Ants take sick days too | smithsonianmag.com

When you catch a cold or the flu, you can choose to keep your distance from others to avoid a similar fate – and these could in turn keep you out of the way. According to a new study, humans are not alone in their efforts to sequester patients. In the presence of contagious pathogens, humble garden ants can also alter their behavior in order to keep contaminated creatures out of the way of other members of the colony.

Ants are social creatures. They live in large groups, communicating and cooperating with each other to ensure that the colony functions as it should. Because they are often in close contact, ants are also vulnerable to contagious diseases. Studies have shown that ants are able to fight the disease through a number of hygiene mechanisms, such as the collection of garbage and the body of dead members of the colony of their nests. Scientists suspected that insects could also alter their social behavior to reduce the spread of infections, but this hypothesis was, until recently, hard to prove.

"Ant colonies have hundreds of individuals," says Nathalie Stroeymeyt, a postdoctoral researcher at the University of Lausanne in Switzerland, who studies the collective behavior of ant colonies. "Until now, there simply was not the technical methodology to measure their interactions at the colony level over long periods."

Fortunately, thanks to an automated tracking system developed by Swiss researchers in 2013, Stroeymeyt and his colleagues have a detailed overview of the behavior of 22 laboratory-grown ant colonies when the disease spreads within them. The team glued tiny 2D barcodes on the ant's chest, giving each insect a unique identifier – "just like a QR code," says Stroeymeyt. A camera above the ant pens took two photos per second, and an algorithm detected and recorded the position of each barcode, giving researchers a wealth of data on ant movements.

For four days, the team let the ants hurry into their paddock. As for the colonies in the wild, some ants worked outside the nest to search for food, while others, like the queen and the "nannies" who were in the wild, occupy brood developing, have remained inside the nest. On the fifth day, the researchers exposed to the fungus some of the foragers of 11 colonies. Metarhizium brunneum, which is frequently found in the soil of garden ants and is known to make them sick. The forage plants of the 11 other colonies were treated with a harmless solution to serve as a control group.

Crucially, previous studies have shown that the M. brunneum It takes at least 24 hours for the fungi to infect the ants, which gave the researchers time to observe the insects before they were really sick.

"We wanted to focus on [this] period … so that we can distinguish the active reaction of the ants themselves from the side effects of disease or parasite manipulation, "says Stroeymeyt.

Write in the newspaper Science, the researchers revealed that when the forage was returned to their pens, contaminated ants spent more time outside the nest, which meant they had less contact with the most valuable members of the colony: the queen, which lays all the eggs of the colony and the interior workers, who are younger than the foragers and therefore have more hours to contribute to the colony. (Older ants are responsible for foraging at risk outside the nest because, as Stroeymeyt says outright, they will "die anyway.")

But most of the study lies in the discovery that contaminated ants are not the only ones to change their behavior. Foragers who were not exposed to the fungus also increased the time spent away from the nest. And nurses inside the nest moved young people further inland and spent more time overlapping, which "could be perceived as spatial isolation from foragers," says Stroeymeyt.

How did the colony learn to take preventive measures even before fungal spores infect certain fodder? Researchers are not sure, but the sense of smell of ants could be the key. Ants sniff with their antennae, which touch and constantly sample the surroundings of insects. According to Stroeymeyt, it is quite possible for an ant to be able to detect a fungus purifying itself on one of the members of its colony, as easily as it would be able to feel a pathogen on his own body.

Why the uncontaminated fodder also reduced the time spent in the nest is another interesting question. As the first line of contact with their coworkers who will soon be sick, they may have somehow known that they stood apart from the important members of the colony. But it is also possible that, having detected pathogens in their foraging companions, they simply spent more time treating infected workers outside the nest. Ants produce formic acid through a gland located at the end of their gastric or abdomen; they can kill fungal spores on each other by picking up formic acid in their mouths and licking the bodies of their pathogen-laden companions.

Although the researchers recorded fewer interactions between foragers and indoor workers, the contacts did not completely stop – which led to another interesting revelation. When they used simulations to model the spread of fungal pathogens in the colony despite changes in the social network of ants, the researchers found that the probability that the queen and nurses would receive a life-threatening load of fungus decreased, but the probability of these large ants receiving a low load are mounted.

"It sounds like vaccination or vaccination in humans," says Stroeymeyt. "These low doses do not cause mortality, but allow the ant to develop some kind of protection against subsequent exposure to the same pathogen. This [finding] It's also something quite new.

In the future, Stroeymeyt plans to study how pathogens cause social changes in wild ant colonies, which can reach several hundred thousand people. She suspects that segregation between workers inside and out could be even more pronounced in these large groups.

Megan Frederickson, Associate Professor of Ecology and Evolutionary Biology at the University of Toronto who did not participate in the new study, qualifies the researchers' findings as "new and exciting discoveries" through the " advanced methods ". She adds that similar technology could help scientists determine if ants are also modifying their social networks to transmit beneficial microbes. And Frederickson thinks "the meaning [of the study] even goes beyond the ants. "

"I wonder," she says, "how often other social animals reorganize their networks to limit the spread of the disease.

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