Wüstennavigatoren en miniature

Desert navigators en miniature Cataglyphis, a strictly diurnal, heat‐tolerant, high‐speed desert ant, employs a path integrator as its main navigational means. By continually measuring directions steered and distances covered the path integrator computes a navigation vector, which can lead the ant directly back to its central place, the nest, and to any point which it has visited before. The path integration vector receives compass information from the pattern of polarized light in the sky (via a set of specialized photoreceptors at the dorsal rim of the eye), and derives information about travel distance from a stride integrator (pedometer) and an optic‐flow meter exploiting self‐induced image motion across the ventral retina. The path integrator is fully functional already at the beginning of the ant's foraging life. Later it keeps running whenever the ant is on a foraging excursion irrespective of whether other navigational tools are at work as well. Finally it provides a scaffold for landmark learning. View‐based landmark information is acquired by taking panoramic “snapshots” at certain places and routes. By comparing this memorized visual information with the actual one received during later journeys the ants are able to return to familiar places and to follow familiar routes even without the aid of the path integrator. The ant's navigational performances known to date can be simulated by designing a decentralized network, in which the individual tools are interconnected in flexible and context dependent ways.     

Evaluating the Strange Situation Procedure (SSP) to Assess the Bond between Dogs and Humans

The Strange Situation Procedure (SSP) is increasingly being used to study attachment between dogs and humans. It has been developed from the Ainsworth Strange Situation Procedure, which is used extensively to investigate attachment between children and their parents. In this experiment, 12 female beagle dogs were tested in two treatments to identify possible order effects in the test, a potential weakness in the SSP. In one treatment (FS), dogs participated together with a ‘familiar person’ and a ‘stranger’. In a control treatment (SS), the same dogs participated together with two unfamiliar people, ‘stranger A’ and ‘stranger B’. Comparisons were made between episodes within as well as between treatments. As predicted in FS, dogs explored more in the presence of the familiar person than the stranger. Importantly, they also explored more in the presence of stranger A (who appeared in the same order as the familiar person and followed the same procedure) than stranger B in SS. Furthermore, comparisons between treatments, where a familiar person was present in FS and stranger A was present in SS, showed no differences in exploration. In combination, these results indicate that the effect of a familiar person on dogs'' exploratory behaviour, a key feature when assessing secure attachment styles, could not be tested reliably due to the order in which the familiar person and the stranger appear. It is proposed that in the future only counterbalanced versions of the SSP are used. Alternatively, since dogs reliably initiated more contact with the familiar person compared to the strangers, it is suggested that future studies on attachment in dogs towards humans should focus either on the behaviour of the dog in those episodes of the SSP when the person returns, or on reunion behaviour in other studies, specially designed to address dog-human interactions at this time.     

A dynamic over games drives selfish agents to win–win outcomes

Understanding human institutions, animal cultures and other social systems requires flexible formalisms that describe how their members change them from within. We introduce a framework for modelling how agents change the games they participate in. We contrast this between-game ‘institutional evolution’ with the more familiar within-game ‘behavioural evolution’. We model institutional change by following small numbers of persistent agents as they select and play a changing series of games. Starting from an initial game, a group of agents trace trajectories through game space by navigating to increasingly preferable games until they converge on ‘attractor’ games. Agents use their ‘institutional preferences'' for game features (such as stability, fairness and efficiency) to choose between neighbouring games. We use this framework to pose a pressing question: what kinds of games does institutional evolution select for; what is in the attractors? After computing institutional change trajectories over the two-player space, we find that attractors have disproportionately fair outcomes, even though the agents who produce them are strictly self-interested and indifferent to fairness. This seems to occur because game fairness co-occurs with the self-serving features these agents do actually prefer. We thus present institutional evolution as a mechanism for encouraging the spontaneous emergence of cooperation among small groups of inherently selfish agents, without space, reputation, repetition, or other more familiar mechanisms. Game space trajectories provide a flexible, testable formalism for modelling the interdependencies of behavioural and institutional evolutionary processes, as well as a mechanism for the evolution of cooperation.     

