Not all colors are equal: predation and color polytypism in the aposematic poison frog Oophaga pumilio
Aposematic organisms are not predicted to show high levels of warning signal diversity because they are expected to be under stabilizing selection to decrease costs of ‘educating’ predators about their unpalatability. However, systematic changes in warning signals (polytypism) can be expected if they represent adaptations to local predators. The aposematic strawberry poison frog (Oophaga pumilio) is red throughout its mainland distribution in Costa Rica and Panamá, but displays high levels of warning signal diversity in the Bocas del Toro Archipelago of Panamá. Both coloration and spot pattern vary in a polytypic sense. Sexual selection contributes to maintaining the polytypism, but little work has investigated the potential influence of predation. We used unspotted models of O. pumilio to determine if predation might help explain the color polytypism on Isla Colón in the Bocas del Toro Archipelago of Panamá. We tested whether attack rates differed among the red mainland morph, green/yellow Isla Colón morph, and the brown control. We found that frog color significantly predicted being attacked. The local green Isla Colón models were attacked more than foreign red or brown models. No difference in attack rate existed between red and brown control models. Our results suggest that the red mainland morph possesses a more effective warning signal, even when it is not the local morph. Honest signaling of unpalatability, neophobia, and the use of search images by local predators are potential explanations. Similarity of the brown model to other local poison frogs might explain the lower attack rate compared to previous work. The attack rate was lower on Isla Colón compared to mainland Costa Rica, which supports the hypothesis that less overall predation in the Bocas del Toro Archipelago may contribute to the overall warning signal diversity in O. pumilio there by relaxing selection for aposematic traits.
KeywordsColor polymorphism Conspicuous coloration Dendrobates pumilio Dendrobatidae Model experiment Bocas del Toro Honest signaling
We thank the Smithsonian Tropical Research Institute (STRI) Bocas del Toro field station and the Institute for Tropical Ecology and Conservation (ITEC) for valuable logistical support. This work was completed with official permission from the Autoridad Nacional del Ambiente (ANAM permit number SE/A-68-08). Jonathan R. Hegna and Humberto Vlades provided assistance in field work preparations. Janna Goldrup’s work at ITEC contributed, in part, to the idea for this study. The manuscript was improved by helpful comments from Johanna Mappes, Craig Guyer, Mike Heithaus, Frank Hensley, Natalie Hyslop, Thomas R. Jones, Monica Isola, Seiichi Murasaki, A. Justin Nowakowski, Kelsey Reider, Janne Valkonen, Steven Whitfield, and the herpetology group at John Carroll University. The manuscript also benefitted from suggestions by editors John Endler and Manuel Leal, along with the anonymous reviewers. We thank Mikael Puurtinen for discussions about the implications of their numerical model. Kenneth G. Gerow graciously provided statistical consulting. Funding was provided by the American Society of Ichthyologists and Herpetologists, the Judith Parker Travel Fund, Organization for Tropical Studies, Greater Cincinnati Herpetological Society, and the Chicago Herpetological Society. A National Science Foundation Postdoctoral Research Fellowship partially supported RAS. This paper is contribution 237 to the program in Tropical Biology at Florida International University.
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