Immunization reduces vocal communication but does not increase oxidative stress in a songbird species

Abstract

Itishypothesizedthatvariation inimmunefunction between individuals is due to costs incurred to sustain it. Sup- port for this hypothesis mostly comes from short-term studies on the either costs of innate responses or a combination of innate and antibody responses. Key studies on the fitness and physiological costs of acquired immunity, in which the antibody response is specifically stimulated over a long peri- od, are lacking. We specifically stimulated the antibody re- sponse against a virus (Newcastle virus) in male European starlings (Sturnus vulgaris) for 2 months to test whether im- munization reduces a fitness-related trait (song rate) and in- creases oxidative stress. Immunization did not affect the total song rate, but it caused a reduction of the undirected song rate (produced away from the nest box and mostly used for estab- lishing dominance hierarchy). We also found that immunized birds had a lower nest-box-oriented song rate (mostly used to attract females) than control birds although the interaction between treatment and sampling period was not significant. Immunization did not cause any changes in the blood oxida- tive status. Starlings with a higher nest-box-oriented song rate had significantly lower levels of oxidative protein damage. Finally, starlings that skipped the antibody response had an oxidative status similar to that of starlings that produced anti- bodies, but they had overall a lower rate of undirected song. Our results suggest that (i) immunized starlings preserved the song used to attract mates but not that used in social interac- tions and (ii) the antibody response incurs costs that are reflected in the expression of song, but also that these costs are unlikely to be determined by oxidative stress. Our results also suggest that bird song might convey information about a male's oxidative status.