Using ‘living fossils’, graduate student investigates evolution and antibiotic resistance

By Meghan Chua

 

All gardeners know what it’s like to try and weed a garden. Even when you keep up with it, sometimes you miss a root or a seed, and the weeds grow back.

As it turns out, this experience applies not only to human gardeners but also to a type of ant that farms its own garden of fungus.

PhD candidate Kirsten Gotting studies evolutionary biology and fungus-growing ants as a member of the Currie Lab in the Department of Bacteriology and the Genetics Training Program. The Currie Lab’s collection of leaf-cutter ants, one of many types of fungus-growing ant, offers a window into the relationships between the ants, the fungus, and other pathogens and bacteria. Gotting hopes this work will provide further insight into antibiotic resistance and how to minimize it.

Kirsten Gotting points to a computer monitor. Another person sits next to her and is looking at the same monitor.
PhD candidate Kirsten Gotting studies a parasite, called Escovopsis, that infects ant colony fungus gardens. Gotting is interested in how Escovopsis has evolved over millennia and how it defends itself against the ants and their antibiotic defenses. (Photo courtesy of Kirsten Gotting)

Leaf-cutter ants harvest pieces of leaves and carry them back to their colonies to feed their fungus gardens. The fungus then breaks down these leaves, creating food for the ants. But, like a gardener contending with the spread of weeds, ants run into challenges keeping their fungus gardens free of pests. Gotting studies a parasite, called Escovopsis, that infects ant colony fungus gardens and how the ants interact with it.

“Just like, when we’re growing crops, we’ll go in and weed out different kinds of weeds that might be preventing the growth of what we want to eat and grow, the ants will go in and search for this parasite fungus that’s coming in and trying to consume the fungus garden … and tear it out,” Gotting said. “And then they’ll take it and carry it to their dumps to manually remove it.”

In addition, the ants have an Actinobacterium on their exoskeletons that helps them fight this parasite and prevent it from growing, which acts as an antibiotic against the parasite.

A Petri dish with a substance that is dark brown in the center and lighter brown on the outside growing within it.
A sample of Escovopsis from one of Gotting’s experiments. (Photo courtesy of Kirsten Gotting)

Gotting is interested in how Escovopsis has evolved over millennia and how it defends itself against the ants and their antibiotic defenses. This year, she was awarded a Smithsonian Fellowship through the Big Ten Academic Alliance to pursue these questions. As a fellow, Gotting has the opportunity to conduct fieldwork at the Smithsonian Tropical Research Institute.

“The great thing about that location is that the institute is in Panama in the middle of the rain forest, so you can collect these ants just by walking outside and going into the forest,” she said. “In that way, it’s sort of more like I’m working [with] and have access to this living collection that is accessible by the location of where the institute is.”

Though she has done fieldwork in Georgia, Gotting said there is less diversity in fungus-growing ant colonies further north.

“By going there, I’ll be able to have access to all of the different lineages of ants and their fungus colonies that I could need to answer all these kinds of questions that I’m interested in,” she said.

For example, Gotting is curious whether different species of Escovopsis are better at avoiding the ants’ weeding behaviors, or whether they have another variation that allows them to avoid the ants’ detection.

“We know that different species of this parasite alternate in how frequently they infect ant colonies. Maybe one parasite is really good at defending itself against this antibiotic pressure from the bacteria, but maybe the other one is really good at avoiding this weeding and grooming behavior from the ants,” she said. “It’s interesting to think that these variants could be alternating in frequency over time, depending on how [well] the ants are able to detect them.”

To conduct this work, Gotting uses molecular analysis to study different species and lineages of fungus-growing ants over time and in different locations. Ant specimens are relatively easily preserved in the fossil record. Even more useful are the “living fossils” she’ll find in the forests of Panama – ants that still exist today, having split off evolutionarily at different points from one another in the past 50 million years.

“There are little snapshots over time,” Gotting said. “We can use that to reconstruct what the evolutionary history might look like.”

Gaining a better understanding of this parasite and how it may evolve to act against the ants’ defenses informs our knowledge of antibiotic resistance in general, Gotting said. There are currently a limited number of antifungals that can be used in a clinical setting without toxic side effects to humans. Gotting’s research could help better understand how new fungal outbreaks occur and help find new antifungals to treat them.

“Understanding the evolutionary history of how parasites evolve over time in the face of this naturally evolved antibiotic implementation could help us inform how we could use antibiotics in a more effective way to minimize the evolution of antibiotic resistance,” Gotting said.

Gotting said that she is not from an academic background, and now, as a graduate student, it’s especially important to her for her research to have broader impacts like this.

“Something that’s really important to me is being able to share that with other people, because for a long time, I didn’t realize that science is for everyone and as scientists, we’re here to serve the community and share research,” she said.

It’s also important for many different people to be able to learn about this research and engage with the lab group, she added. Anyone who wants to visit campus can see a colony of the Currie lab’s leaf-cutter ants that lives on the first floor of the Microbial Sciences building, and lab members are frequent guests at outreach events like the Wisconsin Science Festival and Science Expeditions. Gotting invited anyone who wants to learn more about fungus-growing ants to attend any of those events or email the lab directly for a tour.

Read more about Gotting’s work and the Currie Lab.