The importance of short and near infrared wavelength sensitivity for visual discrimination in two species of lacertid lizards

Abstract

Abstract Males and females from Lacertid lizard species often display conspicuous colourations involved in intraspecific communication. However, visual systems of Lacertidae have rarely been studied and the spectral sensitivity of their retinal photoreceptors remains unknown. Here, we characterised spectral sensitivity of two Lacertid species from contrasted habitats, the wall lizard Podarcis muralis and the common lizard Zootoca vivipara. Both species possess a pure-cone retina with one spectral class of double cones and four spectral classes of single cone photoreceptors. The two species differ in the spectral sensitivity of the LWS cones, the relative abundance of UVS single cones (potentially more abundant in Z. vivipara), and the colouration of oil droplets. Wall lizards have pure vitamin A1-based photopigments while common lizards possess mixed vitamin A1- and A2- photopigments extending spectral sensitivity into near infrared, a rare feature in terrestrial vertebrates. We found that spectral sensitivity in the UV and in the near infrared improves discrimination of small variation in throat colouration among Z. vivipara. Thus, retinal specialisations optimise chromatic resolution in common lizards, which indicates that visual system and visual signals may co-evolve.