Are ants sensitive to the geometry of tunnel bifurcation?

The ability to orient and navigate in space is essential for all animals whose home range is organized around a central point. Because of their small home range compared to vertebrates, central place foraging insects such as ants have for a long time provided a choice model for the study of orientation mechanisms. In many ant species, the movement of individuals on their colony home range is achieved essentially collectively, on the chemical trails laid down by their nest mates. In the initial stage of food recruitment, these trails can cross each other and thus form a network of interconnected paths in which ants have to orient. Previous simulation studies have shown that ants can find the shortest path between their nest and a food source in such a network only if there is a bias in the branch they choose when they reach an asymmetrical bifurcation. In this paper, we studied the choice of ants when facing either a symmetrical or an asymmetrical bifurcation between two tunnels. Ants were tested either on their way to a food source or when coming back to their nest, and either in the presence or in the absence of a chemical trail. Overall, our results show that the choice of an ant at a tunnel bifurcation depends more on the presence/absence of a trail pheromone than on the geometry of the bifurcation itself.     

Field response of acromyrmex crassispinus (forel) to aggression by atta sexdens (linn.) and predation by labidus praedator (fr. smith) (hymenoptera: Formicidae)

Aggression between colonies of the leaf-cutting ants, Acromyrmex crassispinus and Atta sexdens, was followed in the field. A. sexdens dominated the A. crassispinus nest, but did not overcome it. The A. crassispinus nest was subsequently raided by Labidus praedator, which took larvae and pupae without killing the colony. Aggression between the leaf-cutting ant colonies lasted 17 days. Microgyne production and nest displacement in the attacked A. crassispinus colony may be atrributed to stress.     

Ratio-dependent quantity discrimination in quorum sensing ants

To optimise behaviour, organisms require information on the quantity of various components of their environment, and the ability of animals to discriminate quantity has been a subject of considerable recent interest. This body of research hints at generalised mechanisms of quantity discrimination in vertebrates, but data on invertebrates are still relatively scarce. In this study, I present data on the quantification abilities of an invertebrate in a novel context: quorum sensing. Quorum sensing generates a behavioural response in group-living animals once a threshold number of individuals, a ‘quorum’, is detected performing some key action. This process forms the basis for consensus decision-making in many species and allows group-living organisms to decide among mutually exclusive alternatives without compromising group integrity. To determine when a quorum is achieved, individuals must assess the number of group members performing the key action. Social insects employ quorum decisions to decide among potential nest sites when searching for a new home. In the Japanese ant, Myrmecina nipponica, quorum thresholds increase with colony size, providing an opportunity to assess the accuracy of quantity discrimination at different stimulus magnitudes. In this study, I demonstrate that the variation in individual quorum thresholds around the mean increases with increasing colony size. This indicates that the quantity discrimination ability of ants decreases with stimulus magnitude, and thus exhibits ratio dependence in the manner of Weber’s Law. This may have implications for the accuracy of consensus decision-making and other collective actions in a range of group-living organisms.     

Not using the obvious: desert ants, Melophorus bagoti, learn local vectors but not beacons in an arena

Many ant species travel large distances to find food, sometimes covering distances that are up to one million times their body length. Even when these foraging trips follow convoluted paths, the ants usually find their way back to their nest with precision (Wehner et al. in J Exp Biol 199:129–140, 1996). Ants have been shown to use both compass cues in the sky (pattern of polarised light) and landmarks on Earth to return to their nest. We present two experiments conducted on a solitary foraging ant: Melophorus bagoti in their natural habitat in the central Australian desert. Ants were trained and tested in situ. We tested foragers’ ability to exit a circular arena which provided an undifferentiated panorama. Artificial visual landmarks were located near a small exit. On tests in which path integration information was not available, foragers did not use artificial landmarks as beacons. Instead, they oriented in the learned exit direction, whether or not it pointed to the nest. We suggest that M. bagoti foragers learned a context-specific local vector when cued by the context of the circular arena. Our findings present the first evidence that M. bagoti foragers learn context-specific compass directions to chart their initial path home.     

Injury shortens life expectancy in ants and affects some risk-related decisions of workers

Animal Cognition - The Formica cinerea ants are known to be highly territorial and aggressively defend their nest and foraging areas against other ants. During the foraging, workers engage in...     

Idiosyncratic route-based memories in desert ants, Melophorus bagoti: how do they interact with path-integration vectors?

