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Ontogenetic Variation in the Chemical Defenses of Cane Toads (Bufo marinus): Toxin Profiles and Effects on Predators

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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.

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Acknowledgements

We thank the Australian Research Council, Queensland State Government, and Invasive Animals Cooperative Research Center for funding and David Nelson for assistance with bioassay experiments. Procedures involving live animals were approved by the University of Sydney Animal Care and Ethics Committee.

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Correspondence to Richard Shine.

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Table S1

Total amount of each bufadienolide detected (μmol) in each life history stage of the cane toad. Bufadienolides are listed by retention time (RT). All data are shown as mean ± SEM. “−” means below detectable levels. The “metamorph” category refers to small metamorphs (<13 mm SUL), whereas the “juveniles” category refers to metamorphs >16 mm SUL (DOC 72.0 KB)

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Hayes, R.A., Crossland, M.R., Hagman, M. et al. Ontogenetic Variation in the Chemical Defenses of Cane Toads (Bufo marinus): Toxin Profiles and Effects on Predators. J Chem Ecol 35, 391–399 (2009). https://doi.org/10.1007/s10886-009-9608-6

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