Long-term memory involved in nestmate recognition in ants

Abstract

Abstract. The role of long-term memory in nestmate recognition in ants was investigated. Workers of Formica selysi (Formicinae) and Manica rubida (Myrmicinae) were reared in single-species groups or in artificial mixed-species groups, created 5 h after their emergence. In mixed groups, hydrocarbon profiles of both species acquire at least some of the components characteristic of each other. After 3 months, the species reared in mixed groups were separated and each single-species group was divided into two groups for 8, 15, 30, 60 or 90 days, 6 months or 1 year. After the separation period, 'nestmate' recognition was evaluated for individuals of different species previously reared together ('familiar'), and for allospecific individuals from single-species and mixed groups ('unfamiliar'). Even after 1 year of separation, the workers reared in mixed groups recognized familiar allospecific ants, even though their cuticular profiles possessed only trace amounts of allospecific hydrocarbons. Moreover, they were not aggressive towards unfamiliar allospecifics reared in single-species groups. These results suggest that individuals recognized the allospecific cues borne on each individual's body surface, even when they were present in only trace amounts, and/or each individual learned and memorized allospecific recognition cues during its early life. They suggest also that each individual possesses a template encoding the allospecific and the conspecific cues to characterize nestmates.