Search

Visual navigation in ants has long been a focus of experimental study [1-3], but only recently have explicit hypotheses about the underlying neural circuitry been proposed [4]. Indirect evidence suggests the mushroom bodies (MBs) may be the substrate for visual memory in navigation tasks [5-7], while computational modeling shows that MB neural architecture could support this function [8, 9]. There is, however, no direct evidence that ants require MBs for visual navigation. Here we show that lesions of MB calyces impair ants' visual navigation to a remembered food location yet leave their innate responses to visual cues unaffected. Wood ants are innately attracted to large visual cues, but we trained them to locate a food source at a specific angle away from such a cue. Subsequent lesioning of the MB calyces using procaine hydrochloride injection caused ants to revert toward their innate cue attraction. Handling and saline injection control ants still approached the feeder. Path straightness of lesioned and control ants did not differ from each other but was lower than during training. Reversion toward the cue direction occurred irrespective of whether the visual cue was ipsi- or contralateral to the lesion site, showing this is not due simply to an induced motor bias. Monocular occlusion did not diminish ants' ability to locate the feeder, suggesting that MB lesions are not merely interrupting visual input to the calyx. The demonstrated dissociation between innate and learned visual responses provides direct evidence for a specific role of the MB in navigational memory., Competing Interests: Declaration of Interests The authors declare no competing interests., (Copyright © 2020 Elsevier Inc. All rights reserved.)

The ability of bees and ants to learn long visually guided routes in complex environments is perhaps one of the most spectacular pieces of evidence for the impressive power of their small brains. Whereas flying bees can visit flowers in an optimized sequence over kilometers, walking solitary foraging ants can precisely recapitulate routes of up to 100 m in complex environments [1]. It is clear that route following depends largely on learned visual information and we have a good idea of how visual memories can guide individuals along them [2-6], as well as how this is implemented in the insect brain [7, 8]. However, little is known about the mechanisms that control route learning and development. Here we show that ants (Melophorus bagoti and Cataglyphis fortis) navigating in their natural environments can actively learn a route detour to avoid a pit trap. This adaptive flexibility depends on a mechanism of aversive learning based on memory traces of recently encountered stimuli, reflecting the laboratory paradigm of trace conditioning. The views experienced before falling into the trap become associated with the ensuing negative outcome and thus trigger salutary turns on the subsequent trip. This drives the ants to orient away from the goal direction and avoid the trap. If the pit trap is avoided, the novel views experienced during the detour become positively reinforced and the new route crystallizes. We discuss how such an interplay between appetitive and aversive memories might be implemented in insect neural circuitry., Competing Interests: Declaration of Interests The authors declare no competing interests., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Understanding the computational basis of spatial cognition requires observations of natural behaviour and the underlying neural circuits, which are difficult to do simultaneously: however, recent studies show how we might achieve this, combining rich virtual reality set-ups and the use of optogenetics in freely moving animals., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Ants often walk backwards to drag large prey to their nest. New experiments show how they can use information from retinotopically encoded views to follow visual routes even while moving backwards. The mechanisms enabling ants to decouple body orientation and the control of travel direction are likely to be shared with other, flying, insects., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

A study of dung beetles rolling dung balls to safety reveals unexpected facets of the beetle's acquisition and use of celestial information for keeping to a straight path., (Copyright © 2016. Published by Elsevier Ltd.)

Radar studies of a honeybee's flights when it first leaves its nest suggest the features of the surrounding landscape that it learns guide future foraging trips., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Desert ants feeding on dead arthropods forage for food items that are distributed unpredictably in space and time in the food-scarce terrain of the Saharan salt pans [1]. Scavengers of the genus Cataglyphis forage individually and do not lay pheromone trails [2]. They rely primarily on path integration [3] for navigation and, in addition, use visual [4] and olfactory cues [5-7]. While most studies have focused on the navigational mechanisms of ants targeting a familiar place like the nest or a learned feeding site, little is known about how ants locate food in their natural environment. Here we show that Cataglyphis fortis is highly sensitive to and attracted by food odors, especially the necromone linoleic acid, enabling them to locate tiny arthropods over several meters in distance. Furthermore, during the search for food, ants use extensive crosswind walks that increase the chances of localizing food plumes. By combining high sensitivity toward food odors with crosswind runs, the ants efficiently screen the desert for food and hence reduce the time spent foraging in their harsh desert environment., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

Neurogenetic tools of Drosophila research allow unique access to the neural circuitry underpinning visually guided behaviours. New research is highlighting how particular areas in the fly's central brain needed for pattern recognition provide a coarse visual encoding., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

