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A “Simple” but Distributed Cognitive System: Lessons from House Hunting Rock Ants

Nigel R. Franks

School of Biological Sciences, University of Bristol, UK

Social insects exhibit both individual and collective cognition. I will illustrate this distributed decision-making with house hunting in rock ants. Each worker, among the 100 or so in a colony, has less than 100,000 neurones (compared to 10 11 neurones in humans) yet these ants employ the most sophisticated of all consumer strategies when choosing a new nest. Indeed, they can choose the best-of-N among alternative nests even though each has many different and important attributes. I will show how information can cascade through these social networks enabling colonies to benefit from both individual and collective cognition. They use quorum sensing to collate information and to fashion flexible speed accuracy trade-offs. When these ants have achieved a quorum (a sufficient number of nest-mates) in the new nest they switch from tandem running, from the old to the new nest, to social carrying. During tandem runs one leader literally teaches one follower the route between the two nests. Tandem runs seem to be useful even when they do not progress all of the way to the target. I will describe the behaviour of both leaders and followers when tandems break up and show that followers without leaders use Lévy-like searches. I will also describe very recent work, using RFID tags on all workers, that shows how they can choose a better nest that is 9 times further away than a collinear poor one. Certain ants act as consensus breakers to re-route the whole colony. Such ants lead disproportionately more tandem runs first to the poor nest and then onto the more distant better one. These switchers may have better access to the information needed to make well informed but indirect nest comparisons. We have begun to understand this sophisticated decision-making system as a network of threshold dependent decisions where individual responses may depend not only on the physical environment they encounter but also on the social setting. Finally, I suspect that these tiny ants have larger behavioural repertoires than many if not most vertebrates. This begs a question: what are big brains for?