Coevolution of trustful buyers and cooperative sellers in the trust game

Many online marketplaces enjoy great success. Buyers and sellers in successful markets carry out cooperative transactions even if they do not know each other in advance and a moral hazard exists. An indispensable component that enables cooperation in such social dilemma situations is the reputation system. Under the reputation system, a buyer can avoid transacting with a seller with a bad reputation. A transaction in online marketplaces is better modeled by the trust game than other social dilemma games, including the donation game and the prisoner's dilemma. In addition, most individuals participate mostly as buyers or sellers; each individual does not play the two roles with equal probability. Although the reputation mechanism is known to be able to remove the moral hazard in games with asymmetric roles, competition between different strategies and population dynamics of such a game are not sufficiently understood. On the other hand, existing models of reputation-based cooperation, also known as indirect reciprocity, are based on the symmetric donation game. We analyze the trust game with two fixed roles, where trustees (i.e., sellers) but not investors (i.e., buyers) possess reputation scores. We study the equilibria and the replicator dynamics of the game. We show that the reputation mechanism enables cooperation between unacquainted buyers and sellers under fairly generous conditions, even when such a cooperative equilibrium coexists with an asocial equilibrium in which buyers do not buy and sellers cheat. In addition, we show that not many buyers may care about the seller's reputation under cooperative equilibrium. Buyers' trusting behavior and sellers' reputation-driven cooperative behavior coevolve to alleviate the social dilemma.     

Individual contributions to territory defence in a cooperative breeder: weighing up the benefits and costs

While investment in territory defence is expected to be influenced by its benefits, the additional role that costs may play is rarely considered. Here, we quantify both benefits and costs of repelling prospecting males in cooperative meerkats, and demonstrate that both are required to explain the substantial variation in individual contributions to the defence observed. Males benefit more from repelling prospectors than females, as males may lose dominance and be expelled during intrusions. Accordingly, males invest the most in repelling prospectors. We also show that males experience an associated cost in the form of reduced weight gain and, as such, heavier males contribute more to chasing prospectors. Finally, we show evidence of a cost not restricted to individuals engaged in chasing: both males and females reduce their contributions to feeding dependent pups when prospectors are present, resulting in a reduction in pup weight gain in this context. Males appear to adjust their contributions to chasing in light of this cost, chasing at lower rates when their group contains dependent young. Our findings support the view that investment in cooperative behaviours can be attributed to benefits and costs, and highlight the additional importance of considering trade-offs in investment between cooperative behaviours.     

Behavioural dynamics of biparental care in the dung beetle Onthophagus taurus

In the dimorphic dung beetle Onthophagus taurus major males provide assistance during offspring provisioning. We examined the behavioural dynamics of biparental care to quantify directly how males and females allocate time to parental and nonparental behaviours and to determine whether parents adjust their level of investment relative to their partner's contribution. Females allocated more of their time budget to parental behaviours than males. The proportion of time females allocated to parental behaviours increased after oviposition while that of a male decreased. Male paternity assurance behaviours were negatively associated with male and female parental behaviours. Theoretical models predict that the investment provided by the members of a cooperative pair should be negatively correlated and that any shortfall of one parent should be partially compensated for by the other. In the absence of a male, unassisted females allocated more time to parental care, and performed more parental behaviours. However, compensation was incomplete as unassisted females performed fewer parental behaviours than pairs, resulting in significantly lighter brood masses (the egg and its associated dung supply). Males performed more parental behaviours when paired with small females, and small females more than large females. Contrary to prediction, the investments provided by males and females in a cooperative pair were positively correlated. Males coordinated their parental behaviours with the females rather than acting independently. Since parental behaviours were directly related to the weight of brood masses, the observed parental interactions will have important fitness consequences in this species. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.     

