Ants incommunicado: collective decision-making over new nest sites by ants with reduced communication

We study the plasticity of collective decision-making in ants by blocking key aspects of pheromone communication across entire colonies. To achieve this, droplets of paint were applied over the gaster tips of entire worker populations within colonies of the rock ant, Temnothorax albipennis. This treatment should prevent pheromone release potentially from each ant’s Dufour’s, poison, and pygidial glands in addition to the hindgut. We then examined the collective decision-making abilities of treatment and control colonies over alternative new nest sites in binary choice experiments. The performance of treatment colonies was compared with that of control colonies that had also been marked with paint but in such a way as not to disrupt their pheromone excretions from the gaster tip. Our results reveal the importance of “gaster-tip” pheromones during colony emigrations. Treatment-colony emigrations were significantly less successful than those of the controls, as the quality of their nest site assessments was reduced. However, treatment ants presented an extraordinary example of behavioral plasticity as they reduced their quorum thresholds in order to maintain normal emigration completion times. Hence, the ants whose communication systems have been compromised can still emigrate swiftly and maintain low levels of colony exposure.