Individual behavioural type and group performance in Formica fusca ants.

The link between individual and group-level behaviour may help understanding cooperation and division of labour in social animals. Despite the recent surge of studies, especially in social insects, the way individual differences translate into group performance remains debated. One hypothesis is that groups may simply differ in the average personality of their members and this would translate into inter-group differences in collective behaviour. We tested the hypothesis of a linear relationship between individual and group phenotype in the ant Formica fusca by using same-age groups of workers after measuring an individual behavioural trait. Individual exploratory activity in an open-field arena was significantly repeatable. Based on this trait, groups were composed, each consisting of 6 individuals with similar exploration tendency housed with 3 cocoons and a refuge. Individual exploratory activity was associated with the performance in cocoon recovery at the group level: groups composed of high exploratory individuals started transporting displaced cocoons significantly earlier and transported more cocoons into the refuge than groups with low exploratory workers. When in a group, more exploratory animals showed significantly more returns to the refuge than less exploratory ones and tended to transport more cocoons. These results show a direct linear link between individual and collective behaviour, suggesting that colony personality reflects the average personality of workers involved in a given task.