Characterization and geographical variation of the mitochondrial genome in the Azure-winged Magpie (Cyanopica cyanus)

In recent years, studies of mitochondrial genomes have yielded significant insights into the adaptive mechanisms utilized by high-altitude species. However, comparative analyses of mitochondrial genomes in bird species across varying altitudes and latitudes have been rarely conducted. This study delves into the analyses of the mitochondrial genome of the high-altitude Cyanopica cyanus from Gannan, China (3,500 m altitude, near the upper limit of its altitudinal distribution), and compares it with samples from Wuhu, China (10 m altitude), and South Korea (45 m altitude). As a resident bird, C. cyanus offers greater research value for investigating variations in mitochondrial genomes related to elevation and latitude compared to migratory birds. The mitochondrial genomes of three C. cyanus individuals share identical structure and composition. However, the South Korea mitochondrial genome is 6 bp longer in total length than those of the Chinese individuals. The sequence identity between the Gannan and Wuhu is 99.80%, whereas the sequence identity between the Gannan and South Korea is 99.04%. Divergence between two Chinese C. cyanus from different altitudes occurred 0.09 million years ago in the late Pleistocene, while divergence with a South Korea individual happened earlier at ca. 0.80 million years ago during the early Pleistocene. Recent colonization of high-elevation and high-latitude regions, coupled with climate change, may be driving the differentiation of C. cyanus. By conducting a comparative analysis of the mitochondrial genomes from high-altitude Gannan and low-altitude South Korea of C. cyanus, we identified a 6-bp insertion within the ND4 gene in C. cyanus of South Korea. When comparing individuals from high-altitude Gannan with those from low-altitude Wuhu, 15 nucleotide variation sites were detected. However, a comparison with individual from South Korea showed a higher number of nucleotide variation sites, amounting to 128 in total, with 23 of these sites being situated in the ND5 gene. Collectively, these findings suggest that both altitudinal and latitudinal variations play roles in governing intraspecific divergence within C. cyanus. The mitochondrial genome of the high-altitude C. cyanus obtained in this study will provide a valuable resource for future research.