酪蝇的羽化节律和交配行为

【目的】为了明确酪蝇Piophila casei的羽化节律和交配行为,为深入研究酪蝇的性信息素打下基础。【方法】在室内条件[温度(27±1)℃,光周期L︰D=14︰10]下观察了酪蝇的羽化节律和交配行为。【结果】结果表明,化蛹后第8天成虫羽化最多,羽化高峰期出现在由暗期进入光期的前后,雄虫略早于雌虫羽化。观察结果表明,当雄虫接近蛹壳时会表现出"触摸"、"经过"、"扑"、"抱握"等动作,而雌虫仅有"触摸"、"抱握"的动作。当遇到同性成虫或者已交配雌虫时,雄虫会"追逐"对方,当接触到对方时雄虫会表现出"抱握"、"触摸"动作以进行识别,被识别雄虫会"翘起腹部末端"使对方离开,已交配雌虫则猛烈"摆动身体"使对方离开。当遇到处女雌虫时,雄虫跳跃到雌虫背上迅速进行交配。雌虫羽化后1 min即可交配,雄虫羽化后30 min可交配,交配平均持续时间10 min。雄虫间会有交配竞争行为发生,后来者会跳跃到先来者背上,向下弯曲腹部试图越过先来者与雌虫交配。【结论】酪蝇的羽化高峰出现在进入光期前后。成虫对蛹壳有显著趋性,雄虫主动追逐识别异性,较雌虫表现出更强烈的交配欲望。     

Cooperators benefit through reputation-based partner choice in economic games

Explaining unconditional cooperation, such as donations to charities or contributions to public goods, continues to present a problem. One possibility is that cooperation can pay through developing a reputation that makes one more likely to be chosen for a profitable cooperative partnership, a process termed competitive altruism (CA) or reputation-based partner choice. Here, we show, to our knowledge, for the first time, that investing in a cooperative reputation can bring net benefits through access to more cooperative partners. Participants played a public goods game (PGG) followed by an opportunity to select a partner for a second cooperative game. We found that those who gave more in the PGG were more often selected as desired partners and received more in the paired cooperative game. Reputational competition was even stronger when it was possible for participants to receive a higher payoff from partner choice. The benefits of being selected by a more cooperative partner outweighed the costs of cooperation in the reputation building phase. CA therefore provides an alternative to indirect reciprocity as an explanation for reputation-building behaviour. Furthermore, while indirect reciprocity depends upon individuals giving preference to those of good standing, CA can explain unconditional cooperation.     

Development of partner preferences in Japanese Macaques (Macaca fuscata): Effects of gender and kinship during the second year of life

Quantitative data are presented on the effects of subject sex, partner sex,and kinship on the social interactions of 18 juveniles of the Oregon troop of Japanese macaques (Macaca fuscata).Data on these subjects as infants were also used to detail maturational changes in partner sex preferences. Nine males and nine females, whose multiparous mothers represented a cross section of dominance ranks, were observed using a focal-animal technique. Juveniles of both sexes engaged in more proximity, contact, grooming, mounting, aggression, and social play with kin than with nonkin partners. They initiated less contact with females and more contact with males during their second year. They initiated more grooming and aggression during their second year than their first year, with females displaying a strong preference for grooming females and males specifically aggressing males more during the second year. Aggression was higher between same-sexed partners than between opposite-sexed partners. Males engaged in more social interactions with males during the second year than the first year of life. Males played more than females during both years. Males played more with males during the second year than the first year, and males played with males more than did females during the second year. We conclude that sex differences in behavioral frequencies become evident during the first year of life, and sex differences in partner preferences emerge during the second year of life.     

Lek Breeding and Territorial Aggression in White-eared Kob

Territorial aggression in a lek breeding population of white-eared kob (Kobus kob leucotis) was investigated in the Boma National Park region, southern Sudan. The frequency of aggression on leks was positively related to the number of females present, but generally declined over the course of the breeding season. Males fought most strenuously for central territories that were preferred by females. Males with females in their territories were more frequently engaged in fights than unaccompanied males. Such fights often induced females to leave their original partners, especially when large groups of females were involved. Territorial aggression led to damaging injuries in several instances, and mortality of breeding age males was disproportionately high. These results suggest that the intensity of aggression exhibited by territorial males was scaled to potential reproductive benefits.     

