UVB radiation and amphibian resilience: Analyzing skin color, immune suppression and oxidative stress in Rana kukunoris from different elevations

Ultraviolet-B radiation (UVBR), intensified by ozone depletion and climate change, poses a growing ecological threat to amphibians, particularly in high-elevation regions such as the Qinghai-Tibet Plateau. Endemic to this region, Rana kukunoris spans a wide range of elevations, where distinct populations may have evolved unique strategies and regulatory mechanisms to cope with UVBR. However, specific adaptive responses in adult frogs remain underexplored. This study compared the physiological responses of high- and low-altitude Rana kukunoris populations to UVBR exposure, focusing on dorsal color, immune function, antioxidant capacity, and DNA repair gene expression. High-altitude populations exhibited stable, dark pigmentation-potentially reducing the need for rapid melanin synthesis-alongside a robust immune profile and enhanced antioxidant enzyme activity, collectively conferring resilience against oxidative and immune stress under chronic UVBR exposure. Conversely, low-altitude populations exhibited pronounced UVBR-induced responses, including significant skin darkening, heightened immune activation evidenced by increased white blood cell counts, and increased oxidative damage marked by higher malondialdehyde (MDA) levels, coupled with reduced superoxide dismutase (SOD) and catalase (CAT) activities. Furthermore, tissue-specific upregulation of DNA repair genes in high-altitude populations suggested a stable DNA repair capacity adapted to high-UVBR environments. These findings reveal distinct physiological strategies within the same species for coping with UVBR across altitudinal gradients. Amid global increases in UVBR, this study offers novel insights into amphibian resilience in high-UVBR habitats and informs conservation strategies for populations across varying elevations.