Frog farms in the state of São Paulo and its relationship with amphibian chytrids and conservation

Abstract

Amphibian decline and extinction have been taking place around the world, and one of the main causes is the chytridiomycosis, emerging infectious disease caused by the chytrid fungus (filo Chytridiomycota) Batrachochytrium dendrobatidis (Bd). In tadpoles it causes depigmentation of denticles and jaws, but it is usually non-lethal. In post-metamorphic individuals the fungus proliferates in the epidermis, causing hyperkeratosis and generating imbalance of ions and electrolytes, which can lead animals to death. One of the factors that could intensify the threat to amphibians is the invasion of exotic species in nature. In Brazil, the main invasive species is the bullfrog, Lithobates catesbeianus. This species was introduced in Brazil in 1935 for the practice of frog culture and currently it is estimated that 600 frog farms are active in the country. In addition bullfrogs are tolerant to Bd, being recognized as a possible reservoir and carrier of the fungus. Therefore, it can be a major carrier of Bd for others countries, through the international meat trade. Recent studies isolated Bd Brazilian endemic strains were from bullfrogs sold in Michigan and in invasive populations in Japan. Similarly, international trade of frogs may be responsible for the importation of strains from other regions to native fauna of Brazil, or even intensify the flow between strains within Brazil. Besides that, bullfrogs escape from frog farms the invaside surrounding ponds, potentially affecting native species. Native species, have also been found breeding inside frog farms. Such animal flow can contribute to the dissemination and maintenance of the disease in natural environments. Hence, we aim to characterize different frog farms in the state of São Paulo, for the presence, prevalence, and load (infection indices) of Bd in bullfrogs and map the logistics of production and trade of these animals with special attention to the chytrid epidemiology. In addition, we aim to sample native frogs in the vicinity of farms (measuring the infection indices, and genotyping Bd strains). With this information we will be able to determine if there is transmission between bullfrogs and native species. Finally, we aim to propose mitigation and disease eradication actions, helping in national and international amphibian conservation. (AU)