Microorganisms transported by ants induce changes in floral nectar composition of an ant-pollinated plants

Abstract

Premise of the study: Interactions between plants and ants abound in nature and have signifi cant consequences for ecosystem functioning. Recently, it has been suggested that nectar-foraging ants transport microorganisms to fl owers; more specifi cally, they transport yeasts, which can potentially consume sugars and alter nectar composition. Therefore, ants could indirectly change nectar sugar profi le, an important fl oral feature involved in the plant–pollinator mutualism. But this novel role for ants has never been tested. We here investigate the effects of nectarivorous ants and their associated yeasts on the fl oral nectar sugar composition of an ant-pollinated plant. • Methods: Differences in the nectar sugar composition of ant-excluded and ant-visited fl owers were examined in 278 samples by using high-performance liquid-chromatography. The importance of the genetic identity and density of ant-transported basidiomycetous and ascomycetous yeasts on the variation of nectar traits was also evaluated. • Key results: Ant visitation had signifi cant effects on nectar sugar composition. The nectar of ant-visited fl owers contained signifi cantly more fructose, more glucose, and less sucrose than the nectar of ant-excluded fl owers, but these effects were context dependent. Nectar changes were correlated with the density of yeast cells in nectar. The magnitude of the effects of ant-transported ascomycetes was much higher than that of basiodiomycetes. • Conclusions: Ants and their associated yeasts induce changes in nectar sugar traits, reducing the chemical control of the plant over this important fl oral trait. The potential relevance of this new role for ants as indirect nectar modifi ers is a rich topic for future research into the ecology of ant–fl ower interactions.