Joseph H. Manson

Fission-Fusion Dynamics: New Research Frameworks

Renewed interest in fission‐fusion dynamics is due to the recognition that such dynamics may create unique challenges for social interaction and distinctive selective pressures acting on underlying communicative and cognitive abilities. New frameworks for integrating current knowledge on fission‐fusion dynamics emerge from a fundamental rethinking of the term “fission‐fusion” away from its current general use as a label for a particular modal type of social system (i.e., “fission‐fusion societies”). Specifically, because the degree of spatial and temporal cohesion of group members varies both within and across taxa, any social system can be described in terms of the extent to which it expresses fission‐fusion dynamics. This perspective has implications for socioecology, communication, cognitive demands, and human social evolution.

Intergroup aggression in chimpanzees and humans.

The occurrence of fatal attacks during intergroup encounters among chimpanzees suggests that certain aspects of chimpanzee and human intergroup aggression may be explicable in similar ways. This paper addresses three questions: What conditions favor the evolution of lethal raiding in intergroup aggression? Why is intergroup aggression in these two species predominantly the domain of males? Under what circumstances do groups compete over access to females as opposed to material resources? Examination of comparative data on nonhuman primates and crosscultural study of foraging societies suggests that attacks are lethal because where there is sufficient imbalance of power their cost is trivial, that these attacks are a male and not a female activity because males are the philopatric sex, and that it is resources of reproductive interest to males that determine the causes of intergroup aggression.

Social Conventions in Wild White‐faced Capuchin Monkeys

Ten researchers collaborated in a longterm study of social conventions in wild whitefaced capuchin monkeys, involving examination of a 19,000hour combined data set collected on 13 social groups at four study sites in Costa Rica over a 13year period. Five behavior patterns qualified as social traditions, according to the studys criteria: handsniffing, sucking of body parts, and three types of games. Some conventions were independently invented in virtually identical form at multiple sites. The extinction of several conventions was observed during the course of the study; it appears that they rarely last longer than ten years. It is hypothesized that the monkeys are using these group or cliquespecific social conventions to test the quality of their social relationships.Ten researchers collaborated in a longterm study of social conventions in wild whitefaced capuchin monkeys, involving examination of a 19,000hour combined data set collected on 13 social groups at four study sites in Costa Rica over a 13year period. Five behavior patterns qualified as social traditions, according to the studys criteria: handsniffing, sucking of body parts, and three types of games. Some conventions were independently invented in virtually identical form at multiple sites. The extinction of several conventions was observed during the course of the study; it appears that they rarely last longer than ten years. It is hypothesized that the monkeys are using these group or cliquespecific social conventions to test the quality of their social relationships.

Number of males in primate groups: Comparative tests of competing hypotheses

Primate social groups frequently contain multiple males. Male group size has been hypothesized to result from male mating competition, but the selective factors responsible for the evolution of multimale groups are unclear. Short breeding seasons create situations that are not conducive for single males to monopolize mating access to females, and may therefore favor the formation of large male groups. Alternatively, since the costs of mate defense increase with the spatial clumping of females, female group size may be a primary determinant of the number of males in a primate group. We used comparative methods designed to control for the potentially confounding effects of hidden third variables associated with phylogeny to test the breeding season and female group size hypotheses for the evolution of multimale groups. Our results revealed no association between breeding season duration and the number of males in groups. In contrast, we provide support for the female group size hypothesis by demonstrating a strong pattern of correlated evolution between female and male group size.

Measuring female mate choice in Cayo Santiago rhesus macaques

Abstract Few studies of female mate choice have been carried out among free-ranging non-human primates. To qualify as female mate choice, behaviour by oestrous females must predict the occurrence or rate of potentially fertile copulations, in comparisons between heterosexual dyads. In this paper, data are presented to show three behaviour patterns that meet this criterion in free-ranging rhesus macaques, Macaca mulatta , at the island colony of Cayo Santiago: (1) selective cooperation with male sexual solicitations (hip-grasps), (2) restoration of proximity following attacks on females by intruding males, and (3) proximity maintenance (in one of two study groups). Oestrous females maintained proximity preferentially to lower ranking males, but this appeared to reflect differences in the tactics necessary to achieve copulations with males of different dominance ranks, rather than preference for lower ranking mates. Male-oestrous female dyads showed consistency over two consecutive mating seasons in which partner was responsible for proximity maintenance. Male dominance rank was positively correlated with copulatory rate with fertile females. However, in one study group, males to whom oestrous females maintained proximity more actively had higher copulatory rates with fertile females, independent of the effects of male dominance rank.

