Cleverly regulated ant nursing

Ants follow simple rules that result in efficient colony-level disease control. © Sina Metzler & Roland Ferrigato/ISTA

On the trail of cooperative defense against infection: A study shows that the nursing system in ant colonies is characterized by a strategically sensible "patient" order and hygienic behavior. Individuals who are particularly ill and therefore potentially contagious are given preferential treatment. The infected then suspend themselves from nursing duties to prevent further spread of pathogens. It's another glimpse into the secrets of the fascinating insect states' success, the researchers say.

How does a complex unit with amazing performance emerge from a bunch of individuals? Studies in recent years have uncovered some concepts and behaviors in ant colonies that serve community coordination and welfare. Parallels to human societies become clear again and again. This also applies in the case of health management in the insect state. A high population density and frequent and close contact between individuals can also lead to the rapid spread of diseases in social insects.

On the trail of sanitary decision-making

The researchers led by Sylvia Cremer from the Institute of Science and Technology Austria in Klosterneuburg have been investigating how insects deal with this problem for some time. You have already shown that the ants of a colony take care of members who are infected by a harmful fungus that can lead to death if infested excessively: they remove parts of the pathogen from the body surface of those affected and also treat them with disinfecting secretions. This increases the likelihood that the body's defenses will subsequently be able to control the infection. In their current study, the scientists have now looked more closely at the question of how decisions are made about maintenance activities in the ant colony at the individual level.

The scientists carried out studies on the black garden ant (Lasius niger), which is widespread in our country. In the experiments, healthy ants from a colony were each confronted with two colony members infected to different degrees by the harmful fungus. The researchers then examined the extent to which this difference affected caregiving activity and whether other behavioral problems were emerging in caregivers and those being cared for. They also performed model calculations on how certain behaviors affect colonies.

Control suit with protective effect

As the scientists report, in this way they discovered two basic rules that the insects follow: The ants can apparently use certain clues to identify the individuals with the highest disease burden and give them priority in the care efforts. "As a rule, ants select those with the currently highest fungal load, whereby the spore load changes constantly due to sterilization," says Cremer. As the researchers explain, this makes sense from a public health perspective. Because the animals always devote themselves to those ants that currently pose the greatest risk of infection for the community. "In this way, the ants can react dynamically to changes in the disease threat," says Cremer.

The team also found another interesting aspect: an ant stops grooming others once it has been groomed itself. This also makes sense, because the comparatively highly infectious animals do not participate in the work with the intensive contact. The ants not only assess the risk of infecting others, but also respond to the social feedback they receive from the colony about their own risk of infecting others, the scientists explain.

Ultimately, they conclude, this combination of behaviors results in the most infectious colony members always being tended to by the least infectious ones, which is extremely efficient in preventing the spread of disease at the colony level. "The results thus provide new insights into the individual decision-making processes of ants, which underlie their social immunity and cooperative defense against disease," concludes Cremer.

Source: Institute of Science and Technology Austria, specialist article: Nature Communications, doi: 10.1038/s41467-023-38947-y

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