Disease risk and immune strategies in social insects
Group-living has been predicted to have opposing effects on disease risk and immune strategies. First, since repeated contacts between individuals facilitate pathogen transmission, sociality may favour high investment in personal immunity. Alternatively, because social animals can limit disease spread through collective sanitary actions (e.g., mutual grooming) or organisational features (e.g., division of the group’s social network into distinct subsets), sociality may instead favour low investment in personal immunity. The overall goal of this project is to experimentally test these conflicting predictions in ants using advanced data collection and analytical tools. I will first quantify the effect of social organisation on disease transmission using a combination of automated behavioural tracking, social network analysis, and empirical tracking of transmission markers (fluorescent beads). Experimental network manipulations and controlled disease seeding by a robotic ant will allow key predictions from network epidemiology to be tested, with broad implications for disease management strategies. I will then study the effect of colony size on social network structure and disease transmission, and how this in turn affects investment in personal immunity. This will shed light on far-reaching hypotheses about the effect of group size on social organisation ('size-complexity’ hypothesis) and immune investment (‘density-dependent prophylaxis’). Finally, I will explore whether prolonged pathogen pressure induces colonies to reinforce the transmission-inhibiting aspects of their social organisation (e.g., colony fragmentation) or to invest more in personal immunity. This project will represent the first empirical investigation of the role of social organisation in disease risk management, and allow its importance to be compared with other immune strategies. This will constitute a significant advance in our understanding of the complex feedback between sociality and health.