Hanna Granroth-Wilding

PhD thesis

Parasitism, Family Conflict and Breeding Success
University of Edinburgh

Download the thesis (PDF)

Supervisors: Emma Cunningham and Sue Lewis at Edinburgh University, Francis Daunt and Sarah Burthe at the Centre for Ecology & Hydrology.

Wild animals are almost always infected with large numbers of parasites. A parasite infection can be expensive for the host to deal with, leading to negative consequences such as less successful breeding or poorer survival. By altering these vital rates, effects of parasites on individual hosts have the potential to scale up and affect the dynamics of entire populations. However, different hosts suffer these effects to different extents. Intrinsically, some may be more able to cope with an infection, for example because they are in better condition or have more efficient immune systems. Hosts may also be subject to different extrinsic influences, including both their ecological environment, for example food availability, and their social environment, that is how they interact with other individuals. These differences between hosts could be especially important during breeding, when parents must weigh up how much to invest in their own parasite defences against investing in caring for their young, who may be particularly vulnerable to infection. In my PhD thesis, I investigated how parasite infection of nestling chicks and their parents influences these trade-offs between family members and how this affects the outcome of the breeding attempt. Using experimental anti-parasite treatment of the European shag Phalacrocorax aristotelis, I examined the role of gut parasites in chick growth and survival, behavioural interactions between chicks and their parents, parent condition and parents' behaviour during and after the breeding season. As a seabird, the shag is an important indicator of changes in the marine environment, and understanding its responses to these changes requires a full understanding of its ecology. Parasitism is an important part of this ecology that has until recently been overlooked.