Spatio-temporal learning in a mass-recruiting leaf-cutting ant (Acromyrmex subterraneus)

Abstract

The ability to anticipate periodically available resources is observed in several animals and improves performance in obtaining resources and adaptability. Spatio-temporal learning occurs when they associate the correct time and location of future events. We evaluate whether leaf-cutting ants Acromyrmex subterraneus can anticipate the presence of sucrose and examine potential anticipatory effects. Five colonies were used in an experimental setup where, from a central tray, two trails in opposite directions gave access to either the sucrose or to nothing. For 21 consecutive days sucrose was offered at the same place and the same time. Cameras recorded the flow of individuals at 4 different phases: before feeding (10h00-11h00), pre-feeding (11h30-12h00), feeding (12h00-13h00) and after feeding (14h00-15h00). On the 22nd day sugar was not supplied. On the 21st day the ants were marked and the next day, observed. Our results shows that: (1) the ants responded positively to the stimulus presented by forming the foraging trail to collect sucrose; (2) before feeding there was no significant difference in ant flow between the trails, but after feeding, the ant flow was consistently higher on trail that led to sucrose, which we called a keep going behavior; (3) there was a progressive spatio-temporal learning, given that ants began to appear earlier in pre-feeding throghout the weeks; (4) on the 22nd day, the ants presented themselves 10 minutes in advance and remained in the correct place; (5) the marked ants indicated that even without any resource the empty place continued to be explored. The colonies were able to learn where and when to look for food. Due to the adjustment of the ants to the stimuli of the environment it was possible to prepare for the collection of sucrose and the success in foraging for the colony. Summary statementLeaf-cutting ants are capable of spatio-temporal learning and this process has relevance on mass foraging recruitment and overall social organization of the colony.