Alkaloids in bufonid toads melanophryniscus : temporal and geographic determinants for two argentinian species. Bufonid toads of the genus Melanophryniscus represent one of several lineages of anurans with the ability to sequester alkaloids from dietary arthropods for chemical defense. A total of 29 alkaloids were identified in two collections of this population. Eight alkaloids were identified in M. The alkaloid profiles of Melanophryniscus rubriventris collected from four locations in the provinces of Salta and Jujuy, Argentina, contained 44 compounds and differed considerably between locations. Furthermore, alkaloid profiles of M.