No abstract

Genealogical relatedness is thought to be an important causal factor in the evolution of cooperation. We inferred relatedness on the basis of 11 blood protein markers using the Queller and Goodnight index of relatedness in a macaque population with long-term demographic records. This estimate re£ected independently determined pedigree relationships in our data set. Mean relatedness among all members of a social group was 0.10 but much higher levels of relatedness (0.30^0.47) were found among the members of matrilineal families with a high or intermediate social rank. Groups of dispersing males that had been born into the same social group were sometimes closely related (0.43 and 0.58), but they could also be less related (0.08). We found that the pattern of distribution of relatedness was associated with gene £ow and di¡eren-tial reproduction in males, rather than with group ¢ssion and the presence of geographical barriers.

The behaviour of two groups of wedgecapped capuchin monkeys, Cebus olivaceus, a small one (n = 8) and a large one (n = 25) was recorded. Time budgets and other aspects of behaviour depended on group size. The differences can be explained as: adjustment to predation risk and intra-group food competition. In order to evade predation, members of the small groups scan more and stay at greater heights than those of the large group. Higher food competition within the large group was reflected in the composition of its diet, in longer travel distances, and higher levels of social behaviour. In particular during the dry season, the large group exploited unattractive and risky food sources. These results support ALEXANDER'S hypothesis on the causes of group formation.

In a field study of three groups of wild long-tailed macaques, Macaca fascicularis, observations on social behaviour could be related to genetically determined paternity. In contrast to what has been found in many previous studies on captive primate groups, we found a relatively strong correlation between male dominance rank and reproductive success. In a large group the high success of the alpha male compared to other males could be explained only partly by his higher copulation score. His success also resulted partly from better timing of his copulations during maximum fertility of the females, in comparison with other males. We must conclude either that the alpha-male has more access to fertile females, or that females have a preference for the alpha-male during their maximum fertility. The females clearly displayed promiscuous behaviour. This behaviour implies a risk to a female that a male other than the alpha-male with proven qualities will become the father of her offspring. One expects that there must be a social advantage related to this female strategy. In the absence of indications of any direct social advantages to the female of this sexual behaviour pattern, the ultimate explanation for this female promiscuity is most likely is aggression reduction. This could be either through the devaluating of any single copulation, or through the confusion of paternity and a resultant reduction in the risk of infanticide.

ABSTRACT. The relationship between male dominance rank and reproductive success has been a topic of interest since the beginning of primatology. From a theoretical point of view the existence or absence of this relationship has great implications with respect to the meaning of dominance rank and more general of the social relationships between individuals within social groups. Until fairly recently mating behaviour has been used as an indicator of reproductive success, but these two variables need not be correlated. The relations between mating success, reproductive success, and dominance rank indicate whether selective mating is involved (different mating partners at different phases of fertility, for example through male contest or female choice). With the development of genetic techniques to determine reproductive success directly, it has now become possible to investigate these relations.In our study on wild long-tailed macaques (Macacafascicularis) we find a relatively strong correlation between rank and reproductive success which is attributable to selective mating by the alpha male during fertile periods of the females. In most previous studies no such clear results have been obtained, and we discuss the differences in outcome in relation to the study conditions, group sizes, and possible differences between species in terms of reproductive strategies.