Symmetry breaking and pivotal individuals during the reunification of ant colonies

The Power of Population Effect in Temnothorax Ant House-Hunting: A Computational Modeling Approach

The decentralized cognition of animal groups is both a challenging biological problem and a potential basis for bioinspired design. In this study, we investigated the house-hunting algorithm used by emigrating colonies of Temnothorax ants to reach consensus on a new nest. We developed a tractable model that encodes accurate individual behavior rules, and estimated our parameter values by matching simulated behaviors with observed ones on both the individual and group levels. We then used our model to explore a potential, but yet untested, component of the ants' decision algorithm. Specifically, we examined the hypothesis that incorporating site population (the number of adult ants at each potential nest site) into individual perceptions of nest quality can improve emigration performance. Our results showed that attending to site population accelerates emigration and reduces the incidence of split decisions. This result suggests the value of testing empirically whether nest site scouts use site population in this way, in addition to the well-demonstrated quorum rule. We also used our model to make other predictions with varying degrees of empirical support, including the high cognitive capacity of colonies and their rational time investment during decision-making. In addition, we provide a versatile and easy-to-use Python simulator that can be used to explore other hypotheses or make testable predictions. It is our hope that the insights and the modeling tools can inspire further research from both the biology and computer science community.

Ants resort to majority concession to reach democratic consensus in the presence of a persistent minority

Social groups often need to overcome differences in individual interests and knowledge to reach consensus decisions. Here, we combine experiments and modeling to study conflict resolution in emigrating ant colonies during binary nest selection. We find that cohesive emigration, without fragmentation, is achieved only by intermediate-sized colonies. We then impose a conflict regarding the desired emigration target between colony subgroups. This is achieved using an automated selective gate system that manipulates the information accessible to each ant. Under this conflict, we find that individuals concede their potential benefit to promote social consensus. In particular, colonies resolve the conflict imposed by a persistent minority through "majority concession," wherein a majority of ants that hold first-hand knowledge regarding the superior quality nest choose to reside in the inferior one. This outcome is unlikely in social groups of selfish individuals and emphasizes the importance of group cohesion in eusocial societies.

Ants of the Palouse Prairie: diversity and species composition in an endangered grassland

Grasslands are globally imperilled ecosystems due to widespread conversion to agriculture and there is a concerted effort to catalogue arthropod diversity in grasslands to guide conservation decisions. The Palouse Prairie is one such endangered grassland; a mid-elevation habitat found in Washington and Idaho, United States. Ants (Formicidae) are useful indicators of biodiversity and historical ecological disturbance, but there has been no structured sampling of ants in the Palouse Prairie. To fill this gap, we employed a rapid inventory sampling approach using pitfall traps to capture peak ant activity in five habitat fragments. We complemented our survey with a systemic review of field studies for the ant species found in Palouse Prairie. Our field inventory yielded 17 ant species across 10 genera and our models estimate the total ant species pool to be 27. The highest ant diversity was found in an actively-managed ecological trust in Latah County, Idaho, suggesting that restoration efforts may increase biodiversity. We also report two rarely-collected ants in the Pacific Northwest and a microgyne that may represent an undescribed species related to Brachymyrmexdepilis. Our score-counting review revealed that grassland ants in Palouse Prairie have rarely been studied previously and that more ant surveys in temperate grasslands have lagged behind sampling efforts of other global biomes.

Colony size and initial conditions combine to shape colony reunification dynamics

Group cohesion and collective decision-making are important for many social animals, like social insects, whose societies depend on the coordinated action of individuals to complete collective tasks. A useful model for understanding collective, consensus-driven decision-making is the fluid nest selection dynamics of ant colonies. Certain ant species oscillate between occupying multiple nests simultaneously (polydomy) and reuniting at a single location (monodomy), but little is known about how colonies achieve a consensus around these dynamics. To investigate the factors underpinning the splitting-reunification dynamics of ants, we manipulated the availability and quality of nest sites for the ant Temnothorax rugatulus and measured the likelihood and speed of reunification from contrasting starting conditions. We found that pursuing reunification was more likely for smaller colonies, that rates of initial splitting were lower when colonies could coordinate their activity from a central hub, and that diluting colonies among additional sites did not impair reaching consensus on a single nest. We further found mixed support for a specific threshold of social density that prevents reunification (i.e., prolonged polydomy) and no evidence that nest quality influences reunification behavior. Together our data reveal that consensus driven decisions can be influenced by both external and intrinsic group-level factors and are in no way simple stereotyped processes.