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Fungus farming ants work hard to maintain healthy gardens

The secret to a flourishing, healthy garden is to ‘weed early and often.’ Surprisingly, we share this gardening principle with certain ant species. They are master gardeners who have been perfecting this practice over 50 million years.

Just like us, these fungus farming ants carefully weed their underground fungus gardens. However, until recently, the mystery remained: how did ants distinguish between good and bad fungus in their gardens?

Uncovering the secrets of fungus farming ants

On June 15, a diverse group of scientists offered insights into this question in a paper published in PNAS (Proceedings of the National Academy of Sciences).

The team revealed that ants identify the health of their fungal farms not through sight – a luxury they lack in their dark subterranean homes – but rather through an intriguing sense of smell.

Leading the research were Dr. Jonathan Klassen from the University of Connecticut and Dr. Marcy Balunas from the University of Michigan. They discovered that ants identify diseased fungus by sniffing out specific chemicals named peptaibols.

The team focused on the species Trachymyrmex septentrionalis, commonly known as the fungus farming ant. They reside in the pine barren ecosystem stretching from Long Island to East Texas.

Symbiotic relationship between the ants and their fungus

The ants maintain subterranean fungal farms, nourishing the fungus with fresh organic detritus. The fungus reciprocates by growing around the food, digesting it, and producing edible sustenance for the ants. They behave much like an external stomach for the colony.

Katie Kyle, a graduate student from Klassen’s lab and co-first author on the paper, ventured an experimental step further.

Kyle infected the ant nests with Trichoderma, a pathogenic fungus that invades the ants’ gardens naturally. It emerged that the ants redoubled their fungus farming efforts to weed out the infected areas. They increased their waste output in the process.

While the ants took a winter break, the research team delved into the fungal biomes of various nests from different locations. Intriguingly, they found Trichoderma in all the nests.

The curious question remained, were the ants weeding due to the presence of certain compounds, or simply because of the invading pathogenic cells?

To shed light on this, co-first author Dr. Sara Puckett, a recent graduate from the Balunas’ lab, prepared Trichoderma extracts containing the fungus’s organic compounds.

“We were curious to see if the ants were weeding because of compounds produced by the infecting fungus,” Balunas shared.

What the research team learned about fungus farming ants

To the team’s surprise, they found that applying the Trichoderma extract to the fungus garden sent the ants into a frenzy of weeding activity. This mimicked the effect of an actual Trichoderma infection.

The researchers teamed up with scientists from the University of California, San Diego, and the University of North Carolina, Greensboro.

Together, they discovered that the ant nests contained peptaibols. These are chemicals known to be produced by Trichoderma.

Despite this breakthrough, the team faced the daunting challenge of identifying the specific peptaibols responsible for triggering the ants’ weeding activity.

In a meticulous process, they tested pure peptaibols. These included two newly identified compounds called trichokindins VIII and IX.

To their surprise, all the peptaibols tested prompted the ants to weed their gardens to some extent. This suggests that it might not be a specific peptaibol causing the weeding but rather the entire suite of these chemicals.

“This suite of Trichoderma compounds inducing ant behavior is in contrast to many other natural products whose activity can often be attributed to one compound,” Balunas noted.

Many questions answered, many mysteries remain

While their data point towards peptaibols as a signal to weed, what the ants are exactly sensing remains unclear. Are the ants detecting the peptaibols produced by the invading Trichoderma, triggering a weeding response? Or is it a secondary reaction from the fungus garden that alerts the ants?

Klassen suggests that the next phase of the research will be focused on deciphering these complex ant-fungus communication mechanisms. “Maybe the fungus is signaling ‘I’m sick’. Maybe the fungus is detecting the peptaibols. We need to flesh out the chain of signaling,” he elaborated.

Extended defense response

This study uncovers a rare and fascinating phenomenon where an animal reacts to a disease afflicting its symbiotic partner rather than its own body.

Klassen and Balunas have termed this an ‘extended defense response’. It is an intriguing aspect of the ant-fungus relationship that they are keen to unravel further.

The meticulous weeders of the insect world, ants, thus provide an interesting lens into symbiotic relationships and defense mechanisms in nature.

They might not only offer a unique perspective on how to manage a garden but also hold secrets to complex inter-species communications waiting to be decoded.

More about the relationship between ants and fungus

The relationship between certain ant species and fungus is a remarkable example of symbiosis in nature. Particularly notable are leafcutter ants, which are renowned for their fungus farming abilities.

Fungus-farming ants harvest fungus for food

Leafcutter ants, part of the tribe Attini which includes other fungus-growing ants, cultivate fungi for food. They cut pieces of leaves and carry them back to their colonies. Instead of consuming these leaf fragments directly, they use them as a substrate to grow a specialized type of fungus.

This fungus serves as the primary food source for the ant colony. The ants actively tend to the fungus, creating an optimal environment for its growth. They weed out other types of fungi and pests that could potentially harm their crop, much like human farmers.

Fungus benefits from their ant caregivers

In return, the fungus benefits from the care provided by the ants, having a constant source of nutrition from the leaf fragments, and a safe environment in which to grow. This mutual symbiosis has existed for millions of years and is an outstanding example of cooperation in the natural world.

A unique aspect of this relationship is the transfer of fungal strains from one generation to the next. When a new queen leaves her original colony to start a new one, she carries with her a small amount of the fungal mycelium. This ‘starter culture’ is used to establish a new fungal garden in the new colony.

Interestingly, as the original text points out, there is ongoing research into how ants deal with threats to their fungus gardens, such as the harmful fungus Trichoderma. It has been found that ants can detect specific chemicals (peptaibols) produced by this invading fungus, which prompts them to increase their weeding efforts to protect their food source.

Overall, the relationship between ants and fungus is complex and finely balanced, a testament to the intricate and interconnected nature of ecosystems. This symbiotic relationship has significant benefits for both ants and fungus, showcasing the remarkable adaptability and cooperation found within the natural world.

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