An analysis of pre‐ and post‐hatching maternal effects mediated by carotenoids in the blue tit

Maternal effects increase phenotypic plasticity in offspring traits and may therefore facilitate adaptation to environmental variability. Carotenoids have been hypothesized to mediate costs of reproduction in females as well as maternal effects. However, assessing potential transgenerational and population consequences of environmental availability of carotenoids requires a better understanding of mechanisms of maternal effects mediated by these antioxidant pigments. Manipulating dietary availability of carotenoids to egg‐laying female blue tits and subsequently cross‐fostering nestlings between female treatments allowed us to specifically investigate the relative importance of maternal effects through egg carotenoids and through post‐hatching care mediated by antioxidants in females. Nestling body size and mass and plasma antioxidants were not significantly affected by pre‐ or post‐hatching maternal effects mediated by antioxidants, although both types of maternal effects in interaction explained the variation in growth, as measured by wing length. Development of the ability to mount a cell‐mediated immune response as well as its temporal dynamics was influenced by both pre‐ and post‐hatching maternal effects, with an advantage to nestlings originating from, or reared by, carotenoid‐supplemented females. In addition, nestlings reared by carotenoid‐fed females had a lower blood sedimentation rate, indicating that they may have been less infected than nestlings from controls. Finally, prehatching maternal effects in interaction with nestling plasma carotenoid levels affected the development of carotenoid‐based plumage. Maternal effects mediated by carotenoids may thus act as a proximate factor in development and phenotypic plasticity in traits associated with nestling fitness, such as immune response and ability to metabolize and use antioxidants, and ultimately participate in the evolution of phenotypic traits.