Measurements of body temperature and oxidative stress reveal differential costs associated with humoral immune function in a passerine bird

Abstract

Eco-immunology considers resistance to antigens a costly trait for an organism, but actual quantification of such costs appears not straight forward. Costs of the immune response (IR) are e.g., visible in impaired coloration, reduced growth or reproductive success. Activation of the humoral IR is a slow, complex, and long-lasting process, which makes the quantification of its energetic cost a potential losing game. We implemented near continuous measurements of body temperature in zebra finches (Taeniopygia guttata) as a proxy for the energetic cost with particular interests in the body temperature from activation of the humoral IR until the peak of antibody release several days later. At the peak of the antibody release we additionally measured oxygen consumption (open-flow respirometry) and markers of oxidative stress (dROMs, OXY). Birds with activated IR defended a higher night time body temperature during the first four nights after an immune challenge in comparison to controls, implying increased night time energy use. At the peak of antibody production, we did not find differences in night time body temperature and oxygen consumption but observed a differentiated results for oxygen consumption during day time. Immune challenged females had significantly higher oxygen consumption than other groups. Moreover, we found that activation of the humoral IR increases oxidative damage, a potential cost of defending higher night time body temperature crucial at the early stage of the IR. The costs generated by the immune system appear to consist of two components energetic and non-energetic, and these may appear separated in time.