Defending the fortress: comparative studies of disease resistance in ant societies

Parasites represent a considerable and ubiquitous threat to organisms, and studies of host-parasite interactions can demonstrate important insights into key biological processes. Identification and quantification of host defences and their role in parasite resistance is an important part of understanding these effects. Additionally, life-history traits can have significant effects on host-parasite interactions. For example, living in groups has many benefits, but also may have associated costs in terms of increased parasite transmission. Thus group-living animals may be predicted to invest heavily in disease resistance strategies, though which may depend on each species’ parasite pressure. Social insects, and ants in particular, are an ideal model with which to test these evolutionary and ecological hypotheses, as they possess an array of mechanisms to defend themselves against disease and have highly diverse life-histories. However, previous studies into disease resistance tend to have been performed on single species, often looking at just single measures of investment of defence. In this thesis I explore the comparative importance of disease resistance in different ant species. I show that ants possess a variety of defence mechanisms to protect themselves against the threat of parasites and demonstrate how investment into these important defences can vary between individuals and species, and may depend on context, type of parasite, and life-history of the host. Work such as this, demonstrating the costs of individual components of disease resistance in multiple species, is important in developing our understanding of how changes in parasite pressures can influence host biology and how organisms can survive in a world abundant with parasites.