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 Glyptothorax cavia, G. trilineatus, G. annandalei, G. sinensis, and G. granosus, with sequence lengths of 16,529 base pairs (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 the TAA stop codon, although some exhibit incomplete stop codons (T/TA). The majority of the 13 protein-coding genes (PCGs) display a negative guanine-cytosine (GC) skew, except for the (Skew value: 0.53-0.60) NADH dehydrogenase subunit 6 (ND6) gene. In terms of adenine-thymine (AT) (AT Skew value: 0-0.007), eight PCGs have positive values, while cytochrome c oxidase subunit 1 (COX1-), NADH dehydrogenase subunit 3 (ND3), NADH dehydrogenase subunit 4L (ND4L), NADH dehydrogenase subunit 4 (ND4), NADH dehydrogenase subunit 5 (ND5), and cytochrome b (Cytb) exhibit negative values. Genetic distance and non-synonymous to synonymous substitution ratio (Ka/Ks) 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.