Sequential learning of relative size by the Neotropical ant Gigantiops destructor.

The question of whether insects can perform concept learning or can use the geometry of space as in mammals has been recently addressed in Hymenoptera in an extensive way. We investigate here the ability of the tropical ant Gigantiops destructor to perform sequential learning and to use size relationships during navigation. Ants were trained to solve a dichotomic six-stage linear maze relying on the apparent width of two vertical landmarks. Each individual ant first learnt to associate a given landmark width to the motor decision of turning right or left to avoid dead-ends independently of a motor routine. When confronted for the first time with a new intermediate-sized pattern, for which no supposed snapshot could have been stored, ants made directional choices indicating that bar width judgments were not absolute but rather relative to the familiar visual patterns seen in the previous chambers. This result demonstrates that ants can generalize relationship rules by interpolating the relative width of a novel stimulus according to visual information kept in spatial working memory. In conclusion, ants can perform conditional discriminations reliably not only when stimuli are simultaneous but also when they are sequential.