Ontogenetic Variation in the Chemical Defenses of Cane Toads (<Emphasis Type="Italic">Bufo marinus</Emphasis>): Toxin Profiles and Effects on Predators |
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Authors: | R Andrew Hayes Michael R Crossland Mattias Hagman Robert J Capon Richard Shine |
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Affiliation: | (1) Institute for Molecular Bioscience, University of Queensland, Brisbane, Queensland, 4072, Australia;(2) School of Biological Sciences A08, University of Sydney, Sydney, New South Wales, 2006, Australia |
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Abstract: | We conducted a quantitative and qualitative chemical analysis of cane toad bufadienolides—the cardioactive steroids that are
believed to be the principal cane toad toxins. We found complex shifts in toxin composition through toad ontogeny: (1) eggs
contain at least 28 dominant bufadienolides, 17 of which are not detected in any other ontogenetic stage; (2) tadpoles present
a simpler chemical profile with two to eight dominant bufadienolides; and (3) toxin diversity decreases during tadpole life
but increases again after metamorphosis (larger metamorph/juvenile toads display five major bufadienolides). Total bufadienolide
concentrations are highest in eggs (2.64 ± 0.56 μmol/mg), decreasing during tadpole life stages (0.084 ± 0.060 μmol/mg) before
rising again after metamorphosis (2.35 ± 0.45 μmol/mg). These variations in total bufadienolide levels correlate with toxicity
to Australian frog species. For example, consumption of cane toad eggs killed tadpoles of two Australian frog species (Limnodynastes convexiusculus and Litoria rothii), whereas no tadpoles died after consuming late-stage cane toad tadpoles or small metamorphs. The high toxicity of toad eggs
reflects components in the egg itself, not the surrounding jelly coat. Our results suggest a dramatic ontogenetic shift in
the danger that toads pose to native predators, reflecting rapid changes in the types and amounts of toxins during toad development.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. |
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Keywords: | Anuran bufadienolides Bufo marinus toxicity ontogeny bufadienolides cardiac steroids |
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