Do familiar landmarks reset the global path integration system of desert ants?

It is often suggested that animals may link landmark memories to a global coordinate system provided by path integration, thereby obtaining a map-like representation of familiar terrain. In an attempt to discover if desert ants form such associations we have performed experiments that test whether desert ants recall a long-term memory of a global path integration vector on arriving at a familiar food site. Ants from three nests were trained along L-shaped routes to a feeder. Each route was entirely within open-topped channels that obscured all natural landmarks. Conspicuous artificial landmarks were attached to the channelling that formed the latter part of the route. The homeward vectors of ants accustomed to the route were tested with the foodward route, either as in training, or with the first leg of the L shortened or extended. These ants were taken from the feeder to a test area and released, whereupon they performed a home vector. If travelling the latter part of a familiar route and arriving at a familiar food site triggers the recall of an accustomed home vector, then the home vector should be the same under both test conditions. We find instead that the home vector tended to reflect the immediately preceding outward journey. In conjunction with earlier work, these experiments led us to conclude in the case of desert ants that landmark memories do not prime the recall of long-term global path integration memories. On the other hand, landmark memories are known to be linked to local path integration vectors that guide ants along a segment of a route. Landmarks thus seem to provide procedural information telling ants what action to perform next but not the positional information that gives an ant its location relative to its nest

The use of path integration to guide route learning in ants.

Cataglyphid ants travelling between their nest and feeding site follow familiar routes along which they are guided by views of the surrounding landscape. On bare terrain, with no landmarks available, ants can still navigate using path integration. They continually monitor their net distance and direction from the nest, so that they can return home from any point using their computed 'home vector'. Here we ask whether path integration also 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 roughly the correct direction, and that it is appropriate to store those views that can guide subsequent trips to the nest. We tested this hypothesis by training 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 required an ant to discriminate between different pairs of shapes. We show that 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 navigate through an unfamiliar landscape, and assist them to become familiar with it

The use of path integration to guide route learning in ants.

Cataglyphid ants travelling between their nest and feeding site follow familiar routes along which they are guided by views of the surrounding landscape. On bare terrain, with no landmarks available, ants can still navigate using path integration. They continually monitor their net distance and direction from the nest, so that they can return home from any point using their computed 'home vector'. Here we ask whether path integration also 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 roughly the correct direction, and that it is appropriate to store those views that can guide subsequent trips to the nest. We tested this hypothesis by training 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 required an ant to discriminate between different pairs of shapes. We show that 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 navigate through an unfamiliar landscape, and assist them to become familiar with it

Do familiar landmarks reset the global path integration system of desert ants?

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Do Ants Need to Estimate the Geometrical Properties of Trail Bifurcations to Find an Efficient Route? A Swarm Robotics Test Bed

International audienceInteractions between individuals and the structure of their environment play a crucial role in shaping self-organized collective behaviors. Recent studies have shown that ants crossing asymmetrical bifurcations in a network of galleries tend to follow the branch that deviates the least from their incoming direction. At the collective level, the combination of this tendency and the pheromone-based recruitment results in a greater likelihood of selecting the shortest path between the colony's nest and a food source in a network containing asymmetrical bifurcations. It was not clear however what the origin of this behavioral bias is. Here we propose that it results from a simple interaction between the behavior of the ants and the geometry of the network, and that it does not require the ability to measure the angle of the bifurcation. We tested this hypothesis using groups of ant-like robots whose perceptual and cognitive abilities can be fully specified. We programmed them only to lay down and follow light trails, avoid obstacles and move according to a correlated random walk, but not to use more sophisticated orientation methods. We recorded the behavior of the robots in networks of galleries presenting either only symmetrical bifurcations or a combination of symmetrical and asymmetrical bifurcations. Individual robots displayed the same pattern of branch choice as individual ants when crossing a bifurcation, suggesting that ants do not actually measure the geometry of the bifurcations when travelling along a pheromone trail. Finally at the collective level, the group of robots was more likely to select one of the possible shorter paths between two designated areas when moving in an asymmetrical network, as observed in ants. This study reveals the importance of the shape of trail networks for foraging in ants and emphasizes the underestimated role of the geometrical properties of transportation networks in general