Colours of quality: structural (but not pigment) coloration informs about male quality in a polychromatic lizard

Chromatic signals result from the differential absorption of light by chemical compounds (pigment-based colours) and/or from differential scattering of light by integument nanostructures (structural colours). Both structural and pigment-based colours can be costly to produce, maintain and display, and have been shown to convey information about a variety of individual quality traits. Male wall lizards, Podarcis muralis, display conspicuously coloured ventral and lateral patches during ritualized inter- and intrasexual displays: ventral colours (perceived as orange, yellow or white by humans) are pigment based, while the ultraviolet (UV)-blue of the outer ventral scales (OVS), located along the flanks, is structurally produced. We used spectrophotometric data from 372 adult males to examine, considering the entire visual spectrum of lizards, whether ventral and OVS colour variables can predict male quality. Results indicate that the hue and UV chroma of OVS are good predictors of fighting ability (size-independent bite force) and body condition, respectively. This suggests that structural colour patches are condition dependent and function as complex multicomponent signals in this species. In contrast, ventral coloration apparently does not function as a male quality indicator. We suggest that ventral and lateral colour patches may be social signals with different information content, possibly aimed at different receivers.