Physiological effects of immune challenge in captive greenfinches (Carduelis chloris)

It is expected that the costs of exploiting an organism's immune system form the basis of many life-history trade-offs. However, the processes responsible for generating these costs have rarely been quantified in terms of energy expenditures and physiological rearrangements in the organism during the immune response. To determine the physiological changes caused by the immune response, we recorded various condition indices of male captive greenfinches (Carduelis chloris) 1, 4, and 8 days after immune challenge with a nonpathological antigen (sheep red blood cells; SRBC). Measured variables included estimates of total and differential leukocyte counts, serum protein concentrations and profile, serum triglyceride concentration, basal metabolic rate, body mass, spontaneous locomotory activity, and serum total antioxidant capacity. On days 4 and 8 post injection, immune-challenged greenfinches significantly reduced their spontaneous locomotory activity, which suggests a switch to energy conservation. Fourteen hours after injection of SRBC, a transient increase in serum beta-globulin concentration was recorded, indicating an acute-phase response to the anti-en. None of the other condition indices was affected by the treatment, which suggests that when birds maintained on an affluent feeding regimen in captivity mounted an immune response against SRBC, they did not incur any serious physiological impact.