Fijian ants began planting fruit crops millions of years before ancient humans did, a new study revealed.

Researchers from the University of Munich in Germany reconstructed the evolutionary history of the relationship between Fijian ants and fruit plants. They found a mutually beneficial agreement between the two, in which both partners profit from the relationship.

Fijian Farming Ants

Professor Susanne Renner and her student Guillaume Chomicki discovered that Fijian ants started to cultivate fruit plants more than 3 million years ago, long before humans did.

And as it turned out, colonies of the Fijian ant (Philidris nagasau) grow and harvest epiphytes that grow harmlessly upon another tree. These epiphytes include the Squamellaria fruit plants, which grow on branches and are endemic to the island of Fiji.

What happens is that Fijian ants first gather seeds from the Squamellaria fruit plants then seek out fissures or cracks in the bark of the host tree.

If they find one, the ants will plant the seeds in these spaces, where the seed will germinate. Worker ants watch over these planting sites and possibly fertilize them with their feces, researchers said.

As the fruit plants grow, they form large and round hollow structures at the base known as domatia where the Fijian ants will reside instead of building their nests. When the fruit has appeared, the Fijian ants eat them and collect the seeds for future farming. The cycle begins again.

A Network Of Ant Farms

Scientists discovered that each Fijian ant colony farmed dozens of fruit plants at the same time, producing a trail that links them to one another. These connected network of ant farms often spanned several trees that were adjacent to each other.

"The plants colonize three or four tree species," said Renner.

The professor explained that these tree species are attractive for ants either because their bark is especially soft, which helps ants widen the fissures, or because they produce nectar.

Chomicki, who is a graduate student at the university, said dozens of ant colonies have been found to be linked by "ant highways" on a single tree. All these ant colonies are the progeny of a single queen, which lays her nest in the center of the system, said Chomicki.

Profound Symbiosis

Researchers said the mutual benefits for Fijian ants and fruit plants are so profound that neither can survive without the other. This symbiosis may have been the result of evolutionary adaptations that pushed them to be compatible.

Details of the study are published in the journal Nature Plants.

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