Are individual differences in social behaviour a cause or a consequence of endoparasite infection in feral cattle?

Abstract

Host–parasite interactions are often described as ‘vicious circles’, with infected hosts differing from their noninfected conspecifics in ways that can increase their parasitic load and risk of concurrent infections. However, the question of whether individual differences are a cause or a consequence of infection remains challenging to address, as it requires simultaneous quantification of infection and sociality. Concurrent hypotheses address the association of parasite infections and social behaviour, as well as behaviour and infection risk, although these are likely to be system specific. The Hong Kong feral cattle, Bos taurus , population experiences naturally occurring seasonal patterns of infection without anthelmintic treatments and exhibit natural behaviours with minimal management. We assessed social interactions (observations of aggression, affiliation, allogrooming, sexual behaviour, flehmen and dominance) and endoparasite infections (identification of eggs, oocysts and larvae in faecal samples) at the individual level in three herds that varied in size, sex ratio and reproductive status. Following a hypotheses-driven modelling approach, we first assessed the impact of infection on social behaviour by building four generalized linear models. We then modelled the effect of behaviour on parasite infection in the wet season by building four binomial generalized linear models. For all models, we selected the best-fit model using the corrected Akaike information criterion (AICc). Finally, we assessed the association between allogrooming and potential parasite ingestion. Coinfection was an important aspect of infection associated with higher performance of social behaviours and higher dominance rank. Infection status in the dry season remained the most important predictor of infection status in the subsequent (wet) season, regardless of individual differences in social behaviour. We also found an association between the risk of infection with paramphistomids and the type of body part licked during allogrooming bouts. Our results deepen our understanding of the individual differences in host–parasite interactions in free-ranging ungulates.