Light pollution has emerged as a new environmental challenge. Natural light has long been a selecting force in shaping physiological, morphological and behavioral traits across species. The introduction of artificial light at night (ALAN) disrupts the natural light-dark cycle, affecting a broad range of biological processes. In amphibians, ALAN has been suggested as a potential driver behind demographic declines in recent years. In this study, we investigated how exposure to cold LED light affects the development, body length, and oxidative status of the European tree frog (Hyla arborea). Individuals were exposed to ALAN from egg hatching (GS25) to two developmental endpoints: the larvae (GS38) and the juveniles. The experiment included three night-time light conditions: a natural dark control (<0.3 lx), LED light intensity at 20 lx, and LED light intensity at 90 lx. Larvae reared under artificial light reached metamorphosis in a shorter period and exhibited larger body sizes. Nocturnal light also induced changes in oxidative status across life stages. Tadpoles under both 20 lx and 90 lx levels experienced greater oxidative damage of lipids. Likewise, juveniles had higher oxidative damage of proteins and elevated activities of the first-line antioxidant defense enzymes (SOD, CAT and GSH-Px) in response to both light intensities. Our results show that exposure to ALAN shapes development and body size of amphibians, which appears to be accompanied by disturbances in redox balance. Overall, we highlight that ALAN can be a factor affecting amphibian populations, and thus it should be taken into consideration in future conservation strategies.
