Sick ants stay away from the kids
ARS Technica
Ants are the poster children for eusociality. Each ant has a job, and each ant sticks to its job: the foragers forage, the workers work, the nurses nurse, the queen procreates.
It has been assumed that this strict segregation of ant society 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 do the experiment using 22 colonies of Lasius niger, the common black garden ant.
The scientists hailed from various departments in various universities: Ecology and Evolution, Science and Technology, Biorobotics, Intelligent Systems, and Physics of Complex Systems.
They labeled each ant in each colony with what looked like a paper QR code taped to its thorax and used video tracking to follow individual ants, monitoring all of the physical contacts among them.
As predicted, the structure of the colonies inhibited the transmission of pathogens.
The colonies were sorted into discrete communities that were connected, but the nodes at 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 did as well. Those most likely to pick up an infection are the foragers, since the nest is kept scrupulously clean by the workers, which stay inside. Forager ants have fewer connections within the network and are markedly segregated from the queen and the young nurses.
These observations were made by comparing the network of the ant colonies to 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 got infected; 10 percent of the foragers from the other 11 were exposed to a sham solution.) After giving the foragers a day to recover from their treatments, the researchers assayed pathogen loads across all of the ants in the colony. This revealed contact networks, as spores are transferred by physical contact between ants.