by Mary Caperton Morton Thursday, February 9, 2017
A new study in Nature suggests that ants may have invented agriculture as much as 3 million years before humans.
On the Fijian islands of Viti Levu, Vanua Levu and Taveuni, the ant species Philidris nagasau actively cultivates at least six species of Squamellaria plants, using the plants for both food and shelter. All of the Squamellaria are epiphytes, or plants that grow on other plants, using their hosts for support and nutrients. The ants were observed gathering seeds from the fruits of the Squamellaria and inserting them into crevices in host trees. Worker ants constantly patrolled the seeds and, as the seedlings took root in the host, they defecated in the crevices, fertilizing the young plants. As the plants mature, they form hollow chambers at their bases, which the ants were observed using for nests. The ants also harvested the Squamellaria fruit, eating the flesh and collecting seeds for planting.
This kind of symbiosis — known as farming mutualism, in which one organism cultivates another for food and/or shelter — has been documented before in ants. The new study, however, offers a new example of obligate farming mutualism: Both the ants and plants are dependent on one another for survival. For example, Philidris nagasau ants no longer make their own nests, but rather depend on cultivating plants for shelter.
Guillaume Chomicki and Susanne Renner, both of the University of Munich in Germany, observed ant colonies simultaneously farming dozens of plants linked by a network of ant trails. These ant and plant colonies were sometimes found spanning several adjacent trees. Using DNA sequencing, phylogenetic analyses and molecular clock dating techniques, the team also approximated the start of the relationship between Philidris nagasau and Squamellaria to about 3 million years ago, when the plants developed a specific adaptation for bark anchoring, and the ants started their planting behavior.
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