What happens when the lights are left on? Transcriptomic and phenotypic habituation to light pollution

Artificial light at night (ALAN) is one of the most ubiquitous human-induced environmental stressors. ALAN can induce immediate behavioral and physiological changes in animals, sometimes leading to severe health consequences. Nevertheless, many organisms persist in light-polluted environments and may have mechanisms of habituating to ALAN, reducing responses to repeated exposure over time. The capacity for animals to habituate to ALAN has yet to be tested experimentally. We conducted a 6-month repeated-measures experiment with zebra finches (Taeniopygia guttata) to test whether birds can habituate to repeated ALAN exposure. We measured individual changes in behavior, physiology (oxidative stress and telomere attrition), and gene expression to test for concordance among behavioral, physiological, and transcriptomic responses to ALAN. We present evidence of tolerance to chronic ALAN exposure, persistent behavioral responses lasting 8 weeks post-exposure, and habituation to subsequent re-exposure. We found no changes in telomere attrition and a decrease in oxidative stress associated with ALAN exposure, indicating potential protective effects of long-term dim ALAN. Changes in blood transcriptome within individuals revealed unique responses to both previous ALAN exposure and subsequent re-exposure. These results represent organismal resilience to chronic stressors and shed light on the capacity of individuals to persist in an increasingly light-polluted world.