Australian Desert Ant Melophorus Bagoti Research Articles

Nest excavators’ learning walks in the Australian desert ant Melophorus bagoti

The Australian red honey ant, Melophorus bagoti, stands out as the most thermophilic ant in Australia, engaging in all outdoor activities during the hottest periods of the day during summer months. This species of desert ants often navigates by means of path integration and learning landmark cues around the nest. In our study, we observed the outdoor activities of M. bagoti workers engaged in nest excavation, the maintenance of the nest structure, primarily by taking excess sand out of the nest. Before undertaking nest excavation, the ants conducted a single exploratory walk. Following their initial learning expedition, these ants then engaged in nest excavation activities. Consistent with previous findings on pre-foraging learning walks, after just one learning walk, the desert ants in our study demonstrated the ability to return home from locations 2 m away from the nest, although not from locations 4 m away. These findings indicate that even for activities like dumping excavated sand within a range of 5–10 cm outside the nest, these ants learn and utilize the visual landmark panorama around the nest.

Dumping behaviour of Australian desert ants (Melophorus bagoti) (Hymenoptera:Formicidae)

The Central Australian desert ant Melophorus bagoti maintains ground-nesting colonies in the semi-desert habitat. These ants manage waste by dumping items outside the nest. To examine this process, we placed organic and non-organic materials that are associated with either low or high pathogenic risk around or into the nest and observed the nest’s response. We found that generally, ants dumped high-pathogenic-risk materials (dead larvae, dead ants of the colony, foraged food, moth, and non-nest cicada exoskeleton) further from the nest than low-pathogenic-risk ones (sand, buffel grass, cookies), with the exception of (organic) larval shells from their own nest, which were also dumped close to the nest. This pattern of dumping suggests that these ants choose their dumping distance based on how spoilable the experimental materials are.

Ants\u2019 navigation in an unfamiliar environment is influenced by their experience of a familiar route

When displaced experimentally from a food source (feeder) to unfamiliar terrain, ants run off a portion of the homeward vector or its entirety, depending on species and conditions, and then search systematically, turning in loops of ever increasing size. The Australian desert ant Melophorus bagoti runs off a smaller portion of its vector if the test site is more dissimilar to its nest area. Here we manipulated familiarity with the training route between a feeder and the ants’ nest to examine its effects when the ants were displaced to a distant site from the feeder. Naïve ants that arrived at an experimentally provided feeder for the first time were compared with experienced ants that had travelled the route for two days. At the unfamiliar test site, naïve ants ran off a longer portion of their vector from path integration than did experienced ants. Naïve ants also spread out in their systematic search slower than did experienced ants. We conclude that as ants learn the views encountered on their familiar route better, they identify more readily unfamiliar views. A scene distant from their nest area may not look as unfamiliar to a naïve ant as it does to an experienced ant.

Visual scanning behaviours and their role in the navigation of the Australian desert ant Melophorus bagoti

Ants are excellent navigators, using a combination of innate strategies and learnt information to guide habitual routes. The mechanisms underlying this behaviour are little understood though one avenue of investigation is to explore how innate sensori-motor routines are used to accomplish route navigation. For instance, Australian desert ant foragers are occasionally observed to cease translation and rotate on the spot. Here, we investigate this behaviour using high-speed videography and computational analysis. We find that scanning behaviour is saccadic with pauses separated by fast rotations. Further, we have identified four situations where scanning is typically displayed: (1) by naïve ants on their first departure from the nest; (2) by experienced ants departing from the nest for their first foraging trip of the day; (3) by experienced ants when the familiar visual surround was experimentally modified, in which case frequency and duration of scans were proportional to the degree of modification; (4) when the information from visual cues is at odds with the direction indicated by the ant's path integration system. Taken together, we see a general relationship between scanning behaviours and periods of uncertainty.

Multiple sources of celestial compass information in the Central Australian desert ant Melophorus bagoti

The Central Australian desert ant Melophorus bagoti is known to use celestial cues for compass orientation. We manipulated the available celestial cues for compass orientation for ants that had arrived at a feeder, were captured and then released at a distant test site that had no useful terrestrial panoramic cues. When tested in an enclosed transparent box that blocked some or most of the ultraviolet light, the ants were still well oriented homewards. The ants were again significantly oriented homewards when most of the ultraviolet light as well as the sun was blocked, or when the box was covered with tracing paper that eliminated the pattern of polarised light, although in the latter case, their headings were more scattered than in control (full-cue) conditions. When the position of the sun was reflected 180° by a mirror, the ants headed off in an intermediate direction between the dictates of the sun and the dictates of unrotated cues. We conclude that M. bagoti uses all available celestial compass cues, including the pattern of polarised light, the position of the sun, and spectral and intensity gradients. They average multiple cues in a weighted fashion when these cues conflict.

