Diferenças na assimetria flutuante e na massa de fígados em uma população de anfíbios afetada pelo maior desastre ambiental do Brasil

Abstract

The largest environmental disaster in Brazilian history occurred in November 2015 with the collapse of the Fundão dam in the municipality of Mariana, Minas Gerais state, Brazil. The incident released tons of ore tailings into both terrestrial and aquatic environments, leading to high concentrations of heavy metals and exposing organisms, including amphibians, to different levels of toxicity. Amphibians are particularly susceptible to chemical agents and their life cycle usually involves both aquatic and terrestrial phases. As a result, they can provide evidence of contamination through variations in indicators of stress, such as deviations in developmental stability (e.g. fluctuating asymmetry - FA) and changes organs responsible for filtering toxic substances (e.g. liver). To analyze the impact of the disaster, we assessed the fluctuating asymmetry and liver mass of Boana albopunctata (Anura: Hylidae) individuals. We analyzed post-metamorphic specimens collected before the disaster (2014) and at two time points after the disaster (2018 and 2022) from a farm in the municipality of Barra Longa, Minas Gerais state, Brazil, through which the tailings passed. We measured 12 bilateral structures in each individual and calculated FA indices for each structure, using a protocol that analyzes the type of existing asymmetry and possible measurement errors. We also weighed the liver of each specimen using an analytical balance. Finally, we compared the FA indices and liver masses among the three different years, expecting higher FA levels and larger livers after the disaster. Of the total traits measured, three showed FA, while the others were excluded from subsequent analyses due to measurement errors, directional asymmetry, and/or anti-symmetry. We observed lower FA indices in the tympanic area of specimens collected in 2022 compared with previous years, which could be related to the selection of individuals with more symmetrical eardrums seven years after the accident. This is significant, as the importance of symmetrical eardrums in the phonotaxis of female frogs to male calls has been demonstrated. However, we also observed an increase in liver masses of individuals after the accident, specifically when comparing 2014 and 2022. This suggests that the function of this organ remained resilient in individuals and their offspring after exposure to the tailings. Although the observed results may have been influenced by unmeasured ecophysiological processes, our study is the first to demonstrate differential responses of an amphibian population in a natural environment affected by the Fundão dam environmental disaster. We emphasize that the effects of mining on organisms can be multifaceted and indicate the need to conduct more detailed studies with various affected groups to understand the magnitude of this and other similar disasters.