"Hematological health state indices of greenfinches: sources of individual variation and responses to immune system manipulation."
Thesis supervisor: prof Peeter Hõrak, Tartu Ülikool
Opponent: Kevin J. McGraw, juhtivteadur, PhD, Arizona Riiklik Ülikool
The primary goal of immunoecology is to find out the factors, both extrinsic and intrinsic, leading to changes in immune system function, and understand how these changes affect disease susceptibility. Although it has now been accepted that immune responses are costly, the question about the currencies used for paying this cost has remained poorly understood. The main aims of my thesis were (1) to assess the suitability and utility of several widely used methods in ecological research of immunity and oxidative balance systems, and (2) to study some of the most intriguing questions in avian immunoecology. In the first part, I tested the long-term impact of a classic immunoecological technique (PHA skin test), correlations between several indexes of oxidative status and their repeatability in time, and the suitability of wild-caught captive greenfinches for ecophysiological research. In the second part, I studied the association between carotenoids and immune function, oxidative costs of mounting an immune response, and the information content of plumage coloration. Captive greenfinches were used as model organisms. I found that carotenoids may play a role in immune response and in the cost of immune activation, but studying this role is complicated because of several confounding intrinsic factors. I also showed that oxidative damage is a part of the costs of an immune response. According to my results, the bird's ability to control oxidative stress is signaled with its black plumage ornaments, but not in carotenoid-based ornaments. In conclusion, studying captive greenfinches seems to be a promising approach for answering many intriguing questions in immunoecology. Their good captivity tolerance allows studying a wild species in controlled laboratory conditions. Their plumage ornaments allow studying honesty of signal traits. Their common infection with coccidians is easy to follow and manipulate, making them good models for studying the costs of immune activation and the associations between immune system and other traits. At the same time, although some model systems and methods might seem to be widely accepted and technically completed, work with old and new methods must always continue in order to find possible flaws, better interpretation possibilities and new solutions. Continuous methodological work will eventually help to bind together immunology and ecology, and this synthesis will enable scientists to find solutions to many questions that both disciplines separately would fail to answer.