A positive effect of flowers rather than eye images in a large-scale, cross-cultural dictator game

People often consider how their behaviour will be viewed by others, and may cooperate to avoid gaining a bad reputation. Sensitivity to reputation may be elicited by subtle social cues of being watched: previous studies have shown that people behave more cooperatively when they see images of eyes rather than control images. Here, we tested whether eye images enhance cooperation in a dictator game, using the online labour market Amazon Mechanical Turk (AMT). In contrast to our predictions and the results of most previous studies, dictators gave away more money when they saw images of flowers rather than eye images. Donations in response to eye images were not significantly different to donations under control treatments. Dictator donations varied significantly across cultures but there was no systematic variation in responses to different image types across cultures. Unlike most previous studies, players interacting via AMT may feel truly anonymous when making decisions and, as such, may not respond to subtle social cues of being watched. Nevertheless, dictators gave away similar amounts as in previous studies, so anonymity did not erase helpfulness. We suggest that eye images might only promote cooperative behaviour in relatively public settings and that people may ignore these cues when they know their behaviour is truly anonymous.     

No Evidence for Audience Effects in Reciprocal Cooperation of Norway Rats

Norway rats (Rattus norvegicus) cooperate according to indirect reciprocity, which implies the involvement of a reputation mechanism. Here, we test whether the rats employ such mechanism in repeated cooperative interactions. Focal subjects were first trained individually to pull food towards a social partner. During the experiment, the focal rats were confronted with two types of trained social partners: one always cooperated and the other one always defected, either in the presence or in the absence of an audience. Based on the hypotheses that the rats possess a reputation mechanism involving image scoring, we predicted them to be more helpful in the presence of an audience, independently of the partner's cooperative behaviour. If, in contrast, reputation involved a standing strategy, we predicted the rats to distinguish more between cooperators and defectors in the presence of an audience than in its absence. The rats helped cooperative partners more than defectors, but against both predictions the presence or absence of an audience did not influence their helping propensity. This indicates that either reputation is not included in the decision of rats to help an individual that has helped others, or that reputation is neither involving image scoring nor a standing strategy. Although the rats have been shown to modulate their decision to help a social partner based on its helpful behaviour towards others, they do not seem to adjust their behaviour strategically to the presence of an audience.     

Rejection of unfair offers can be driven by negative emotions, evidence from modified ultimatum games with anonymity

The rejection of unfair offers can be affected by both negative emotions (e.g. anger and moral disgust) and deliberate cognitive processing of behavioral consequences (e.g. concerns of maintaining social fairness and protecting personal reputation). However, whether negative emotions are sufficient to motivate this behavior is still controversial. With modified ultimatum games, a recent study (Yamagishi T, et al. (2009) Proc Natl Acad Sci USA 106:11520-11523) found that people reject unfair offers even when this behavior increases inequity, and even when they could not communicate to the proposers. Yamagishi suggested that rejection of unfair offers could occur without people's concerning of maintaining social fairness, and could be driven by negative emotions. However, as anonymity was not sufficiently guaranteed in Yamagishi's study, the rejection rates in their experiments may have been influenced by people's concerns of protecting personal reputation (reputational concerns) in addition to negative emotions; thus, it was unclear whether the rejection was driven by negative emotions, or by reputational concerns, or both. In the present study, with specific methods to ensure anonymity, the effect of reputational concerns was successfully ruled out. We found that in a private situation in which rejection could not be driven by reputational concerns, the rejection rates of unfair offers were significantly larger than zero, and in public situations in which rejection rates could be influenced by both negative emotions and reputational concerns, rejection rates were significantly higher than that in the private situation. These results, together with Yamagishi's findings, provided more complete evidence suggesting (a) that the rejection of unfair offers can be driven by negative emotions and (b) that deliberate cognitive processing of the consequences of the behavior can increase the rejection rate, which may benefit social cooperation.     

Public charity offer as a proximate factor of evolved reputation-building strategy: an experimental analysis of a real-life situation

Although theoretical considerations suggest that a considerable portion of human altruism is driven by concerns about reputation, few experimental studies have examined the psychological correlates of individual decisions in real-life situations. Here we demonstrate that more subjects were willing to give assistance to unfamiliar people in need if they could make their charity offers in the presence of their group mates than in a situation where the offers remained concealed from others. In return, those who were willing to participate in a particular charitable activity received significantly higher scores than others on scales measuring sympathy and trustworthiness. Finally, a multiple regression analysis revealed that while several personality and behavior traits (cooperative ability, Machiavellianism, sensitivity to norms, and sex) play a role in the development of prosocial behavior, the possibility of gaining reputation within the group remains a measurable determinant of charitable behavior.     

