Genetic Diversity and Differentiation Pattern of Mastacembelus armatus in the Dongjiang and Ganjiang River Sources

To explore the genetic diversity and evolutionary differentiation of Mastacembelus armatus from the headwaters of the Dongjiang and Ganjiang Rivers, we performed whole-genome resequencing on three populations, including Xunyushui (XW) and Jiuqu River (DN) from the Dongjiang River source as well as Taojiang River (XF) from the Ganjiang River source. We analyzed population structure, genetic differentiation, nucleotide diversity (π), pairwise FST, linkage disequilibrium, kinship, and neutrality tests (Tajima’s D, Fu and Li’s D). A total of 209.05 Gbp of clean data were obtained, with high quality and reliable alignment. Average nucleotide diversity (π) was higher in XW (0.00490 ± 0.00248) and DN (0.00478 ± 0.00312) and lower in XF (0.00463 ± 0.00158). Pairwise FST values revealed moderate differentiation between XW and DN (FST = 0.12) and strong divergence between XF and the other two populations (FST = 0.19 and 0.17). Neutrality tests showed no significant deviation from neutrality. XW and DN exhibited positive values, indicating stable demography, while XF showed negative values, suggesting a tendency of population expansion. Phylogenetic, admixture, and PCA analyses supported that all three populations belonged to one evolutionary clade with two ancestral components. XF showed the slowest linkage disequilibrium decay and distant kinship, indicating a small effective population size. Significant genetic divergence was primarily driven by geographic isolation and limited gene flow. This study reveals the genetic diversity and differentiation pattern of M. armatus and provides a genomic basis for its conservation and management.