Nicola F. Koyama

Interchange of grooming and agonistic support in chimpanzees

We investigated the temporal relationship between grooming given and agonistic support received in a group of chimpanzees at Chester Zoo, U.K. We compared grooming levels the day before a conflict-with-support to those the day before a conflict-without-support and to baseline to investigate whether individuals groom potential supporters in anticipation of the need for support. We also compared grooming and aggression levels the day after conflicts-with-support to levels the day after conflicts-without-support and to baseline levels to determine whether chimpanzees reward individuals that support them or punish those that do not. Finally, we compared grooming and aggression levels the day after conflicts-with-unsuccessful-solicitations-for-support to those the day after conflicts-with-support and to baseline to examine the behavioral consequences of not providing support when an individual had solicited but did not receive it. Future recipients of support groomed future supporters more the day before receiving support, compared to the day before conflicts-without-support, indicating that grooming increased the likelihood of support. The relationship between prior grooming and support held true only for aggressor and not victim support and is consistent with behavior expected if chimpanzees anticipated the need for agonistic support and groomed their supporter the day before to increase the likelihood of support. We found evidence of a system of reward and punishment. Individuals experienced significantly lower rates of aggression after conflicts in which they provided support than at baseline and after conflicts in which they did not provide support. The finding was true only for aggressor support. We found no evidence that chimpanzees punished individuals whom or that they unsuccessfully solicited with aggression or a reduction in grooming. However, solicitors groomed individuals that they solicited for support significantly more after unsuccessful solicitations than after individuals provided support (but with no difference from baseline), indicating that individuals may attempt to recement their relationship after an unsuccessful solicitation. The findings are consistent with a mechanism of calculated interchange in chimpanzees.

Anticipation of conflict by chimpanzees

Captive chimpanzees appear to anticipate the occurrence of conflict during feeding by grooming and being in proximity at increased rates during the hour prior to feeding. The effect is more marked when food is clumped than when it is dispersed, suggesting that the proximate cause is the anticipation of increased levels of competition. Chimpanzees did not choose high ranking individuals more often as prefeed grooming partners; rather, they preferred to associate with their normal grooming partners (as reflected in post-feed grooming preferences) and close kin. A strong correlation between prefeed association patterns and spatial proximity during clumped feeding sessions suggests that their main concern is to be allowed to feed near individuals who are able to monopolize food sources.

Postconflict Behavior Among Male Japanese Macaques

Reconciliation was first described more than 20 years ago. Since then, it has been observed in many mammals (mainly primates) but data on postconflict behavior among males are still scarce because they usually aggressively compete for mating partners, rarely maintain amicable relationships with one another. Accordingly, reconciliation is expected to occur at low rates. Although this is true for Japanese macaque males, the subspecies on Yakushima Island (Macaca fuscata yakui) seems to represent an exception as grooming among males occurs often. We analyzed postconflict behavior among them and discuss the possible factors that may favor the occurrence of grooming and reconciliation. Selective attraction between former opponents—reconciliation—occurred soon after conflicts. Consolation—affiliative interactions between a focal animal and group members other than the former opponents occurring earlier in PCs than in MCs—was absent among males. Conciliatory tendency is higher for Yakushima macaque males (0.31) versus that in studies on the other subspecies Macaca fuscata. We discuss differences in the behavioral ecology of the 2 subspecies, the ecological and social factors that may favor the occurrence of reconciliation, and the possible benefits that males gain from grooming exchange and reconciliation.

Analysing the effects of group size and food competition on Japanese macaque social relationships

Socio-ecological models predict group size to be one major factor affecting the level of food competition. The aims of this study were to analyse how grooming distribution and reconciliation were affected by differences in group size and food competition in a habitat where predation risk is absent. Data were collected on two groups of different size of wild Japanese macaques (Macaca fuscata yakui), living on Yakushima Island, Japan. The large group faced a greater level of intra-group scramble and a lower level of inter-group food competition. However, intra-group food competition appeared to be greater in the small group as evidenced by the stronger rank-related effects on diet composition in the small group. Grooming and reconciliation were more matrilineally kin-biased and more directed toward close-ranking monkeys in the small group than in the large group. Reconciliation was more frequent in the small group, but monkeys in the large group spent more time grooming and had a greater number of grooming partners. These results indicate that social relationships within the two groups were the result of the combination of group size differences and of the balance between the benefits and costs of a lower/greater level of inter- and intra-group food competition.

Seasonal Effects on Reconciliation in Macaca fuscata yakui

Dietary composition may have profound effects on the activity budgets, level of food competition, and social behavior of a species. Similarly, in seasonally breeding species, the mating season is a period in which competition for mating partners increases, affecting amicable social interactions among group members. We analyzed the importance of the mating season and of seasonal variations in dietary composition and food competition on reconciliation in wild female Japanese macaques (Macaca fuscata yakui) on Yakushima Island, Japan. Yakushima macaques are appropriate subjects because they are seasonal breeders and their dietary composition significantly changes among the seasons. Though large differences occurred between the summer months and the winter and early spring months in activity budgets and the consumption of the main food sources, i.e., fruits, seeds, and leaves, the level of food competition and conciliatory tendency remained unaffected. Conversely, conciliatory tendency is significantly lower during the mating season than in the nonmating season. Moreover, conciliatory tendency is lower when 1 or both female opponents is in estrous than when they are not. Thus the mating season has profound effects on reconciliation, whereas seasonal changes in activity budgets and dietary composition do not. The detrimental effects of the mating season on female social relationships and reconciliation may be due to the importance of female competition for access to male partners in multimale, multifemale societies.

