In a wide range of social species, when an animal is sick, it takes itself away from its group. Ant pupae are unable to move, however, so they've developed a unique mechanism that leads them to sacrifice their own life for the betterment of the nest.
Researchers in Austria have discovered that when an ant pupae is infected with an incurable infection, it releases a particular scent that is detectable only on the outside of its cocoon. When worker ants inspect the pupae and encounter the scent, they get busy unpacking the cocoon and creating small openings in the pupae's body by biting it. Next, they disinfect the pupae with formic acid, an antimicrobial poison that the ants produce. Not only does the acid remove any trace of infection, but it also kills the pupae.
"What appears to be self-sacrifice at first glance is, in fact, also beneficial to the signaler: it safeguards its nestmates, with whom it shares many genes," says first study author Erika Dawson from the Institute of Science and Technology Austria (ISTA). "By warning the colony of their deadly infection, terminally ill ants help the colony remain healthy and produce daughter colonies, which indirectly pass on the signaler’s genes to the next generation."
The finding supports the idea of an ant colony functioning like a superorganism, in which individual ants act much like the cells in our body. In this case, the researchers liken the worker ants who carry out the disinfection process to our own immune cells which are attracted to diseased cells by chemical signals. This process is known by immunologists as the "find-me-and-eat-me signal."
To test out their discovery, the ISTA scientists, in conjunction with Thomas Schmitt from the University of Würzburg, transferred the scent molecules from diseased ant pupae to the cocoons of healthy ant pupae. Sure enough, the worker ants destroyed the disease-scented pupae.
Interestingly, the researchers discovered that only the pupae of worker ants emitted the find-me-and-eat-me scent. Queen ant pupae did not because, the researchers theorize, they have stronger immune systems and could better survive infection.
This research dovetails with another finding from earlier this year in which it was found that ants infected with fungal spores began social distancing themselves from other ants in the nest, to the point of building different nest entrances and tunnels. It has also been well known that ants that are approaching the end of their lives remove themselves from the nest to die, a process known as "terminal altruism."
The researchers have named this new study, which has been published in the journal, Nature Communications, "Altruistic disease signaling in ant colonies."
