Sickness behaviour within cleaning interactions

When facing diseases, strategies such as social distancing have proven effective in preventing disease spread. Cleaning interactions are social interactions where cleaner organisms remove ectoparasites from clients. These interactions can be potential vectors of infectious diseases in reef fishes. Here, we aimed to determine if cleaner wrasses (Labroides dimidiatus) employ social distancing and other behavioural tactics to prevent disease spread within the context of cleaning interactions. To this end, we used bacterial lipopolysaccharides (LPS) immunostimulation to induce "sickness" behaviour in cleaners. After LPS injection, we performed four behavioural trials: social preference (from cleaner and client perspectives), social interaction, and bystander cooperativeness tests. In the social preference test, LPS-injected cleaners showed lower activity rates but no change in their social preference. However, some clients preferred "sick" cleaners. Contrarily, during the social interaction test, cleaners reduced the number of interactions, despite clients willingness to interact. For the bystander test, LPS-injected cleaners were unable to adjust their behaviour to be more cooperative. Reduced activity levels revealed lethargy, which may lead to passive self-isolation, allowing for some social distancing of healthy individuals. This suggests that immune-stimulated cleaners undergo changes in their behaviour which can be viewed as a passive social distancing preventing disease spread.