Floral deception in dioecious Actinidia polygama (Actinidiaceae) revealed by differential nitrogen investment in male organs

Abstract

Animal‐pollinated plants have evolved rewards and advertisements to attract pollinators, which learn to associate advertisements with rewards. Pollen‐collecting insects, such as bees, associate stamens with pollen (a reward) essential for brood rearing. In some dioecious plants, female flowers have stamens with sterile pollen grains to mimic male flowers. It is not yet fully understood whether females offer less nutritious pollen to pollinators in order to conserve nutrition. Here, we tested this hypothesis in a perennial vine, Actinidia polygama, which bears nectarless flowers. We quantified flower production and measured the dry mass of floral parts as well as carbon and nitrogen concentrations in floral parts and pollen in both sexes. Males produced more flowers per inflorescence and more inflorescences per shoot than females, while the dry mass of each flower was greater in females. The carbon allocation pattern was similar to that of biomass, but nitrogen allocation exhibited a remarkable reduction in sterile stamens and pollen of female flowers. In addition, as sterile pollen of females was sparse, when compared at the same volume, it was lighter than the pollen of males. Sterile pollen produced in female flowers appears to be as voluminous as that of male flowers but extremely poor in nutrients, especially in nitrogen, which clearly suggests that A. polygama females deceive pollen‐collecting pollinators for brood rearing.