When large-brained humans invented agriculture, we were millions of years behind ants that have been farming fungi since soon after the dinosaurs were startled by an incoming asteroid. The relationships between the farmer and the farmed provide an indication of how their interactions shape each other. A new study of insect/fungus co-evolution also tells us something about what we are doing to ourselves and our crops.

More than 240 ant species have adapted to farming fungi, feeding nutrients to their charges to encourage growth and getting a reward that makes it all worthwhile. These ants even produce their own antibiotics to protect their precious crops. Different ants, living side-by-side in an area of rainforest the size of a large room, have adopted divergent approaches, with some maximizing productivity while others prioritize crops better able to survive in varying conditions.

"Atta ants evolved huge agro-industrial farms. They have giant colonies with millions of workers. But they have miniscule brains and no detectable culture, so the big question is 'How do they know exactly what their crop needs?'" said Dr Jonathan Shik of the University of Copenhagen in a statement. 

Yet the ants do indeed know what will suit their favorite fungus. "They walk past many resources to pick up a tiny piece of insect poop that is exactly what they were looking for. They take it back to the nest and use it to grow a fungus," Shik said.

 Credit: Video by Jon Shik

Shik and colleagues camped in the Panamanian rainforest, collecting the items that different species of ants delivered to their fungal charges and measuring their nutritional content to understand why items much sought by one ant were ignored by others. In Nature Ecology and Evolution, they reveal that the ants could assess with stunning accuracy whether an item they had never encountered before would suit the specific fungus they were farming.

For example, too much protein can kill the fungi, and ants would reject extremely high protein synthetic foods Shik offered them, even starving to death rather than overfeeding their crop. Novel carbohydrate-rich foods, however, were accepted eagerly.

Leafcutter ants are considered among the more evolved fungal farmers, becoming the agribusiness of the ant world with thousands of workers per colony, in contrast to palaeoattines' family farm-style of 10-100 workers. In doing so, however, they have adapted a fungus that is very productive, but also highly specialized in the conditions it can thrive.

"In parallel to human cultural evolution where farmers and their crops have become increasingly co-dependent, so too have the ants and their fungal cultivar,” said co-author Dr Bill Wcislo of the Smithsonian Tropical Research Institute.

Humans have not had time to biologically adapt to the products we farm, with the notable exception of the spread of the gene for adult lactose tolerance. Nevertheless, there are parallels with the way we have become socially conditioned to use a narrow range of highly productive versions of particular foods, neglecting strains that might provide the genetic diversity to ride out crises.