Natural history, coloration pattern and conservation status of the threatened South Brazilian red bellied toad, Melanophryniscus macrogranulosus Braun, 1973 (Anura, Bufonidae)

Efforts to find and gather data on natural history, including geographic records, of species considered threatened are an important tool to assess and update its conservation status. Little is known about the threatened South American red belly toad, Melanophryniscus macrogranulosus, endemic from northeastern Rio Grande do Sul, southern Brazil. The main goal of this article is to provide information on natural history, geographic distribution, morphology and conservation of this toad, including new geographic records, and new data on color pattern, habitat use, and reproductive and defensive behavior. We conducted 30 field expeditions from 2005 to 2013 to the type locality and surroundings and examined the three major herpetological collections from Rio Grande do Sul. We described the live color pattern of juveniles and adults. The data on reproductive and defensive behavior was obtained in the field. We rediscovered the species on its type locality, after 45 years from previous records, and revealed the presence of M. macrogranulosus in five new localities. The color pattern varies ontogenetically from metamorphosed juveniles to adults. Newly metamorphosed individuals have dark gray dorsum and pale, partially translucent ventral surface. Adults have dorsum from light to dark green and ventral surface exhibiting a green or grayish blue coloration pattern with white spots and red patches. Associated with this suspected aposematic coloration we observed individuals employing unken reflex when disturbed. Reproductive activity was recorded after heavy rains in all four seasons. Males call during day and night, in small, shallow pools along temporary streams with clear water. Amplexus and struggles between males also involving a female were registered inside the water in the reproductive site. All records of M. macrogranulosus are inside the limits of the Atlantic forest, considered one of the most endangered Biome of Brazil. However, none is inside the limits of a protected area. Some possible threats observed include fragmentation and habitat destruction, pollution (improper discard of human waste) and the recent duplication of a paved road near the reproductive site. These impacts associated with the small extent of occurrence, justify the species category as Endangered (EN).