LSU AgCenter mycologist Vison P.Doyle and LSU Department of Biological Sciences professor Brant C.Faircloth worked alongside Smithsonian Institution entomologist Ted Schultz to lead a study that showed that ants began farming fungi after the asteroid that killed the dinosaurs 66 million years ago.
Fungus farming ants?
The study, published in the journal Science, analysed genetic data from 475 species of fungi and 276 species of ants to create detailed evolutionary trees. By creating this, it allowed researchers to pinpoint when ants would have begun farming fungi millions of years ago, which ants still do today.
The publication of this paper falls on the 150 th anniversary of the discovery of fungus farming by ants made by Thomas Belt and Fritz Mueller.
“ Ants have been practising agriculture and fungus farming for much longer than humans have existed,” Schultz said. “We could probably learn something from the agricultural success of these ants over the past 66 million years.”
The team thought that decaying leaf litter became the food for fungi that grew during this period, which would bring them into close contact with ants. The ants then began to use the fungi as a food source and continued to rely on this food since the time of the extinction event.
“To really detect patterns and reconstruct how this association has evolved through time, you need lots of samples of ants and their fungal cultivars,” Schultz said.
According to Faircloth, more DNA sequence data is needed to be able to reconstruct the evolutionary history of both of these groups. Collecting these data types from fungal cultivars and ants is where Doyle and Faircloth came in. They developed a molecular method used to capture genetic data from ants and fungi.
Doyle said that ideas about fungal farming by ants are generally assumed to be that there was a single origin of this behaviour, but what was hampering a deeper insight into questions regarding how ants started farming was trying to accumulate sufficient DNA sequence data from the fungi that the ants ate. During the last 15 years, the cost of genome sequencing has gone down, and the techniques used for collecting different types of genome data have improved, making studies such as this one easier to complete.
“If you have a mushroom, it’s relatively straightforward to sequence its genome,” Doyle said. “But when you have teeny-tiny fragments of a fungus that an ant is carrying inside of it, it’s hard to get enough fungal material to generate sufficient genome sequence data to analyse. That’s where the fungal bait sets we created come in. They allowed us to pull the DNA from minuscule bits of fungi, amplify it, sequence it and analyse it.”
More data needed
Doyle says that “capture-based” approaches to collect sequence data from fungi allow researchers to study the symbiotic relationships between organisms in a way that hasn’t been possible before.
An example he used was of doctoral student Spenser Babb-Biernacki, who he is co-advising with Jake Esselstyn. Babb-Biernacki is studying a genus of fungus that occurs in the lungs of mammals called Pneumocystis, which is commonly known as fungal pneumonia.
“It’s hard to get DNA from the lungs of mammals when you have 100 million host cells and just a few fungal cells, ” he said. “We’re using the same approach from this study to pull out genome-wide data, allowing us to start to understand the evolutionary history of the diverse group of organisms and address interactions between symbionts and their hosts.”
Doyle’s main interest is the influence of agriculture on fungi, saying that a pathogen does not usually originate in agricultural populations.
“It’s out there in the wild, then because of agriculture, it jumps in and starts to change in the agricultural environments,” he said. “This is similar, but it’s studying the coevolution of the ants and fungus and looking at the impact of ant agriculture on fungal evolution and vice versa.”
Doyle said there are parallels between what the researchers see happening in the fungi that the ants are cultivating and crops that humans have cultivated.
“The more examples you have of domestication across distantly related groups of organisms, the better you can start to develop a model for how domestication evolves and what happens to the genomes of organisms that become domesticated,” he said. “This study provides an example from millions and millions of years before humans started domesticating plants, but it seems like t he process is actually rather similar.”
Schultz, T.R., Sosa-Calvo, J., Kweskin, M.P., Lloyd, M.W., Dentinger, B., Kooij, P.W., Vellinga, E.C., Rehner, S.A., Rodrigues, A., Montoya, Q.V., Hermógenes Fernández-Marín, Ješovnik, A., Niskanen, T., Liimatainen, K., Leal-Dutra, C.A., Solomon, S.E., Gerardo, N.M., Currie, C.R., Bacci, M. and Vasconcelos, H.L. (2024). The coevolution of fungus-ant agriculture. Science, 386(6717), pp.105–110.