Kin-biased social behaviour in wild adult female white-faced capuchins, Cebus capucinus

*Department of Anthropology and Center for Behavior, Evolution and Culture,University of California, Los AngelesyMax Planck Institute for Evolutionary AnthropologyzDepartment of Psychology, Indiana University(Received 16 October 2007; initial acceptance 30 October 2007;final acceptance 4 January 2008; published online 27 May 2008; MS. number: A10889R)Studies of kin bias in the distribution of social behaviour in group-living matrifocal species generallyunderline the importance of bonds among female kin. However, few studies examine either how kinbias may be affected by variation in the availability of kin or the relevance of paternal kin. In this study,we used genetic and behavioural data to analyse correlates of coalition formation, proximity, groomingand dominance relations among female white-faced capuchins over a 10-year period during which thenumber of adult females in the group varied from 6 to 10. Females sided with the most closely relatedof two opponents when joining coalitions. Both dominance rank and kinship influenced proximity andgrooming patterns. In particular, when group size was small, mean relatedness high and interdyadic var-iation in relatedness low, rank distance was a better predictor of proximity and grooming than was kinshipdistance. However, when group size was large, mean relatedness lower and interdyadic variation in relat-edness higher, females significantly biased their grooming and spatial proximity towards kin. Dominancerank was not so tightly associated with relatedness as in provisioned female-bonded cercopithecines;females did not follow the ‘youngest sister ascendancy rule’. Full sisters, maternal half sisters andmotheredaughter dyads associated at statistically indistinguishable rates, and all associated significantlymore often than paternal half sisters. Paternal half sisters did not associate more often than distantlyrelated femaleefemale dyads (r < 0.125). These and similar results call into question the general impor-tance of paternal kin ties in wild primates.

White-faced capuchin monkeys show triadic awareness in their choice of allies

The social intelligence hypothesis, which holds that social challenges have selected for increased intelligence and social skills, has been supported by evidence that, in catarrhine primates, individuals know about the characteristics of groupmates’ social relationships. Evidence for such ‘triadic awareness’ has not been sought for platyrrhine primates, although two platyrrhine genera, capuchins, Cebus, and squirrel monkeys, Saimiri, are among the most highly encephalized primates. We examined patterns of coalitionary recruitment in wild white-faced capuchins, C. capucinus. Analyses have shown that more dominant individuals are more likely to join aggressive coalitions than low-rankers, and that individuals preferentially support those with whom they have stronger affiliative relationships. Data from 110 fights, analysed using simulation techniques that produced distributions of results expected under null hypotheses, revealed that contestants preferentially solicited prospective coalition partners that (1) were dominant to their opponents, and (2) had better social relationships (higher ratios of affiliative/ cooperative interactions to agonistic interactions) with themselves than with their opponents. Further analyses showed that soliciting dominant partners could be explained by either of two simpler rules, ‘Solicit an ally that outranks yourself’ or ‘Solicit the highest-ranking available individual’. However, soliciting partners with better social relationships appears to indicate triadic awareness, because subjects did not preferentially solicit the nearby individual with whom they shared the highest-quality social relationship. Effects of relative relationship quality on coalition solicitation decisions were independent of effects of dominance rank.

Nonconceptive Sexual Behavior in Bonobos and Capuchins

Sexual behavior by infecundable females, and by same-sex and adult-immature dyads, occurs in wild and captive bonobos (Pan paniscus). Proposed functions of these behaviors, in social primates generally, include practice, paternity confusion, exchange, and communication as well as appeasement. We used this framework to interpret and to compare observations of sexual behavior in a captive bonobo group and a wild white-faced capuchin (Cebus capucinus) group. In both species, (a) sexual behavior was no more frequent in cycling females than in pregnant or lactating females and (b) same-sex and adult-immature dyads engaged in as much mounting or genitogenital contact as adult heterosexual dyads did. The species differed in that (a) bonobos engaged in sexual behavior 65 times as frequently as capuchins, (b) only bonobos engaged in sexual contact other than ventrodorsal mounting during focal observation, and (c) bonobo sexual contact was concentrated most heavily in socially tense situations in adult female–female dyads, whereas capuchin sexual contact was concentrated most heavily in socially tense situations in adult male–male dyads. These data and published literature indicate that (a) practice sex occurs in both species, (b) paternity confusion may be a current function of C. capucinus nonconceptive sex, (c) exchange sex remains undemonstrated in capuchins, and (d) communication sex is more important to members of the transferring sex—female bonobos and male capuchins—than to members of the philopatric sex.

Father–daughter inbreeding avoidance in a wild primate population

Supplemental tables, acknowledgements, experimental procedures, and referencesxDownload (.15 MB ) Supplemental tables, acknowledgements, experimental procedures, and references

Male dominance and reproductive success in wild white-faced capuchins (Cebus capucinus) at Lomas Barbudal, Costa Rica.

Theory and a growing body of empirical evidence suggest that higher ranking males experience reproductive advantages in group‐living mammals. White‐faced capuchins (Cebus capucinus) exhibit an interesting social system for investigating the relationship between dominance and reproductive success (RS) because they live in multimale multifemale social groups, in which the alpha males can have extraordinarily long tenures (i.e. they coreside with daughters of reproductive age). Genetic paternity was determined from fecal samples for 120 infants born into three social groups of wild C. capucinus at Lomas Barbudal Biological Reserve, Costa Rica. Alpha males produced far more offspring than expected by chance, and significantly high Nonacs B indices (a measure of deviation from a random distribution of RS among potentially breeding individuals) were a feature of six out of eight male tenures. The likelihood of the alpha male siring a particular offspring was predicted by the kin relationship between the mother and the alpha male, as well as the total number of males and females in the group. The almost complete lack of father–daughter inbreeding [Muniz et al., 2006] constitutes an impediment to alpha male reproductive monopolization in this population, particularly toward the end of long alpha male tenures. Am. J. Primatol. 72:1118–1130, 2010.