Avoiding infection: perspectives from Papionini and Hominini

Abstract

To what extent do primates - our closest phylogenetic relatives and thus the most relevant to understanding the origins of human hygiene practices - exhibit counterstrategies when faced with risk of infection? To address this, we conducted feeding-related infection-avoidance experiments with 5 species of Papionini and Hominini: Macaca fuscata fuscata, Macaca fascicularis, Mandrillus sphinx, Pan troglodytes troglodytes, and Pan paniscus. First, we found that free ranging Japanese macaques vary in their sensitivity to infection risk during foraging under both experimental and natural conditions, and the ‘hygienic tendencies’ of individuals were good predictors of their current levels of geohelminth infection. Then, we expanded our experimental protocol to include visual, olfactory and tactile cues of feces and other contaminants such as blood, semen, rotten meat and rotten fruit with captive chimpanzees, semi-free-ranging mandrills, group-housed long-tailed macaques and semi-free-ranging bonobos. Results indicate that subjects demonstrated risk-sensitivity to these potential contaminants, manifest as increased latencies to consumption of food rewards, maintenance of greater distances from contaminants, and/or outright refusals to consume food in test versus control conditions. Current work is testing whether risk-averse individuals with greater tendencies to avoid potential sources of contamination are less prone to infection and thus characterized by better general health than risk-prone individuals. These studies are aimed at better understanding behavioral immunity to infection among primates, which is fundamental to the understanding of the origins of human hygiene.