Age- and sex-related differences in dominance and foraging behaviour of nuthatches Sitta europaea

Nuthatches collecting sunflower seeds from feeders were observed. In summer, but not in autumn, adults collected more seeds per visit than juveniles. From summer to autumn, juveniles increased both the number of seeds collected per unit time and the total number taken per visit. This was probably due to an increase in both experience and ability to handle seeds, possibly associated with beak growth. Males were dominant over females, and adults over juveniles of the same sex. Dominance relations were important in determining the length of visits; males made longer visits. Males also took more seeds per visit. However, females obtained more seeds per unit time, probably to avoid being supplanted by males.     

Social Dominance among Male Meadow Voles is Inversely Related to Reproductive Success

Intrasexual selection can occur through direct aggressive interactions between males for access to females. We tested the relationship between social dominance and male reproductive success among meadow voles, Microtus pennsylvanicus. Dominance ranks of wild‐caught males were determined using neutral arena trials, with the winner of two of three trials considered dominant. These males were then released into field enclosures and allowed to visit females housed in nestboxes for 8 wk, and males’ home range sizes were determined using weekly grid trapping. Male reproductive success was determined using molecular paternity analysis (six microsatellite primers) for all pups born during the field experiment. Males with higher dominance ranks had larger home ranges. However, male dominance rank was not predictive of the number of total visits to females’ nestboxes or the number of visits to each male's most frequently visited nestbox. Males that made more visits to nestboxes sired more litters. Males that had higher dominance ranks sired fewer litters. These results suggest that there is a reproductive disadvantage to having higher dominance rank among male meadow voles.     

Transcranial Direct Current Stimulation of the Left Dorsolateral Prefrontal Cortex Shifts Preference of Moral Judgments

Attitude to morality, reflecting cultural norms and values, is considered unique to human social behavior. Resulting moral behavior in a social environment is controlled by a widespread neural network including the dorsolateral prefrontal cortex (DLPFC), which plays an important role in decision making. In the present study we investigate the influence of neurophysiological modulation of DLPFC reactivity by means of transcranial direct current stimulation (tDCS) on moral reasoning. For that purpose we administered anodal, cathodal, and sham stimulation of the left DLPFC while subjects judged the appropriateness of hard moral personal dilemmas. In contrast to sham and cathodal stimulation, anodal stimulation induced a shift in judgment of personal moral dilemmas towards more non-utilitarian actions. Our results demonstrate that alterations of left DLPFC activity can change moral judgments and, in consequence, provide a causal link between left DLPFC activity and moral reasoning. Most important, the observed shift towards non-utilitarian actions suggests that moral decision making is not a permanent individual trait but can be manipulated; consequently individuals with boundless, uncontrollable, and maladaptive moral behavior, such as found in psychopathy, might benefit from neuromodulation-based approaches.     

Simultaneous EEG-fMRI during a Working Memory Task: Modulations in Low and High Frequency Bands

Background

EEG studies of working memory (WM) have demonstrated load dependent frequency band modulations. FMRI studies have localized load modulated activity to the dorsolateral prefrontal cortex (DLPFC), medial prefrontal cortex (MPFC), and posterior parietal cortex (PPC). Recently, an EEG-fMRI study found that low frequency band (theta and alpha) activity negatively correlated with the BOLD signal during the retention phase of a WM task. However, the coupling of higher (beta and gamma) frequencies with the BOLD signal during WM is unknown.

Methodology

In 16 healthy adult subjects, we first investigated EEG-BOLD signal correlations for theta (5–7 Hz), alpha1 (8–10), alpha2 (10–12 Hz), beta1 (13–20), beta2 (20–30 Hz), and gamma (30–40 Hz) during the retention period of a WM task with set size 2 and 5. Secondly, we investigated whether load sensitive brain regions are characterised by effects that relate frequency bands to BOLD signals effects.