Looking and homing: how displaced ants decide where to go

We caught solitary foragers of the Australian Jack Jumper ant, Myrmecia croslandi, and released them in three compass directions at distances of 10 and 15 m from the nest at locations they have never been before. We recorded the head orientation and the movements of ants within a radius of 20 cm from the release point and, in some cases, tracked their subsequent paths with a differential GPS. We find that upon surfacing from their transport vials onto a release platform, most ants move into the home direction after looking around briefly. The ants use a systematic scanning procedure, consisting of saccadic head and body rotations that sweep gaze across the scene with an average angular velocity of 90° s⁻¹ and intermittent changes in turning direction. By mapping the ants’ gaze directions onto the local panorama, we find that neither the ants’ gaze nor their decisions to change turning direction are clearly associated with salient or significant features in the scene. Instead, the ants look most frequently in the home direction and start walking fast when doing so. Displaced ants can thus identify home direction with little translation, but exclusively through rotational scanning. We discuss the navigational information content of the ants’ habitat and how the insects’ behaviour informs us about how they may acquire and retrieve that information.     

The Effect of Trail Pheromone and Path Confinement on Learning of Complex Routes in the Ant Lasius niger

Route learning is key to the survival of many central place foragers, such as bees and many ants. For ants which lay pheromone trails, the presence of a trail may act as an important source of information about whether an error has been made. The presence of trail pheromone has been demonstrated to support route learning, and the effect of pheromones on route choice have been reported to persist even after the pheromones have been removed. This could be explained in two ways: the pheromone may constrain the ants onto the correct route, thus preventing errors and aiding learning. Alternatively, the pheromones may act as a ‘reassurance’, signalling that the learner is on the right path and that learning the path is worthwhile. Here, we disentangle pheromone presence from route confinement in order to test these hypotheses, using the ant Lasius niger as a model. Unexpectedly, we did not find any evidence that pheromones support route learning. Indeed, there was no evidence that ants confined to the correct route learned at all. Thus, while we cannot support the ‘reassurance’ hypothesis, we can rule out the ‘confinement’ hypothesis. Other findings, such as a reduction in pheromone deposition in the presence of trail pheromones, are remarkably consistent with previous experiments. As previously reported, ants which make errors on their outward journey upregulate pheromone deposition on their return. Surprisingly, ants which would go on to make an error down-regulate pheromone deposition on their outward journey, hinting at a capacity for ants to gauge the quality of their own memories.     

Age‐dependent and task‐related volume changes in the mushroom bodies of visually guided desert ants,Cataglyphis bicolor

Desert ants of the genus Cataglyphis are skillful long‐distance navigators employing a variety of visual navigational tools such as skylight compasses and landmark guidance mechanisms. However, the time during which this navigational toolkit comes into play is extremely short, as the average lifetime of a Cataglyphis forager lasts for only about 6 days. Here we show, by using immunohistochemistry, confocal microscopy, and three‐dimensional reconstruction software, that even during this short period of adult life, Cataglyphis exhibits a remarkable increase in the size of its mushroom bodies, especially of the visual input region, the collar, if compared to age‐matched dark‐reared animals. This task‐related increase rides on a much smaller age‐dependent increase of the size of the mushroom bodies. Due to the variation in body size exhibited by Cataglyphis workers we use allometric analyses throughout and show that small animals exhibit considerably larger task‐related increases in the sizes of their mushroom bodies than larger animals do. It is as if there were an upper limit of mushroom body size required for accomplishing the ant's navigational tasks. © 2006 Wiley Periodicals, Inc. J Neurobiol, 2006     

Scene perception and the visual control of travel direction in navigating wood ants

This review reflects a few of Mike Land''s many and varied contributions to visual science. In it, we show for wood ants, as Mike has done for a variety of animals, including readers of this piece, what can be learnt from a detailed analysis of an animal''s visually guided eye, head or body movements. In the case of wood ants, close examination of their body movements, as they follow visually guided routes, is starting to reveal how they perceive and respond to their visual world and negotiate a path within it. We describe first some of the mechanisms that underlie the visual control of their paths, emphasizing that vision is not the ant''s only sense. In the second part, we discuss how remembered local shape-dependent and global shape-independent features of a visual scene may interact in guiding the ant''s path.     

