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

Abstract

Male and female Lacertid lizards often display conspicuous coloration that is 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 characterise the spectral sensitivity of two Lacertid species from contrasting 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 cones. 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 coloration of oil droplets. Wall lizards have pure vitamin A1-based photopigments, whereas common lizards possess mixed vitamin A1 and A2 photopigments, extending spectral sensitivity into the near infrared, which is a rare feature in terrestrial vertebrates. We found that spectral sensitivity in the UV and near infrared improves discrimination of small variations in throat coloration among Z. vivipara. Thus, retinal specialisations optimise chromatic resolution in common lizards, indicating that the visual system and visual signals might co-evolve.

Shaping communicative colour signals over evolutionary time

“…We followed Martin et al . [56] in assuming that receptor noise does not depend on light intensity, using a Weber fraction of 0.05 as used for amphibians [53] and a measure of standard daylight irradiance (D65 spectrum, [57]). Following Macedonia et al .…”

Visual Pigments, Ocular Filters and the Evolution of Snake Vision

“…The spectral location of the k max of a pigment depends on the constituent chromophore as well as the amino acid residues present at so-called tuning sites in the opsin protein (see Yokoyama 2008 and references cited therein). We made predictions of k max by assuming a vitamin A 1 chromophore because an A 2 chromophore has not been reported in snakes (Sillman et al 1997;Davies et al 2009;Hart et al 2012;Simões et al 2015Simões et al , 2016Schott et al 2016), though is known to occur in some lizards (Martin et al 2015). For the three visual pigments found in snakes, spectral tuning sites are generally highly conserved and similar to those found in other vertebrates, such that it is possible to predict the k max for RH1 (Nathans 1990;Hunt et al 1996Hunt et al , 2001Fasick and Robinson 2000;Simões et al 2016), SWS1 Sekharan et al 2013;Hunt and Peichl 2013;Simões et al 2016), and LWS (Yokoyama 1995 Visual Pigments, Ocular Filters and the Evolution of Snake Vision .…”

“…Visual opsins in some vertebrates have been studied intensely over the past 20 years, to the extent that changes in specific ("spectral tuning") amino acid sites are known to change the peak absorbance wavelength (k max ) of the visual pigments (Yokoyama 2008;Yokoyama et al 2014). However, there is no universal consensus about the tuning impacts of all such mutations (Hauser et al 2014), with some data suggesting that additional mechanisms to change spectral sensitivity may exist Martin et al 2015).…”

UV coloration influences spatial dominance but not agonistic behaviors in male wall lizards

“…1 and 2). This UV reflectance can be perceived by wall lizards, which possess a UV-sensitive visual system (Martin et al 2015;. During male-male interactions, wall lizards perform push-ups and present one flank to the sight of their opponent, suggesting that the blue spots on their marginal ventral scales might be involved in intraspecific communication.…”