Morphophysiological traits of an amphibian exposed to historical industrial pollution in a Brazilian biodiversity hotspot

Industrial pollution is a significant global threat to biodiversity, but its consequences on rainforest ecosystems remain poorly understood. Amphibians are especially susceptible to pollutants released on natural environments due to their aquatic-terrestrial life cycle. Here, we explored the association of severe historical air, water, and soil pollution with physiological and morphological alterations on Rhinella ornata individuals, an endemic toad species of Atlantic Forest, a world biodiversity hotspot. We hypothesized that individuals sampled in sites closer to the pollution source will present worse indicators of health. As predicted, toads at decreasing distances from the pollution source presented enlargement of organs related to detoxification function (liver and kidneys) and compensatory immunological function (spleen). Contrary to our predictions, however, we do not found significant effects of proximity to the pollution source on individuals' body condition index, on the indicative of fertility (testicles masses) or on macroparasite infection's response (eosinophil counts). Surprisingly, proximity to the pollution source was associated with lower chronic stress levels (neutrophil/lymphocyte ratio) on individuals. We discuss which processes could promote the alterations found on the toads. We also discuss the possible acquirement of local resistance to contamination on toads populations closer from pollution source, giving the more than 60 years of exposure to chemical contaminants in the area.