Genetic composition of social groups influences male aggressive behaviour and fitness in natural genotypes of Drosophila melanogaster

Indirect genetic effects (IGEs) describe how an individual''s behaviour—which is influenced by his or her genotype—can affect the behaviours of interacting individuals. IGE research has focused on dyads. However, insights from social networks research, and other studies of group behaviour, suggest that dyadic interactions are affected by the behaviour of other individuals in the group. To extend IGE inferences to groups of three or more, IGEs must be considered from a group perspective. Here, I introduce the ‘focal interaction’ approach to study IGEs in groups. I illustrate the utility of this approach by studying aggression among natural genotypes of Drosophila melanogaster. I chose two natural genotypes as ‘focal interactants’: the behavioural interaction between them was the ‘focal interaction’. One male from each focal interactant genotype was present in every group, and I varied the genotype of the third male—the ‘treatment male’. Genetic variation in the treatment male''s aggressive behaviour influenced the focal interaction, demonstrating that IGEs in groups are not a straightforward extension of IGEs measured in dyads. Further, the focal interaction influenced male mating success, illustrating the role of IGEs in behavioural evolution. These results represent the first manipulative evidence for IGEs at the group level.     

Individual-learning ability predicts social-foraging strategy in house sparrows

Social foragers can use either a ‘producer’ strategy, which involves searching for food, or a ‘scrounger’ strategy, which involves joining others'' food discoveries. While producers rely on personal information and past experience, we may ask whether the tendency to forage as a producer is related to being a better learner. To answer this question, we hand-raised house sparrow (Passer domesticus) nestlings that upon independence were given an individual-learning task that required them to associate colour signal and food presence. Following the testing phase, all fledglings were released into a shared aviary, and their social-foraging tendencies were measured. We found a significant positive correlation between individual''s performance in the individual-learning task and subsequent tendency to use searching (producing) behaviour. Individual-learning score was negatively correlated with initial fear of the test apparatus and with body weight. However, the correlation between individual learning and searching remained significant after controlling for these variables. Since it was measured before the birds entered a social group, individual-learning ability could not be the outcome of being a producer. However, the two traits may be initially associated, or individual learning could facilitate producing behaviour. To our knowledge, this is the first evidence that associates individual-learning abilities with social-foraging strategies in animal groups.     

Power through ‘Us’: Leaders’ Use of We-Referencing Language Predicts Election Victory

Leaders have been observed to use distinct rhetorical strategies, but it is unclear to what extent such strategies are effective. To address this issue we analyzed the official election campaign speeches of successful and unsuccessful Prime Ministerial candidates in all 43 Australian Federal elections since independence from Britain in 1901 and measured candidates'' use of personal (‘I’, ‘me’) and collective pronouns (‘we’, ‘us’). Victors used more collective pronouns than their unsuccessful opponents in 80% of all elections. Across all elections, victors made 61% more references to ‘we’ and ‘us’ and used these once every 79 words (vs. every 136 words for losers). Extending social identity theorizing, this research suggests that electoral endorsement is associated with leaders'' capacity to engage with, and speak on behalf of, a collective identity that is shared with followers whose support and energies they seek to mobilize.     

The Effects of Extra-Somatic Weapons on the Evolution of Human Cooperation towards Non-Kin

