Como a água do entorno de lagoas artificiais afetam a composição, diversidade e a saúde de anuros neotropicais

Abstract

Agricultural practices can reshape the environment and affect the survival of aquatic organisms. In modified landscapes, artificial ponds used for fish farming often provide excellent habitat opportunities for amphibian populations, contributing to the maintenance of local diversity. Data point to a predominant role of the habitat around these lakes and of the water quality for amphibians, suggesting that the characteristics of the terrestrial and aquatic environment act as an environmental filter on these animals. Thus, these systems can be good study models to assess the relationships between amphibians and anthropic changes in their habitat. Contamination of these ponds can also increase disease pressure, where the mechanisms underlying this pattern are not always known. For example, artificial ponds that receive nutrient enrichment should strongly influence the selection of environmental bacteria, which have the potential to alter the microbiome composition of aquatic animals and their vulnerability to disease. However, these changes in the host microbiome associated with diseases of aquatic organisms have received little attention when related to the enrichment of nutrients of animal origin. We analyzed how anthropogenic environmental changes in landscape and water quality affect the composition, diversity and health of anuran amphibians in artificial ponds in southern Brazil. We sampled a set of artificial ponds with different landscapes and levels of contamination from the point of view of frog diversity as well as the effects of water quality on the composition of the host's skin microbiome and its relationship with chytridiomycosis, caused by the fungus Batrachochytrium dendrobatidis (Bd). Our results indicate that this integrated farming system of fish and swine was responsible for outbreaks of fecal coliforms, disturbing the bacterial communities of the amphibian skin, so that the hosts recruited higher proportions of Bd-facilitating bacteria and had higher intensity and prevalence of infection. Our findings also highlight that despite the risk of chytridiomycosis, these artificial lakes can act as important breeding sites for anurans, especially in anthropic habitats with low availability of breeding sites. But the ability to offer reproductive opportunities, and consequently, help maintain anuran populations, depends on the configuration of the habitat in which these ponds are located. The physical-chemical parameters of the water and the configuration of the habitat around the ponds are the elements that most explained the variation in frog diversity. However, the characterization of the surrounding environment played a predominant role in the differences between communities. The level of soil exposure in the surrounding area was the component that most acted on the 4 turnover component of beta diversity. We expose here that the species turnover process is a consequence of the landscape simplification caused by the removal of the original vegetation cover (forests), culminating in biotic homogenization. Among the water parameters, only the phosphate concentration proved to be relevant for the configuration of the communities. Phosphate spikes can be derived from sewage or fertilizer contamination. Both types of contamination are likely to occur in the study area, even though it is characterized by low human population density and whose economic activity is based on small-scale (family) agriculture. Despite the enormous potential of artificial lakes in the maintenance of regional frog communities, these may be acting as ecological traps and their effectiveness will depend on the presence of forest remnants as well as on the quality of the water.