Trace Metals Affect Early Maternal Transfer of Immune Components in the Feral Pigeon

Maternal early transfers of immune components influence eggs' hatching probability and nestlings' survival. They depend on females' own immunity and, because they are costly, on their physiological state. Therefore, trace metals, whether toxic and immunosuppressive (e.g., lead, cadmium, etc.) or necessary and immunostimulant (e.g., zinc, copper, iron, etc.), are likely to affect the amount of immune components transferred into the eggs. It may also vary with plumage eumelanin level, which is known to be linked to immunity, to transfer of antibodies, and to metal detoxification. In feral pigeons (Columba livia) injected with an antigen and experimentally exposed to lead and/or zinc (two highly abundant trace metals in urban areas), we measured specific antibody transfer and concentrations of two antimicrobial proteins (lysozyme and ovotransferrin) in eggs. As expected, lead had negative effects on specific antibody transfer, while zinc positively affected lysozyme egg concentrations. Moreover, eggs from lead-exposed females exhibited higher ovotransferrin concentrations; because it binds metal ions, ovotransferrin may enable egg detoxification and embryo protection. Finally, eggs' lysozyme concentrations increased with plumage darkness of females not exposed to zinc, while the relation was opposite among zinc-exposed females, suggesting that benefits and costs of plumage melanism depend on trace metal environmental levels. Overall, our study underlines the potential ecotoxicological effects of trace metals on maternal transfers of immune components and the role of plumage melanism in modulating these effects.