Principal Findings

We found negative theta-BOLD signal correlations in the MPFC, PPC, and cingulate cortex (ACC and PCC). For alpha1 positive correlations with the BOLD signal were found in ACC, MPFC, and PCC; negative correlations were observed in DLPFC, PPC, and inferior frontal gyrus (IFG). Negative alpha2-BOLD signal correlations were observed in parieto-occipital regions. Beta1-BOLD signal correlations were positive in ACC and negative in precentral and superior temporal gyrus. Beta2 and gamma showed only positive correlations with BOLD, e.g., in DLPFC, MPFC (gamma) and IFG (beta2/gamma). The load analysis revealed that theta and—with one exception—beta and gamma demonstrated exclusively positive load effects, while alpha1 showed only negative effects.

Conclusions

We conclude that the directions of EEG-BOLD signal correlations vary across brain regions and EEG frequency bands. In addition, some brain regions show both load sensitive BOLD and frequency band effects. Our data indicate that lower as well as higher frequency brain oscillations are linked to neurovascular processes during WM.     

Male preference for a subtle posture cue that signals spawning readiness in female sticklebacks

We presented territorial male three-spined sticklebacks, Gasterosteus aculeatus, two stationary dummies simultaneously, each simulating an equally gravid female. Both dummies featured the head-up orientation indicative of a sexually receptive female but differed in more subtle aspects of posture. In one dummy the back and tail were moulded in a relaxed straight posture and the other was moulded with the raised tail and concave back posture (lordosis), which mating tests revealed to be a strong predictor of spawning readiness in females. Males courted both dummies but directed more to the lordosis posture. Male sticklebacks thus recognize and respond appropriately to relatively subtle features of female posture in addition to other cues such as the head-up angle and dorsal barring reported in earlier studies. Physiological or morphological constraints may make the lordosis posture a reliable, and hence relatively honest, indicator of spawning readiness in females. Males may therefore enhance their fitness by preferentially courting females that assume this posture. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.     

Multiple reputation domains and cooperative behaviour in two Latin American communities

Reputations are a ubiquitous feature of human social life, and a large literature has been dedicated to explaining the relationship between prosocial reputations and cooperation in social dilemmas. However, humans form reputations in domains other than prosociality, such as economic competency that could affect cooperation. To date, no research has evaluated the relative effects of multiple reputation domains on cooperation. To bridge this gap, we analyse how prosocial and competency reputations affect cooperation in two Latin American communities (Bwa Mawego, Dominica, and Pucucanchita, Peru) across a number of social contexts (Dominica: labour contracting, labour exchange and conjugal partnership formation; Peru: agricultural and health advice network size). First, we examine the behavioural correlates of prosocial and competency reputations. Following, we analyse whether prosocial, competency, or both reputation domains explain the flow of cooperative benefits within the two communities. Our analyses suggest that (i) although some behaviours affect both reputation domains simultaneously, each reputation domain has a unique behavioural signature; and (ii) competency reputations affect cooperation across a greater number of social contexts compared to prosocial reputations. Results are contextualized with reference to the social markets in which behaviour is embedded and a call for greater theory development is stressed.     

Effects of Low Frequency Prefrontal Repetitive Transcranial Magnetic Stimulation on the N2 Amplitude in a GoNogo Task

During the last decade, repetitive transcranial magnetic stimulation (rTMS) of the prefrontal cortex has become established as a treatment for various mental diseases. The rational of prefrontal stimulation has been adapted from the mode of action known from rTMS using motor-evoked potentials though little is known about the precise effect of rTMS at prefrontal sites. The objective of the current study is to investigate the inhibitory effect of prefrontal 1 Hz rTMS by stimulating the generators of event-related potentials (ERP) which are located in the prefrontal cortex. Thus, 1 Hz rTMS was applied offline over the left dorsolateral prefrontal cortex (DLPFC) and the medial prefrontal cortex (MPFC) in 18 healthy subjects who subsequently underwent a GoNogo task. Both active conditions were compared to sham rTMS within a randomized and counterbalanced cross-over design in one day. ERPs were recorded during task performance and the N2 and the P3 were analysed. After 1 Hz rTMS of the left DLPFC (but not of the MPFC), an inhibitory effect on the N2 amplitude was observed, which was related to inhibitory control. In contrast, after 1 Hz rTMS of the MPFC (but not at the left DLPFC) a trend towards an increased P3 amplitude was found. There was no significant modulation of latencies and behavioural data. The results argue in favour of an inhibitory effect of 1 Hz rTMS on N2 amplitudes in a GoNogo task. Our findings suggest that rTMS may mildly modulate prefrontally generated ERP immediately after stimulation, even where behavioural effects are not measurable. Thus, combined rTMS-ERP approaches need to be further established in order to serve as paradigms in experimental neuroscience and clinical research.     