Happy hamsters? Enrichment induces positive judgement bias for mildly (but not truly) ambiguous cues to reward and punishment in Mesocricetus auratus

Recent developments in the study of animal cognition and emotion have resulted in the ‘judgement bias’ model of animal welfare. Judgement biases describe the way in which changes in affective state are characterized by changes in information processing. In humans, anxiety and depression are characterized by increased expectation of negative events and negative interpretation of ambiguous information. Positive wellbeing is associated with enhanced expectation of positive outcomes and more positive interpretation of ambiguous information. Mood-congruent judgement biases for ambiguous information have been demonstrated in a range of animal species, with large variation in the way tests are administered and in the robustness of analyses. We highlight and address some issues using a laboratory species not previously tested: the Syrian hamster (Mesocricetus auratus). Hamsters were tested using a spatial judgement go/no-go task in enriched and unenriched housing. We included a number of controls and additional behavioural tests and applied a robust analytical approach using linear mixed effects models. Hamsters approached the ambiguous cues significantly more often when enriched than unenriched. There was no effect of enrichment on responses to the middle cue. We discuss these findings in light of mechanisms underlying processing cues to reward, punishment and true ambiguity, and the implications for the welfare of laboratory hamsters.

Matrilineal Cohesion and Social Networks in Macaca fuscata

In a provisioned troop of Japanese macaques (Macaca fuscata) in Arashiyama, Japan, greater adherence to Kawamuras rules of matrilineal rank inheritance and youngest ascendancy occurred among high-ranking females versus low-ranking females. Accordingly, high-ranking females formed more clustered hierarchies and low-ranking females had more dispersed hierarchies. A proximate explanation for this finding may be related to differences in how females maintain their social networks. To determine whether the clustering in the hierarchy was reflected in patterns of social cohesiveness, I compared network sizes of coalition and grooming partners for females in each third of the hierarchy. I calculated the proportion of available partners that were coalition and grooming partners within each category of relatedness (0.5 ≥ r ≤ 0.004 and r = 0). High-ranking females formed coalitions with a large proportion of their close relatives and a small proportion of their distant relatives; middle-ranking females supported an intermediate proportion of their close relatives and a small proportion of their distant relatives; and, low-ranking females formed coalitions with very few available close and distant relatives. High-ranking females groomed nearly all available close relatives and an intermediate proportion of distant relatives, whilst middle- and low-ranking females groomed a large proportion of available close relatives and a very small proportion of distant relatives. Thus, levels of clustering within the hierarchy appeared to reflect levels of social cohesion, in terms of grooming and coalition formation.

Supply and demand predict male grooming of swollen females in captive chimpanzees, Pan troglodytes

The notion of a biological marketplace as a framework for explaining cooperative acts among animals is well supported. However, direct evidence for a biological market in a mating context is limited to a handful of studies. We collected data over a 3-year period to test supply/demand predictions of male grooming of swollen females according to a biological market in captive chimpanzees while controlling for other potential interchange. Females received more grooming from and gave less grooming to males when swollen than when not swollen, with parous females receiving more grooming from males than nulliparous females. The central tenet of a biological market that the market value of a commodity should vary according to its availability was supported. Males groomed swollen females less as the availability of swollen females in the group increased. There was also an effect of male dominance rank such that higher ranking males groomed swollen females less than lower ranking males. Taken together, our findings provide evidence for male grooming of swollen females according to a biological market while controlling for potential confounds.

Female sexual advertisement reflects resource availability in twentieth-century UK society

Evolutionary theory suggests that men and women differ in the characteristics valued in potential mates. In humans, males show a preference for physical attractiveness, whereas females seek cues that relate to resources and future earning potential. If women pursue marriage as an economic strategy, female sexual advertisement should increase during periods of poor economic conditions when the number of high-quality male partners becomes a limited resource. To test this prediction, measures of skin display and clothing tightness were taken for clothes portrayed in UK Vogue magazine from 1916 to 1999. These estimates of sexual advertisement were analyzed in relation to an index of economic prosperity (GDP), while controlling for general increases in economic conditions and sexual display over the course of the past century. The results indicate that female sexual display increases as economic conditions decline, with the level of breast display and the tightness of clothing at the waist and hips the key factors underlying this increase. Breast size and symmetry and female body form are secondary sexual characteristics that play an important role in sexual attractiveness. Since advertisement of these features increases as levels of competition for high-quality partners increases, females appear to use marriage as an economic strategy. Patterns of female fashion appear to be underpinned by evolutionary considerations relating resource availability to female reproductive success.

Managing Conflict: Evidence from Wild and Captive Primates

After the first published study of the reconciliatory kiss in Pan troglodytes (de Waal and van Roosmalen, 1979), research into preand postconflict behavior in primates gained rapid momentum throughout the 1980s and 1990s. During the burst of activity, much effort centered on the systematic demonstration of postconflict behavior in a variety of primate and some nonprimate species. Theoretical work developed hypotheses to explain the functions of reconciliation: valuable relationship hypothesis and the stress reduction hypothesis, for which supporting evidence is growing. More recently Aureli et al. (2002) proposed a framework to predict its occurrence in social animals. Given the backdrop of intense activity and the fact that researchers have systematically described postconflict behavior in many primate species, we organized a symposium on current developments in the field to highlight new directions for research. The 7 articles are from