Individually foraging desert ants of central Australia, Melophorus bagoti, exhibit amazingly precise mechanisms of visual landmark guidance when navigating through cluttered environments. If trained to shuttle back and forth between the nest and a feeder, they establish habitual outbound and inbound routes, which guide them idiosyncratically across the natural maze of extended arrays of grass tussocks covering their foraging areas. The route-based memories that usually differ between outbound and inbound runs are acquired already during the first runs to the nest and feeder. If the ants are displaced sideways of their habitual routes, they can enter their stereotyped routes at any place and then follow these routes with the same accuracy as if they had started at the usual point of departure. Furthermore, the accuracy of maintaining a route does not depend on whether homebound ants have been captured at the feeder shortly before starting their home run and, hence, with their home vector still fully available (full-vector ants), or whether they have been captured at the nest after they had already completed their home run (zero-vector ants). Hence, individual landmark memories can be retrieved independently of the state of the path-integration vector with which they have been associated during the acquisition phase of learning. However, the ants display their path-integration vector when displaced from the feeder to unfamiliar territory.     

Visual discrimination,sequential learning and memory retrieval in the Australian desert ant <Emphasis Type="Italic">Melophorus bagoti</Emphasis>

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.     

Rapid spatial learning in a velvet ant (<Emphasis Type="Italic">Dasymutilla coccineohirta</Emphasis>)

Spatial learning has been examined in a variety of animals to determine what cues are used to navigate through a complex environment. A common feature of previously studied vertebrates and invertebrates is their need to return to a previously visited site for mating, nesting, foraging or predator avoidance. Velvet ants (Hymenoptera: Mutillidae) are cursorial parasitoids with flightless females that must walk through complex terrain to find ground dwelling host larvae burrows. Velvet ants are not central-place foragers (they do not return to an established nest site) so much of the previous work on spatial learning does not directly apply in this context. It was assumed that females primarily use chemosensory cues for navigation and burrow location instead of visual learning. This study, however, demonstrates that velvet ant females are able to use visual landmarks to find an inconspicuous exit in an aversion-motivation spatial learning task. A significant number of velvet ants learned to locate the exit after seven training trials and went to the previous location of the exit even after the maze had been rotated, showing that landmarks external to the maze were used to learn the escape location.     

Aggression in wood ants (Formica polyctena Foerst., Hymenoptera,Formicidae)

The relationship between aggression and predation was surveyed in Red wood ants, in the field as well as under laboratory conditions. Aggression between wood ant nests is highest in early spring, and many wood ant wars break out then. The end of these wars coincides with a strong increase in prey density. Since the casualties are taken as food to the warring nests, a hypothesis is formulated that warfare between wood ant nests only occurs in periods when prey demand exceeds the supply. Protein-rich food in early spring is mainly for the benefit of the queens and the sexual larvae. Although the most obvious function of warfare is the defence of a foraging area, the main function may be the advancement of the mating flight dates of the queens in order to make the chance of propagating their genes greatest.     

The Effect of Stress on Spontaneous Nest Leaving Behavior in the Mouse: An Improved Model of Stress-Induced Behavioral Pathology

The present experiments were conducted to develop a more sensitive and reliable model of stress-induced behavioral pathology in the mouse. Male mice were housed singly in nest cages connected to either a circular tunnel, a recreational cage or a large box with food foraging apparatus. Spontaneous nocturnal out of nest activity or food foraging behavior in these environments was continuously monitored for a two week period during which time the effects of stress were examined. It was found that both repeated restraint and aggression stress markedly and persistently reduced out of nest nocturnal activity or food foraging behavior in all 3 environments but did not alter activity in a novel open field or plus maze or food or saccharin intake in the nest cage. In a preliminary experiment the reduction in out of nest activity by stress was attenuated by prior chronic treatment with the antidepressant, desmethylimipramine. Plasma corticosterone was elevated immediately after aggression stress but reduced 5 hr after chronic aggression stress. The reduction in activity did not appear the result of increased anxiety as measured by spontaneous risk assessment behavior in the nest. It is concluded that the decrease in out of nest activity after stress in the present studies models a withdrawn behavioral state and may be due to either or both a decrease in appetitive motivation to leave the nest or an increased aversion to the external environment which does not apparently involve anxiety.     

