Information content of visual scenes influences systematic search of desert ants (original) (raw)
Related papers
Behavioral Ecology and Sociobiology, 2016
Two species of Australian desert ants, one inhabiting a visually rich environment (Melophorus bagoti) and one inhabiting a visually barren environment (as yet unnamed and dubbed Melophorus sp.), were tested on path integration and subsequent search. For each species, prominent landmarks were placed near the nest, and ants were trained to visit a feeder. After training over two days, an ant was captured at the feeder when it had grabbed some food, and tested, just once individually, in homing with the training landmarks either present or absent. Their subsequent search was also recorded on gridded paper according to a grid marked at the test site. Both species headed initially in the feeder-nest direction, but directional scatter was larger when training landmarks were absent. Melophorus bagoti ran a shorter distance before starting to search on tests with the landmarks absent, but Melophorus sp. ran a similar distance in both conditions. In both species, the variance in distance run was larger when landmarks were absent. In searching, both species expanded their search pattern more when landmarks were absent than when landmarks were present. Contrary to predictions, the distribution of the lengths of search segments was best described as a single exponential function on tests with landmarks absent, and as a double exponential function with landmarks present.
Ants might use different view-matching strategies on and off the route
Journal of Experimental Biology, 2012
Individual foraging ants are known to rely on views of their surroundings for route learning and for pinpointing goals. Different strategies have been proposed to explain how ants might process visual information for navigation, but little is known about the actual development and nature of the view-based strategies used by ants in complex natural environments. Here, we constrained the knowledge of Melophorus bagoti ants to either the nest vicinity or a curved route (length 10m) and analysed their initial direction when released at both novel and familiar locations. In parallel, we used 360deg pictures of the scene as a basis for modelling different navigational strategies. We propose here a new hypothesis based on skyline height comparison to explain how ants home from novel locations. Interestingly, this strategy succeeded well at novel locations but failed on familiar terrain. By contrast, the use of a visual compass strategy failed at novel locations but could explain the results on familiar routes. We suggest that ants might switch between skyline height comparison and a visual compass strategy, depending on whether they are on familiar terrain or not. How ants could switch between strategies and how their memories develop are discussed in turn.
Ants are known to use the terrestrial visual panorama in navigation. Recent evidence has accumulated for the use of the currently perceived visual panorama to determine a direction to head in. The pattern of the height of the terrestrial surround, the skyline, is one key cue for the Central Australian red honey ant Melophorus bagoti in determining a direction of travel. But ants might also possess some mechanism to match the skyline heights encountered during training, which functions to steer away from regions whose skyline is too high and towards regions whose skyline is too low. We made an initial test of this hypothesis by training ants to visit a feeder centred between two experimentally constructed walls of black cloth. Trained ants were then tested for their initial homing direction with the walls retaining their heights as encountered in training (controls), with one of the walls lowered or raised in height, or with one wall lowered and the opposite wall raised. Wall-height manipulations deflected the initial headings of ants towards the lower wall, with combined wall lowering and wall raising changing the initial headings by~30°w hen compared with controls. The results suggest that the ants combined the dictates of the panorama in determining the best direction of travel (a heading towards the nest) with some attractor mechanism that functions to establish the skyline heights of training conditions (a heading towards the lower wall).
Behavioral Ecology and Sociobiology, 2007
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.
Visual associative learning in two desert ant species
Behavioral Ecology and Sociobiology, 2010
Visual cues are important navigational tools for many solitary foraging insects. In addition to information provided by path integration, desert ants learn and use visual cues for homing back to their nest. In this study, we compared the visually based learning of two desert ant species: the North African Cataglyphis fortis and the Australian Melophorus bagoti, each of which lives in ecologically similar but visually different environments. In our experiment, ants' choice performance was measured by training foragers in a channel system. We used a decision box with two visual stimuli during their homebound trips, with one of the stimuli always being the correct one that provided thoroughfare. To determine any habitat effects on learning, we examined intraspecific comparisons in C. fortis with different nest surroundings. The intraspecific comparison in C. fortis revealed no differences in learning the task. In general, C. fortis showed little learning in our task and the results were similar for ants from barren and cluttered environments. Overall, M. bagoti learned the task faster and had a higher level of accuracy than C. fortis. One explanation for this species-specific difference could be that the cluttered habitat of M. bagoti favours the evolution of visual associative learning more so than the plain habitat of C. fortis.
Search strategies of ants in landmark-rich habitats
Search is an important tool in an ant’s navigational toolbox to relocate food sources and and the inconspicuous nest entrance. In habitats where landmark information is sparse, homing ants travel their entire home vector before searching systematically with ever increasing loops. Search strategies have not been previously investigated in ants that inhabit landmark-rich habitats where they typically establish stereotypical routes. Here we examine the search strategy in one such ant, Melophorus bagoti, by confining their foraging in one-dimensional channels to determine if their search pattern changes with experience, location of distant cues and altered distance on the homebound journey. Irrespective of conditions, we found ants exhibit a progressive search that drifted towards the active nest and beyond. Segments moving away from the start of the homeward journey were longer than segments heading back towards the start. The right tail distribution of segment lengths was well fitted by a power function, but slopes less than -3 on a log-log plot indicate that the process cannot be characterized as Lévy searches that have optimal slopes near –2. A double exponential function fits the distribution of segment lengths better, supporting another theoretically optimal search pattern, the composite Brownian walk.
Views, landmarks, and routes: how do desert ants negotiate an obstacle course?
Journal of Comparative Physiology A, 2011
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.
Non-numerical Distance and Size Effects in an Ant
Journal of Biology and Life Science, 2020
The distance effect (the fact that the individuals’ discrimination between two similar elements increases with the magnitude of the distance between them) as well as the size effect (the fact that the individuals’ discrimination between two similar elements decreases with the size of these elements) have been largely reported in vertebrates but not in invertebrates. Here, we demonstrate their existence in an ant, using operant conditioning to visual cues (black circles) of different dimensions. The two effects were obvious and differed from one another. Both effects could be accounted for Weber’s law, but it was here not tempted to verify if they are in line with this law by defining the just noticeable difference the ants can perceive between the cues.