This final altruistic act could be an attempt to save the ant colony from contamination.
Some baby ants don’t ask for help when they contract deadly infections: they ask to be killed.
Terminally ill worker ant pupae actively emit a chemical signal “find me and destroy me”prompting other workers to eliminate them, behavioral ecologist Sylvia Cremer and colleagues report December 2 in Natural communications. This last altruistic act may be an attempt to save the colony from contamination and ensure its survival.
“Just as the cells of a body coordinate to maintain the health of the entire organism, individual ants work collectively to protect the colony,” says Cremer, of the Austrian Institute of Science and Technology in Klosterneuburg.
In previous work, Cremer and his team showed that workers of ant species Lasius was neglected Quickly detect fungal diseases spreading among their brood of baby ants. After detecting cuticular hydrocarbons (chemical alarm signals that pupae emit through their hard exteriors, or cuticles), worker ants launch into “destructive disinfection” opening the cocoons, piercing the cuticles and spraying formic acid inside. This antimicrobial spray kills both fungal spores and diseased pupae.
In the new study, researchers found that the pupae’s immune genes become activated after contracting a fungal infection, implying an immune response. But infected pupae only emit the hydrocarbons in the presence of a mature worker, not when they are alone.
“We were fascinated to discover that pupae can sense their environment and adjust their chemical signals based on whether workers are present,” says co-author Erika Dawson, a former biologist in Cremer’s lab and now a grant writer at Sorbonne University in Paris.
The team also found that a higher infection load did not trigger more chemical releases. Together, the results indicate that the signals are not passive: “The ants are proactively signaling their destruction,” says Mark Bulmer, a molecular ecologist at Towson University in Maryland who was not involved in the study.
Infected royal pupae, on the other hand, do not emit this self-sacrificing signal because their advanced immune systems curb the infection before it gets out of control, the researchers found. Because of their ability to reproduce, queens are more valuable than workers, which could potentially explain their better immune systems.
This altruistic signaling shows how ant colonies function as a single living entityor superorganism. Ants in a colony are more like cells in our bodies, says Erik Frank, an animal ecologist at the University of Würzburg in Germany. Immune cells sometimes self-destruct to prevent the spread of infection, thereby protecting other cells.
“Humans are very interested in individual fitness; because we can all reproduce, we want to maximize our own genes, while social insects all [except the queen] are sterile, and they can only really benefit from that by helping the queen reproduce as much as possible,” Frank says. “It makes sense that individual workers would sacrifice themselves for the inclusive fitness of the colony rather than their own selfish individual fitness.”
Although adult ants exposed to pathogens can practice social distancing Or leave the nest to die terminallythe pupae confined in their cocoons must rely on the distress signal. Workers, the researchers note, are able to detect and destroy only infected pupae and not kill brood indiscriminately. Cremer wants to test whether pupae would sacrifice themselves so easily if their infection levels were much lower and if they could recover. “We hope the ants won’t take that risk,” she says. Neglecting even a single pupa that could release fungal spores “can have devastating effects on the colony,” she adds.