Human cooperation and altruism towards non-kin is a major evolutionary puzzle, as is ‘strong reciprocity’ where no present or future rewards accrue to the co-operator/altruist. Here, we test the hypothesis that the development of extra-somatic weapons could have influenced the evolution of human cooperative behaviour, thus providing a new explanation for these two puzzles. Widespread weapons use could have made disputes within hominin groups far more lethal and also equalized power between individuals. In such a cultural niche non-cooperators might well have become involved in such lethal disputes at a higher frequency than cooperators, thereby increasing the relative fitness of genes associated with cooperative behaviour. We employ two versions of the evolutionary Iterated Prisoner''s Dilemma (IPD) model – one where weapons use is simulated and one where it is not. We then measured the performance of 25 IPD strategies to evaluate the effects of weapons use on them. We found that cooperative strategies performed significantly better, and non-cooperative strategies significantly worse, under simulated weapons use. Importantly, the performance of an ‘Always Cooperate’ IPD strategy, equivalent to that of ‘strong reciprocity’, improved significantly more than that of all other cooperative strategies. We conclude that the development of extra-somatic weapons throws new light on the evolution of human altruistic and cooperative behaviour, and particularly ‘strong reciprocity’. The notion that distinctively human altruism and cooperation could have been an adaptive trait in a past environment that is no longer evident in the modern world provides a novel addition to theory that seeks to account for this major evolutionary puzzle.     

Social network- and community-level influences on contraceptive use: evidence from rural Poland

The diffusion of ‘modern’ contraceptives—as a proxy for the spread of low-fertility norms—has long interested researchers wishing to understand global fertility decline. A fundamental question is how local cultural norms and other people''s behaviour influence the probability of contraceptive use, independent of women''s socioeconomic and life-history characteristics. However, few studies have combined data at individual, social network and community levels to simultaneously capture multiple levels of influence. Fewer still have tested if the same predictors matter for different contraceptive types. Here, we use new data from 22 high-fertility communities in Poland to compare predictors of the use of (i) any contraceptives—a proxy for the decision to control fertility—with those of (ii) ‘artificial’ contraceptives—a subset of more culturally taboo methods. We find that the contraceptive behaviour of friends and family is more influential than are women''s own characteristics and that community level characteristics additionally influence contraceptive use. Highly educated neighbours accelerate women''s contraceptive use overall, but not their artificial method use. Highly religious neighbours slow women''s artificial method use, but not their contraceptive use overall. Our results highlight different dimensions of sociocultural influence on contraceptive diffusion and suggest that these may be more influential than are individual characteristics. A comparative multilevel framework is needed to understand these dynamics.     

Regime shifts in exploited marine food webs: detecting mechanisms underlying alternative stable states using size-structured community dynamics theory

Many marine ecosystems have undergone ‘regime shifts’, i.e. abrupt reorganizations across trophic levels. Establishing whether these constitute shifts between alternative stable states is of key importance for the prospects of ecosystem recovery and for management. We show how mechanisms underlying alternative stable states caused by predator–prey interactions can be revealed in field data, using analyses guided by theory on size-structured community dynamics. This is done by combining data on individual performance (such as growth and fecundity) with information on population size and prey availability. We use Atlantic cod (Gadus morhua) and their prey in the Baltic Sea as an example to discuss and distinguish two types of mechanisms, ‘cultivation-depensation’ and ‘overcompensation’, that can cause alternative stable states preventing the recovery of overexploited piscivorous fish populations. Importantly, the type of mechanism can be inferred already from changes in the predators'' body growth in different life stages. Our approach can thus be readily applied to monitored stocks of piscivorous fish species, for which this information often can be assembled. Using this tool can help resolve the causes of catastrophic collapses in marine predatory–prey systems and guide fisheries managers on how to successfully restore collapsed piscivorous fish stocks.     

Never Say No … How the Brain Interprets the Pregnant Pause in Conversation

In conversation, negative responses to invitations, requests, offers, and the like are more likely to occur with a delay–conversation analysts talk of them as dispreferred. Here we examine the contrastive cognitive load ‘yes’ and ‘no’ responses make, either when relatively fast (300 ms after question offset) or delayed (1000 ms). Participants heard short dialogues contrasting in speed and valence of response while having their EEG recorded. We found that a fast ‘no’ evokes an N400-effect relative to a fast ‘yes’; however, this contrast disappeared in the delayed responses. ''No'' responses, however, elicited a late frontal positivity both if they were fast and if they were delayed. We interpret these results as follows: a fast ‘no’ evoked an N400 because an immediate response is expected to be positive–this effect disappears as the response time lengthens because now in ordinary conversation the probability of a ‘no’ has increased. However, regardless of the latency of response, a ‘no’ response is associated with a late positivity, since a negative response is always dispreferred. Together these results show that negative responses to social actions exact a higher cognitive load, but especially when least expected, in immediate response.     

