Influência de fatores ambientais sobre a composição, diversidade funcional e doenças infecciosas em comunidades de girinos no Sul do Brasil

Abstract

Landscape changes impact biodiversity, altering the species composition of a community and threatening the more vulnerable species with extinction. Amphibians are highly susceptible to environmental changes and are negatively affected by habitat fragmentation and loss, climatic changes, exotic species, and diseases. Due to this, amphibians are considered the most threatened group on the planet, with several species already extinct or threatened with extinction. The largest number of threatened species in Brazil occur in the Atlantic Forest. Therefore, knowing the composition, functional diversity attributes, and dynamics of the infection caused by pathogens such as chytridiomycosis and ranavirosis is extremely important for amphibian conservation in this biome. In Brazil’s South Region, remnants of the Atlantic Forest form a mosaic with areas of pastures, agriculture and urbanization. Studies on the ecology of tadpole communities are scarce in this portion of the Atlantic Forest. Here, we present unprecedented studies on anuran community composition, functional diversity attributes, and infection by pathogens of emergent diseases (chytridiomycosis and ranavirosis) using tadpoles as study models. We conducted field collections between October 2018 and March 2019 in waterbodies (streams and ponds) located in forest remnants in Brazil’s South Region. The study area included seven forest remnants in the states of Paraná, Santa Catarina, and Rio Grande do Sul. We collected about 3000 tadpoles from 22 species in 30 waterbodies. In the laboratory, we identified the tadpoles and determined the presence of deformities in the oral apparatus and zoosporangia of the fungus Batrachochytrium dendrobatidis (Bd) and performed morphological measurements. We also used qPCR to identify ranavirus in the studied communities. We used satellite images to assess land use of the sampled areas, analyzed morphological data of the microenvironments and physical and chemical parameters of the water in the waterbodies. We showed that the dissimilarity in the composition of tadpole communities was influenced by larger areas of forest and pasture, with the habitat-specialist species being associated with forests. Attributes of tadpole functional diversity were selected by physicochemical characteristics of the water and morphological characteristics of the habitat, which act differently on lentic and lotic waterbodies. We did not record the presence of ranavirus in the studied communities but found a high prevalence of Bd. Tadpole communities in landscapes with larger forest areas were indicators of the Bd fungus. Similarly, two habitat-specialist species (Boana curupi and Crossodactylus schmidti) and one habitat-generalist (Boana faber) were Bd- 7 indicator species, the latter using forest areas as shelter. Thus, we conclude that the southern Atlantic Forest has a high prevalence of Bd, and forest environments have a greater influence on the dynamics of this fungus in the aquatic environments. Our study provides important data on the composition, functional diversity, and vulnerability to emergent pathogens in anuran communities in a little-known region of the Atlantic Forest.