Abstract: A popular view is that high population density promotes behavioural pathology, particularly increased aggression. In contrast, according to a coping model, some primates have behavioural mechanisms (e.g. formal displays, reconciliation and grooming) that regulate social tensions and control the negative consequences of crowding. Seven captive rhesus monkey groups, Macaca mulattawere observed over a wide range of population densities where high-density groups were over 2000 times more crowded than low-density free-ranging groups. As density increased, male rhesus monkeys increased grooming and huddling but did not increase rates of aggression. Females increased all categories of behaviour examined (heavy aggression, mild aggression, formal bared-teeth displays, grooming and huddling), but the increases were not distributed uniformly to all classes of partners. Females increased only grooming, huddling and appeasement displays to males, increased only aggression and huddling with kin and increased all categories of behaviour to non-kin adult females. There were no differences in the percentage of aggressive conflicts reconciled across density conditions. Increased density had different effects on particular relationships. Relationships between females and males were characterized by a coping pattern in which animals modified their behaviour in ways that may decrease aggression under crowded conditions. Female relationships with kin and non-kin were characterized by increases in both aggression and friendly interactions as density increased. The different patterns of response to higher density may reflect different strategies depending on the strength and stability of relationships and the potential consequences if certain relationships are disrupted.1997The Association for the Study of Animal Behaviour

Abstract: A grooming posture previously reported for two wild chimpanzee (Pan troglodytes) communities developed spontaneously in a captive group of the same species. This offered a unique opportunity to follow the propagation of a new social custom. The posture consists of two partners grasping hands--either both right hands or both left hands--and raising the arms in an A-frame above their heads while mutually grooming with their free hands. The propagation of this pattern was followed over a 5 year period. In the beginning, handclasps were always initiated by the same adult female. This female initiated the posture mainly with her adult female kin. In subsequent years, these relatives became frequent participants in the posture with each other as well as with nonrelatives. Over the years the posture increased in frequency and duration and spread to the majority of adults and also to a few adolescents and older juveniles. The pattern persisted after removal of the apparent originator.

Abstract: Following aggressive interactions, dominant female baboons, Papio cynocephalus ursinusoccasionally grunt to their victims. To examine the effect of these apparently reconciliatory grunts on victims' subsequent behaviour, a series of playback experiments was designed to mimic reconciliation. Victims were played their opponents' grunts in the minutes immediately following a fight and then observed for half an hour. After hearing these grunts, victims approached their former opponents and also tolerated their opponents' approaches at significantly higher rates than they did under control conditions. They were also supplanted by their opponents at significantly lower rates. By contrast, playbacks of control females' grunts did not influence victims' behaviour. Playbacks of reconciliatory grunts did not increase the rate at which opponents approached or initiated friendly interactions with their former victims. Playbacks of reconciliatory grunts, therefore, appeared to influence victims', but not opponents', perception of recent events.

Abstract: It has been argued that intraspecific mate-choice copying can be adaptive under certain conditions. Dugatkin's (1992,Am. Nat.139, 1384-1389) work with guppies,Poecilia reticulataremains the most influential experimental demonstration of this phenomenon. We replicated Dugatkin's work using several choice criteria to ensure that our results were not dependent upon any single method of judging mate choice. We also tested our findings against two null hypotheses of differing stringency. Irrespective of the choice criteria or null hypothesis used, we did not observe any relationship between female mate choice and copying. We conclude that further experimental evidence of female mate-choice copying is required before the existence of this behaviour can be affirmed.

Abstract: At present, the most general evolutionary theory of honest communication is Grafen's model of Zahavi's 'handicap' signalling system, in which honesty of signals about the signaller's quality (e.g. mate suitability or fighting ability) is maintained by the differentially high cost of signals to signallers having lower quality. The latter model is here further generalized to include any communication between signallers and receivers that are genetically related (e.g. parents and begging offspring, cooperative or competing siblings). Signalling systems involving relatives are shown to be evolutionarily stable, despite a potential pay-off for false signalling, if the Zahavian assumption of differential signal costs holds and there are diminishing reproductive returns to the signaller as the receiver's assessed value of its attribute increases, or if, regardless of whether the Zahavian assumption holds, signallers with high values of the attribute benefit more from a given receiver assessment than signallers with low values (e.g. begging chicks that are hungrier benefit more from being fed). In stable systems of signalling among kin, it is also shown to be generally true that (i) levels of signalling and thus observed signal costs will decline as relatedness increases or as the receiver's reproductive penalty for erroneous assessment increases, and (ii) receivers will consistently, altruistically overestimate the true value of the signalled attribute.