Researchers from the Cavanilles Institute of Biodiversity and Evolutionary Biology (ICBiBE) and the University of Oporto have identified and characterized iridescence in the dorsal coloration of the brown lizard (Podarcis liolepis), an optical phenomenon whereby the colours reflected by a surface change according to the angle between the observer and the light source. Podarcis liolepis, a species common in the east of the Iberian Peninsula, shows this phenomenon on its back, and for the first time it has been evaluated how these chromatic changes are perceived by observers with different color vision systems, such as lizards, birds and humans
The work published in the Journal of Zoology suggests that iridescence may be much more widespread among reptiles than is thought, and that its apparent rarity may be due more to a lack of adequate studies than to its true scarcity, according to Javier Ábalos, a researcher at the Department of Ethology at the Cavanilles Institute for Biodiversity and Evolutionary Biology (ICBiBE), located in the scientific-academic area of the Science Park of the Universitat de València. Iridescence is the basis of many of the most striking colors in nature (such as butterfly wings or bird feathers), although little is known about whether these changes are noticeable to animals that see them.
Another relevant aspect of the study is the use of visual models to compare how iridescence-induced color changes are perceived from the perspective of different observers: lizards, birds of prey and humans. This is the first work on reptiles that applies this comparative approach between visual systems, which allows us to evaluate not only physical changes in reflected light, but also its real perceptual impact. This distinction is key to understanding whether iridescence can have adaptive functions, such as communication or camouflage.
The results also show that, in certain contexts, dorsal iridescence of P. liolepis may be more visible to avian predators (and humans) than to individuals themselves. This introduces a sensory dimension to the phenomenon: the same spectral changes may be more or less detectable depending on how they overlap with the sensitivity of the observer’s photoreceptor cones. Thus, iridescence can be understood not only as a physical trait, but also as an interaction between optical structure and sensory perception, as explained in the research in which Guillem Pérez de Lanuza and Enrique Font have also worked, both professors of the Faculty of Biological Sciences of the Universitat de València, and Ferrán de la Cruz (University of Porto).
This is the first work on reptiles that applies this comparative approach between visual systems, which allows us to evaluate not only the physical changes in reflected light, but also its real perceptual impact
Specifically, the iridescence in the dorsal coloration of Podarcis liolepis has been analyzed, comparing two populations with marked differences in their coloration: one in the Botanical Garden of Valencia (brown tones) and another in the Municipal Natural Park of La Murta de Alzira (more greenish and intense colors). The coloration of 87 adult lizards has been measured from three different viewing angles and visual models have been used to estimate how other lizards, birds and humans would perceive these colors.
The results explain that, although the lizards of the Botanist seem to exhibit a less apparent iridescence, their spectral properties change with the viewing angle as much as those of La Murta. However, these changes are more apparent on La Murta due to a greater coincidence between the affected wavelengths and visual sensitivity of all observers examined, including humans.
Thus, the work shows that chromatic variation within the species, for example between sexes or populations, influences the detectability of iridescence. Although the spectral shifts are similar, they generate a greater chromatic difference in some populations than others, partly due to background color characteristics. This interaction between basal coloration and iridescence means that their visibility may be modulated by other phenotypic traits and the environment, opening up new avenues for exploring their ecological significance.
Photographs of the same male lizard (Podarcis liolepis) from the Botanical Garden, with seconds of difference, and from two different viewing angles to illustrate the apparent change in dorsal coloration due to iridescence. Photo: UV News
The study questions the reliability of human perception as the only tool for describing animal coloration. The observed differences among observers suggest that many descriptions based on direct observation or standard photography may be underestimating actual chromatic variability, especially when phenomena such as iridescence come into play.
This research has received an Ayuda Margarita Salas to Javier Ábalos (ref. MS21-053), another to FCT Ayuda to Ferrán de la Cruz (ref. 2022.14105.BD), and project AICO/2021/113 of the Conselleria of Innovation, University, Science and Digital Society and the PID2019 104721GB I00 project of the Ministry of Science and Innovation.
Source: UV News