The outline of a worm cluster as it moves across a circular food patch over time. Image credit: Ding et al. (CC BY 4.0)
Anyone who has watched a flock of birds maneuver through the sky has probably wondered how so many animals coordinate their movements. Often, these seemingly complex group behaviors can be explained by a few simple rules that govern the behavior of the individuals in the group. For example, if each bird flies and reacts to its neighbors in a certain way, the whole flock’s flight pattern results from these individual choices.
Computer simulations can help researchers to test how individual behaviors contribute to coordinated group movements. Ding, Schumacher et al. have now used a simulation to uncover the rules that control the behavior of small worms called Caenorhabditis elegans, which form large groups while feeding on bacteria.
To gather the data needed to form the computer model, Ding, Schumacher et al. genetically engineered C. elegans worms to produce fluorescent proteins. The fluorescence allows the movements of the worms to be monitored automatically in time-lapse movies made from a series of microscope images. The movies show that worm clusters move together over a patch of food, consuming it as they go. As the food disappears, the whole worm cluster moves to a new area in search of more food.
The computer simulation that Ding, Schumacher et al. developed to recreate how the clusters move revealed that individual worms in the group interact according to three rules. Firstly, worms slow down when they have more neighbors. Secondly, when a worm leaves its cluster, it will reverse to rejoin the group. And finally, worms will move towards areas with more neighbors.
It is still not known why the C. elegans worms form clusters, but understanding how the individuals in the group interact could help future studies to uncover this reason. Many other organisms benefit from forming similar groups, from single celled bacteria to animals such as birds and fish. The results presented by Ding, Schumacher et al. will therefore help researchers to consider whether there are universal rules that control group behavior.
