The highest-elevation frog provides insights into mechanisms and evolution of defenses against high UV radiation.

Abstract

Defense against ultraviolet (UV) radiation exposure is essential for survival, especially in high-elevation species. Although some specific genes involved in UV response have been reported, the full view of UV defense mechanisms remains largely unexplored. Herein, we used integrated approaches to analyze UV responses in the highest-elevation frog, <i>Nanorana parkeri</i>. We show less damage and more efficient antioxidant activity in skin of this frog than those of its lower-elevation relatives after UV exposure. We also reveal genes related to UV defense and a corresponding temporal expression pattern in <i>N. parkeri</i>. Genomic and metabolomic analysis along with large-scale transcriptomic profiling revealed a time-dependent coordinated defense mechanism in <i>N. parkeri</i>. We also identified several microRNAs that play important regulatory roles, especially in decreasing the expression levels of cell cycle genes. Moreover, multiple defense genes (i.e., <i>TYR</i> for melanogenesis) exhibit positive selection with function-enhancing substitutions. Thus, both expression shifts and gene mutations contribute to UV adaptation in <i>N. parkeri</i>. Our work demonstrates a genetic framework for evolution of UV defense in a natural environment.