Consensus driven by a minority in heterogenous groups of the cockroach Periplaneta americana
Many social species are able to perform collective decisions and reach consensus. However, how the interplay between social interactions, the diversity of preferences among the group members and the group size affects these dynamics is usually overlooked. The collective choice between odourous and odourless shelters is tested for three groups of social cockroaches (Periplaneta americana) which are solitary foragers: naïve (individuals preferring the odorous shelter); conditioned (individuals without preference); and mixed (combining, unevenly, conditioned and naïve individuals). The robustness of the consensus is not affected by the naïve individuals’ proportion, but its rate and the selection frequency of the odorous shelter are correlated to this proportion. In mixed groups, the naïve individuals act as influencers. Simulations based on the mechanisms highlighted in our experiments predict that the consensus emerges only for intermediate group sizes. The universality of these mechanisms suggests that such phenomena are widely present in social systems.