A review of chemical defense in harlequin toads (Bufonidae: Atelopus)

Abstract

Toads of the genus Atelopus are chemically defended by a unique combination of endogenously synthesized cardiotoxins (bufadienolides) and neurotoxins which may be sequestered (guanidinium alkaloids). Investigation into Atelopus small-molecule chemical defenses has been primarily concerned with identifying and characterizing various forms of these toxins while largely overlooking their ecological roles and evolutionary implications. In addition to describing the extent of knowledge about Atelopus toxin structures, pharmacology, and biological sources, we review the detection, identification, and quantification methods used in studies of Atelopus toxins to date and conclude that many known toxin profiles are unlikely to be comprehensive because of methodological and sampling limitations. Patterns in existing data suggest that both environmental (toxin availability) and genetic (capacity to synthesize or sequester toxins) factors influence toxin profiles. From an ecological and evolutionary perspective, we summarize the possible selective pressures acting on Atelopus toxicity and toxin profiles, including predation, intraspecies communication, disease, and reproductive status. Ultimately, we intend to provide a basis for future ecological, evolutionary, and biochemical research on Atelopus.

Graphical abstract

Highlights

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  We review the quantity and diversity of toxins in Atelopus toads.

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  Sampling and methodological biases likely affect known toxin quantity and diversity.

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  Atelopus extinctions threaten the loss of undescribed toxins.

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  Few data exist on the ecology and evolution of Atelopus chemical defenses.

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  Atelopus is a promising study system for toxin sequestration and synthesis.