The impact of chemical pollution across major life transitions: a meta-analysis on oxidative stress in amphibians

Among human actions threatening biodiversity, the release of anthropogenic chemical pollutants – which have become ubiquitous in the environment – is a major concern. Chemical pollution can induce oxidative stress and damage by causing the overproduction of reactive oxygen species (ROS), and affecting the antioxidant system. In species undergoing metamorphosis (i.e., the vast majority of the extant animal species), antioxidant responses to chemical pollution may differ between pre- and post-metamorphic stages. Here, we meta-analysed (N = 104 studies, k = 2,283 estimates) the impact of chemical pollution on the redox balance across the three major amphibian life stages (embryo, larva, adult). Before metamorphosis, embryos did not experience any redox change but larvae activate their antioxidant pathways and do not show increased oxidative damage against pollutants. In contrast, post-metamorphic individuals show unnoticeable antioxidant responses, and a marked oxidative damage in lipids. Also, type of pollutant (i.e., organic vs inorganic) promotes contrasting effects across amphibian life stages. Our findings show a divergent evolution of the redox balance in response to pollutants across life transitions of metamorphosing amphibians, likely linked to the characteristics of each life stage. Further comparative mechanistic approaches to wildlife responses to global changes will improve our understanding of these eco-evo-devo processes.