Benevolent Characteristics Promote Cooperative Behaviour among Humans

Cooperation is fundamental to the evolution of human society. We regularly observe cooperative behaviour in everyday life and in controlled experiments with anonymous people, even though standard economic models predict that they should deviate from the collective interest and act so as to maximise their own individual payoff. However, there is typically heterogeneity across subjects: some may cooperate, while others may not. Since individual factors promoting cooperation could be used by institutions to indirectly prime cooperation, this heterogeneity raises the important question of who these cooperators are. We have conducted a series of experiments to study whether benevolence, defined as a unilateral act of paying a cost to increase the welfare of someone else beyond one''s own, is related to cooperation in a subsequent one-shot anonymous Prisoner''s dilemma. Contrary to the predictions of the widely used inequity aversion models, we find that benevolence does exist and a large majority of people behave this way. We also find benevolence to be correlated with cooperative behaviour. Finally, we show a causal link between benevolence and cooperation: priming people to think positively about benevolent behaviour makes them significantly more cooperative than priming them to think malevolently. Thus benevolent people exist and cooperate more.     

Theft in an ultimatum game: chimpanzees and bonobos are insensitive to unfairness

Humans, but not chimpanzees, punish unfair offers in ultimatum games, suggesting that fairness concerns evolved sometime after the split between the lineages that gave rise to Homo and Pan. However, nothing is known about fairness concerns in the other Pan species, bonobos. Furthermore, apes do not typically offer food to others, but they do react against theft. We presented a novel game, the ultimatum theft game, to both of our closest living relatives. Bonobos and chimpanzee ‘proposers’ consistently stole food from the responders'' portions, but the responders did not reject any non-zero offer. These results support the interpretation that the human sense of fairness is a derived trait.     

Being Sticker Rich: Numerical Context Influences Children’s Sharing Behavior

Young children spontaneously share resources with anonymous recipients, but little is known about the specific circumstances that promote or hinder these prosocial tendencies. Children (ages 3–11) received a small (12) or large (30) number of stickers, and were then given the opportunity to share their windfall with either one or multiple anonymous recipients (Dictator Game). Whether a child chose to share or not varied as a function of age, but was uninfluenced by numerical context. Moreover, children’s giving was consistent with a proportion-based account, such that children typically donated a similar proportion (but different absolute number) of the resources given to them, regardless of whether they originally received a small or large windfall. The proportion of resources donated, however, did vary based on the number of recipients with whom they were allowed to share, such that on average, children shared more when there were more recipients available, particularly when they had more resources, suggesting they take others into consideration when making prosocial decisions. Finally, results indicated that a child’s gender also predicted sharing behavior, with males generally sharing more resources than females. Together, findings suggest that the numerical contexts under which children are asked to share, as well as the quantity of resources that they have to share, may interact to promote (or hinder) altruistic behaviors throughout childhood.     

Host acceptance and sex allocation of Nasonia wasps in response to conspecifics and heterospecifics

Species recognition is an important aspect of an organism''s biology. Here, we consider how parasitoid wasps vary their reproductive decisions when their offspring face intra- and interspecific competition for resources and mates. We use host acceptance and sex ratio behaviour to test whether female Nasonia vitripennis and Nasonia longicornis discriminate between conspecifics and heterospecifics when ovipositing. We tested pairs of conspecific or heterospecific females ovipositing either simultaneously or sequentially on a single host, using strains varying in their recent history of sympatry. Both N. vitripennis and N. longicornis rejected parasitized hosts more often than unparasitized hosts, although females were more likely to superparasitize their own species in the sequential treatment. However, sex ratio behaviour did not vary, suggesting similar responses towards conspecifics and heterospecifics. This contrasts with theory predicting that heterospecifics should not influence sex ratios as their offspring do not influence local mate competition, where conspecifics would. These non-adaptive sex ratios reinforce the lack of adaptive kin discrimination in N. vitripennis and suggest a behavioural constraint. Discrimination between closely related species is therefore context dependent in Nasonia. We suggest that isolating mechanisms associated with the speciation process have influenced behaviour to a greater extent than selection on sex ratios.     