Kompass im Kopf

Ant compass – how desert ants learn to navigate Successful spatial orientation is a daily challenge for many animals. Cataglyphis desert ants are famous for their navigational performances. They return to the nest after extensive foraging trips without any problems. How do ants take their navigational systems into operation? After conducting different tasks in the dark nest for several weeks, they become foragers under bright sun light. This transition requires both a drastic switch in behavior and neuronal changes in the brain. Experienced foragers mainly rely on visual cues. They use a celestial compass and landmark panoramas. For that reason, naïve ants perform stereotype learning walks to calibrate their compass systems and acquire information about the nest's surroundings. During their learning walks, the ants frequently look back to the nest entrance to learn the homing direction. For aligning their gazes, they use the earth's magnetic field as a compass reference. This magnetic compass in Cataglyphis ants was previously unknown.     

Local vectors in desert ants: context-dependent landmark learning during outbound and homebound runs

Desert ants, Cataglyphis fortis, associate nestward-directed vector memories (local vectors) with the sight of landmarks along a familiar route. This view-based navigational strategy works in parallel to the self-centred path integration system. In the present study we ask at what temporal stage during a foraging journey does the ant acquire nestward-directed local vector information from feeder-associated landmarks: during its outbound run to a feeding site or during its homebound run to the nest. Tests performed after two reversed-image training paradigms revealed that the ants associated such vectors exclusively with landmarks present during their homebound runs.     

Nest Etiquette—Where Ants Go When Nature Calls

Sanitary behaviour is an important, but seldom studied, aspect of social living. Social insects have developed several strategies for dealing with waste and faecal matter, including dumping waste outside the nest and forming specialised waste-storage chambers. In some cases waste material and faeces are put to use, either as a construction material or as a long-lasting signal, suggesting that faeces and waste may not always be dangerous. Here we examine a previously undescribed behaviour in ants – the formation of well-defined faecal patches. Lasius niger ants were housed in plaster nests and provided with coloured sucrose solution. After two months, 1–4 well defined dark patches, the colour of the sucrose solution, formed within each of the plaster nests. These patches never contained other waste material such as uneaten food items, or nestmate corpses. Such waste was collected in waste piles outside the nest. The coloured patches were thus distinct from previously described ‘kitchen middens’ in ants, and are best described as ‘toilets’. Why faeces is not removed with other waste materials is unclear. The presence of the toilets inside the nest suggests that they may not be an important source of pathogens, and may have a beneficial role.     

Distributed Patterns of Event-Related Potentials Predict Subsequent Ratings of Abstract Stimulus Attributes

Exposure to pleasant and rewarding visual stimuli can bias people''s choices towards either immediate or delayed gratification. We hypothesised that this phenomenon might be based on carry-over effects from a fast, unconscious assessment of the abstract ‘time reference’ of a stimuli, i.e. how the stimulus relates to one''s personal understanding and connotation of time. Here we investigated whether participants'' post-experiment ratings of task-irrelevant, positive background visual stimuli for the dimensions ‘arousal’ (used as a control condition) and ‘time reference’ were related to differences in single-channel event-related potentials (ERPs) and whether they could be predicted from spatio-temporal patterns of ERPs. Participants performed a demanding foreground choice-reaction task while on each trial one task-irrelevant image (depicting objects, people and scenes) was presented in the background. Conventional ERP analyses as well as multivariate support vector regression (SVR) analyses were conducted to predict participants'' subsequent ratings. We found that only SVR allowed both ‘arousal’ and ‘time reference’ ratings to be predicted during the first 200 ms post-stimulus. This demonstrates an early, automatic semantic stimulus analysis, which might be related to the high relevance of ‘time reference’ to everyday decision-making and preference formation.