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In wild primates, social behaviour influences exposure to environmentally acquired and directly transmitted microorganisms. Prior studies indicate that gut microbiota reflect pairwise social interactions among chimpanzee and baboon hosts. Here, we demonstrate that higher-order social network structure--beyond just pairwise interactions--drives gut bacterial composition in wild lemurs, which live in smaller and more cohesive groups than previously studied anthropoid species. Using 16S rRNA gene sequencing and social network analysis of grooming contacts, we estimate the relative impacts of hierarchical (i.e. multilevel) social structure, individual demographic traits, diet, scent-marking, and habitat overlap on bacteria acquisition in a wild population of Verreaux's sifaka (Propithecus verreauxi) consisting of seven social groups. We show that social group membership is clearly reflected in the microbiomes of individual sifaka, and that social groups with denser grooming networks have more homogeneous gut microbial compositions. Within social groups, adults, more gregarious individuals, and individuals that scent-mark frequently harbour the greatest microbial diversity. Thus, the community structure of wild lemurs governs symbiotic relationships by constraining transmission between hosts and partitioning environmental exposure to microorganisms. This social cultivation of mutualistic gut flora may be an evolutionary benefit of tight-knit group living. [ABSTRACT FROM AUTHOR]

Three brown lemurs, Eulemur fulvus, and two black lemurs, Eulemur macaco, were trained to select consistently the photograph of the face of a known individual (KI: belonging to the same social group) when it was presented simultaneously with a photograph of the face of an unfamiliar individual (UI: belonging to another social group). After the learning phase, the subjects were presented with new pairs of photographs (KI versus UI: photographs that were not used in the learning phase), the same pairs presented in different associations, and finally pairs of photographs that were completely novel (50 different pairs). All the subjects selected the KI significantly more often than the UI under all conditions. Additional tests showed that the subjects preferentially selected photographs of a UI belonging to their own species versus a UI belonging to the other species. No preference was observed when the subjects were presented with two KI or with their own photograph associated with a UI. These results reveal that the face contains information allowing lemurs to discriminate familiar individuals from unfamiliar ones. [Copyright &y& Elsevier]

Tight energetic constraints on reproductively active females are hypothesized to be an important determinant of the phenomenon of female dominance in Propithecus verreauxi, a primate endemic to Madagascar. Five wild sifakas were captured in the Beza Mahafaly Special Reserve in southern Madagascar, and resting metabolic rates (RMR) were measured. Levels were low, as predicted, with the exception of a possibly pregnant female. Although the data were not conclusive, they were consistent with the hypothesis. [ABSTRACT FROM AUTHOR]