Social familiarity modulates personality trait in a cichlid fish

Personality traits, such as exploration–avoidance, are expected to be adaptive in a given context (e.g. low-risk environment) but to be maladaptive in others (e.g. high-risk environment). Therefore, it is expected that personality traits are flexible and respond to environmental fluctuations, given that consistency across different contexts is maintained, so that the relative individual responses in relation to others remains the same (i.e. although the magnitude of the response varies the differences between high and low responders are kept). Here, we tested the response of male cichlid fish (Oreochromis mossambicus) to a novel object (NO) in three different social contexts: (i) social isolation, (ii) in the presence of an unfamiliar conspecific, and (iii) in the presence of a familiar conspecific. Males in the familiar treatment exhibited more exploratory behaviour and less neophobia than males in either the unfamiliar or the social isolation treatments. However, there were no overall correlations in individual behaviour across the three treatments, suggesting a lack of consistency in exploration–avoidance as measured by the NO test in this species. Moreover, there were no differences in cortisol responsiveness to an acute stressor between the three treatments. Together, these results illustrate how behavioural traits usually taken as measures of personality may exhibit significant flexibility and lack the expected consistency across different social contexts.     

Context‐dependent alarm signalling in an insect

Animals often respond to danger by raising alarm to inform others. Alarm signals come in many different forms, such as visual or mechanical display, sound or odour. Some animals produce vocal alarm signals that vary with the level of danger. For chemical alarm signals, virtually nothing is known about such context‐dependent signalling due to a general notion that alarm pheromones have fixed compositions. Here, we show that larvae of the Western Flower Thrips (Frankliniella occidentalis) produce an alarm pheromone whose composition varies with the level of danger they face: the presence of a relatively harmless predator or a very dangerous predator, that is either actually attacking or not. The frequency of alarm pheromone excretion increases with the level of danger. Moreover, the composition of excreted alarm pheromone varies in the relationship between total and relative amount of the putative two components, decyl acetate (DAc) and dodecyl acetate (DDAc). When pheromone is excreted with a predator present but not attacking, the percentage DDAc increases with the total amount of pheromone. When a predator does attack, however, the relationship between percentage DDAc and total amount of pheromone is reversed. Taken together, the alarm signal of thrips larvae appears to be context dependent, which to our knowledge is the first report of context‐dependent composition of an alarm pheromone.     

Attentiveness to eyes predicts generosity in a reputation-relevant context

Eyes play a vital role in human social interactions. In fact, some prior work indicates that simply the presence of eyes or eye-like stimuli increases people's prosocial behavior, arguably because the eyes serve as cues of being watched and thus elicit reputational concerns. The current study was designed to address two questions in this regard. First, we examined how salient the eyes are among the human features. Second, we asked whether individual differences in attentiveness to eyes (but not other human features such as ears or hands) are predictive of reputation-enhancing behavior. Using an eye-tracking paradigm, we found that participants looked longest to eyes compared to other human features. Critically, greater attentiveness to eyes correlated with greater generosity on a donation task, but only in a reputation-relevant context (i.e., when donations were public but not when they were anonymous). Attentiveness to other human features did not predict donation behavior. Eyes are thus an especially salient human feature, and attentiveness to eyes may signal individuals' concerns about their reputations.     

Social monitoring via close calls in meerkats

Social monitoring of the actions of group members is thought to be a key development associated with group living. Humans constantly monitor the behaviour of others and respond to them in a flexible way depending on past interactions and the current social context. While other primates have also been reported to change their behaviour towards other group members flexibly based on the current state of their relationship, empirical evidence is typically linked to contextually specific events such as aggressive or reproductive interactions. In the cooperatively breeding meerkat (Suricata suricatta), we investigated whether subordinate females use frequently emitted, non-agonistic close calls to monitor the location of the dominant female and whether they subsequently adjust their response based on recent social interactions during conflict and non-conflict periods. Subjects discriminated between the close calls of the dominant female and control playbacks, responding by approaching the loudspeaker and displaying submissive behaviour only if they were currently threatened by eviction. Our results suggest that meerkats assess the risk for aggressive interactions with close associates depending on social circumstances, and respond accordingly. We argue that social monitoring based on non-agonistic cues is probably a common mechanism in group-living species that allows the adjustment of behaviour depending on variation in relationships.     

Hidden altruism in a real-world setting

Concerns for reputation can promote cooperative behaviour. Individuals that behave cooperatively stand to benefit if they gain in influence, status or are more likely to be chosen as interaction partners by others. Most theoretical and empirical models of cooperation predict that image score will increase with cooperative contributions. Individuals are therefore expected to make higher contributions when observed by others and should opt to make contributions publicly rather than privately, particularly when contributions are higher than average. Here, however, I find the opposite effect. Using data from an online fundraising website, I show that donors are more likely to opt for anonymity when making extremely low and extremely high donations. Mid-range donations, on the other hand, are typically publicized. Recent work has shown that extremely generous individuals may be ostracized or punished by group members. The data presented here suggest that individuals may hide high donations to avoid these repercussions.     

