Sexual differences in oxidative stress in two species of Neotropical manakins (Pipridae)

Because of differences in energetic investments in reproduction, natural and sexual selection are expected to impact males and females differentially, driving the evolution of sexual dimorphism. Thus, males and females are predicted to also differ in how they respond to environmental stressors and how they restore and maintain body homeostasis. Oxidative stress has been suggested to be one potential indicator of the impact of environmental stressors on wildlife. In this paper, we evaluate, for the first time, the oxidative stress in two sympatric lekking species of Neotropical manakins: the Red-headed Manakin (Ceratopipra rubrocapilla) and the White-crowned Manakin (Pseudopipra pipra). Specifically, we test the hypothesis that females of these two species have higher levels of oxidative stress than males because, among Neotropical manakins, only females provide parental care. We found no support for this hypothesis. In fact, males had higher levels of oxidative stress than females. All three hypotheses (predation stress, oxidation handicap, and aerobic activity) available to explain our results have limitations, so further field and laboratory studies on oxidative stress in manakins are required.