Uncovering Evolutionary and Phylogenetic Relationships in Glyptothorax Species through Comparative Mitochondrial Genomics

The mitochondrial genome serves as a crucial molecular marker for studying phylogenetic relationships and molecular evolution in fish. Despite their ecological significance in freshwater ecosystems, Glyptothorax fishes have limited evolutionary research, with only a few complete mitochondrial genomes reported. The present study examines the complete mitochondrial DNA (mtDNA) of G. cavia, G. trilineatus, G. annandalei, G. sinensis, and G. granosus, with sequence lengths of 16,529 bp, 16,539 bp, 16,541 bp, 16,531 bp, and 16,540 bp, respectively. Our comprehensive analysis reveals that most protein-coding genes (PCGs) begin with the ATG codon and terminate with TAA, although some exhibit incomplete stop codons (T/TA). The majority of the 13 PCGs display a negative GC skew, except for the ND6 gene. In terms of AT skew, eight PCGs have positive values, while COX1, ND3, ND4L, ND4, ND5, and Cytb exhibit negative values. Genetic distance and Ka/Ks ratio analyses indicate purifying selection acting on the 13 PCGs, with selection pressures potentially influenced by environmental adaptations. Phylogenetic and evolutionary analyses identify G. sinensis, G. annandalei, and G. granosus as closely related species.