Mechanisms of collective decision-making in the slave-making ant, Protomognathus americanus

Although research on the mechanisms of collective decision-making in social insects has largely focused on how colonies forage or locate new nest-sites, social insects collectively solve a variety of problems unique to their life-history and ecology. Such untapped diversity presents opportunities to discover alternative mechanisms of collective decision-making. Here, I present a collective decision-making system in colonies of the slave-making ant, Protomognathus americanus, that integrates information in a time-dependent manner. These obligate slave-makers are an ideal model for studying collective decisions because their survival depends on coordinated attacks at heterospecific ant nests, requiring that the colony reach a consensus over where direct their slave-raid. Scouts recruit back home after discovering a slave nest, but vary considerably in the time needed to successfully elicit a raiding party. I investigate how the quality of a discovered slave nest influences the latency to raid. I focus on the slave colony’s size, their number of brood, the ratio of workers to brood, and the relative size of slave-maker and slave colonies as measures of quality. In addition, I quantify the costs and benefits of each raid in terms of worker mortality and slave brood gained to determine what makes a high quality option. I then illustrate that the duration of the attack latency is inversely correlated with the quality of the chosen nest, such that higher quality nests are raided more rapidly whereas lower quality nests have longer latencies. Finally, I propose that attack latencies based upon a candidate slave nest’s quality leads to collective decisions that favor the best option when available, but also ensures that colonies settle for a mediocre nest when better alternatives are unavailable.