Cutaneous immune activity, but not innate immune responsiveness, covaries with mass and environment in nestling house wrens (Troglodytes aedon).

Immunological measures are increasingly being applied to ecological and evolutionary studies of wild vertebrates, yet frequently it is not clear how condition and environmental factors correlate with various immune parameters. We used mixed-model ANOVA to examine the effects of several measures of condition (both morphological and physiological) and environmental factors on two measures of immune responsiveness in nestling house wrens (Troglodytes aedon L.) to test the hypothesis that nestlings in good condition mount stronger immune responses than those in poor condition. Based on previous studies, we predicted that the innate bactericidal response would be less likely to be affected by condition-related factors than the cutaneous response, which includes both innate and the more costly adaptive components. Both cutaneous immune activity (i.e., phytohaemagglutinin [PHA] response) and innate immune responsiveness (i.e., plasma bactericidal activity) varied significantly among broods. Nestling PHA response was significantly influenced by year, mass, and the time of day that the challenge was administered. However, besides nest of origin, no other variable examined had a significant effect on bactericidal activity. Morphological condition, assessed as body mass adjusted for structural size, differed significantly among nests and years and was positively correlated with hematocrit but not plasma albumin/gamma-globulin proteins, indicating that these are measures of different aspects of health state.