Immune challenge affects female condition and egg size in the grey partridge

As maintenance of the immune system is energetically costly and resource-limited, trade-offs among immune function, body condition, and reproductive allocation are expected. In this study, we experimentally test the possible trade-off between immune response, self maintenance, and reproductive output in breeding grey partridges Perdix perdix. Before laying, half the females were immune challenged with a novel antigen vaccine (Newcastle disease virus, NDV). The challenged females showed a higher erythrosedimentation rate, a serum parameter related to worsened health conditions, but their cell-mediated immune reaction (PHA test) did not differ from that of controls. The NDV-treated females laid smaller eggs (mass, length, and breadth), while the concentrations of antibacterial substances (lysozyme and avidin, two enzymes that confer innate antibacterial immunity) were unrelated to the hen's immune challenge. Our study suggests that an immune challenge can have physiological consequences in terms of self-maintenance and reproductive allocation to the egg.