Abstract

Artificial light at night is a worldwide expanding form of pollution. Studies evaluating the effects of artificial light at night have often overlooked their impact on the photoreceptor, the basic functional structure of animals to absorb light. This is essential to understand the mechanisms by which this stressor may be impacting species. This study examined the photoreceptor (rhabdom) of two sandy beach crustaceans exhibiting different light tolerances at night: the amphipod Orchestoidea tuberculata and the isopod Tylos spinulosus. We developed a novel protocol to measure these species' photoreceptor areas and quantify the damage caused by artificial light at night using histological sections and scanning electron microscopy. In the isopod, a species naturally adapted to lower light intensities at night than the amphipod, the rhabdom surface was 20-times larger, and presented a tapetum, an adaptive feature found in species living in low light conditions. A brief exposure to artificial light caused 3–6 times more damage in the isopod's rhabdom. In fact, the light caused structural damage in the isopod's rhabdom but not in the amphipod's rhabdom, with no signs of recovery after 1 and 24 h. These findings suggest that the damage induced by artificial light at night on an organism's photoreceptors is more severe and persistent in species naturally adapted to lower light levels at night. Hence, this type of sensory ecological stressor may act as a novel selection pressure on these species, a concern with wide implications given the ubiquity among animals of the photoreceptor structure and its response to light.