Urine Washing and Sniffing in Wild White-faced Capuchins (<Emphasis Type="Italic">Cebus capucinus</Emphasis>): Testing Functional Hypotheses

Urine washing (UW) is taxonomically widespread among strepsirhines and platyrrhines, yet its functional significance is still unclear. We used 2274 h of focal follows of 35 adult and subadult wild white-faced capuchins (Cebus capucinus) to test 1) the intergroup signaling, intragroup social signaling, and thermoregulatory hypotheses for UW and 2) the hypothesis that individuals sniff each other's urine and other traces to gather socially significant information. Males engaged in significantly more UW than females. All 5 α-males engaged in more UW than subordinate males did, including 4 α-males that increased their UW rate above that of their male groupmates after their rise to α rank. Males engaged in significantly less UW while in view of other males than at other times. Male-male sniffing rates do not correlate with either aggression rate or dominance rank distance. Urine washing rates did not increase while subjects were in parts of their home range where more intergroup encounters occurred. Urine washing rates were highest early in the morning and late in the afternoon, presumably when temperatures were coolest. The data do not support either the thermoregulatory or social signaling hypothesis. We suggest that experiments with captive capuchins are necessary to resolve the issue of the function of urine washing in the taxon.     

Is This Car Looking at You? How Anthropomorphism Predicts Fusiform Face Area Activation when Seeing Cars

Anthropomorphism encompasses the attribution of human characteristics to non-living objects. In particular the human tendency to see faces in cars has long been noticed, yet its neural correlates are unknown. We set out to investigate whether the fusiform face area (FFA) is associated with seeing human features in car fronts, or whether, the higher-level theory of mind network (ToM), namely temporoparietal junction (TPJ) and medial prefrontal cortex (MPFC) show a link to anthropomorphism. Twenty participants underwent fMRI scanning during a passive car-front viewing task. We extracted brain activity from FFA, TPJ and MPFC. After the fMRI session participants were asked to spontaneously list adjectives that characterize each car front. Five raters judged the degree to which each adjective can be applied as a characteristic of human beings. By means of linear mixed models we found that the implicit tendency to anthropomorphize individual car fronts predicts FFA, but not TPJ or MPFC activity. The results point to an important role of FFA in the phenomenon of ascribing human attributes to non-living objects. Interestingly, brain regions that have been associated with thinking about beliefs and mental states of others (TPJ, MPFC) do not seem to be related to anthropomorphism of car fronts.     

Indirect reciprocity under incomplete observation

Indirect reciprocity, in which individuals help others with a good reputation but not those with a bad reputation, is a mechanism for cooperation in social dilemma situations when individuals do not repeatedly interact with the same partners. In a relatively large society where indirect reciprocity is relevant, individuals may not know each other's reputation even indirectly. Previous studies investigated the situations where individuals playing the game have to determine the action possibly without knowing others' reputations. Nevertheless, the possibility that observers of the game, who generate the reputation of the interacting players, assign reputations without complete information about them has been neglected. Because an individual acts as an interacting player and as an observer on different occasions if indirect reciprocity is endogenously sustained in a society, the incompleteness of information may affect either role. We examine the game of indirect reciprocity when the reputations of players are not necessarily known to observers and to interacting players. We find that the trustful discriminator, which cooperates with good and unknown players and defects against bad players, realizes cooperative societies under seven social norms. Among the seven social norms, three of the four suspicious norms under which cooperation (defection) to unknown players leads to a good (bad) reputation enable cooperation down to a relatively small observation probability. In contrast, the three trustful norms under which both cooperation and defection to unknown players lead to a good reputation are relatively efficient.     

