Ant Agriculture
D. Maya, Kolkata

Today you enjoy your yennai-katirikkai or bisi-bele-bhath. Can you imagine a time before humans began to grow crops? You would forage around and eat whatever was growing around you. How did those ancient humans find out what was edible and what was poisonous? There lies the curiosity of human beings, and the beginning of farming, some 12,000 years ago.
When agriculture began, humans altered the future of our species forever. Our ancestors were ecological pioneers, discovering and cultivating the most valuable crops, scaling them up to feed entire communities and transforming wild crops so fundamentally that they became dependent on humans for their survival.
But humans were late to the game. By the time our ancestors had launched their world-changing Neolithic Revolution, ants had already been farming fungi in South American rainforests for 60 million years! Not only do they use sophisticated techniques, but the fungus they grow can no longer survive without the ants to take care of them. So the fungi are fully domesticated!

Where do these ants farm?
There are about 240 species of these ants. They are called attine ants—ants which farm fungi! Most common among them are the leafcutters in the Americas and the Caribbean. And their farms are completely underground! Strangely, they are often located in dry, inhospitable habitats where fungi do not normally grow. That's because you most often see fungi growing on wet decaying plant matter.
The ants forage for bits of vegetation. For instance, the leaf-cutters, as their name suggests, use their mandibles to cut portions of leaf. They do not eat it themselves, but use the plant matter to grow their crops! They later feed on the fungus themselves. Some of the ant colonies contain millions of ants, so they grow fungi on an industrial scale. Not only is it an industry, it is a sustainable one, efficient, and also resistant to diseases and pests. How do they achieve this?

Growing a farden
Attine ants perform a variety of farming behaviors to maintain the fungal colony. The colonies are located in shallow, below-ground nests and often found in natural holes between rocks and roots. To optimize the growth of their fungal cultivar, attine ants open and close tunnels to maintain the ideal temperature and humidity in their below-ground structures for fungus farming. Secretions from specialised glands are applied across the surface of the fungus to inhibit the growth of harmful pathogens. Any weeds or infected parts are removed by chewing off sections and discarding the waste material to prevent the spread of pathogens through the colony.
The fungi are completely isolated in their underground gardens. They cannot escape, meaning wild fungi growing in the wild, and fungi domesticated by the ants can’t get together and swap genes. As a result of this isolation, the domesticated fungi have evolved so they are completely dependent on their ant farmers for survival. This is like many of the crops that humans grow: they are so highly modified that they exist in forms no longer found in the wild. The ants also in turn depend on the fungi: when a queen's daughter founds a new colony, she takes with her a piece of her mother's fungal garden to begin her own.

How did this happen?
Some scientists believe this happened due to a severe climate change that occurred some 30 million years ago. The DNA data suggests that this leap coincided with dramatic changes in ancient climate. About 35 millions years ago, there was a global cooling of the earth. The wet rain forests of the ants gave way to dryer environments. But the ants were used to feeding on fungi that grow only in wet conditions. As you know, fungi are usually seen on moist decaying vegetable matter. So the ants very likely evolved this complex mechanism by growing the fungi underground, in controlled conditions. The fungi learned to live off fresh (rather than decaying) plant matter, and the ants got their favourite food.
One of the key findings is that these ants likely lost the ability to make a key amino acid called arginine. This is most likely because fungi have arginine and so they did not need to make it themselves. Such dependence on each other for existence is called symbiosis. In particular, since the dependence is mutual, it is called mutualism.

Lessons for humans
Like some industrial farmers, fungus-farming ants grow a single type of crop. However, they manage to do so without succumbing to foes like disease or pests that threaten human crops when they lose genetic diversity. Ants achieve this remarkable feat by keeping their underground garden rooms spotless to limit the possibility of disease, and by producing a sort of natural antibiotic that acts as a pesticide, battling a parasitic fungus that threatens their food source.
The key difference is that these strategies effectively keep pathogens in check but don’t completely destroy them, as humans tend to do. Instead, ants have achieved a sustainable balance, by allowing all kinds of bacteria and other microbes that might be benign or even beneficial. Perhaps they have discovered the optimal ecological blend of microbes that's the best for healthy soil and healthy food.
Adapted from https://www.smithsonianmag.com/author/brian-handwerk and Wikipedia