Meeting Abstract
Perception of ultraviolet (UV) light, mediated by the SWS1 opsin, is widespread in reptiles. Many species reflect UV light as part of their coloration, but its role is understudied, because humans cannot perceive it. The UV reflectance of geckos in particular has not been investigated. The nocturnal ancestry of geckos has left them with a unique trichromatic visual system, with opsins sensitive to UV, blue, and green light, but not red. I have used objective multispectral photography and cone-catch modeling to determine how different signals stimulate the gecko visual system, so that their coloration can be interpreted in a biologically relevant context. I specifically focus on the sexually dimorphic coloration displayed by members of the diurnal genus Lygodactylus Gray, 1864. Several species in the genus exhibit a yellow head with a blue-grey (and UV) body, a pattern which has evolved convergently in other, independently diurnal clades. This indicates that the yellow-headed phenotype is an efficient signal for the gecko visual system in a diurnal light environment. I find that to the gecko visual system, the UV-blue-grey body and the yellow head are each most conspicuous against different natural backgrounds, providing a good signal in complex lighting and background conditions. The chromatic contrast between the head and body is higher than either against any background; this contrast may be an important component of the signal regardless of visual context. As geckos lack a red sensitive cone type, the yellow head cannot be distinguished from the green color of foliage, and for this reason has been lost in the canopy dwelling species. This species, the critically endangered L. williamsi, has evolved bright blue coloration with a strong UV component, highlighting the importance of UV reflectance for signaling in this clade.
