Loss of conspicuous coloration has co-evolved with decreased body size in populations of poison dart frogs
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Larger signal size is known to facilitate the learning process of predators to warning signals. Further, smaller objects are generally harder to detect than large, which suggests that smaller sized prey are less likely to benefit from an aposematic strategy compared to crypsis. However, whether body size changes in concert with shifts between crypsis and aposematism in natural populations, remains largely unexplored. I tested whether body size was larger in visually conspicuous population than in cryptic populations among recently diverged populations of the Strawberry Poison frog, Oophaga pumilio. By analysing spectral reflectance and body size data from individuals from 18 discrete populations I found a larger mean body size in conspicuous populations, which was confirmed by an analysis of a subset of 12 populations accounting for phylogenetic history. This shows that the loss of conspicuous colour likely co-evolved repeatedly with a decrease in body size. Thus, selection on body size may influence evolutionary shifts between aposematism and crypsis and vice versa.
KeywordsDendrobates pumilio Warning signal Crypsis Population differentiation Anura Amphibia
I thank the Panamanian authorities A.N.A.M for the scientific permit (SE/A-100-07); Dirección Nacional de Politica Indigenista, community leaders and landholders of Bocas del Toro and Comarca Ngäbe-Buglé. I thank the Smithsonian Tropical Research Institute staff at Bocas del Toro and Martin Breed and Simon Hultby for help in the field. Thanks to Alejandro Gonzalez Voyer for discussions on the statistics and helpful comments, I. Wang and B. Shaffer for kindly providing the phylogeny, Anders Ödeen and Olle Håstad for technical advice related to spectrophotometry and visual modelling, Anna Qvarnström, Jacob Höglund, Niclas Kolm, David Wheatcroft, Katarzyna Kulma, Jason L. Brown and two anonymous reviewers for comments on earlier versions of the manuscript and Björn Rogell for fieldwork and comments. The work was funded by The Swedish Research Council, The Royal Swedish Academy of Sciences and Stiftelsen för zoologisk forskning.
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