Light induced changes in starry flounder (Platichthys stellatus) opsin expression and its influence on vision estimated from a camouflage-based behavioural assay.

Abstract

Correlations between variation in opsin expression and variation in vision are often assumed but rarely tested. We exposed starry flounder (Platichthys stellatus) to either broad spectrum sunlight or green-filtered light in outdoor aquaria for seven weeks and then combined digital-PCR and camouflage experiments to test two hypotheses: i) short-wavelength sensitive opsin expression decreases in a green light environment, and ii) if observed, this change in opsin expression influences colour vision as estimated using a camouflage-based behavioural assay. Of the eight visual opsins measured, Sws1 (UV sensitive) and Sws2B (blue sensitive) expression was significantly lower in fish exposed to green light. However, opsin expression in fish transferred to an arena illuminated with white LED light for three hours after the green light treatment did not differ from broad spectrum controls. Changes in opsin expression in response to artificial light environments have been reported before, but rapid changes over three hours rather than days or weeks is unprecedented. We did not observe a significant difference in a flounders camouflage response based on light environment, although broad spectrum fish increased and green-filter fish decreased the pattern contrast when on the blue-green substrate, and this difference approached significance. This pattern is intriguing considering green-filter fish expressed fewer UV and blue opsins and we recommend increased statistical power for future experiments. Together, our results show that starry flounder opsin expression changes rapidly in response to changes in light environment, however, there is no apparent effect on their visually mediated camouflage.