Predator learning favours mimicry of a less-toxic model in poison frogs (original) (raw)

Nature volume 440, pages 208–211 (2006)Cite this article

Abstract

Batesian mimicry—resemblance of a toxic model by an edible mimic—depends on deceiving predators1. Mimetic advantage is considered to be dependent on frequency because an increase in mimic abundance leads to breakdown of the warning signal2,3. Where multiple toxic species are available, batesian polymorphism4 is predicted—that is, mimics diversify to match sympatric models. Despite the prevalence of batesian mimicry in nature5, batesian polymorphism is relatively rare6. Here we explore a poison-frog mimicry complex comprising two parapatric models and a geographically dimorphic mimic that shows monomorphism where models co-occur. Contrary to classical predictions, our toxicity assays, field observations and spectral reflectances show that mimics resemble the less-toxic and less-abundant model. We examine “stimulus generalization”7 as a mechanism for this non-intuitive result with learning experiments using naive avian predators and live poison frogs. We find that predators differ in avoidance generalization depending on toxicity of the model, conferring greater protection to mimics resembling the less-toxic model owing to overlap of generalized avoidance curves. Our work supports a mechanism of toxicity-dependent stimulus generalization8, revealing an additional solution for batesian mimicry where multiple models coexist.

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Acknowledgements

We thank L. Coloma, J. C. Santos, and S. Ron for discussions on poison frogs; D. Cannatella for frog photos in Fig. 1, assistance with assays and discussion; M. Domjan for advice on predator learning experiments; E. Tapia, S. Padilla, M. Bustamante, P. Menéndez-Guerrero and D. Paucar for assistance in the field; J. Cassaday for assistance with toxicity assays; and M. Ryan for comments on the manuscript. This work was supported by University of Texas at Austin EEB graduate program fellowships, a UT Continuing Fellowship, and the Explorer's Club Exploration Fund.

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  1. Section of Integrative Biology, University of Texas, 1 University Station, 78712, Austin, Texas, USA
    Catherine R. Darst & Molly E. Cummings

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  1. Catherine R. Darst
  2. Molly E. Cummings

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Correspondence toCatherine R. Darst.

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Reprints and permissions information is available at npg.nature.com/reprintsandpermissions. The authors declare no competing financial interests.

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Darst, C., Cummings, M. Predator learning favours mimicry of a less-toxic model in poison frogs.Nature 440, 208–211 (2006). https://doi.org/10.1038/nature04297

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Editorial Summary

Don't eat me

One of the earliest tests of Darwin's theory of natural selection was defensive mimicry, and this act of deception continues to cast light into hidden corners of evolutionary biology. Few frogs catch the eye like poison frogs — and such is their intent. Their garish colours advertise toxicity, and ‘cheating’ species mimic the warning coloration without the toxins to back it up. A study in the Amazonian rainforest in Ecuador has produced the surprising finding that edible frogs mimic the less toxic of two poison-frogs in the vicinity. Why mimic the less potent deterrent? The answer, discovered through learning experiments, lies in avoidance psychology. Extreme noxiousness makes predators avoid things that only slightly resemble the noxious object; however, with less severity, predator avoidance becomes specific. So the mimics of the less toxic poison frog gain total protection; they are avoided by predators learning on either the more or less toxic frogs.

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