Amphibians in the border region between Uruguay and Brazil: Updated species list with comments on taxonomy and natural history (Part I: Bufonidae)1

Abstract

The border region between Uruguay and the Brazilian state of Rio Grande do Sul comprises four major biomes, i. e. the coastal dune zone, adjacent wetlands, low hill ranges (cuchillas), and grassland (pampas). All these environments provide different microhabitats for amphibians, such as continental lagoons, rivers, small streams, ponds and temporary water bodies. This habitat diversity is reflected by high species diversity, but the amphibian fauna in this region is yet poorly studied. Recent fieldwork revealed several new records for anurans, including a recently described species of toad, Chaunus achavali. In our publication we provide an updated check list of the species belonging to the family Bufonidae (toads) occurring in this region, including taxonomical comments, conservation issues, natural history notes, zoogeographical considerations and an updated bibliography. A total amount of 12species of Bufonidae is known from the study area belonging to the genera Chaunus (formerly Bufo) and Melanophryniscus. Chaunus is represented by seven species in three taxonomic groups (C. marinus, C. granulosus and C. crucifer groups), whereas Melanophryniscus is represented by six species in three groups (M. stelzneri, M. moreirae and M. tumifrons groups). We present a key for the identification of these bufonid species in the study region. Based on geographical distribution patterns of the species involved, we distinguish five main ecological groups: Coastal species inhabiting sandy soil layers (Chaunus arenarum and Melanophryniscus montevidensis); species shared with the Argentinean mesopotamic region (Chaunus granulosus group); species characteristic for the chacoan region (Chaunus schneideri); species associated with the low hill regions of Uruguay and southern Rio Grande do Sul (most taxa belonging to Melanophryniscus); two species of Chaunus (C. ictericus, C. henseli) are associated with the Atlantic forest biome further to the north being untypical for the border region.