Ultraviolet vision in lacertid lizards: evidence from retinal structure, eye transmittance, SWS1 visual pigment genes, and behaviour

Abstract

Ultraviolet (UV) vision and UV colour patches have been reported in a wide range of taxa and are increasingly appreciated as an integral part of vertebrate visual perception and communication systems. Previous studies with Lacertidae, a lizard family with diverse and complex coloration, have revealed the existence of UV-reflecting patches that may function as social signals. However, confirmation of the signalling role of UV coloration requires demonstrating that the lizards are capable of vision in the UV waveband. Here we use a multidisciplinary approach to characterize the visual sensitivity of a diverse sample of lacertid species. Spectral transmission measurements of the ocular media show that wavelengths down to 300 nm are transmitted in all the species sampled. Four retinal oil droplet types can be identified in the lacertid retina. Two types are pigmented and two are colourless. Fluorescence microscopy reveals that a type of colourless droplet is UV-transmitting and may thus be associated with UV-sensitive cones. DNA sequencing shows that lacertids have a functional SWS1 opsin, very similar at 13 critical sites to that in the presumed ancestral vertebrate (which was UV sensitive) and other UV-sensitive lizards. Finally, males of Podarcis muralis are capable of discriminating between two views of the same stimulus that differ only in the presence/absence of UV radiance. Taken together, these results provide convergent evidence of UV vision in lacertids, very likely by means of an independent photopigment. Moreover, the presence of four oil droplet types suggests that lacertids have a four-cone colour vision system.

Colour variation between different lineages of a colour polymorphic lizard

“…Most available results agree with the hypothesis that sexual selection is important for the maintenance of this polymorphism P erez i de Lanuza et al, 2013bP erez i de Lanuza et al, , 2017Abalos et al, 2016). However, evidence from geographic variation of local morph composition and habitat use by morphs in sympatry suggests that this polymorphism is also environmentally constrained (P erez i de Lanuza & Carretero, 2018;P erez i de Lanuza et al, 2018a,b).…”

Lens transmittance shapes ultraviolet sensitivity in the eyes of frogs from diverse ecological and phylogenetic backgrounds

“…Our results show that lens transmittance among anurans spans a range similar to that of other vertebrates such as fishes, snakes, lizards, birds and mammals [5,6,8,[16][17][18][19] Figure 2. Relationship between the cornea and lens transmittance for a subset of the species used in the study.…”

Photoreception and vision in the ultraviolet

“…Tetrapod SWS1 pigments, however, apparently shifted from UV into violet or blue sensitivity independently on multiple occasions in each lineage (Yokoyama et al, 2016;Hunt and Peichl, 2014). The ancestral amphibian, reptile and mammal presumably all expressed a UV SWS1, and modern reptiles have no reported violet SWS1 opsins (de Lanuza and Font, 2014). It is possible that the common reptilian ancestor of birds had a violet SWS1, but that some avian groups reevolved UV sensitivity, often through the alternative tuning site at position 90 (Hunt et al, 2004;Ödeen and Håstad, 2013).…”