Learning of views and flexibility of cue use in navigation in Australian ants
Solitarily foraging ants face the recurrent challenge of navigating to find food and bringing it back to the nest. They show considerable navigational abilities, including path integration and view-based navigation. Ants inhabiting a visually cluttered environment, such as the red honey ant Melophorus bagoti and the nocturnal bull ant Myrmecia midas, depend on cues from the visual panorama around them. Empirical evidence shows that solitarily foraging ants combine information from various navigational cues flexibly. Foragers can choose the optimal weighting of various information sources. Ants of many species perform a series of exploratory walks around the nest to acquire visual landmark information before their first foraging trip. Firstly, we investigated how naïve red honey ants perform these learning walks trial by trial before they become foragers. Ant foragers retain memories of the visual panorama around their nest, memorized during the learning walks. When away from the nest, they can compare these stored views with their current vision to return to their nest. Our observations suggest that during learning walks, naïve red honey ants increased the search area around the nest with successive walks. During these walks, the ants performed stereotypical saccadic body movements in what are called pirouettes. They performed complete body rotations with stopping phases as well as small circular walks without stops known as voltes. Secondly, we investigated whether spatially restricted red honey ant foragers can generalise their memory of visual cues to unexperienced nearby sites. After naïve red honey ants were restricted to an arena around their nest of 1 m in radius for 3 days, they were able to correctly orient to the nest from displacement sites up to 8 m from the nest. We concluded that M. bagoti ants can generalise their views learned from foraging in a restricted area when given unrestricted views. Thirdly, we also examined whether M. midas foragers generalise their views similarly under daylight and dim (night) conditions from displacement sites at different distances to their nest. We found that M. midas foragers exhibit differences in initial orientation, path straightness, and initial navigational behaviours at displacement sites under daylight and dim (night) conditions. Lastly, we also examined how nocturnal bull ants adjust their navigational strategies in their natural terrain if their usual home route does not lead to their entry into their home. We examined whether foragers showed any changes in their path characteristics. After the nocturnal bull ants M. midas made the first trip from the foraging tree displacement site to their nest, they were picked up near their nest and rewound (placed back on the route that they had travelled) repeatedly. It was observed that they decreased their path straightness and increased the number of scans over rewinding trials, suggesting increased navigational uncertainty.