1. Parental effects can have profound consequences on offspring phenotype. Still, little is known about the relative influence of prenatal versus postnatal parental effects of parasite exposure of parents on offspring traits.
2. In this study, we investigated the respective role of a prenatal and a postnatal immune challenge of parent feral pigeons (Columba livia) on offspring humoral immunity, growth and survival. We used a cross-fostering design and antigen injections in biological and foster parents. Feral pigeons are particularly suitable for studying the effects of parental immune challenges because they can affect the phenotype of their young through the transmission of prenatal antibodies in the egg and postnatal antibodies in the ‘crop milk’, a substance produced in the crop of both parents.
3. Results show that a prenatal immune challenge of biological parents with keyhole limpet haemocyanin (KLH) antigen decreased the humoral response against KLH of nestlings injected at 14 days of age. In contrast, a postnatal immune challenge of foster parents with KLH enhanced the humoral response of 1-year-old juveniles exposed to a second KLH injection, but only when these juveniles had received their first injection at 3 days of age.
4. No effect on nestling and juvenile response to another antigen (NDV) was observed, indicating that the changes in humoral responses were specific to the KLH injected in parents. In addition to this, prenatal and postnatal parental immune challenges had an interaction effect on fledging body mass, but no effect on juvenile survival.
5. This study shows that pre- and postnatal exposure to antigens in parents has contrasted effects on offspring humoral response and growth. Moreover, it shows that the timing of an early exposure to antigens in nestlings has important effects on their specific humoral response.
6. This study thus suggests that pre- and postnatal parental effects have distinct roles in shaping the phenotype of the offspring on different time scales and calls for further investigations on the potential adaptive role of combined parental effects. Moreover, it suggests that pigeon milk has positive effects on offspring humoral immunity and thus could potentially have a similar immune role as mammalian milk.