By Alice Klein
Ants beat us to it. A Fijian ant first started planting fruit crops 3 million years ago, long before human agriculture evolved.
The ant – Philidris nagasau – grows and harvests Squamellaria fruit plants that grow on the branches of various trees.
First, the ants insert seeds of the fruit plant in the cracks in tree bark. Workers constantly patrol the planting sites and fertilise the seedlings, probably with their faeces.
As the plants grow, they form large, round hollow structures at their base called domatia that the ants live in instead of building nests. When the fruit appears, the ants eat the flesh and collect the seeds for future farming.
Guillaume Chomicki at the University of Munich, Germany, and his colleagues discovered that each ant colony farmed dozens of Squamellaria plants at the same time, with trails linking each thriving hub. The connected plant cities often spanned several adjacent trees.
The researchers found that Squamellaria plants are completely dependent on the ants to plant and fertilise their seeds. At the same time, Philidris nagasau ants cannot survive without the food and shelter provided by the plants. The Fijian phenomenon is the first documented example of ants farming plants in a mutually dependent relationship.
Trees in nearby Australia have been observed with similar-looking ant-filled plants growing along their branches, but no one has known why, says Simon Robson at James Cook University in Australia. The plants are from the same family as Squamellaria, suggesting they have the same symbiotic farming relationship with ants.
Chomicki’s team also conducted a genetic analysis to study the history of the Fijian ant-plant interactions. The results showed that the ants lost their ability to build nests around 3 million years ago, at the same time as the plants developed roots that could grow in bark. This signals the beginning of the mutual relationship, which emerged when Fiji and Australia were still connected.
Only a handful of other species have been found to farm their food. For example, Yeti crabs cultivate bacteria on their claws and sloths grow algae gardens on their fur. Ants have been known to cultivate fungi, but this is the first time they have been found to plant crops in such a mutualistic manner.
The fact that ants have developed such sophisticated food production skills confirms the impressive teamwork of ants, says Kirsti Abbott at the University of New England, Australia.
“Ants are a lot smarter than we think they are – we call them superorganisms because they form networks that are much like our brains,” she says. “The information flow among ant colonies is just insane compared to human social systems, so this finding does not surprise me in the slightest.”
Journal reference: Nature Plants, DOI: 10.1038/nplants.2016.181