Costs and benefits of immune system activation on physiology, behavior and offspring phenotype from an immunoecological perspective

Abstract: Pathogen challenges and host immune defenses can have substantial impact on life history patterns of animals. Biotic and abiotic factors may affect immunity in wild animals, influencing e.g., population dynamics and sexual selection. The overall aim of this thesis was to assess costs and benefits of immune system activation on physiology, behavior and offspring phenotype. The conducted research has been in two of the major branches within the field of immunoecology; (i) direct and indirect effects related to the costs induced by immune system activation and (ii) different aspects of maternal transfer of antibodies to offspring. We found that immune-challenged zebra finches (Taenopygia guttata) demonstrated some of the general sickness behaviors, such as reduction in appetite and activity. However, zebra finches showed a circadian pattern in their thermoregulatory response, manifested as fever at night and hypothermia at day. In addition, they reduced their energy consumption several days after the immune-challenge. Immune-challenged zebra finch mothers also increased investment in the current breeding event, in line with a ‘terminal investment’ strategy. When examining the effects of immune system activation on the energy budget on wild birds during winter, we found that immune-challenged great tits (Parus major) attenuated their energy saving nighttime hypothermia and immune-challenged blue tits (Cyanistes caeruleus) were more inclined to expose themselves to perceived predation risk in order to save energy by using nest boxes for nighttime roosting. When assessing maternal antibody transmission to offspring, we found that immune-challenged zebra finch mothers transferred antigen-specific antibodies to their offspring in relation to antibody concentration in her circulation by the time of egg laying. These maternal antibodies persisted in the offspring until at least 5 days of age. In addition, we demonstrated that mothers are able to transfer functional antigen-specific antibodies to their offspring five months after the mothers were exposed to the antigen. Collectively, this work shows how immune system activation can have significant effects on physiology, behavior and offspring phenotype, with important implications for avian life history evolution.