ORIGINAL PAPER Sexual dimorphism and intra-populational colour pattern variation in the aposematic frog Dendrobates tinctorius Bibiana Rojas • John A. Endler Received: 11 September 2012 / Accepted: 21 March 2013 Ó Springer Science+Business Media Dordrecht 2013 Abstract Despite the predicted purifying role of stabilising selection against variation in warning signals, many aposematic species exhibit high variation in their colour patterns. The maintenance of such variation is not well understood, but it has been suggested to be the result of an interaction between sexual and natural selection. This interaction could also facilitate the evolution of sexual dichromatism. Here we analyse in detail the colour patterns of the poison frog Dendrobates tinctorius and evaluate the possible correlates of the variability in aposematic signals in a natural population. Against the theoretical pre- dictions of aposematism, we found that there is enormous intra-populational variation in colour patterns and that these also differ between the sexes: males have a yellower dorsum and bluer limbs than females. We discuss the possible roles of natural and sexual selection in the maintenance of this sexual dimorphism in coloration and argue that parental care could work synergistically with aposematism to select for yellower males. Keywords Aposematism Á Polymorphism Á Sexual dimorphism Á Parental care Á Poison frog Introduction Aposematism is an anti-predator strategy by which some animals warn their predators about their unprofitability with conspicuous colours or patterns (Poulton 1890; Ruxton et al. 2004). Because variation in aposematic signals makes it difficult for predators to learn and retain the association between colour patterns and distastefulness, warning signals are expected to be simple and uniform (Endler 1988; Joron and Mallet 1998; Endler and B. Rojas Á J. A. Endler Centre for Integrative Ecology, School of Life and Environmental Sciences, Deakin University at Waurn Ponds, 75 Pigdons Road, Geelong, VIC 3217, Australia B. Rojas (&) Centre of Excellence in Biological Interactions, Department of Biological and Environmental Science, University of Jyva ¨skyla ¨, PO Box 35, 40014 Jyva ¨skyla ¨, Finland e-mail: bibiana.rojas@jyu.fi 123 Evol Ecol (2013) 27:739–753 DOI 10.1007/s10682-013-9640-4