In a study published today in the journal Nature Communications, researchers revealed that the ant pupa – a larva that develops before becoming an adult – lasius neglectus Ant species actively produce a chemical signal that causes other members of the colony to destroy them. The findings further strengthen the view of the ant colony as a “superorganism” that behaves as a single unit rather than a community of many individuals.
selfless ants
“Ill individuals often hide their illness status to group members, which may prevent social exclusion or aggression,” the researchers write in the paper. On the other hand, researchers have documented sick adult ants leaving their colonies to avoid spreading their disease. However, the pupae are encased in cocoons and cannot get out, so they resort to an extreme strategy.-Emitting a chemical signal essentially calling for self-destruction.
“Adult ants that approach death leave the nest to die outside the colony. Similarly, workers exposed to fungal spores practice social distancing,” Sylvia Kramer, group leader of the Kramer Group at the Institute of Science and Technology Austria (ISTA) and co-author of the study, said in a statement from ISTA. “Yet, this is only possible for mobile individuals. Ant babies within the colony, like infected cells in tissue, are largely immobile and lack this option.”
Once worker ants receive the signal, they remove the pupae from the cocoon, drill holes in them, and inject formic acid into them – an antimicrobial poison that acts like a self-made disinfectant. It kills not only the pathogens but also the pupae.
While previous research had shown that worker ants could recognize sick pupae and kill them to disinfect the nest, scientists did not know whether passive signaling or intentional signaling by sick pupae produced this dynamic. To shed light on the matter, the scientists behind the new study infected lasius neglectus Ants with fungal pathogen.
BO as a warning
During the experiment, sick worker pupae emitted a modified body odor (chemical signal) that warned adult ants to destroy them. Only sick ants near adult worker ants produced this signal, indicating that this signal is not simply an immune response or a side effect of infection. When researchers applied the odor to healthy pupae, they too were destroyed, confirming the chemical’s role in triggering the response.
Because workers destroy specific pupae within a mass of the entire brood (eggs, larvae and pupae), “the odor cannot simply spread through the nest chamber, but must be directly associated with the diseased pupae,” explained Thomas Schmidt, co-author of the study and a chemical ecologist at the University of Wurzburg. “Accordingly, the signals do not involve volatile compounds, but rather are composed of non-volatile compounds on the surface of the pupa body.”
While colonies are technically communities made up of many individual ants, they operate as a single superorganism. The ants within a colony are like the cells in our body. For example, ant queens are responsible for producing offspring, and non-fertile workers are responsible for the maintenance and health of the colony. Similarly, our germ cells are responsible for producing offspring, and our somatic cells carry out all other vital functions. Along the same lines, the signal from terminally ill pupae mirrors the way our body’s cells release chemical signals – called “find me and eat me signals” – to our immune cells, which then identify and destroy the signaling cells to eliminate the risk of infection.
Queen ants do not need to be destroyed
For ants, “What at first glance appears to be self-sacrifice is, in fact, also beneficial for the signaler: It protects its nestmates, with whom it shares many genes. By warning the colony of their deadly infection, terminally ill ants help the colony stay healthy and produce daughter colonies, which indirectly transmit the signaler’s genes to the next generation,” said the study’s first author and Erica Dawson, a behavioral ecologist at ISTA, explained. If a terminally ill ant pretends to be healthy and dies, it can become infectious and put the entire colony at risk.
Interestingly, the researchers did not see the queen pupa emitting a chemical signal. They have stronger immune defenses than worker pupae and can fend off infection independently. However, the worker pupae could not control the infection and alarmed the colony.
Sick pupae emit signals only when the infection is out of control, giving fellow ants the right to intervene in situations of real danger, while pupae that may recover are spared their destruction. Kramer concluded, “This precise coordination between the individual and colony level is what makes this altruistic disease signaling so effective.”
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