Intraspecific variation in the design, information content and reliability of a lizard ultraviolet ornament

Animals communicate through a diverse range of signals that vary across multiple levels. Interpopulation variation offers valuable insights into the function and evolution of these signals. Here, we use more than 3,000 European wall lizards (Podarcis muralis) from 55 populations in the Pyrenees to study interpopulation variation in a chromatic signal: the ultraviolet (UV)-blue patches. We aim to describe interpopulation variation in the design, information content, and reliability of the signal, and to assess to what extent this variation can be explained by the local signaling environment. We found geographic variation in the size and chromatic properties of the signal. The area and number of UV-blue patches was positively correlated with UV chroma and hue, suggesting a pattern of coupling components for signal redundancy. The relationship between the UV-blue patches and body size varied across localities, suggesting that the condition-dependence of this signal is geographically variable. Signal reliability was also found to vary among populations with informative signals. Geographic variation in signal design was explained by local adaptation to the signaling environment, including climatic conditions and the social context. These results highlight the relevance of the signaling environment driving the evolution of signals and the importance of analyzing multiple populations.