Differential responses of rural and urban populations to artificial light at night in the Spiny toad

Abstract The ongoing expansion of urban areas and increased use of electric lighting has led to the surge of artificial light at night (ALAN) worldwide. ALAN alters the physiology and behavior of animals and is considered as a threat to biodiversity. Nevertheless, many species have colonized the urban environment. For these, urban individuals may have become less sensitive to ALAN than individuals from rural environments. We tested this hypothesis in rural and urban spiny toads Bufo spinosus in western France. Individuals housed in outdoor mesocosms were exposed to 0.5 lx or to the dark at night throughout the experiment. We measured their behavioral responses to ALAN exposure (movement and use of space in arenas) in three experiments measuring their general activity, sensitivity to glare and propensity to cross a light strip. We also measured pupillary light reflex and change in body condition. ALAN-exposed individuals were less disturbed by light than controls while urban toads were less sensitive to light during the tests than rural toads. Urban toads exposed to ALAN also had a lower gain in body condition than controls while the gain was similar in both groups of rural toads. Origin and treatment did not influence the pupillary light response. Overall, the larger influence of origin on toad’s response may arise from broader behavioral differences making urban individuals generally more tolerant to stressful conditions at the behavioral level. However, our results show that higher tolerance to nocturnal light in urban toads may increase their exposure and induce physiological costs.