Humans first started farming plants around 10,000 years ago in the Near East, but it seems we were pipped to the post by at least 3 million years. Scientists have discovered for the first time that ants in Fiji have been found to cultivate plants, harvesting seeds, planting, and fertilizing them, and then moving into their new homes.
The plants that are cultivated by the ants are all from the genus Squamellaria, which are a type of epiphyte. This means that they grow exclusively on other plants, usually trees. They are not parasites, because they don’t often harm the host tree, but they do have reduced roots, which means that they can’t take up nutrients from the soil in the usual way plants do. This is where the ant species Philidris nagasau comes in.
These epiphytes naturally grow on a few species of tree that are also beneficial to the ants, as they provide nectar, while also being the perfect host due to their soft bark. So after eating the flesh of the epiphytes fruit, the insects collect the seeds of the Squamellaria plants and insert them into cracks in the host trees' bark.
The plants germinate and then develop a small growth, or tuber, which naturally has a small hole in it. This allows the ants to climb inside, which the insects then use, in effect, as a toilet. By pooping in the tubers the ants provide the epiphytes with valuable nutrients that helps the seedlings grow. As the plants get bigger, so the tuber grows too, forming a network of chambers that the ants then move into and colonize. Reserving one part as the restroom, the ants continue to provide the epiphyte with fertilizer, while they set up another chamber as a nursery for their growing larvae.
As the ant colony grows, they plant more and more seeds, until they create a tiny ant “village” in the host tree, connected to each other by little ant highways. “One often finds dozens of colonies, connected by ant highways, on a single tree,” said Guillaume Chomicki, who co-authored the study published in Nature Plants. “All of these individuals are the progeny of a single queen, whose nest is located in the center of the system.” When the cultivated plants then develop fruit, the ants have a ready supply of food, and more seeds.
While humans may have only just picked up on this incredible symbiosis, it seems that the ants and plants have been working together for millions of years. By looking into their DNA, the researchers found that the species first started their relationship at least 3 million years ago, and that they have coevolved for such a long time that now neither species can exist without the other.