Male-infant relationships in semifree-ranging Barbary macaques (Macaca sylvanus) of affenberg salem/FRG: Testing the “male care” hypothesis

The infant-directed behavior of Barbary macaque males was analyzed in order to determine whether it is essential for an infant's survival during the first year and whether males interact selectively with closely related infants. Dyadic male-infant contacts were recorded in a large group of semifree-ranging Barbary macaques. Data collected during the first 12 weeks of life on each infant born in 1983 (n = 36) were analyzed. All adult and almost all subadult males established strong relationships with at least one infant. Almost two-thirds of the infants (22) had frequent contacts with one or several males. Males showed no preference for closely related infants. Sexual associations with an infant's mother during the preceding mating season had no significant effect. Natal males did not prefer infants of their own matrilineage. There was no evidence that contacts with males had a positive influence on infant survival or that other benefits to the infants resulted from these contacts. Instead, excessive carrying by males and females led to starvation of some very young infants and was a major cause of neonatal deaths in this population. Males interacted preferentially with infants that were born early in the birth season, had a high-ranking multiparous mother, and were male. Younger males established strong relationships with male infants only, while mother's rank was more important for older males. It is suggested that certain mothers prevented early contacts between their infants and males so that the observed preferences for certain infants were also a result of easier access to them. All results suggested that males interacted with infants for their own benefit.     

Brown spider monkeys (Ateles hybridus): a model for differentiating the role of social networks and physical contact on parasite transmission dynamics

Elevated risk of disease transmission is considered a major cost of sociality, although empirical evidence supporting this idea remains scant. Variation in spatial cohesion and the occurrence of social interactions may have profound implications for patterns of interindividual parasite transmission. We used a social network approach to shed light on the importance of different aspects of group-living (i.e. within-group associations versus physical contact) on patterns of parasitism in a neotropical primate, the brown spider monkey (Ateles hybridus), which exhibits a high degree of fission–fusion subgrouping. We used daily subgroup composition records to create a ‘proximity’ network, and built a separate ‘contact’ network using social interactions involving physical contact. In the proximity network, connectivity between individuals was homogeneous, whereas the contact network highlighted high between-individual variation in the extent to which animals had physical contact with others, which correlated with an individual''s age and sex. The gastrointestinal parasite species richness of highly connected individuals was greater than that of less connected individuals in the contact network, but not in the proximity network. Our findings suggest that among brown spider monkeys, physical contact impacts the spread of several common parasites and supports the idea that pathogen transmission is one cost associated with social contact.     

Infectious disease and group size: more than just a numbers game

Increased risk of infectious disease is assumed to be a major cost of group living, yet empirical evidence for this effect is mixed. We studied whether larger social groups are more subdivided structurally. If so, the social subdivisions that form in larger groups may act as barriers to the spread of infection, weakening the association between group size and infectious disease. To investigate this ‘social bottleneck’ hypothesis, we examined the association between group size and four network structure metrics in 43 vertebrate and invertebrate species. We focused on metrics involving modularity, clustering, distance and centralization. In a meta-analysis of intraspecific variation in social networks, modularity showed positive associations with network size, with a weaker but still positive effect in cross-species analyses. Network distance also showed a positive association with group size when using intraspecific variation. We then used a theoretical model to explore the effects of subgrouping relative to other effects that influence disease spread in socially structured populations. Outbreaks reached higher prevalence when groups were larger, but subgrouping reduced prevalence. Subgrouping also acted as a ‘brake’ on disease spread between groups. We suggest research directions to understand the conditions under which larger groups become more subdivided, and to devise new metrics that account for subgrouping when investigating the links between sociality and infectious disease risk.     

Phylogenetic reconstruction of carnivore social organizations

It is generally assumed that carnivore social organizations evolved directionally from a solitary ancestor into progressively more advanced forms of group living. Although alternative explanations exist, this evolutionary hypothesis has never been tested. Here, I used literature data and maximum likelihood reconstruction on a complete carnivore phylogeny to test this hypothesis against two others: one assuming directional evolution from a non-solitary ancestor, and one assuming parallel evolutions from a socially flexible ancestor, that is, an ancestor with abilities to live in a variety of social organizations. The phylogenetic reconstructions did not support any of the three hypotheses of social evolution at the root of Carnivora. At the family level, however, there was support for a non-solitary and socially flexible ancestor to Canidae, a socially flexible or solitary ancestor to Mustelidae, a solitary or socially flexible ancestor to Mephitidae, a solitary or group living ancestor to Phocidae, a group living ancestor to Otariidae and a solitary ancestor to Ursidae, Felidae, Herpestidae and Viverridae. There was equivocal support for the ancestral state of Procyonidae and Hyaenidae. It is unclear whether the common occurrence of a solitary ancestry at the family level was caused by a solitary ancestor at the root of Carnivora or by multiple transitions into a solitary state. The failure to support a solitary ancestor to Carnivora calls for caution when using this hypothesis in an evolutionary framework, and I suggest continued investigations of the pathways of the evolution of carnivore social organizations.     

Ontogenic development of dyadic social relationships: Assessing individual roles

Socialization processes lead to creation and differentiation of social relationships. It is often difficult to qualify them, especially due to ontogenic changes of social behavior. In this paper, an attempt is made to assess the role of each partner in a dyad by defining the quality of their overall relationship. A Social Investment Index (SII) was devised to describe these roles throughout ontogeny. SII is expressed as (G% — R%)/2, where G% and R% represent the difference between the sum of cohesive behaviors and that of disruptive behaviors divided by the overall sum of these behaviors given (G%) or received (R%) by one individual in a dyad. Results from a longitudinal study of the development of social behavior in one infant mangabey (Cercocebus albigena albigena) are used as an example. The developmental changes of the SII are presented in three dyads in a single-male group: mother-infant; “aunt”-infant; and juvenile male-infant.     

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. © 1996 Wiley-Liss, Inc.