Coevolution of honest signaling and cooperative norms by cultural group selection

Evolution of cooperative norms is studied in a population where individual and group level selection are both in operation. Individuals play indirect reciprocity game within their group and follow second order norms. Individuals are norm-followers, and imitate their successful group mates. Aside from direct observation individuals can be informed about the previous actions and reputations by information transferred by others. A potential donor estimates the reputation of a potential receiver either by her own observation or by the opinion of the majority of others (indirect observation). Following a previous study (Scheuring, 2009) we assume that norms determine only the probabilities of actions, and mutants can differ in these probabilities. Similarly, we assume that individuals follow a stochastic information transfer strategy. The central question is whether cooperative norm and honest social information transfer can emerge in a population where initially only non-cooperative norms were present, and the transferred information was not sufficiently honest.It is shown that evolution can lead to a cooperative state where information transferred in a reliable manner, where generous cooperative strategies are dominant. This cooperative state emerges along a sharp transition of norms. We studied the characteristics of actions and strategies in this transition by classifying the stochastic norms, and found that a series of more and more judging strategies invade each other before the stabilization of the so-called generous judging strategy. Numerical experiments on the coevolution of social parameters (e.g. probability of direct observation and the number of indirect observers) reveal that it is advantageous to lean on indirect observation even if information transfer is much noisier than for direct observation, which is because to follow the majorities’ opinion suppresses information noise meaningfully.     

Behavior of giant pandas (Ailuropoda melanoleuca) in captive conditions: Gender differences and enclosure effects

The behavior of giant pandas (Ailuropoda melanoleuca) was studied under captive conditions. Both male and female pandas spent similar amounts of time engaged in eating and locomotion. Males performed anogenital‐marking more but rested less than females, which suggests a sexually dimorphic pattern of behavior. Furthermore, females housed in the seminatural environment spent significantly less time engaged in stereotyped behavior than did females housed in the traditional enclosure, indicating that an enclosure environment affects the behavior of giant pandas. These data illustrate the importance of careful management and facility design for captive giant pandas. Zoo Biol 22:77–82, 2003. © 2003 Wiley‐Liss, Inc.     

Inferring reputation promotes the evolution of cooperation in spatial social dilemma games

In realistic world individuals with high reputation are more likely to influence the collective behaviors. Due to the cost and error of information dissemination, however, it is unreasonable to assign each individual with a complete cognitive power, which means that not everyone can accurately realize others' reputation situation. Here we introduce the mechanism of inferring reputation into the selection of potential strategy sources to explore the evolution of cooperation. Before the game each player is assigned with a randomly distributed parameter p denoting his ability to infer the reputation of others. The parameter p of each individual is kept constant during the game. The value of p indicates that the neighbor possessing highest reputation is chosen with the probability p and randomly choosing an opponent is left with the probability 1-p. We find that this novel mechanism can be seen as an universally applicable promoter of cooperation, which works on various interaction networks and in different types of evolutionary game. Of particular interest is the fact that, in the early stages of evolutionary process, cooperators with high reputation who are easily regarded as the potential strategy donors can quickly lead to the formation of extremely robust clusters of cooperators that are impervious to defector attacks. These clusters eventually help cooperators reach their undisputed dominance, which transcends what can be warranted by the spatial reciprocity alone. Moreover, we provide complete phase diagrams to depict the impact of uncertainty in strategy adoptions and conclude that the effective interaction topology structure may be altered under such a mechanism. When the estimation of reputation is extended, we also show that the moderate value of evaluation factor enables cooperation to thrive best. We thus present a viable method of understanding the ubiquitous cooperative behaviors in nature and hope that it will inspire further studies to resolve social dilemmas.