Amphibian Alkaloids

Abstract

This chapter discusses that amphibians have elaborated an astonishing array of alkaloids, most of which are known only from the skin or skin glands of adult amphibians. These substances are probably released defensively against predators and/or microorganisms onto the skin surface from the cutaneous granular “poison” glands that develop during metamorphosis. Such glands are present even in frogs that do not seem to have elaborated a defensive substance. The origin of amphibian alkaloids is even less clear. Many represent unique structural classes, while others occur in certain insects. Ants contain simple pyrrolidines, piperidines, pyrrolizidines, and indolizidines; beetles contain tricyclic coccinellines; and a millepede contains a possible precursor for the pyrrolizidine oxime class. The phylogenetic distribution of alkaloids in amphibians discusses for genetic control through specific sets of biosynthetic enzymes. The involvement of symbiotic microorganisms, dietary precursors, or cofactors, or other environmental factors in alkaloid production in amphibians cannot be excluded, although genetic factors play a role. © 1993, Academic Press, Inc.