Information content of ultraviolet-reflecting colour patches and visual perception of body coloration in the Tyrrhenian wall lizard Podarcis tiliguerta

Colour signals are ubiquitous in nature but only recently have researchers recognised the potential of ultraviolet (UV)-reflecting colour patches to function as signals of quality. Lacertid lizards often display UV-blue patches on their flanks and black spots over their entire body, both of which are under sexual selection. They also have a cryptic dorsum and some species have a conspicuous, polymorphic ventral coloration. In this study, we use the Tyrrhenian wall lizard Podarcis tiliguerta to investigate the information content of the lateral UV-blue patches and black melanin spots of males by assessing the relationship between colour features and individual quality traits. In addition, we use a visual modelling procedure to examine whether the coloration of the different body parts and different colour morphs can be distinguished by a wall lizard visual system. We found that larger males had more numerous and larger UV-blue patches, with a higher UV chroma, UV-shifted hue, but a lower spectral intensity than smaller males. The extent of black on the throat, dorsum, and flanks also correlated with male body size and size-corrected head length but not with colour features of the UV-blue patches. These results suggest that the UV-blue and melanic colour patches may provide different, non-redundant information about male resource holding potential, and thus act as condition-dependent indicators of male quality. Finally, we found that the different body parts can be chromatically distinguished from each other, and that the UV-blue patches are the most conspicuous while the dorsum is the least conspicuous. SIGNIFICANCE STATEMENT: Many animals use their coloration to convey information about their quality as rivals or mates. Yet, until recently researchers have not recognised the potential of ultraviolet colour patches to function as signals of quality. In this study, we first show that male Tyrrhenian wall lizards display ultraviolet-blue and black colour patches that correlate positively with some aspect of their quality such as body or head size. Furthermore, our visual modelling procedure suggests that these lizards are able to distinguish the colours of their body parts from each other, with dorsal colours being the least conspicuous and ultraviolet-blue coloration being the most conspicuous.