Variability of nest relocation behavior among acorn ant species

The so-called “acorn ants” (i.e., the Formicoxenus genus group, comprised of the closely related genera Formicoxenus, Harpagoxenus, Temnothorax, Leptothorax, Vombisidris, and Gauromyrmex) are model systems for studying collective decision-making. This is because of the well-understood algorithms workers use to select nests during relocation. However, the details of these algorithms are based on data from relatively few species. This taxonomic neglect threatens to provide a distorted sense of how colonies in general execute collective decision-making and the obscure variation in algorithms that can be used to accomplish this task. We observed nest relocations in 18 species of acorn ants and compared our data to previously collected data from emigrations in T. curvispinosus to obtain a more thorough survey of nest relocation behavior in this group of ants. We found that the basic sequence of emigration behaviors in most species was no different from those reported in previous studies. However, we found a few notable deviations from standard Temnothorax emigration behavior that appear to be common in Leptothorax. Compared to Temnothorax, species of Leptothorax showed elevated rates of worker participation in scouting for a new nest and fewer adults were carried to the new nest. This difference could not be explained by colony size, the latitude of colony origin, or whether colonies were social parasites that captured workers from colonies of other species. Furthermore, we found that the timing of transports in Leptothorax is structured so that brood transports are prioritized; adults are carried to the new nest near the end of emigrations after all brood items have already been relocated.