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Primates exhibit diverse social systems that are intricately linked to their biology, behavior, and evolution, all of which influence the acquisition and maintenance of their gut microbiomes (GMs). However, most studies of wild primate populations focus on taxa with relatively large group sizes, and few consider pair-living species. To address this gap, we investigate how a primate's social system interacts with key environmental, social, and genetic variables to shape the GM in pair-living, red-bellied lemurs (Eulemur rubriventer). Previous research on this species suggests that social interactions within groups influence interindividual microbiome similarity; however, the impacts of other nonsocial variables and their relative contributions to gut microbial variation remain unclear. We sequenced the 16S ribosomal RNA hypervariable V4-V5 region to characterize the GM from 26 genotyped individuals across 11 social groups residing in Ranomafana National Park, Madagascar. We estimated the degree to which sex, social group identity, genetic relatedness, dietary diversity, and home range proximity were associated with variation in the gut microbial communities residing in red-bellied lemurs. All variables except sex played a significant role in predicting GM composition. Our model had high levels of variance inflation, inhibiting our ability to determine which variables were most predictive of gut microbial composition. This inflation is likely due to red-bellied lemurs' pair-living, pair-bonded social system that leads to covariation among environmental, social, and genetic variables. Our findings highlight some of the factors that predict GM composition in a tightly bonded, pair-living species and identify variables that require further study. We propose that future primate microbiome studies should simultaneously consider environmental, social, and genetic factors to improve our understanding of the relationships among sociality, the microbiome, and primate ecology and evolution., (© 2024 The Author(s). American Journal of Primatology published by Wiley Periodicals LLC.)

Infant handling (holding or carrying) by adult males is rare in mammals; however, high levels have been reported in some primates. Though infant handling is a costly behaviour, there are many benefits that male handlers can accrue. Infant handling by males is most conspicuous in platyrrhines and tends to be uncommon in catarrhines. In the latter species, research on male-infant interactions has focused on low-cost behaviours, such as proximity and grooming. However, to better understand the evolution of infant handling by males, more data on its occurrence across the Primate order are essential, even in species where it is relatively uncommon. We compare the occurrence of infant handling by males in three closely related species of catarrhine: Colobus vellerosus, C. guereza, and C. angolensis ruwenzorii. We collected focal animal samples on infants to quantify infant handling rates and durations, and found that adult male C. a. ruwenzorii handled infants much more frequently and for much longer than males in the other two species. We discuss how C. a. ruwenzorii's unique social organization may explain high levels of infant handling by adult males in this species. More long-term and detailed comparisons of infant handling across species and populations will shed light on how sociality has shaped the evolution of this behaviour in the Primate order.

Neuroendocrine evidence suggests that paternal care is mediated by hormonal mechanisms, where hormonal changes in expectant and new fathers facilitate infant care. In species with obligate and extensive paternal care such as humans, androgen levels decline once males are paired and have offspring, and in direct response to offspring care. Facultative infant care is widespread in the Order Primates, but the underlying hormonal mechanisms are largely unknown. We found that wild, red-bellied lemurs living in family groups (two adults and their presumed offspring) varied in the amount of care they provided infants. The more fathers invested in helping infants (measured as a composite of carrying, holding, huddling, grooming, and playing), and specifically the more they huddled and groomed with infants, the higher their fecal androgen (fA) levels, contrary to expectations. Carrying was negatively related to fA levels. Helping by subadults and juveniles was not related to their own fA levels. Elevated fA levels during infant dependence have been observed in other vertebrate species, and are thought to reflect reinvestment in mating rather than investment in dependent offspring. However, red-bellied lemurs do not mate until after infants are weaned, and they have long-term pair-bonds, suggesting that elevated fA levels play a role in offspring care. These results support a growing body of research suggesting that elevated androgen levels do not inhibit protective infant care., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Vertebrate gut microbiota form a key component of immunity and a dynamic link between an individual and the ecosystem. Microbiota might play a role in social systems as well, because microbes are transmitted during social contact and can affect host behaviour. Combining methods from behavioural and molecular research, we describe the relationship between social dynamics and gut microbiota of a group-living cooperative species of primate, the red-bellied lemur (Eulemur rubriventer). Specifically, we ask whether patterns of social contact (group membership, group size, position in social network, individual sociality) are associated with patterns of gut microbial composition (diversity and similarity) between individuals and across time. Red-bellied lemurs were found to have gut microbiota with slight temporal fluctuations and strong social group-specific composition. Contrary to expectations, individual sociality was negatively associated with gut microbial diversity. However, position within the social network predicted gut microbial composition. These results emphasize the role of the social environment in determining the microbiota of adult animals. Since social transmission of gut microbiota has the potential to enhance immunity, microbiota might have played an escalating role in the evolution of sociality., (© 2017 The Authors. Journal of Animal Ecology © 2017 British Ecological Society.)

Ruffed lemurs (genus Varecia) are often described as having a flexible social organization, such that both cohesive (low fission-fusion dynamics) and fluid (high fission-fusion dynamics) grouping patterns have been observed. In ruffed lemur communities with high fission-fusion dynamics, group members vary in their temporal and spatial dispersion throughout a communally defended territory. These patterns have been likened to those observed in several haplorrhine species that exhibit the most fluid types of fission-fusion social organization (e.g., Pan and Ateles). To substantiate and further refine these claims, we describe the fission-fusion dynamics of a black-and-white ruffed lemur (Varecia variegata) community at Mangevo, an undisturbed primary rainforest site in Ranomafana National Park, Madagascar. We collected instantaneous group scan samples from August 2007-December 2008 (4,044 observation hours) to study and characterize patterns of subgroup size, composition, cohesion, and social association. In 16 consecutive months, we never found all members of the community together. In fact, individuals spent nearly half of their time alone. Subgroups were small, cohesive, and typically of mixed-sex composition. Mixed-sex subgroups were significantly larger, less cohesive, and more common than either male-only or female-only subgroups. Subgroup dynamics were related to shifts in climate, phenology of preferred fruit species, and female reproductive state. On average, association indices were low. Males and females were equally gregarious; however, adult male-male associations were significantly weaker than any other association type. Results presented herein document striking differences in fission-fusion dynamics between black-and-white ruffed lemurs and haplorrhines, while also demonstrating many broad-scale similarities to haplorrhine taxa that possess the most fluid fission-fusion societies., (© 2015 Wiley Periodicals, Inc.)