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Summary: Chimpanzees make lethal coalitionary attacks on members of other groups . This behavior generates considerable attention because it resembles lethal intergroup raiding in humans . Similarities are nevertheless difficult to evaluate because the function of lethal intergroup aggression by chimpanzees remains unclear. One prominent hypothesis suggests that chimpanzees attack neighbors to expand their territories and to gain access to more food . Two cases apparently support this hypothesis, but neither furnishes definitive evidence. Chimpanzees in the Kasekela community at Gombe National Park took over the territory of the neighboring Kahama community after a series of lethal attacks . Understanding these events is complicated because the Kahama community had recently formed by fissioning from the Kasekela group and members of both communities had been provisioned with food. In a second example from the Mahale Mountains, the M group chimpanzees acquired part of the territory of the adjacent K group after all of the adult males in the latter disappeared . Although fatal attacks were suspected from observations of intergroup aggression, they were not witnessed, and as a consequence, this case also fails to furnish conclusive evidence. Here we present data collected over 10 years from an unusually large chimpanzee community at Ngogo, Kibale National Park, Uganda. During this time, we observed the Ngogo chimpanzees kill or fatally wound 18 individuals from other groups; we inferred three additional cases of lethal intergroup aggression based on circumstantial evidence (see ). Most victims were caught in the same region and likely belonged to the same neighboring group. A causal link between lethal intergroup aggression and territorial expansion can be made now that the Ngogo chimpanzees use the area once occupied by some of their victims. [Copyright &y& Elsevier]

Survival in primates is facilitated by commensal gut microbes that ferment otherwise indigestible plant matter, resist colonization by pathogens, and train the developing immune system. 1,2 However, humans are unique among primates in that we consume highly digestible foods, wean early, mature slowly, and exhibit high lifelong investments in maintenance. 3–6 These adaptations suggest that lifetime trajectories of human-microbial relationships could differ from those of our closest living relatives. Here, we profile the gut microbiota of 166 wild chimpanzees aged 8 months to 67 years in the Kibale National Park, Uganda and compare the patterns of gut microbial maturation to those previously observed in humans. We found that chimpanzee gut microbial alpha-diversity, composition, density, interindividual variation, and within-individual change over time varied significantly with age. Notably, gut microbial signatures in infants <2 years old were distinct across all five metrics. Infant chimpanzee guts were enriched in some of the same taxa prevalent in infant humans (e.g., Bifidobacterium, Streptococcus , and Bacteroides), and chimpanzee gut microbial communities, like those of humans, exhibited higher interindividual variation in infancy versus later in life. However, in direct contrast to human infants, chimpanzee infants harbored surprisingly high-diversity rather than low-diversity gut bacterial communities compared with older conspecifics. These data indicate differential trajectories of gut microbiota development in humans and chimpanzees that are consistent with interspecific differences in lactation, diet, and immune function. Probing the phenotypic consequences of differential early-life gut microbial diversity in chimpanzees and other primates will illuminate the life history impacts of the hominid-microbiome partnership. • We profiled changes in the wild chimpanzee gut microbiota over the life course • 600+ samples collected over 3 years from 166 individuals aged 8 months to 67 years • Unlike humans, gut microbial diversity in chimpanzees is highest in infancy (<2 years old) • Divergent patterns may reflect interspecific differences in lactation, diet, and immunity Reese et al. profile the gut microbiota of wild chimpanzees over the life course. High gut microbial diversity among infants <2 years old contrasts sharply with the low diversity observed in human infants. This divergence could relate to interspecific differences in lactation, diet, and immunity and may contribute to lifelong differences in physiology. [ABSTRACT FROM AUTHOR]