 recent work, published in the American Journal of Botany, De Vega and Herrera investigated whether flowers visited by these ants differed from flowers that were not visited by ants in their sugar chemistry, and whether sugar-chemistry was correlated with the abundance of ant-transmitted yeasts found in the nectar.
By excluding ants from visiting inflorescences of a perennial, parasitic plant, Cytinus hypocistis, and comparing the nectar chemistry to inflorescences that were visited by ants, the authors tested these ideas experimentally.
When the authors compared the sugar content in the nectar of flowers visited by ants versus those enclosed in nylon mesh bags to exclude ants, they found that nectar of flowers exposed to ants had higher levels of fructose and glucose, but lower levels of sucrose compared with the ant-excluded flowers.
Interestingly, in flowers visited by ants, there was a high correlation between yeast cell density and sugar content. Nectar that had higher densities of yeast had more fructose and less sucrose, suggesting that the types of yeasts change the sugar content of the nectar. Flowers that were excluded from ants did not have any yeast in their nectar.
"Our study has revealed that ants can actually change the nectar characteristics of the flowers they are pollinating," says de Vega. "The microorganisms, specifically yeasts, that are present on the surface of ants change the composition of sugar in the flower´s nectar."
"This means that nectar composition is not completely controlled by the flower—it is something created in cooperation with the ants that visit the flower," she notes. "We also think that these ant-transported yeasts might have the potential to affect plant reproduction."
Indeed, if a plant cannot control the sugar content of its nectar, then it may lose some of its target pollinators, which would potentially affect overall seed set and plant fitness.
Moreover, if introducing these yeasts to nectar changes the chemistry of the very components that serve to attract pollinators, then perhaps ants are indirectly changing the foraging behavior of subsequent flower visitors and thereby affecting seed dispersal patterns.
This study has revealed an additional layer in the complex association between ants and flowering plants, as pollinating ants alter sugar-nectar chemistry in flowers via sugar-consuming yeasts. But the story does not end here. De Vega plans to continue researching the role that these nectarivorous yeasts play on the reproduction of plants.
"I plan to study the whole interaction of plants, yeasts, and pollinators—how are they interrelated and what mechanisms shape these relations?"
Explore further: Nectar is not a simple soft drink
Clara de Vega and Carlos M. Herrera. 2013. Microorganisms transported by ants induce changes in floral nectar composition of an ant-pollinated plant. American Journal of Botany 100(4): 792-800. DOI: 10.3732/ajb.1200626 http://www.amjbot.org/content/100/4/792.full.pdf+html