Humans began to farm about 11,000 years ago, when temperatures around the planet warmed, and people could settle down and start to grow plants. But we don't have a monopoly on agriculture; ants started their own farms millions of years before humans even appeared on the scene. A new study has suggested that ant agriculture arose about 66 million years ago, when Earth was struck by an asteroid that wiped out the dinosaurs.
Ants started to cultivate fungi long ago, and this relationship has continued for millions of years, up to the present. Using genetic data obtained from hundreds of different species of ants and fungi, researchers created evolutionary trees for comparison. This work enabled them to determine exactly when ants began to farm fungi. The findings have been reported in Science.
There are four types of farming ants, which are classified based on how they cultivate fungi. For example, leafcutter ants practice higher agriculture, in which they use pieces of fresh vegetation to enrich fungi that grow ant food known as gongylidia. Their complex colonies, which are supported by this effort, can have members that may have millions of residents.
“Ants have been practicing agriculture and fungus farming for much longer than humans have existed,” said lead study author Ted Schultz, the curator of ants at the Smithsonian’s National Museum of Natural History. “We could probably learn something from the agricultural success of these ants over the past 66 million years.”
During fieldwork on over thirty trips to various locations throughout the Americas and Caribbean, Schultz has observed ant behavior and collected thousands of genetic samples of both ants and fungi. There are around 250 species of farming ants living in the region.
In this work, the researchers analyzed the genetics of about 288 fungi that are cultivated by ants, as well as another 200 fungal species, in addition to 276 ant species, of which 208 are fungi farmers. Thus, evolutionary trees of these different groups could be created, and wild species of fungi could be compared to those being farmed. This work also showed when ants started to use certain fungal species in agriculture.
The scientists revealed that ants and fungi have been working together for 66 million years, since about the same time an asteroid hit the planet and filled the atmosphere with debris. The light of the sun was blocked, and photosynthesis came to a halt for years. A mass extinction ensued, and about half of all the plants on Earth were destroyed.
But fungi fared well. The massive amounts of dead plants material were perfect for them. As the fungi moved into the decaying plant matter, they likely began to interact with ants. The insects were able to use the fungi for their own needs, and survive extinction.
This study also showed that it still took about another 40 million years for ants to engage in more complex, higher agriculture. Around 27 million years ago, the planet cooled, which changed the environment. Drier regions emerged in places like South America, and ants moved fungi from a wet to dry climate. Fungi were then isolated from their wild ancestors, and they started to rely on the ants to help them survive. This is thought to have led to practices used by leafcutter ants, which provide sustenance for the fungi.
“The ants domesticated these fungi in the same way that humans domesticated crops,” Schultz said. “What’s extraordinary is now we can date when the higher ants originally cultivated the higher fungi.”
