Individual cognition and collective behaviour in ants

Eusocial insects are impressive on individual and collective level. Collectively, they build nests and efficiently exploit and monopolise nearby resources by sharing information amongst their members. Such collective behaviours are shaped by remarkable and multi-facetted individual abilities and decision-making processes. By revealing and investigating factors which influence individual decision making, this thesis provides a deeper insight into the cognitive lives of ants while contributing to a more cohesive understanding of colony behaviour as a whole. In chapter 2, we demonstrated that foraging ants form expectations about value-neutral qualities of a food source – such as its taste – and dislike food which deviates from those expectations. As such dislike is translated into reduced recruitment, it will have a direct impact on colony-level behaviour. Expectations are thus a potential driver of foraging decisions. Ants excel in navigation, and we showed in chapter 3 that ants can rapidly learn olfactory or spatial cues to localise food sources. Moreover, when those two types of private information where put into conflict, ants exclusively relied on olfaction. This demonstrates that one type of information can entirely dominate decisions in certain situations. While we demonstrated that ants learn simple associations rapidly, nothing was known about their ability to learn abstract relations between stimuli, although concept learning has been reported in honeybees. Thus, in chapter 4, we trained ants to learn a relational rule of same/different, but found that the ants, instead of solving such a complex task via learning, resorted to heuristics such as ‘go left’ or ‘go to the more salient cue’. Intriguingly, the heuristics used varied between individual ants. Learning is dependent on reward and motivation and in chapter 5 we investigated whether those factors alone could explain individual and collective foraging behaviour. While we only found small effects of reward magnitude and motivation on learning, persistence rates varied dramatically in lower motivated colonies. An agent-based model using the empirical data further demonstrated that individual decisions alone can cause ecologically sensible colony-level foraging behaviour. Finally, in chapter 6 we explored whether colonies could make sensible collective decisions in the context of trail-clearing by Australian meat ants. We found that ant colonies preferentially cleared trails toward a food source if the alternative detours were long. The underlying mechanisms seem to be dependent on individual propensities to remove obstacles which leads to the emergence of paths. Taken together, the results of this thesis broaden our understanding of individual cognition in ants and demonstrate that properties inherent to individuals, such as experience or task propensities, systematically influence decisions and thus impact the collective