Behavior in Transition: Recovery of Behavior by an Obligate Parasitic Ant (Formica subintegra) Following Host Removal

Abstract

Dulosis is a type of social parasitism in which a parasitic ant has become dependent on captured workers (hosts) of a closely related species. Dulosis can be either facultative or obligate depending on the degree of dependence on host workers. As parasites become more specialized over evolutionary time, their domestic abilities degenerate until they become unable to survive without the host. However, depending on the degree of specialization, the “lost” behaviors may display some degree of recovery when host workers are unavailable to do the tasks. The 12 species of the Formica sanguinea group are all traditionally considered to be facultative parasites. However, recent studies suggest that one member of the group, F. subintegra, has characteristics that are more consistent with obligate parasitism. To explore the degree to which F. subintegra has become obligate, this study examined the degree of recovery of foraging and nest excavation behaviors of parasites when hosts are removed. When parasites were isolated from hosts, they spent more time foraging and feeding regurgitated food to nestmates (oral trophallaxis), and tended to begin feeding sooner following a period of fasting than when hosts were present. Isolated parasites were able to excavate suitable tunnels and engaged in nest building behavior significantly more often than parasites in groups with hosts. These results indicate that F. subintegra demonstrates some recovery of its foraging and nest excavation abilities, and can be considered a less specialized (more primitive) obligate parasite. Formica subintegra and its facultative relatives can be used as models for studying the progression of dulotic evolution within a closely related group of social parasites, and may shed light on which factors contribute to the transition from facultative to obligate parasitism.