PhD defence Merijn Driessen
Merijn Driessen (BPE/TRÊS)
Promotores: Prof. S. Verhulst, Prof. I.R. Pen, Prof. B.I. Tieleman
Trading off immunity
Disentangling life-history and environmental effects on zebra finch innate immunity
In this thesis we provide novel insights into the effects of environmental and life-history variables on six measures of baseline immunity, in an effort to identify causal variables driving asynchrony in immune function and immunosenescence. Our populations of zebra finch were housed in outdoor aviaries, exposed to natural cycles in temperature, wind, humidity and light. There, we utilized experimental manipulation of developmental period (brood size), foraging environment and opportunity to reproduce. An essential part of our approach is that all experimental manipulations are done in ways that mimic natural settings. For instance, our manipulation of foraging environment was realized through altering the amount of activity required to obtain a unit of food. Birds could increase foraging effort to obtain more food, like they can in nature.
Our most striking results came from the effort of reproducing, with animals in breeding aviaries showing increased values in three out of six measures of baseline immunity, and the expected reductions nowhere to be seen. Taken together with a decreased ability to mount an immune response observed in other studies, we hypothesize that our unexpected increase in immune levels points to a shift within the immune system, prioritizing stability and consistency over efficiency. Ageing patterns for these three measures revealed that they did decline with age, showing that reproduction does come at a long term cost.