Making the Invisible Visible: Verbal but Not Visual Cues Enhance Visual Detection

Background

Can hearing a word change what one sees? Although visual sensitivity is known to be enhanced by attending to the location of the target, perceptual enhancements of following cues to the identity of an object have been difficult to find. Here, we show that perceptual sensitivity is enhanced by verbal, but not visual cues.

Methodology/Principal Findings

Participants completed an object detection task in which they made an object-presence or -absence decision to briefly-presented letters. Hearing the letter name prior to the detection task increased perceptual sensitivity (d′). A visual cue in the form of a preview of the to-be-detected letter did not. Follow-up experiments found that the auditory cuing effect was specific to validly cued stimuli. The magnitude of the cuing effect positively correlated with an individual measure of vividness of mental imagery; introducing uncertainty into the position of the stimulus did not reduce the magnitude of the cuing effect, but eliminated the correlation with mental imagery.

Conclusions/Significance

Hearing a word made otherwise invisible objects visible. Interestingly, seeing a preview of the target stimulus did not similarly enhance detection of the target. These results are compatible with an account in which auditory verbal labels modulate lower-level visual processing. The findings show that a verbal cue in the form of hearing a word can influence even the most elementary visual processing and inform our understanding of how language affects perception.     

Hunt or hide: How insularity and urbanization affect foraging decisions in lizards

Foraging decisions should reflect a balance between costs and benefits of alternative strategies. Predation risk and resource availability in the environment may be crucial in deciding how cautious individuals should behave during foraging. These costs and benefits will vary in time and context, meaning that animals should be able to adjust their foraging behaviour to new or altered environments. Studying how animals do this is essential to understand their survival in these environments. In this study, we investigated the effect of both insularity and urbanization on risk‐taking and neophobia during foraging in the Dalmatian wall lizard (Podarcis melisellensis). Small islets tend to have both a lower number of predators and less resources. Therefore, islet populations were expected to show more risk‐taking behaviour and less neophobia in a foraging context. Previous studies on behaviour of urban lizards have yielded inconsistent results, but due to a lack of both predators and arthropod prey in urban habitats, we expected urban lizards to also take more risks and behave less neophobic. We sampled several inhabited and uninhabited locations on Vis (Croatia) and surrounding islets. Risk‐taking behaviour was tested by measuring the latency of lizards to feed in the presence of a predator model, and neophobia by measuring the latency to feed in the presence of a novel object. We found that islet lizards do indeed take more risks and were less vigilant, but not less neophobic. Urban and rural lizards did not differ in any of these behaviours, which is in sharp contrast with previous work on mammals and birds. The behavioural differences between islet and island lizards were novel, but not unexpected findings and are in line with the theory of “island tameness”. The effect of urbanization on the behaviour of animals seems to be more complex and might vary among taxa.     

Contextual determinants of female-female mounting in laboratory rats

Female-female mounting is widespread among mammalian species, but little is known about the proximal function of this behaviour. While such mounting is often regarded as a 'masculine' trait, its widespread occurrence may indicate that it serves specific functions within the context of female-female social behaviour. We valuated female mounting behaviour in Long-Evans rats in standard observation chambers and in a seminatural enclosure. Under these conditions, we examined a number of potential factors that might influence mounting, including the oestrous cycle, social hierarchy, familiarity and male presence. The female's mounting was not influenced by her own oestrous cycle, but did vary with the oestrous cycle of the stimulus female. Socially dominant females mounted significantly more than subordinate females, and mounting by the dominant female was most frequent when the subordinate female was sexually receptive. Females mounted (and fought with) unfamiliar females significantly more than they did with familiar cagemates. Female-female mounting was dramatically reduced when males were present. Further testing showed that female mounting did not affect the induction of the progestational state of pregnancy, suggesting that female mounting does not function as a pseudomale behaviour that can substitute for genital stimulation provided by the male. Based on these data, female mounting does not appear to function as a sexual behaviour per se, but may serve as a form of female social behaviour related to maintenance of the female's social status within female groups. In this regard, the results of this study suggest that female mounting is part of the normal female's complex behavioural repertoire and does not necessarily reflect masculinization of some underlying neural substrate. Copyright 1999 The Association for the Study of Animal Behaviour.     

