Non-visual functions of opsins in Crustacea: a review

Opsins are transmembrane proteins that have a covalent bond with a chromophore 11-cis-retinal in the intracellular region, opsins transiently bind to a G protein, which in turn is alternatively coupled to GTP or GDP. These characteristics allow opsins to function as photopigments and, after reacting with light, they launch the cascade of intracellular communication processes known as phototransduction. Commonly referred to as the starting point of the visual pathway, phototransduction as initiated by opsins, can also mediate physiological processes as varied as taxis, metabolic synchronization, and seasonal migration. This review analyzes such functions performed by opsins in crustaceans, a group with a huge diversity of species that, owing to their plasticity, have been able to invade habitats that other arthropods or terrestrial vertebrates have been unable to occupy. Our analysis emphasizes the way in which opsins take part in crustacean behavioral display under extreme habitat conditions as in the case of cave fauna), as well as in essential ontogenic events. The many functions of opsins have been scarcely investigated due to bias generated by their participation in visual processes. Attention to the non-visual activity of opsins can break new grounds towards an integrative understanding of animal physiology.