Individual and Geographic Variation of Skin Alkaloids in Three Swamp-Forest Species of Madagascan Poison Frogs (Mantella)

Nirina R. Andriamaharavo, National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
H. Martin Garraffo, National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Thomas F. Spande, National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Lesley Ann Giddings, Middlebury College
David R. Vieites, CSIC - Museo Nacional de Ciencias Naturales (MNCN)
Miguel Vences, Technische Universität Braunschweig
Ralph A. Saporito, John Carroll University


Seventy skins of three mantellid frog species from Madagascan swamp-forest habitats, Mantella aurantiaca, M. crocea, and M. milotympanum, were individually examined for skin alkaloids using GC/MS. These poison frogs were found to differ significantly in their alkaloid composition from species of Mantella originating from non-flooded rainforest in eastern Madagascar, which were examined in earlier work. Only 16 of the previously detected 106 alkaloids were represented among the 60 alkaloids from the swamp-forest frogs of the present study. We hypothesize this difference is related mainly to habitat but cannot exclude a phylogenetic component as the three swamp-forest species are a closely related monophyletic group. The paucity of alkaloids with unbranched-carbon skeletons (ant-derived) and the commonness of alkaloids with branched-carbon skeletons (mite-derived) indicate that oribatid mites are a major source of alkaloids in these species of mantellids. Furthermore, most of the alkaloids have an oxygen atom in their formulae. Differences in alkaloids were observed among species, populations of the same species, and habitats. In M. aurantiaca, small geographic distances among populations were associated with differences in alkaloid profiles, with a remote third site illustrating even greater differences. The present study and an earlier study of three other mantellid species suggest that oribatid mites, and not ants, are the major source of alkaloids in the species of mantellids examined thus far.