Growth and pruning of mushroom body Kenyon cell dendrites during worker behavioral development in the paper wasp, Polybia aequatorialis (Hymenoptera: Vespidae)

Adult workers of some social insect species show dramatic behavioral changes as they pass through a sequence of task specializations. In the paper wasp, Polybia aequatorialis, female workers begin adult life within the nest tending brood, progress to maintaining and defending the nest exterior, and ultimately leave the nest to forage. The mushroom body (MB) calyx neuropil increases in volume as workers progress from in-nest to foraging tasks. In other social Hymenoptera (bees and ants), MB Kenyon cell dendrites, axons and synapses change with the transition to foraging, but these neuronal effects had not been studied in wasps. Furthermore, the on-nest worker of Polybia wasps, an intermediate task specialization not identified in bees or ants, provides the opportunity to study pre-foraging worker class transitions. We asked whether Kenyon cell dendritic arborization varies with the task specialization of Polybia workers observed in the field near Monteverde, Costa Rica. Golgi-impregnated arbors in the lip and collar calyces, which receive a predominance of olfactory and visual input, respectively, were quantified using Sholl’s concentric circles and a novel application of virtual spherical probes. Arbors of the lip varied in a manner reminiscent of honeybees, with foragers having the largest and in-nest workers having the smallest arbors. In contrast, arbors of the collar were largest in foragers but smallest in on-nest workers. Thus, progression through task specializations in P. aequatorialis involves subregion specific dendritic growth and regression in the MB neuropil. These results may reflect the sensitivity of Kenyon cell dendritic structure to specialization dependent social and sensory experience.     

The contribution of private and public information in foraging by Australasian gannets

Predators that forage on foods with temporally and spatially patchy distributions may rely on private or public sources of information to enhance their chances of foraging success. Using GPS tracking, field observations, and videography, we examined potential sites and mechanisms of information acquisition in departures for foraging trips by colonially breeding Australasian gannets (Morus serrator). Analyses of the bill-fencing ceremony between mated pairs of breeding gannets did not detect correlations between parameters of this reciprocal behavior and foraging trips, as would have been predicted if gannets used this behavior as a source of private information. Instead, 60 % of the departing birds flew directly to join water rafts of other conspecific en route to the feeding grounds. The departure of solitary birds from the water rafts was synchronized (within 60 s) with the arrival of incoming foragers and also among departing birds. Furthermore, solitary departing birds from the rafts left in the same directional quadrant (90º slices) as the prior arriving (67 %) and also prior departing forager (79 %). When associated plunge dives of conspecific were visible from the colony, providing a public source of information, gannets more often departed from the water rafts in groups. Our study thus provides evidence for the use of water rafts, but not the nest site, as locations of information transfer, and also confirms the use of local enhancement as a strategy for foraging flights by Australasian gannets.     

Foraging in a simulated natural environment: There's a rat loose in the lab

Rats were required to earn their food in a large room having nine boxes placed in it, each of which contained food buried in sand. In different phases of the experiment the amount of time allowed for foraging, the amount of food available in each food patch, and the location of the different available amounts were varied. The rats exhaustively sampled all patches each session but seemed to have fairly strong preferences for certain locations over others. If position preferences were for patches containing small amounts of food, the sensitivity to amount available was increased so that when location was compensated for, a pattern of optimal foraging was evident. The importance of environmental constraints in producing optimal behavior and the relation of the observed behavior to laboratory findings are discussed.     

Attack and defensive behaviors in the albino mouse

Attack by dominant male colony mice on intruders included chasing and lateral attack behaviors, while the corresponding intruder behaviors were flight, boxing, and checking. Both of these are similar to the attack and defensive behaviors of colony rats and intruders. However, mice did not show a significant constraint on bites to ventral areas, and the rat defensive behavior of lying on the back, which is effective because of this constraint, was rare; the corresponding “on-top” behavior of attackers was almost absent in mice. These findings strongly support the view that intraspecific attack and defensive behaviors, and target sites for bites, are interrelated factors facilitating effective but nonlethal agonistic interactions in muroid rodents.     

Bee-eaters (<Emphasis Type="Italic">Merops orientalis</Emphasis>) respond to what a predator can see

Two sets of experiments are reported that show that the small green bee-eater (Merops orientalis, a small tropical bird) can appreciate what a predator can or cannot see. Bee-eaters avoid entering the nest in the presence of a potential nest predator. In the first set of experiments bee-eaters entered the nest more frequently when the predator was unable to see the nest from its position, as compared to an approximately equidistant position from which the nest could be seen. In the second set of experiments bee-eaters entered the nest more frequently when the predator was looking away from the nest. The angle of gaze from the nest was associated significantly positively with the probability of entering the nest whereas the angle from the bird was not. Birds showed considerable flexibility as well as individual variation in the possible methods of judging the predator's position and direction of gaze. Electronic Publication     

Orangutans (Pongo abelii) "play the odds": information-seeking strategies in relation to cost, risk, and benefit

