Parasites alter interaction patterns in fish social networks

Social networks influence the spread of parasites through populations. Although we know how parasites are transmitted as a product of social interactions, we have a limited understanding of how social networks are affected by parasites over time. Host–parasite interactions and the networks they form, are typically examined as static networks, and while topological descriptions at a specific time point are useful, both behaviour and the infection process are dynamic. By monitoring replicate populations of Trinidadian guppies (Poecilia reticulata) daily before and during infection with the ectoparasite Gyrodactylus turnbulli, we show how parasitism drives social network dynamics. Specifically, infected individuals increased their connections in networks affected by parasitism. In contrast, uninfected control shoals showed no change in network metrics. The structure of subnetworks (motifs) and networks, however, did not change in response to infection status. These findings provide further evidence of reciprocal host behaviour–parasite feedback mechanisms, and highlight that infected fish alter their interactions in order to ‘off-load’ their parasites. Understanding how these reciprocal interactions affect the structure and function of natural systems, as well as understanding how these interactions may alter with future environmental change, are key areas of future research.