The Individual Contribution to Cooperative Transport in the ant Novomessor albisetosus

The desert ant, Novomessor albisetosus, is an ideal model system for studying collective transport in ants and self-organized cooperation in natural systems. Small teams collect and stabilize around objects encountered by these colonies in the field, and the teams carry them in straight paths at a regulated velocity back to nearby nest entrances. The puzzling finding that teams are slower than individuals contrasts other cases of cooperative transport in ants. The statistical distribution of speeds has been found to be consistent with the slowest-ant model, but the key assumption that individual ants consistently vary in speed has not been tested. To test this, information is needed about the natural distribution of individual ant speeds in colonies and whether some ants are intrinsically slow or fast. To investigate the natural, individual-level variation in ants carrying loads, data were collected on single workers carrying fig seeds in arenas separated from other workers. Using three separate, small arenas, the instantaneous speed of each seed-laden worker was recorded when she picked up a fig seed and transported within the arena. Instantaneous speeds were measured by dividing the distance traveled in each frame by how much time had passed.
There were nine ants who transported a fig seed numerous times and there was a clear variation in their average instantaneous speed. Within an ant, slightly varying speeds were found as well, but within-ant speeds were not as varied as speed across ants. These results support the conclusion that there is intrinsic variation in the speed of an individual which supports the slowest-ant model, but this may require further experimentation to test thoroughly. This information aids in the understanding of the natural variation of ants cooperatively carrying larger loads in groups.