. Scientific Frontline: Like mushroom out ants

Thursday, February 2, 2023

Like mushroom out ants

Argentine ant workers with brood. Ants react immediately to contamination with pathogens and not only to the later developing symptoms of a disease. The nest comrades efficiently clean colony members of infectious particles.
Photo Credit: Sina Metzler & Roland Ferrigato / ISTA

An Austrian-German research team discovered how disease-causing fungi adapt to the collective hygiene measures of ants.

Ants show many social behaviors. For example, they care for sick individuals and make it difficult to spread pathogens among the people with joint hygiene measures. Germs not only have to outsmart the immune system of individual ants, but also the health care of the whole group.

A new study, the journal, shows how the pathogens do this Nature Ecology & Evolution is published. It was presented by the team of Professor Sylvia Cremer from the Institute of Science and Technology Austria (ISTA) in cooperation with the animal ecologist Professor Thomas Schmitt from the Biozentrum of the Julius Maximilians University in Würzburg (JMU).

Fungal outgrowth in ants. The insects get sick when enough fungal spores infect them internally. Metarhizium is dependent on killing its host, so it can then grow out new spores that spread from the carcass.
Photo Credit: Matthias Konrad/ISTA

Cleaning behavior of the ants has consequences

The researchers have the interactions between Argentine ants (Linepithema humile) and disease-causing metarhicium fungi under the microscope.

“The mushrooms infect the ants from the body surface and then continue to grow in the host body. The fungal spores are mostly cleaned by nest comrades before they can cause an internal infection at all,” explains Barbara Milutinović, former postdoc in Sylvia Cremers group and now Marie Curie Sklodowska scholarship holder at the Ruđer Bošković Institute in Croatia.

In response to the cleaning measures of the ant workers, the mushrooms changed fundamentally: the mushrooms increased their spore production over ten infection cycles. "This helps the mushroom to counteract social spore removal," explains Sylvia Cremer. “However, it was surprising that the ants suddenly cleaned fewer and fewer spurs. This suggests that they no longer recognized the spurs so easily."

Mushrooms lay down their typical chemical profile

Why did the ants have problems identifying the mushrooms?? To find out, the ISTA researchers teamed up with the Würzburg professor Thomas Schmitt. "The mushrooms adapted to the social hosts showed a strong reduction in their membrane component ergosterol," said the expert in chemical ecology. “Ergosterol is an essential building material for all mushrooms, which makes it a mushroom identifier."

If one exposed the ants to pure ergosterol or the similar vertebrate analog, it was shown that only the fungus-specific substance triggered an intensive cleaning behavior in the ants. Milutinović sums up: “Sickness pathogens, in this case mushrooms, react to the presence of nourishing ants by reducing characteristic signals - they are then no longer perceived as a danger and can therefore escape the social immunity of the colony."

The results illustrate the great influence that the group behavior of social hosts can have on pathogens. “It is fascinating how collective hygiene measures trigger very specific alternative strategies for the pathogen. It would be exciting to see how the ants react - perhaps by recognizing lower and lower fungal instructions,” said Sylvia Cremer.

Funding: For this study, Sylvia Cremer received funding from the German Research Foundation (CR118 / 3-1) as part of the priority program SPP 1399 and from the European Research Council (ERC) as part of the research and innovation program Horizon 2020 of the European Union (No. 771402; EPIDEMICSonCHIP).

Published in journalNature Ecology & Evolution

Source/CreditUniversity of Würzburg

Reference Number: en020223_01

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