Does the Australian desert ant Melophorus bagoti approximate a Lévy search by an intrinsic bi-modal walk?

We suggest that the Australian desert ant Melophorus bagoti approximates a Lévy search pattern by using an intrinsic bi-exponential walk and does so when a Lévy search pattern is advantageous. When attempting to locate its nest, M. bagoti adopt a stereotypical search pattern. These searches begin at the location where the ant expects to find the nest, and comprise loops that start and end at this location, and are directed in different azimuthal directions. Loop lengths are exponentially distributed when searches are in visually familiar surroundings and are well described by a mixture of two exponentials when searches are in unfamiliar landscapes. The latter approximates a power-law distribution, the hallmark of a Lévy search. With the aid of a simple analytically tractable theory, we show that an exponential loop-length distribution is advantageous when the distance to the nest can be estimated with some certainty and that a bi-exponential distribution is advantageous when there is considerable uncertainty regarding the nest location. The best bi-exponential search patterns are shown to be those that come closest to approximating advantageous Lévy looping searches. The bi-exponential search patterns of M. bagoti are found to approximate advantageous Lévy search patterns.

Selection pressures give composite correlated random walks Lévy walk characteristics

Composite correlated random walks have been posited as a strong alternative to Lévy walks as models of multi-scale forager movement patterns. Here it is shown that if plastic then intrinsic composite correlated random walks will, under selection pressures, evolve to resemble optimal Lévy walks when foraging is non-destructive. The fittest composite correlated random walkers are found to be those that come closest to being optimal Lévy walkers. This may explain why such a diverse range of foragers have movement patterns that can be approximated by optimal Lévy walks and shows that the ‘Lévy-flight foraging’ hypothesis has a broad hinterland. The new findings are consistent with recent observations of mussels Mytilus edulis and the Australian desert ant Melophorus bagoti which suggest that animals approximate a Lévy walk by adopting an intrinsic composite movement strategy with different modes.

Foraging patterns and strategies in an Australian desert ant

AbstractThe Australian desert ant Melophorus bagoti (Formicidae) is a thermophilic, solitary foraging ant that inhabits the semi‐arid regions of Australia. In recent years, it has become a model species for the study of navigation. However, its ecological traits are not well understood, especially on the level of the entire colony. Here, we investigated this species daily activity schedule and diet composition, and examined its foraging behaviour. Foraging activity is confined to a window of roughly 50–70°C soil surface temperature, and foragers reacted quickly to temperature changes. Consequently, the pattern of daily outbound traffic during summer is unimodal on warm days and bimodal on very hot days. Foragers are opportunistic scavengers; dead insects make up a large proportion of food items, but grass seeds are also occasionally brought back to the nest in large amounts. Diet composition changes with the seasonal availability of certain food groups. Melophorus bagoti foragers have the ability to recruit nestmates to profitable food sources. Recruitment seems to function without the use of pheromone trails, but the exact mechanism requires further investigation.

Finding food: outbound searching behavior in the Australian desert ant Melophorus bagoti

Foragers of Melophorus bagoti often return to previously rewarding sites to search for more food items. They are opportunistic scavengers that exploit both protein and carbohydrate food sources. Under natural foraging conditions, protein food items are distributed sparsely and randomly, whereas carbohydrates come in patches that are often renewable. This makes for vastly different foraging scenarios that a single forager is confronted with. In theory, foraging performance can be greatly improved if foragers are able to adjust their strategy to different food item distributions. This could be achieved through individual foraging experience or by employing pre-existing, intrinsic foraging strategies. We investigated this by offering both kinds of food with the same distribution: as a renewable food source at a fixed location. After removal of the food source, outbound foragers displayed an area-restricted search centered on its location. Searches for protein had a greater spread than those for carbohydrates, which matches the natural distribution pattern of these food types. However, searches for both kinds of food follow the same general strategy, which is best described as a Brownian-like walk. We suggest that the observed adaptive behavior is a result of differential learning effort.

Vector-based and landmark-guided navigation in desert ants of the same species inhabiting landmark-free and landmark-rich environments

The central Australian desert ant Melophorus bagoti lives in a visually cluttered semi-arid habitat dotted with grass tussocks, bushes and trees. Previously, it was shown that this species has a higher propensity to switch from vector-based navigation to landmark-guided navigation compared with the North African desert ant Cataglyphis fortis, which usually inhabits a visually bare habitat. Here, we asked whether different colonies of M. bagoti, inhabiting more and less cluttered habitats, show a similar difference. We compared ants from typically cluttered habitats with ants from an exceptional nest located in an open field largely devoid of vegetation. Ants from both kinds of nests were trained to forage from a feeder and were then displaced to a distant test site on the open field. Under these conditions, ants from cluttered habitats switched more readily from vector-based navigation to landmark-guided navigation than ants from the open field. Thus, intraspecific differences caused by the experience of particular landmarks encountered en route, or of particular habitats, influence navigational strategies in addition to previously found interspecific, inherited differences due to the evolutionary history of living in particular habitats.

