Diverse mitogenomic variations contribute to population differentiation in Eurasian tree sparrows ( Passer montanus)

Mitochondrial genomes (mitogenomes) play a crucial role in species adaptation to diverse evolutionary pressures. Although adaptive changes in mitochondrial genes have been reported under extreme conditions, large-scale analyses of mitogenomic evolution across ecologically diverse habitats are still limited. The Eurasian tree sparrow ( Passer montanus), one of the most widely distributed avian species, occupies variable habitats, providing an ideal model for investigating mitochondrial responses to environmental heterogeneity. This study examined mitogenomic variation in tree sparrow populations sampled across China, revealing pronounced mitochondrial divergence in geographically isolated populations, particularly those in southern Xizang on the Qinghai-Xizang Plateau and the continental islands of Hainan and Taiwan. In the high-altitude population of southern Xizang, non-synonymous substitutions in COX2 and COX3 may enhance protein stability, potentially facilitating adaptation to cold and hypoxic conditions. In contrast, substitutions in ATP6 (Hainan) and ND5 (Taiwan) may reduce protein stability, implying distinct mitogenomic responses to local environmental constraints. Moreover, distinct tRNA mutations in the Hainan populations may confer increased structural flexibility, potentially contributing to island-specific adaptation. These findings highlight the role of mitochondrial genomes in responding to ecological variation and geographic barriers, underscoring the prospective functional consequences of mitogenomic evolution.