The mutually beneficial relationship between acacias and the ants that guard them is a little better understood, thanks to researchers in the UK and Sweden. They found that the ants are deterred from entering the flowers–and thus competing with pollinators–by a chemical the plant produces. This chemical is produced in addition to the food rewards provided to the ants.
The ants are well-studied as highly protective defenders of the acacia plants, even to the point of attacking large herbivores. In return the plants provide shelter and food to the ants via specialized structures, extrafloral nectaries (for sugars) and beltian bodies (proteins).
“They have very open flowers, but still, the ants don’t seem to go on to them. We wanted to know why,” lead researcher Nigel Raine from University of London said in a BBC news interview.
Production of the chemical is correlated with pollen production, and it repellant only to the ants. The discovery of an additional signal paints a picture of a complex, chemically mediated co-evolution between the two organisms.