Chapter 4 The Nature and Origin of Amphibian Alkaloids

The chapter discusses the nature and origin of amphibian alkaloids. The sructures of amphibian alkaloids were reviewed in detail, most recently in 1993. The distribution of various alkaloids among some 40 species of frogs of the neotropical family Dendrobatidae was presented in 1987. Synthetic efforts leading to amphibian alkaloids were reviewed, most recently in 1986. Since the 1993 review, many more alkaloids have been detected in amphibian skin extracts using gas chromatographic (GC) mass spectral and GC-Fourier-transform infrared (FTIR) spectral analyses. Structural classes have been defined, and, most importantly, evidence has been obtained that indicates that alkaloid-bearing amphibians—with the exception of the European fire salamander—probably do not synthesize their skin alkaloids, but instead rely on dietary sources and merely efficiently sequester and store for extended periods alkaloids that they obtain from ants, beetles, millipedes, and probably other small arthropods. The amphibian-skin alkaloids thus represent a remarkable instance of a chemical ecology, wherein the amphibian is wholly dependent on dietary arthropods as a source of the alkaloids that comprise the active principles in its defensive skin secretions.