RESUMO
Several hypotheses have been proposed to explain the biogeographic processes that generate the high species richness of the Amazon basin. We tested two of them in a terra firme (upland) forest frog species, Physalaemus petersi: (1) the riverine barrier hypothesis; and (2) the elevational gradient hypothesis. Mitochondrial DNA sequence data (2.4 kb) from the 12S, 16S, and intervening valine tRNA genes were obtained from 65 P. petersi individuals and 4 outgroup taxa and analyzed with a combination of phylogenetic and population genetic approaches. Moderate support for the riverine barrier hypothesis was found for one of the three rivers examined, but little evidence was found for the elevational gradient hypothesis. Phylogenetic analyses revealed that high levels of sequence divergence (an average of 4.57-4.79%) separate three well-supported clades from the northwestern, southwestern, and eastern Amazon. Strong evidence for recent population expansion in P. petersi in the southwestern region of the Amazon basin was also uncovered.