Colour variation between different lineages of a colour polymorphic lizard

Colour polymorphic animals offer useful models to study the evolution of polymorphisms and studies with colour polymorphic lizards have contributed many advances in this field. Unfortunately, few studies address basic questions such as how observers (e.g. conspecifics) perceive the polymorphism or whether there is chromatic variability among evolutionary lineages or distant geographic areas within a species' range. The common wall lizard (Podarcis muralis) shows a striking colour polymorphism in its ventral surface, presenting up to five alternative colour morphs, that is white, yellow and orange/red (depending on the lineage), and two intermediate mosaic morphs: white-orange and yellow-orange. Here we compare this polymorphism in two geographically distant areas, the Po valley (Northern Italy) and the Eastern Pyrenees (Iberian Peninsula), corresponding to separate phylogeographic lineages. Using objective techniques of colour measurement and lizard vision models, we examine the chromatic differences between these two polymorphic lineages. We also search for chromatic differences in other colour traits present in P. muralis: the cryptic dorsal coloration and the ultraviolet-blue spots of the outer ventral scales (UV-blue OVS) used for intraspecific communication. Although we detected significant differences among lineages in colour variables, the main variation was found between the alternative ventral colour morphs. The most striking inter-lineage divergence was between the orange Pyrenean morph and the red Italian morph, mainly caused by achromatic (but not chromatic) differences. In addition, although the UV-blue OVS show strong chromatic and achromatic variation between lineages, the dorsal coloration shows the smallest degree of variation, and mainly between localities rather than lineages. Overall, the ventral colour pattern of P. muralis is shared by at least two geographically and phylogenetically distant lineages. Nevertheless, body coloration also shows signs of historical divergence (Pyrenean orange vs. Italian red) and local adaptation (mainly in the dorsal pattern).