between selection from pollinators and herbivores. The herbivory of flowers is particularly costly to plants, as these are the reproductive organs. In Namaqualand, South Africa, daisies flower en-masse each year, and many of these daisies have flowers that are closed at night and for 5-6 daylight hours. We test whether these closing daisies have evolved camouflaged colours on the petal surfaces that are exposed during the times when flowers are closed and herbivores are active. By modelling the colour of the exposed petal surfaces in the vision of multiple herbivores, we showed that these daisies indeed have lower petal surfaces that cannot be distinguished from the green leaf background. We also show that flowers that close at night have different colours on the upper surfaces (which are exposed to pollinators) and lower surfaces (which are exposed to herbivores). Experiments using vertebrate herbivores show that flowers are easily detected when the upper petal surfaces are exposed, but that herbivores were unable to distinguish lower petal surfaces against a leaf background, resulting in reduced flower herbivory. Our results show the important role of herbivores in selection on floral traits. Visual camouflage of flowers may be an effective anti-herbivory strategy during times when pollinators are inactive. Further, visual camouflage potentially provides an alternative to chemical defence, which often involves costs to pollination.