Group Mobbing Behaviour and Nest Defence in a Cooperatively Breeding Australian Bird

Cooperatively breeding noisy miners (Manorina melanocephala) are well known in Australia for their persistent and very vocal group mobbing of heterospecifics. Here I investigated the nature of this extraordinary behaviour, in particular its role in nest defence, in a colour banded population of noisy miners in south‐east Queensland, Australia. I focused on two questions. First, did the intensity of mobbing vary according to factors such as the threat to the nest, or the ‘value’ of a clutch? Secondly, what role did group mobbing play in the success of a nest? To answer these questions, I experimentally manipulated the nest defence behaviour by placing one of three stuffed models near active noisy miner nests. The response of noisy miners to intruders was not indiscriminate. However, I found that the number of birds that mobbed a model did not simply reflect the potential threat posed. The response of noisy miners to raptors and other potential nest predators may have reflected their rarity as well as the threat posed. The number of mobbers did not vary with the age or size of a brood. In this study, the fate of nests was independent of the number of mobbers or visitors at nests. Finally, up to 80% of mobbers were never seen to make any other type of contribution to a nest, and many could not be related to the brood that they were ‘defending’. Hence, for some noisy miner ‘helpers’ the benefits that they accrued were probably not wholly dependent on the survival of the broods. I suggest that, in this gregarious species, mobbing behaviour at the nest may be a display of social status or individual quality. This hypothesis warrants further investigation.     

The ontogeny of human prosociality: behavioral experiments with children aged 3 to 8

Humans regularly engage in prosocial behavior that differs strikingly from that of even our closest living relatives, the chimpanzees (Pan troglodytes). In laboratory settings, chimpanzees are indifferent when given the opportunity to deliver valued rewards to conspecifics, while even very young human children have repeatedly been shown to behave prosocially. Although this broadly suggests that prosocial behavior in chimpanzees differs from that of young human children, the methods used in prior work with children have also differed from the methods used in studies of chimpanzees in potentially crucial ways. Here we test 92 pairs of 3–8-year-old children from urban American (Los Angeles, CA, USA) schools in a face-to-face task that closely parallels tasks used previously with chimpanzees. We found that children were more prosocial than chimpanzees have previously been in similar tasks, and our results suggest that this was driven more by a desire to provide benefits to others than a preference for egalitarian outcomes. We did not find consistent evidence that older children were more prosocial than younger children, implying that younger children behaved more prosocially in the current study than in previous studies in which participants were fully anonymous. These findings strongly suggest that humans are more prosocial than chimpanzees from an early age and that anonymity influences children's prosocial behavior, particularly at the youngest ages.     

Effects of a Major Tree Invader on Urban Woodland Arthropods

Biological invasions are a major threat to biodiversity; however, the degree of impact can vary depending on the ecosystem and taxa. Here, we test whether a top invader at a global scale, the tree Robinia pseudoacacia (black locust or false acacia), which is known to profoundly change site conditions, significantly affects urban animal diversity. As a first multi-taxon study of this kind, we analyzed the effects of Robinia dominance on 18 arthropod taxa by pairwise comparisons of woodlands in Berlin, Germany, that were dominated by R. pseudoacacia or the native pioneer tree Betula pendula. As a negative effect, abundances of five arthropod taxa decreased (Chilopoda, Formicidae, Diptera, Heteroptera, Hymenoptera); 13 others were not affected. Woodland type affected species composition of carabids and functional groups in spiders, but surprisingly did not decrease alpha and beta diversity of carabid and spider assemblages or the number of endangered species. Tree invasion thus did not induce biotic homogenization at the habitat scale. We detected no positive effects of alien dominance. Our results illustrate that invasions by a major tree invader can induce species turnover in ground-dwelling arthropods, but do not necessarily reduce arthropod species abundances or diversity and might thus contribute to the conservation of epigeal invertebrates in urban settings. Considering the context of invasion impacts thus helps to set priorities in managing biological invasions and can illustrate the potential of novel ecosystems to maintain urban biodiversity.     

Reduced Gaze Following and Attention to Heads when Viewing a "Live" Social Scene

Social stimuli are known to both attract and direct our attention, but most research on social attention has been conducted in highly controlled laboratory settings lacking in social context. This study examined the role of social context on viewing behaviour of participants whilst they watched a dynamic social scene, under three different conditions. In two social groups, participants believed they were watching a live webcam of other participants. The socially-engaged group believed they would later complete a group task with the people in the video, whilst the non-engaged group believed they would not meet the people in the scene. In a third condition, participants simply free-viewed the same video with the knowledge that it was pre-recorded, with no suggestion of a later interaction. Results demonstrated that the social context in which the stimulus was viewed significantly influenced viewing behaviour. Specifically, participants in the social conditions allocated less visual attention towards the heads of the actors in the scene and followed their gaze less than those in the free-viewing group. These findings suggest that by underestimating the impact of social context in social attention, researchers risk coming to inaccurate conclusions about how we attend to others in the real world.