Guest blog post by Cássio Pereira
The Zeyheria montana shrub is quite common in the Brazilian Cerrado and is known to have extrafloral nectaries on the leaf blade that attract patrolling ants such as the aggressive Ectatomma tuberculatum. The ant, in turn, defends the leaves against the action of herbivores. However, extrafloral nectaries can distract ants on the leaves, segregating them from the reproductive parts and preventing them from driving away pollinators, which can benefit the action of florivores and nectar robbers.
Surprisingly, in southeastern Brazil, we observed a second defensive mutualism occurring on the reproductive tissues of these shrubs between E. tuberculatum and the treehopper Guayaquila xiphias, which provides the ant with honeydew in exchange for protection. This trophobiosis relationship (interaction between ants and phytophagous hemipterans that secrete sugary exudates) seems to be effective not only in the defense of floral buds and flowers, but also of the fruit, which, despite being dry, contains a lot of water in its formation and is attacked by beetles of the Curculionidae family.
As far as we know, this is the first case reported in the literature of a double defensive mutualism occurring simultaneously on a single plant species. Given this record, important questions arise regarding these interactions. Is the trophobiosis that occurs in reproductive organs capable of increasing the fitness of these plants? Although these ants are probably also scaring away possible pollinating insects, could the fact that Z. montana is primarily pollinated by hummingbirds offset this loss given that hummingbirds are larger and perhaps immune to ant attacks?
Our record raises more questions than it answers. Long-term Z. montana population studies would help improve our ecological understanding of these interactions.