Abstract

Acute increases in ultraviolet-B (UVB) radiation, driven by ozone depletion and climate change, function as a non-chemical environmental contaminant that can inflict rapid physiological and molecular damage. Yet ecotoxicological assessments focusing on acute high-intensity UV events are scarce. Here, we treat UVB as a hazardous environmental stressor and use the Qinghai–Tibetan Plateau endemic frog Rana kukunoris to compare high-altitude (HA) and low-altitude (LA) populations’ multi-level responses to a controlled acute UVB challenge (4   h, 1800 μW cm −2 ) and recovery (4–48   h post-exposure, HPE). By integrating skin histology/pigmentation, oxidative and antioxidant indices, DNA damage, apoptosis, and gene expression, we revealed pronounced altitude-dependent differences in defense strategies. HA frogs displayed a thicker epidermis and darker baseline pigmentation with a smaller UVB-induced darkening amplitude, whereas LA frogs had lighter baseline coloration and stronger darkening (reflectance minima at 4 HPE in both populations), together indicating contrasting pigmentary buffering capacities. HA frogs further showed rapid antioxidant mobilization (skin and liver T-AOC peaked at 4 HPE), faster DNA repair (alkaline comet tail length and TDNA% decreased at 5.3   AU   h −1 and 2.8% h −1 over 0–12 HPE), and apoptosis peaking at 12 HPE, indicating early containment with reduced downstream investment. LA frogs showed delayed antioxidant activation (T-AOC peaked at 24 HPE in skin and 12 HPE in liver), slower repair (3.6   AU   h −1 and 0.8% h −1 ), delayed apoptosis (24 HPE), and stronger hepatic induction of repair/apoptosis pathways (CPD photolyase 33.7-fold; OGG1 35.2-fold vs 2.8- and 6.4-fold in HA), consistent with compensatory, higher-demand responses. Together, these findings demonstrate that acute UVB exposure elicits altitude-specific, multi-level defense