Beneficial divisions of labour in ants develop with increasing colony size - starting with just six individuals - reports a paper published online this week in Nature. The finding improves our understanding of how complex sociality emerges.
The ability to improve efficiency by dividing up tasks is a major benefit of group living, and a hallmark of human society. Even more elaborate labour divisions are found in social insect colonies in which activities are split between specialized and physically distinct castes - for example, fertile queens and drones, or sterile workers. It has been unclear, however, how this division of labour initially evolved in the solitary ancestors of these insects.
Daniel Kronauer and colleagues studied 100 colonies of Ooceraea biroi, the clonal raider ant, which live in small groups. O. biroi colonies have no queens; instead, they are all identical workers that breed together. During the colony’s brood phase, when the ants are most mobile, some workers forage while others nurse larvae. The authors tagged ants with spots of paint, and tracked their movements during the brood phase with digital cameras.
The authors find that the division of labour can emerge in colonies of as few as six ants. As colonies grow in numbers, individual workers grow more specialized in their activities and colonies become more behaviourally diverse. In addition, the colony fitness per individual - as exhibited by survival rates, reproduction levels and developmental timing - also increases.