Developing and adult reef fish show rapid, reversible light-induced plasticity in their visual system

Abstract

The visual capabilities of fish are optimised for their ecology and light environment over evolutionary time. Similarly, fish vision can adapt to regular changes in light conditions within their lifetime, e.g., ontogenetic or seasonal variation. However, we do not fully understand how vision responds to irregular short-term changes in the light environment, e.g., algal blooms and light pollution. In this study, we investigated the effect of short-term exposure to unnatural light conditions on opsin gene expression and retinal cell densities in larval and adult diurnal reef fish (convict surgeonfish; Acanthurus triostegus). Results revealed phenotypic plasticity in the retina across ontogeny, particularly in the larvae. The most substantial differences at both molecular and cellular levels were found under constant dim light, while constant bright light or simulated artificial light at night had a lesser effect. Under dim light, larvae and adults increased expression of the cone opsin genes, sws2a, rh2c and lws, within a few days and larvae also decreased densities of cones, inner nuclear layer cells and ganglion cells. These changes likely enhanced vision under the altered light conditions. Thus, our study suggests that plasticity mainly comes into play when conditions are extremely different to the species natural light environment, i.e., a diurnal fish in constant night. Finally, in a rescue experiment on adults, shifts in opsin expression were reverted within 24 hours. Overall, our study showed rapid, reversible light-induced changes in the retina of A. triostegus, demonstrating phenotypic plasticity in the visual system of a reef fish throughout life.