Ecotoxicologia em tempos de emergência climática: Os impactos da contaminação agroquímica em girinos amazônicos sob estresse térmico

Abstract

The global decline of amphibian populations is driven by multiple anthropogenic stressors, most notably chemical pollution and climate change. In the Amazon, the conversion of forests into agricultural land has intensified pesticide use, coinciding with projections of rising regional temperatures. In this context, this thesis investigated the isolated and combined effects of the carbamate insecticide methomyl and IPCC-projected global warming on tadpoles of native Amazonian species. Across four chapters, we explored aspects related to a review of the current scenario, acute and chronic toxicity, behavioral and neuroendocrine alterations, and larval development costs. In the first chapter, through a literature review, we diagnosed the scarcity of ecotoxicological data for Amazonian species and discussed how the thermal physiology of tropical ectotherms may render them particularly vulnerable to synergistic interactions between contaminants and high temperatures. In the second chapter, we determined acute lethality in Osteocephalus taurinus and Scinax ruber. We observed that elevated temperature (30°C) significantly potentiated methomyl toxicity for O. taurinus, corroborating the climate-induced toxic sensitivity hypothesis, whereas S. ruber proved to be more sensitive to the pesticide regardless of temperature, with no alterations in critical thermal maximum (CTmax) for either species. In the third chapter, we evaluated sublethal behavioral and physiological responses. While O. taurinus exhibited lethargy, a preference for dark substrates, and an unexpected increase in acetylcholinesterase (AChE) activity under thermal and chemical stress, S. ruber maintained behavioral and enzymatic stability but showed a significant elevation in cortisol, indicating distinct coping strategies between the species. In the fourth chapter, we investigated chronic effects in Leptodactylus knudseni throughout metamorphosis. Exposure to methomyl accelerated larval development but resulted in smaller individuals with lower body mass, evidencing an energetic trade-off. There was an inhibition of AChE and activation of the antioxidant system (increased superoxide dismutase - SOD), suggesting metabolic costs of detoxification. We conclude that the interaction between pesticides and global warming affects Amazonian tadpoles in a complex and species-specific manner, ranging from acute mortality to hidden developmental and physiological costs. This underscores the need to include thermal variables in environmental risk assessments for biodiversity conservation in the region.