Scientists have discovered a key transition in the agricultural evolution of insects, dating back 30 million years, when the planet cooled down and dry areas spread.
Millions of years before humans discovered agriculture, vast agricultural systems were thriving beneath the Earth's surface. The underground farms, which produced various types of mushrooms, were cultivated and maintained by colonies of ants, whose descendants continue to practice agriculture today.
This transition allowed ants to reach higher levels of complexity in agriculture, rivaling the agricultural practices of humans: the domestication of crops that remained permanently isolated from their wild habitats and therefore depended on their farmers for their evolution. and survival.
The work, which was published this Wednesday, April 12, in 'Proceedings of Royal Society B' by scientists from the Smithsonian National Museum of Natural History, reveals that the transition of ants probably occurred when agricultural ants began to live in dry climates, where moisture-loving fungi couldn't survive on their own. The finding comes from a genetic analysis showing the evolutionary relationships of agricultural and non-agricultural ants from wet and dry habitats throughout the Neotropics.
In the Americas and the Caribbean, about 250 species of ants have been found cultivated in tropical forests, deserts, and grasslands, and these species are divided into two different groups, based on the level of complexity of their agricultural societies: lower agriculture and higher. All agricultural ants begin new mushroom gardens when a queen's daughter leaves her mother's nest to go and find her own nest, taking with her a piece of the mushroom from the original colony to start the farm for the next colony.
In the lower primitive forms of ant agriculture - found largely in humid tropical forests - fungi occasionally escape their ant colonies and return to the wild. Lesser ants also occasionally collect their wild-grown mushrooms and carry them back to their nests to replace faltering crops. These processes allow wild and cultivated fungi to interbreed and limit the degree of influence that lower ants have on the evolution of their crops.
But, as with certain crops, they have been so modified by human breeders that they can no longer reproduce and live alone in the wild. These superior agricultural ants grow highly domesticated crops, allowing them to live in vast communities and work through division of labor to fertilize their fungal crops, transport waste, keep pathogens at bay, and maintain ideal growing conditions.
"IMPORTANT LESSONS" FOR THE HUMAN BEING
"These ant farming societies have been practicing sustainable agriculture on an industrial scale for millions of years," emphasizes entomologist Ted Schultz, museum ant curator and leader of the task force, who argues that the study of dynamics and evolution of ant-fungal relationships can offer "important lessons" for human challenges with their agricultural practices.
"Ants have established a form of agriculture that provides all the food necessary for their societies using a single crop that is resistant to disease, pests and droughts at a scale and level of efficiency that rivals human agriculture," he adds.
Today, many species of agricultural ants are threatened by habitat destruction, and as part of his studies, Schultz has been collecting specimens from the field and preserving them in the museum's cryogenic biological repository for future genomic studies. In the present analysis, he and his colleagues compared the genomes of 119 modern ant species, most of which were collected during their decades of field expeditions.
Using powerful new genomic tools, the scientists compared DNA sequences at each of the more than 1,500 genomic sites for 78 species of fungi and 41 species of non-agricultural fungi.
Their analysis clarifies the closest nonfarm relative of today's fungus-producing ants and allows Schultz and his team to begin examining the geographic backgrounds of these species and deduce when, where, and under what conditions particular traits emerged.
"If things are getting too dry, the ants go out to find water and add it," Schultz explains. "If they are too wet, they do the opposite." Thus, even when conditions above the surface become inhospitable, fungi can thrive within the heated, subterranean chambers of an agricultural ant colony. In this situation, the fungi can depend on their ants.
"If they have taken you to a dry habitat, your destiny is going to be equal to the destiny of the colony you are in," says Schultz. "At that moment, you are tied to a relationship with those ants in which you were not tied when you were. in a humid forest. " In his view, the conditions present during this evolutionary transition illustrate how an organism can become domesticated, even if its farmers are not consciously selecting desirable characteristics as humans do.
The ants that moved their fungi to new habitats would have isolated the organism from its wild relatives, just like humans do when they domesticate a crop. This isolation creates an opportunity for cultivated species to evolve independently of wild species, adopting new traits.