Social animals are particularly exposed to infectious diseases. Pathogen-driven selection pressure has thus favoured the evolution of behavioural adaptations to decrease transmission risk, such as “social distancing”. Yet, such strategy might deprive individuals from valuable social interactions, generating a cost-benefit trade-off between pathogen avoidance and social opportunities. Recent studies revealed that hosts differ in the expression of these behavioural defences but the determinants driving such inter-individual variation remain poorly understood. Using 5 years of detailed behavioural and parasite data obtained on a large natural population of non-human primates, we show that, during grooming interactions, some female mandrills (Mandrillus sphinx) consistently avoid their conspecifics’ peri-anal region, where oro-faecally transmitted gastro-intestinal parasites accumulate, while others do not. This hygienic trait is further highly repeatable across the years and hygienic females are less parasitized on average than non-hygienic females. While age, dominance rank and sociality level do not influence hygienic tendencies, close maternal kin exhibit similar levels of hygiene suggesting social inheritance from mothers to daughters. Our study thus emphasizes that social inheritance of hygienic tendencies may structure behavioural resistance to pathogens in host populations, with unforeseen consequences on the dynamics of infectious diseases.

The table entitled "Table_model1" indicates for each grooming event collected during 6 study years (n = 3429): the season ("LD" : Long-dry, "LR": Long-rainy, "I": intermediate), the identity of the female groomer, the average population protozoan richness (during a period ranging from two weeks before to two weeks after that grooming event), and whether or not this grooming event included the peri-anal region ("PAR": 0/1) of the social partner.

The table entitled "Table_model2" gives protozoan richness of each female, each study month (n = 357 female.months), as well as female age, dominance rank ("HR": high-rank, "MR": medium-rank, "LR": low-rank) and proportion of risky grooming events (i.e., including groupmates' peri-anal region) for each female each study year ("female_annual_PRG"). "Population monthly protozoan richness" corresponds to the average protozoan richness in the population the corresponding month.

The table entitled "Table_model3" gives hygienic index for each female each study year ("female_annual_HI") as well as female age, dominance rank, and sociality level.