Discovery of skin alkaloids in a miniaturized eleutherodactylid frog from Cuba

Abstract

Four phylogenetically independent lineages of frogs are currently known to sequester lipid-soluble skin alkaloids for which a dietary source has been demonstrated. We report here a remarkable fifth such instance, in Eleutherodactylus iberia and Eleutherodactylus orientalis , two species of miniaturized frogs of the family Eleutherodactylidae from Cuba. Six pumiliotoxins and two indolizidines were found in E. iberia , one of the smallest frogs in the world and characterized by a contrasting colour pattern for which we hypothesize an aposematic function. Analyses of stomach content indicated a numerical prevalence of mites with an important proportion of oribatids—a group of arthropods known to contain one of the pumiliotoxins detected in E. iberia . This suggests that miniaturization and specialization to small prey may have favoured the acquisition of dietary skin alkaloids in these amphibians.