Artificial Light at Night (ALAN): An Anthropogenic Challenge for Urban Lizard Behavior and Physiology

Artificial light at night (ALAN) is a byproduct of anthropogenic illumination that disrupts the behaviors and physiologies of organisms as diverse as mammals, birds, non-avian reptiles, fishes, and insects. In a time of increasing urbanization, discovering the impacts of ALAN on urban organisms is crucial to conservation efforts. In this study, we investigated the impacts of ALAN on the behaviors and physiology of the green anole lizard (Anolis carolinensis). Two groups of 24 urban wild-caught adult green anoles (12 males, 12 females per group) were exposed to two different light-dark cycles in a controlled lab setting for six weeks. One group was exposed to a light-dark cycle that simulated the natural light-dark cycle of a summer day in San Antonio, Texas, and the other group was exposed, in addition to the natural light-dark cycle, to an ALAN source that simulated the light intensity of the streetlights on an urban university campus. After an acclimation period, we conducted a series of behavioral trials. Three trials were repeated during mid-day and mid-night: open field tests, to examine exploratory behavior; foraging trials, to examine prey consumption; and conspecific trials, to examine same-sex interactions. The fourth trial examined behavioral time allocation over two 24 h periods. At the conclusion of behavioral trials, we measured each lizard’s body mass and snout-vent length (SVL) and the mass of its abdominal fat pads, liver, and reproductive tissues. Our data demonstrate that lizards exposed to ALAN were more likely to be awake at night. While they were awake, lizards exposed to ALAN used the light to explore, forage, and display to conspecifics. However, during the day, lizards exposed to ALAN were more likely to be asleep, were slower to move and forage, and females displayed less frequently than females not exposed to ALAN. Lizards exposed to ALAN had heavier fat pads and males had heavier testes, but ALAN did not impact liver mass, overall body mass, or female reproductive tissue mass. In sum, ALAN appears to cause behavioral trade-offs between diurnal and nocturnal activity and alters metabolic and reproductive processes within green anoles. These behavioral and physiological changes could cause the lizards to be exposed to novel situations and impact higher-level organization within the urban environment