Leveraging genetics to discover promising sensory systems in marine animals: extraocular photoreception and its implications for bioinspiration

Vision is a critical sensory system, playing a key role for many animals in facilitating essential ecological processes such as locating prey, selecting mates, and avoiding predators. Whereas vision is best understood to occur using the eyes, recent studies employing methods in genetics have revealed that photoreceptor proteins, such as visual opsins, are occasionally expressed in tissues outside of the eyes including skin and light organs. The presence of visual opsins across a diverse array of tissue types implies they may allow for light sensitivity outside of the retina, a phenomenon defined as extraocular photoreception. Presently, extraocular photoreception has been linked to various ecologically significant processes, including circadian photoentrainment, phototactic responses, bioluminescence detection, and color-changing camouflage across both vertebrates and invertebrates. Despite growing interest, there has yet to be a comprehensive review of the methodologies used to identify and study these extraocular visual opsins. In this work, we review the genetic methods used to investigate these systems and examine case studies to outline how to identify functional extraocular photoreception, building on previous research. We found that RNA sequencing (RNASeq) and quantitative PCR (qPCR) analysis were common genetic methodologies, allowing for the identification of visual opsins outside of the eye by comparing expression across retinal and extraretinal tissues. By synthesizing current techniques and findings, we propose a framework for reliably identifying functional extraocular photoreception in diverse species. Understanding these systems not only advances conservation efforts by enhancing our understanding of ecologically and economically important species, but also offers valuable insights for bioinspired technologies utilizing non-ocular light detection.