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Highlights • Ants have a navigational toolbox that includes learned cues across multiple senses. • We review current work on learning panoramas as well as non-visual cues. • We call for more experimental ethology focussed on learning processes. Abstract Foraging desert ants are repeatedly presented with the challenge of leaving the nest, searching the scorching desert landscape to find food, and then transporting it back home. To accomplish this task, foragers have a navigational toolbox, which relies on olfactory, idiothetic, visual and magnetic cues. Desert ants have been widely studied with regards to these abilities, including a heavy focus on learned visual cues, the most prominent being the terrestrial panorama. Nest cues are first acquired during pre-foraging learning walks. Once foragers leave the nest area, they also learn a number of cues to aid them when returning both back to the nest and to known food sites, using experience of previous trips to navigate on future trips. In this review, we describe the learning processes involved in accurate navigation in desert ants. We first focus on recent research on nest-site panorama learning during pre-foraging learning walks as well as panorama learning away from the nest during foraging. We also review learning cues beyond the terrestrial panorama, including tactile, magnetic, olfactory and vibrational cues. These studies provide a basis for future work to further explore how these navigators, despite their small brains, acquire, retain and use many cue sets present in their environments. We call for more experimental ethology focussed on learning processes, both by exploring run-by-run and step-by-step acquisition of information for navigation, as well as for other natural tasks in an animal's life. [ABSTRACT FROM AUTHOR]

Solitary foraging ants commonly use visual cues from their environment for navigation. Foragers are known to store visual scenes from the surrounding panorama for later guidance to known resources and to return successfully back to the nest. Several ant species travel not only on the ground, but also climb trees to locate resources. The navigational information that guides animals back home during their descent, while their body is perpendicular to the ground, is largely unknown. Here, we investigate in a nocturnal ant, Myrmecia midas , whether foragers travelling down a tree use visual information to return home. These ants establish nests at the base of a tree on which they forage and in addition, they also forage on nearby trees. We collected foragers and placed them on the trunk of the nest tree or a foraging tree in multiple compass directions. Regardless of the displacement location, upon release ants immediately moved to the side of the trunk facing the nest during their descent. When ants were released on non-foraging trees near the nest, displaced foragers again travelled around the tree to the side facing the nest. All the displaced foragers reached the correct side of the tree well before reaching the ground. However, when the terrestrial cues around the tree were blocked, foragers were unable to orient correctly, suggesting that the surrounding panorama is critical to successful orientation on the tree. Through analysis of panoramic pictures, we show that views acquired at the base of the foraging tree nest can provide reliable nest-ward orientation up to 1.75 m above the ground. We discuss, how animals descending from trees compare their current scene to a memorised scene and report on the similarities in visually guided behaviour while navigating on the ground and descending from trees. [ABSTRACT FROM AUTHOR]

Foraging ants are known to use multiple sources of information to return to the nest. These cue sets are employed by independent navigational systems including path integration in the case of celestial cues and vision-based learning in the case of terrestrial landmarks and the panorama. When cue sets are presented in conflict, the Australian desert ant species, Melophorus bagoti, will choose a compromise heading between the directions dictated by the cues or, when navigating on well-known routes, foragers choose the direction indicated by the terrestrial cues of the panorama against the dictates of celestial cues. Here, we explore the roles of learning terrestrial cues and delays since cue exposure in these navigational decisions by testing restricted foragers with differing levels of terrestrial cue experience with the maximum (180°) cue conflict. Restricted foragers appear unable to extrapolate landmark information from the nest to a displacement site 8 m away. Given only one homeward experience, foragers can successfully orient using terrestrial cues, but this experience is not sufficient to override a conflicting vector. Terrestrial cue strength increases with multiple experiences and eventually overrides the celestial cues. This appears to be a dynamic choice as foragers discount the reliability of the terrestrial cues over time, reverting back to preferring the celestial vector when the forager has an immediate vector, but the forager's last exposure to the terrestrial cues was 24 hr in the past. Foragers may be employing navigational decision making that can be predicted by the temporal weighting rule. [ABSTRACT FROM AUTHOR]

Visual cues commonly aid solitary foraging ants. Specifically, foragers can use the skyline where terrestrial landmarks meet the sky. Foraging ants show a remarkable affinity to retain these terrestrial cues, developing lifelong memories of the nest site panorama. Here we explore foragers' ability to retain skyline cues of resource locations at some distance from the nest through experiments with artificial skylines erected around a resource location. We also tested the foragers' memories of one skyline at several time points after the skyline was replaced by a different one. During retention testing, foragers appear able to retain robust memories of these skylines over periods (5 days) that surpass their average life span. Exposure to the nest panorama during these periods did not interfere with navigational performance at the distant skyline. Foragers in the replacement experiment initially oriented correctly to both skylines. Thereafter, the foragers' headings in tests with the first skyline gradually shifted away from the correct homeward direction. We argue that new skyline memories cause retroactive interference in the retention of previously learned skylines. Skyline memories may compete during memory retrieval, or may be retrieved in association with context cues present in the current testing paradigm such as vector length. [ABSTRACT FROM AUTHOR]

Harsh environments and severe winters have been hypothesized to favor improvement of the cognitive abilities necessary for successful foraging. Geographic variation in winter climate, then, is likely associated with differences in selection pressures on cognitive ability, which could lead to evolutionary changes in cognition and its neural mechanisms, assuming that variation in these traits is heritable. Here, we focus on two species of food-caching chickadees (genus Poecile), which rely on stored food for survival over winter and require the use of spatial memory to recover their stores. These species also exhibit extensive climate-related population level variation in spatial memory and the hippocampus, including volume, the total number and size of neurons, and adults' rates of neurogenesis. Such variation could be driven by several mechanisms within the context of natural selection, including independent, population-specific selection (local adaptation), environment experience-based plasticity, developmental differences, and/or epigenetic differences. Extensive data on cognition, brain morphology, and behavior in multiple populations of these two species of chickadees along longitudinal, latitudinal, and elevational gradients in winter climate are most consistent with the hypothesis that natural selection drives the evolution of local adaptations associated with spatial memory differences among populations. Conversely, there is little support for the hypotheses that environment-induced plasticity or developmental differences are the main causes of population differences across climatic gradients. Available data on epigenetic modifications of memory ability are also inconsistent with the observed patterns of population variation, with birds living in more stressful and harsher environments having better spatial memory associated with a larger hippocampus and a larger number of hippocampal neurons. Overall, the existing data are most consistent with the hypothesis that highly predictable differences in winter climate drive the evolution and maintenance of differences among populations both in cognition and in the brain via local adaptations, at least in food-caching parids. [ABSTRACT FROM AUTHOR]