Visual discrimination, sequential learning and memory retrieval in the Australian desert ant Melophorus bagoti

Bees, wasps and ants--so-called central-place foragers--need potent homing strategies to return to their nest. Path integration and view-based landmark guidance are the key strategies for the ants' navigation. For instance, they memorise different views in a sequence (sequential memory) but also have a step counter that informs them about the covered distance during each foraging trip (odometer). The sequential memory and the odometer information can act as contextual cues during travel for retrieving the appropriate stored view. When and which cue is used at different stages and lengths of the foraging trips is still unknown. In this study, we examined how the Australian desert ant Melophorus bagoti uses sequential memory and odometric information to retrieve visual memories. Using a set-up made out of channels and two-choice boxes (Y-mazes), we demonstrate first that M. bagoti foragers are able to learn and discriminate a variety of visual stimuli in a sequence of views along the inbound trip back to the nest. We then forced the homing ants to encounter a fixed sequence of two visual patterns during their inbound trips. By manipulating the position and distance of the visual stimuli and decision boxes, we could set the two contextual cues (sequential memory and odometer) into conflict. After the short 4-m outbound distance, a preference for odometric information as a contextual cue was found, but after the long 8-m outbound distance, ants relied primarily on their sequential memory retrieval. Odometer precision deteriorates with increasing travel distance, and accordingly, our findings imply that desert ants may be relying on the most reliable contextual cue for retrieving visual memories.

The properties of the visual system in the Australian desert ant Melophorus bagoti

The Australian desert ant Melophorus bagoti shows remarkable visual navigational skills relying on visual rather than on chemical cues during their foraging trips. M. bagoti ants travel individually through a visually cluttered environment guided by landmarks as well as by path integration. An examination of their visual system is hence of special interest and we address this here. Workers exhibit distinct size polymorphism and their eye and ocelli size increases with head size. The ants possess typical apposition eyes with about 420–590 ommatidia per eye, a horizontal visual field of approximately 150° and facet lens diameters between 8 and 19 μm, depending on body size, with frontal facets being largest. The average interommatidial angle Δϕ is 3.7°, the average acceptance angle of the rhabdom Δρrh is 2.9°, with average rhabdom diameter of 1.6 μm and the average lens blur at half-width Δρl is 2.3°. With a Δρrh/Δϕ ratio of much less than 2, the eyes undersample the visual scene but provide high contrast, and surprising detail of the landmark panorama that has been shown to be used for navigation.

Ocelli contribute to the encoding of celestial compass information in the Australian desert antMelophorus bagoti

Many animal species, including some social hymenoptera, use the visual system for navigation. Although the insect compound eyes have been well studied, less is known about the second visual system in some insects, the ocelli. Here we demonstrate navigational functions of the ocelli in the visually guided Australian desert ant Melophorus bagoti. These ants are known to rely on both visual landmark learning and path integration. We conducted experiments to reveal the role of ocelli in the perception and use of celestial compass information and landmark guidance. Ants with directional information from their path integration system were tested with covered compound eyes and open ocelli on an unfamiliar test field where only celestial compass cues were available for homing. These full-vector ants, using only their ocelli for visual information, oriented significantly towards the fictive nest on the test field, indicating the use of celestial compass information that is presumably based on polarised skylight, the sun's position or the colour gradient of the sky. Ants without any directional information from their path-integration system (zero-vector) were tested, also with covered compound eyes and open ocelli, on a familiar training field where they have to use the surrounding panorama to home. These ants failed to orient significantly in the homeward direction. Together, our results demonstrated that M. bagoti could perceive and process celestial compass information for directional orientation with their ocelli. In contrast, the ocelli do not seem to contribute to terrestrial landmark-based navigation in M. bagoti.

Views, landmarks, and routes: how do desert ants negotiate an obstacle course?

The Australian desert ant Melophorus bagoti often follows stereotypical routes through a cluttered landscape containing both distant panoramic views and obstacles (plants) to navigate around. We created an artificial obstacle course for the ants between a feeder and their nest. Landmarks comprised natural objects in the landscape such as logs, branches, and tussocks. Many ants travelled stereotypical routes home through the obstacle course in training, threading repeatedly the same gaps in the landmarks. Manipulations altering the relations between the landmarks and the surrounding panorama, however, affected the routes in two major ways. Both interchanging the positions of landmarks (transpositions) and displacing the entire landmark set along with the starting position of the ants (translations) (1) reduced the stereotypicality of the route, and (2) increased turns and meanders during travel. The ants might have used the entire panorama in view-based travel, or the distal panorama might prime the identification and use of landmarks en route. Despite the large data set, both options (not mutually exclusive) remain viable.

