The use of path integration to guide route learning in ants

Cataglyphid ants travelling between their nest and feeding site follow fami liar routes along which they are guided by views of the surrounding landsca pe(1-5). On bare terrain, with no landmarks available, ants can still navig ate using path integration(6). They continually monitor their net distance and direction from the nest, so that they can return home from any point us ing their computed 'home vector'(7). Here we ask whether path integration a lso provides signals to reinforce the learning of visual landmarks. A fall in the value of the home vector indicates when a homing ant moves in roughl y the correct direction, and that it is appropriate to store those views th at can guide subsequent trips to the nests. We tested this hypothesis by tr aining the ant Cataglyphis cursor to negotiate a variety of mazes that led from a feeding site back to the nest. Efficient passage of each maze requir ed an ant to discriminate between different pairs of shapes(9). We show tha t if the value of the home vector drops while the ant approaches and passes a shape, the shape's appearance is learnt, but if the vector grows, or is absent, no visual learning occurs. Path integration may both help ants navi gate through an unfamiliar landscape, and assist them to become familiar wi th it.