Recent research has examined whether animals possess metacognition, or the ability to monitor their knowledge states. However, the extent to which animals actively control their knowledge states is still not well delineated. Although organisms might be capable of seeking information when it is lacking, it does not mean that it is always adaptive to do so. In the present set of experiments, we examined the flexibility of this behavior in captive orangutans (Pongo abelii; two adults and one juvenile) in a foraging task, by varying the necessity of information-seeking, the cost associated with it, the likelihood of error, and the value of the reward. In Experiment 1, subjects searched for information most often when it was "cheapest" energetically. In Experiment 2, subjects searched for information most often when the odds of making an error were the greatest. In Experiment 3, subjects searched for information more when the reward was doubled in value. In Experiment 4, adult subjects adapted to risk/benefit trade-offs in their searching behavior. In every experiment, subjects sought information more often when they needed it than when they already knew the solution to the problem. Therefore, the current research suggests that information-seeking behavior in orangutans shows a sophisticated level of flexibility, comparable to that seen in human children, as they appear to "play the odds" when making the decision to seek information or not.     

Perception of Maximum Reaching Height When the Means of Reaching Are No Longer in View

Previous research has shown that perception of maximum reaching height is relative to reaching ability even when the means of performing this behavior would bring about (future) changes in reaching ability. Two experiments investigate whether this continues to be the case even when the means of reaching are no longer in view. The results show perception of maximum reaching height reflects impending changes to reaching ability both when the means of performing the reaching task (and changing reaching ability) are present and when they are no longer in view. The results are discussed in the context of prospectivity, retrospectivity, and flexibility—3 fundamental hallmarks of goal-directed behavior.     

Geometry, features, and panoramic views: ants in rectangular arenas

When tested in rectangular arenas, the navigational behavior of the ant Gigantiops destructor can produce results similar to vertebrates. Such results are usually interpreted as supporting the ability of animals to segregate spatial geometry and features. Here, we combine a detailed analysis of ants' paths with panoramic images taken from the ant's perspective that can serve as a basis for developing view-based matching models. The corner choices observed in ants were better predicted by the use of panoramic views along with a simple matching process [rotational image difference function (rIDF)] than by models assuming segregation of geometry and features (G/F). Our view-based matching model could also explain some aspects of the ants' path (i.e., initial direction, length) resulting from the different visual conditions, suggesting that ants were using such a taxon-like strategy. Analyzed at the individual level, the results show that ants' idiosyncratic paths tend to evolve gradually from trial to trial, revealing that the ants were partially updating their route memory after each trial. This study illustrates the remarkable flexibilities that can arise from the use of taxon-like strategies and stresses the importance of considering them in vertebrates.     

Capacitive sensors for detecting proximity and response

We have implemented an inexpensive circuit that indicates when a subject is in close proximity to a specified area of arbitrary shape and size. The circuit can transform an easily created metal surface or a preexisting metal object into an experimental sensor. The subject need not make physical contact with the sensor to activate the mechanism, which enables the detection of subjects through nonconductive materials, such as wood and plastics. The technology is readily adapted to existing experimental setups. Applications of this technology, using pigeons, rats, and mice, demonstrate its flexibility: a nose-poke/peck sensor for response or choice detection; a subject location detector that can be placed on a floor, wall, or ceiling; and a perch that detects when a bird is present. This technology can also be applied to the study of behavior in primates and many other animal species.     

Female degus (Octodon degus) monitor their environment while foraging socially

Vigilance or scanning involves interruptions in foraging behavior when individuals lift their heads and conduct visual monitoring of the environment. Theoretical considerations assume that foraging with the "head down", and scanning ("head up") are mutually exclusive activities, such that foraging precludes vigilance. We tested this generalization in a socially foraging, small mammal model, the diurnal Chilean degu (Octodon degus). We studied spontaneous bouts of scanning of captive degus when foraging in pairs of female sibs and non-sibs. We examined the extent to which foraging (head down postures) and scanning (head up postures) were mutually exclusive in subjects exposed to none, partial, and complete lateral visual obstruction of their partners. In addition, we monitored the orientation of their bodies to examine the target of attention while foraging and scanning. Lastly, we examined the temporal occurrence of scanning events to assess the extent of scanning coordination, and whether this coordination is kin-biased. Visual obstruction had a significant influence on degu vigilance. Focal degus increased their quadrupedal and semi-erect scanning when foraging under a partially obstructed view of their partners. Degus oriented their bodies toward partners when foraging and scanning. Despite this, degus did not coordinate scanning bouts; instead, they scanned independently from one another. Relatedness among cage mates did not influence any aspect of degu behavior. Contrary to theoretical expectations, these results indicate that foraging and vigilance are not mutually exclusive, and that kinship per se does not influence scanning behavior and coordination.