Which portion of the natural panorama is used for view-based navigation in the Australian desert ant?

Ants that forage in visually rich environments often develop idiosyncratic routes between their nest and a profitable foraging ground. Such route knowledge is underpinned by an ability to use visual landmarks for guidance and place recognition. Here we ask which portions of natural visual scenes are essential for visually guided navigation in the Australian desert ant Melophorus bagoti whose foragers navigate through a habitat containing grass tussocks, shrubs and trees. We captured M. bagoti foragers after they had returned to their nest from a feeder, but before they had entered their nest, and tested their ability to home accurately from a series of release locations. We used this simple release paradigm to investigate visually guided navigation by monitoring the accuracy of nestwards orientation when parts of the ants' visual field were obscured. Results show that the lower portion of the visual panorama is more important for visually guided homing than upper portions. Analysis of panoramic images captured from the release and nest locations support the hypothesis that the important visual information is provided by the panoramic contour, where terrestrial objects contrast against sky, rather than by a limited number of salient landmarks such as tall trees.

Traveling in clutter: Navigation in the Central Australian desert ant Melophorus bagoti

The Central Australian desert ant Melophorus bagoti is the most thermophilic ant on the continent. It comes out to forage during the hottest part of the day in the summer months. The ant shares a cluttered, plant-filled habitat with other arthropods and uses a range of navigational strategies. We review recent studies on this species concerning its use of habitual routes, distant landmarks, landmarks around the nest, and path integration, which is keeping track of the distance and direction traveled from one's starting point. Functional predictions concerning the acquisition, retention, and integration of memories of distances and of landmarks are also reviewed, illuminating the behavioral ecology of spatial cognition.

Learning, retention and coding of nest-associated visual cues by the Australian desert ant, Melophorus bagoti

A variety of social insects use visual cues for homing. In this study, we examine the possible factors affecting the learning and retention of nest-associated visual cues by the Australian desert ant Melophorus bagoti and the manner in which such cues are encoded by foraging ants. We placed four prominent cylindrical landmarks around a nest and trained foragers from that nest to a food source. Ants were tested with the landmark array in a distant testing field after (1) a known number of exposures to the landmarks (1, 3, 7 or 15 trials, spread over a period of 1 day, 2 days or ≥3 days) and (2) after a known period of delay (0, 24, 48, 96 or 192 h). The results show that a combination of an increase in training trials and an increase in number of training days affected the acquisition of landmark memory. Moreover, once the landmarks were learnt, they became a part of long-term memory and lasted throughout the ants’ foraging lifetime. To examine visual cue encoding behaviour, ants trained under similar conditions for 4 days were tested with (1) an identical landmark array, (2) landmarks of the same size used in training, but placed at twice the distance from each other, and (3) landmarks whose dimensions were doubled and placed at twice the distance from each other. In conditions (1) and (3), the ants searched extensively at the centre of the four landmarks, suggesting that, similar to the Saharan ant (genus Cataglyphis) and the honeybee, M. bagoti too uses a snapshot to match the view of the landmarks around the nest. But contrary to the snapshot model, in condition (2), the ants did not search extensively at the centre of the landmarks, but searched primarily 0.5 m from the landmark, the distance from each landmark to the nest during training. We discuss how various search models fare in accounting for these findings.

Acquiring, retaining and integrating memories of the outbound distance in the Australian desert ant Melophorus bagoti

Estimation of distance travelled (odometry) forms a vital part of navigation for solitarily foraging ants. In this study we investigated the properties of odometric memory in the Australian desert ant Melophorus bagoti. Ants were trained to travel in linear channels to a feeder placed at 6 m or 12 m from the nest. We determined if the ability to estimate distances accurately increased with experience. We also determined the delay at which the odometric memory started to decay at both these distances. Ants with six trials of experience did not get better at estimating distances and the odometric memory decayed after a 24 h delay. We then determined if ants integrated their latest odometric memory with their previous memories. We did this by training two groups of ants for five trials, one group to 6 m and another to 12 m, and then halving or doubling the outbound distance on their sixth trip, respectively. The ant's estimate was noted when the ants were released either immediately or after a 24 h delay. Ants always estimated their last outbound distance when released immediately. However, they switched to route-based navigation rather than estimating distances after a 24 h delay (at which time their odometric memory would have decayed).