Animals sometimes take sinuous paths to a goal. Insects, tracking an odor trail on the ground [1-3] or moving up an odor plume in the air [4, 5], generally follow zigzag paths. Some insects [6-8] take a zigzag approach to visual targets, perhaps to obtain parallax information. How does an animal keep its overall path in the direction of the goal without disrupting a zigzag pattern? We describe here the wood ant's strategy when guided by a familiar visual scene. If their travel direction is correct, ants face the goal briefly after each turning point along their zigzag path. If the direction is wrong, they turn rapidly at this point to place the scene correctly on their retina. Such saccade-like turns are rare elsewhere in the zigzag. Similarly, when the scene is made to jump to a new position on their retina, ants wait until an expected goal-facing phase of the zigzag before turning to correct the imposed error. Correctly timed, intermittent control allows an animal to adjust its path without compromising additional roles for the zigzag pattern in gathering visual information or in using odor cues for guidance., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

Ants, like honeybees, can set their travel direction along foraging routes using just the surrounding visual panorama. This ability gives us a way to explore how visual scenes are perceived. By training wood ants to follow a path in an artificial scene and then examining their path within transformed scenes, we identify several perceptual operations that contribute to the ants' choice of direction. The first is a novel extension to the known ability of insects to compute the "center of mass" of large shapes: ants learn a desired heading toward a point on a distant shape as the proportion of the shape that lies to the left and right of the aiming point--the 'fractional position of mass' (FPM). The second operation, the extraction of local visual features like oriented edges, is familiar from studies of shape perception. Ants may use such features for guidance by keeping them in desired retinal locations. Third, ants exhibit segmentation. They compute the learned FPM over the whole of a simple scene, but over a segmented region of a complex scene. We suggest how the three operations may combine to provide efficient directional guidance., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

A recent study shows that desert ants use a precise behaviour, based on the internal cues of path integration, to facilitate the learning of visual landmark information. This raises fascinating questions about how insects encode familiar terrain., (Copyright (c) 2010 Elsevier Ltd. All rights reserved.)

Ants are so low to the ground that slight undulations in the terrain over which they navigate will cause large and unpredictable changes to their view of the scene around them. We describe here evidence of a form of motor learning that helps ants follow their usual route when guiding landmarks vanish from sight. Wood ants were trained to approach a vertical bar presented at varying positions on a LCD screen. In different experiments, the bar was either stationary, moved smoothly, or jumped between two stationary positions. Ants trained in these three ways followed straight, curved, or two-leg routes, respectively. Once ants were accustomed to approaching the bar from different starting points, the bar was made to disappear during their approach. Ants often continued their straight or curved or two-leg paths, despite the missing landmark, showing that they can perform complex routes with no more than intermittent visual feedback.

Background: Even on short routes, ants can be guided by multiple visual memories. We investigate here the cues controlling memory retrieval as wood ants approach a one- or two-edged landmark to collect sucrose at a point along its base. In such tasks, ants store the desired retinal position of landmark edges at several points along their route. They guide subsequent trips by retrieving the appropriate memory and moving to bring the edges in the scene toward the stored positions., Results: The apparent width of the landmark turns out to be a powerful cue for retrieving the desired retinal position of a landmark edge. Two other potential cues, the landmark's apparent height and the distance that the ant walks, have little effect on memory retrieval. A simple model encapsulates these conclusions and reproduces the ants' routes in several conditions. According to this model, the ant stores a look-up table. Each entry contains the apparent width of the landmark and the desired retinal position of vertical edges. The currently perceived width provides an index for retrieving the associated stored edge positions. The model accounts for the population behavior of ants and the idiosyncratic training routes of individual ants., Discussion: Our results imply binding between the edge of a shape and its width and, further, imply that assessing the width of a shape does not depend on the presence of any particular local feature, such as a landmark edge. This property makes the ant's retrieval and guidance system relatively robust to edge occlusions.

Animals typically have several navigational strategies available to them. Interactions between these strategies can reduce navigational errors and may lead to the emergence of new capacities.

Insects are thought to pinpoint a place by using memorized "snapshots," i.e., two-dimensional retinotopic views of the surrounding landmarks recorded when at the place (reviewed in ). Insects then reach the place by moving until their current view matches their snapshot. To determine when snapshots are recalled, and how differences between view and snapshot are translated into appropriate movements, we analyzed the approaches of wood ants to a feeding site that was located in the center of an array of two or three cylinders. In ants, contrary to flying hymenopterans, body orientation and direction of travel are collinear, so that an ant approaching an object always looks at it with frontal visual field. On their way to a food site, ants fixated and approached a cylinder predominantly when its angular size was smaller than when viewed from the food site. This finding implies that ants store snapshots at this place while fixating landmarks with frontal retina, so simplifying the later alignment of snapshots with their current view. It also means that ants recall snapshots well in advance of reaching the place. Although snapshots are centered on a landmark, we show that they extend at least 120 degrees into the periphery.