Baseline innate immunity does not affect the response to an immune challenge in female great tits (Parus major)

Abstract

The immune system is an important defence against pathogens but requires resources that hosts may also use otherwise. Thus, trade-offs between investment in immunity versus other life-history traits may exist, especially during resource-demanding periods such as reproduction. Here, we investigated the potential trade-off between an activated immune system and parental care in free-living great tits. We also studied whether variation in baseline immune indices prior to immunization contributes to individual differences in the responses to an immune challenge. To this end, we injected free-living great tit females with either phosphate-buffered saline (PBS) or with bacterial lipopolysaccharides (LPS) when nestlings were 9 days old and subsequently recorded parental feeding rates. We quantified potential fitness consequences via the growth and survival of their nestlings. Exposure to LPS tended to decrease female feeding rates. However, nestling body mass was not affected by the maternal immune challenge, probably because males compensated for the change in feeding rate of their partner. We found a negative relationship between haptoglobin levels and female feeding rates pre-treatment, but not with any of the other innate immune traits. Although there was substantial variation in female innate immune indices, we found no evidence that baseline immunity affected how females reacted to an immune challenge in terms of changes in parental behaviour.