Ants are the poster children for eusociality. Every ant has a job and every ant keeps to its job: the foragers forage, the workers work, the nurses care, the queen reproduces. It was believed that this strict segregation of the ant community into age and task groups could help prevent epidemics, but this assumption had never been tested. Finally, a group of scientists got together and figured out how to run the experiment with 22 colonies Lasius nigerthe common black garden ant.
A division of more than labor
The scientists came from different departments of different universities: Ecology and Evolution, Science and Technology, Biorobotics, Intelligent Systems and Physics of Complex Systems. They labeled each ant in each colony with what appeared to be a paper QR code taped to its thorax and used video tracking to track individual ants, monitoring all physical contacts between them.
As predicted, the structure of the colonies inhibited the transmission of pathogens. The colonies were sorted into separate communities that were connected, but the nodes to which they were connected were limited. This organization also protected the most vulnerable members: the queen and young workers.
Not only did the entire network function to limit disease transmission, but individual ants as well. The feeders most at risk of infection are the foragers, as the nest is scrupulously kept clean by the workers, who stay indoors. Forager ants have fewer connections within the network and are clearly separated from the queen and the young nurses.
These observations were made by comparing the network of the ant colonies with other types of networks in simulated infections, but then they were confirmed with real infections. The scientists randomly infected 10 percent of a colony’s foragers with the spores of a fungal ant pathogen, Metarhizium brunneum. (Only 11 of the colonies became infected; 10 percent of the collectors of the other 11 were exposed to a sham solution.) After giving the collectors a day to recover from their treatments, the researchers analyzed the pathogens of all the ants in the colonies. colony. This revealed contact networks, as spores are transmitted through physical contact between ants.
Untreated foragers ended up with much higher pathogens than the queen and the young nurses locked in their nest. After nine days, more foragers had died than ants of any other caste; all queens were still alive.
Exposure to pathogens and not the sham treatment altered the ants’ behavior in ways that further protected the colony. Infected foragers spent more time outdoors, ventured further from the colony and did not move much when entering the nest. Nurses moved the brood deeper into the nest. We don’t know how they knew, but these behavioral changes reduced both the chance of infection and the number of spores transmitted through touch. They also functioned to vaccinate the queen by allowing her to be exposed to only a low level of pathogen contamination.
One of the practical ramifications of this finding — that the strict division of the ant community into hives helps protect their young and their queens from epidemics — is that if you give your child one of those ant colony toys for Christmas, the resulting ant infestation will infest your home. long lasting and resistant to epidemics.
Science2018. DOI: 10.1126/science.aat4793 (About DOIs).