Summary:

The physiological mechanisms involved in the cost of reproduction are poorly understood. In addition, the interaction between reproduction and infection with pathogens is still not resolved. Birds infected with pathogen may be more impacted by physiological mechanisms such as oxidative stress, because of the double physiological cost of reproduction and resistance to pathogens. In this case, an increased metabolism is expected and should lead to a physiological stress involving higher oxidative stress driven by an increased in oxidant production, a higher antioxidant recruitment and/or more oxidative damage to biomolecules. Here, we investigated the effect of reproductive investment and infectious status on parental oxidative stress measures in three wild populations of the great tit, Parus major, naturally infected by Plasmodium spp. Different physiological measures involved in both oxidant production and resistance to oxidative stress were taken from parents when chicks were 14 days old: erythrocyte superoxide production, a proxy of erythrocyte mitochondria quantity (cardiolipin content), and erythrocyte membrane resistance to oxidative attacks. We found a sex dependent effect of reproductive effort on membrane resistance. We also found that parental infection with Plasmodium spp. was linked to an increased production of superoxides, which in turn indirectly decreased membrane resistance. This study suggests that breeding birds incur an additional physiological cost of reproduction linked to infection with malaria parasites.