Trejo-Reveles, V.; Anderson, G. E.; Jonhston, A. R.; Meddle, S.; Johnson, M.

Extra-retinal photoreception is widely observed across vertebrates, facilitating species-specific regulation of physiological and behavioral responses to diverse photic environments. Yet, the roles of non-visual opsins remain poorly understood, as their distribution and function have not yet been systematically investigated. This study provides the first comprehensive evidence of non-visual opsin expression across the reptile body. Using predicted sequences for extra-retinal photoreceptors, non-visual opsins were confirmed in the brain, eye, testes, liver, and skin. Specifically, OPN3 (encephalopsin) exhibited the highest expression across all tissues, particularly in the testes, corroborating findings in mammals. OPN5 (neuropsin) was detected predominantly in the testes, marking the first such report in reptiles. Moderate expression of OPN4 (melanopsin) in the brain and eye supports its roles in both visual and deep-brain photoreception. In the skin, a distinct pattern of higher opsin expression was observed in the dorsal skin compared to ventral skin. OPN3-3 was most abundant and exhibited a unique expression profile, potentially linking opsins to light-mediated processes influencing chromatophore-driven color changes. Findings from this research provide a critical evolutionary context for understanding the role and conservation of non-visual opsins in reptiles and their relevance to vertebrate lineages, including mammals and birds.