Some plants provide ants with food and shelter, in return for protection and means of spreading seeds. Biologists have finally established how their union began.
The union of insects and plants has an exceptionally long history and covers the most diverse aspects of their coexistence. Trees can provide food to ants and grow thorns, creating for them excellent protected habitats so that they, in turn, protect them from pests and help spread the seeds. Under the influence of each other, they strongly modified: some trees are able to secrete nectar on the trunk and leaves, luring ants, or form hollow spines for arranging the nest.
The question of the origin of these close relationships is reminiscent of the problem of chicken and egg: can we figure out how their symbiotic existence began? Perhaps the plants were the first to “tame” the insects, luring them with nectar and spreading the seeds? Or did the ants begin to feed on nectar, and only then did the plants take advantage of it? Or was some other scenario realized? This story dates back to the Mesozoic era, and paleontological evidence of it is almost not preserved.
Therefore, Matthew Nelsen and his colleagues from the Field Museum of Natural History in Chicago approached the issue from the other side – and studied the genomes of 1,700 species of ants and more than 10 thousand plants to establish the appearance of signs that are important for symbiosis. The results of the study they presented in an article published in Proceedings of the National Academy of Sciences. “In our work, we linked the behavioral and physiological characteristics of ants and plants to determine when ants began to feed and live on plants and when plants acquired the ability to produce structures useful for them,” explains Nielsen.
Judging by their results, the ants, who rose from the ground and spent a lot of time on plants in search of prey, “started” the first. This made it possible for the predatory insects to switch to feeding on the resources of the plant itself, after which they began to produce more nectar or juicy fruit pulp. Finally it was completed already in the Cenozoic, several tens of millions of years ago, when the herbivorous diet finally changed the way of life of these ants – and they began to place their nests on the plants.