Indel variation in the mitochondrial ND5 region supports monophyly of the tribe Hippoglossoidini (sensu Vinnikov et al. 2018) within the family Pleuronectidae

Indel (insertion–deletion) events observed in the genome represent irreversible mutational processes, making indel regions crucial characteristics for discussing phylogenetic relationships. The tribe Hippoglossoidini is a recently proposed taxonomic group based on the molecular phylogenetic analyses of both mitochondrial (mt) and nuclear DNA sequences. However, no synapomorphic characteristics have been identified within this tribe, either morphologically or molecularly. In the present study, we sequenced the ND5 region of mtDNA in the righteye flounder species and conducted interspecific comparisons. We found a 12 bp indel immediately upstream of the stop codon in the ND5 region. A comparative analysis of this region with outgroup species from the Paralichthyidae revealed that the indel was a unique insertion shared by the common ancestor of the Hippoglossoidini species, providing irreversible evidence to support the monophyly of this taxonomic group (synapomorphic characters).