The behavior of peripheral males during the mating season inMacaca fuscata

Flexibility in the social structure of male chimpanzees (Pan troglodytes schweinfurthii) in the Budongo Forest, Uganda

Individuals of social species experience competitive costs and social benefits of group living. Substantial flexibility in humans' social structure and the combination of different types of social structure with fission-fusion dynamics allow us to live in extremely large groups-overcoming some of the costs of group living while capitalizing on the benefits. Non-human species also show a range of social strategies to deal with this trade-off. Chimpanzees are an archetypical fission-fusion species, using dynamic changes in day-to-day association to moderate the costs of within-group competition. Using 4 years of association data from two neighbouring communities of East African chimpanzees (Pan troglodytes schweinfurthii), we describe an unexplored level of flexibility in chimpanzee social structure. We show that males from the larger Waibira community (N = 24-31) exhibited additional structural levels of semi-stable core-periphery society, while males from the smaller Sonso community (N = 10-13) did not. This novel core-periphery pattern adds to previous results describing alternative modular social structure in other large communities of chimpanzees. Our data support the hypothesis that chimpanzees can incorporate a range of strategies in addition to fission-fusion to overcome costs of social living, and that their social structures may be closer to that of modern humans than previously described.

Mismatches in resident and stranger serotonin transporter genotypes lead to escalated aggression, and the target for aggression is mediated by sex differences in male and female rhesus monkeys (Macaca mulatta)

A variety of studies show that the s-allele of the serotonin transporter genotype (5-HTT) is related to aggression. However, influences of sex and 5-HTT genotype of both subject and opponent have not received as much attention in aggression research. Using a nonhuman primate model, the present study explores differences in rates of aggression exhibited by 201 group-housed male and female rhesus monkeys (Macaca mulatta; 122 females; 79 males) exposed to an unfamiliar age- and sex-matched stranger while in the presence of other same-sex members of their social group. The study also assesses whether the rates of aggression increase when the home-cage resident, the unfamiliar stimulus animal, or both possess the short (s) allele of the 5-HTT. Results showed that, when compared to females, males exhibited higher rates of physical aggression toward the stranger, and when both the male resident and the male stranger possessed the s-allele, rates of physical aggression toward the stranger increased five-fold. Resident females also engaged in higher rates of physical aggression when they possessed the s-allele, although unlike the males, their physical aggression was directed toward familiar same-sex members of their social group. The findings of this study indicate that rates of physical aggression are modulated by 5-HTT resident and stranger suggest a role of sexual competition in the phenotype of the 5-HTT genotype. Importantly, when two males with impulse deficits, as a function of the s-allele, are placed together, rates of violence exhibited by the dyad escalate substantially.

Genotyping from semen of wild Japanese macaques (Macaca fuscata)

The noninvasive collection of animal cells is crucial for DNA analyses in wild populations that cannot be disturbed by capture. We describe the collection of 68 semen samples following copulation and masturbation events in wild habituated and nonhabituated troops of Japanese macaques on the protected island of Yakushima. We used this DNA to amplify 390 base pairs (bp) of the mitochondrial DNA control region in 16 individuals from eight troops, and found a monomorphic pattern in agreement with the low variability imposed by geographic isolation and female philopatry. We also amplified two microsatellite loci from samples collected after the resident males of a focal troop had copulated with different females. We found several different allele combinations in samples collected after the observed mating of a single male, indicating the presence of contaminant DNA, presumably from males that had previously mated with the same female. This discovery made it impossible to assign a given sample to a specific male except when the samples were recovered after masturbation events. Thus, it was not possible to test for kinship or estimate allele frequencies from the semen samples. The mixing of semen, and the pattern of sample collection observed in morphologically identified individuals support the notion that strong mating and sperm competition exists among resident and nonresident males.