Artificial light at night disrupts immune rhythms in wild rodents under semi-natural conditions

Artificial light at night (ALAN) is a rapidly expanding form of environmental pollution that disrupts natural light-dark cycles and alters behavioral and physiological rhythms across species. Because immune function is tightly linked to environmental cues, studying ALAN within an ecoimmunological framework is essential for understanding its real-world impacts on wildlife fitness. In natural settings, immune rhythms are shaped by multiple, interacting environmental pressures, and evaluating ALAN against this broader ecological backdrop is critical for interpreting its physiological consequences. We investigated how low-intensity ALAN affects immune and endocrine rhythmicity, antibody responses, and survival in two wild rodent species with opposing activity patterns, the nocturnal Acomys dimidiatus and the diurnal Acomys russatus, maintained in semi-natural outdoor enclosures. Under natural light-dark conditions, both species exhibited daily oscillations in circulating lymphocyte frequencies, and in A. dimidiatus, fecal cortisol also showed a clear daily rhythm. These rhythms were disrupted or dampened under ALAN. Moreover, antibody titers were significantly higher when immunization occurred during the species-specific rest phase, but ALAN exposure disrupted these rhythms, eliminating time-of-day variation in antibody responses. Overall, ALAN increased the mortality risk by 2.35-fold. Although controlled laboratory experiments have been essential for advancing immunology, they offer limited insight into how environmental disturbances like light pollution affect wildlife under realistic conditions. By studying wild rodents in semi-natural habitats, we reveal that ALAN exposure alters immune rhythms, endocrine patterns, and survival in ways that emerge only when animals experience natural ecological variation. These results highlight that immune baselines in the wild are products of complex environmental interactions and that ALAN can disrupt these integrated physiological systems. Together, these findings underscore the need for ecoimmunological approaches to assess how expanding light pollution threatens wildlife health and resilience. Significance Statement. Artificial light at night (ALAN) is a growing anthropogenic disturbance with wide-ranging ecological and physiological impacts. While its disruptive effect on circadian rhythms is well documented, its effects on immune function remain underexplored. Our findings show that ALAN alters immune rhythmicity and weakens time-dependent antibody responses in wild rodents under semi-natural conditions, potentially increasing susceptibility to infection. Studying the effects of light pollution on wild species under natural conditions is essential not only for understanding its impact on ecosystem health, but also for assessing how altered immune function may influence the emergence and spread of zoonotic diseases. These insights underscore the need to investigate immunity in ecologically relevant contexts beyond traditional laboratory models and conditions.