Molecular phylogeny of orthopteroid insects based on the mitochondrial cytochrome oxidase II gene

Phylogenetic relationships among 18 species of orthopteroid insects (Blattaria: cockroaches, Isoptera: termites, Mantodea: mantids, Grylloblattodea: grylloblattids, Phasmatodea: stick-insects, Orthoptera-Caerifera: locusts, Orthoptera-Ensifera: crickets, and Dermaptera: earwigs), were estimated based on DNA sequencing of the mitochondrial cytochrome oxidase II gene. Our results drew attention to the need for caution in using third codon positions for tree construction, since it was likely that base pair substitutions of third codon positions in the COII gene were saturated among taxa used in the present study. We also detected that there were many phylogenetically informative sites in first codon positions. Phylogenetic trees using first and second codon positions based on both the neighbor-joining method and parsimony analysis indicated that the topology was nearly identical to each other. The phylogenetic relationships among these taxa differ from the current classification based on morphological characters. The inferred trees showed that grylloblattids were not a primitive group, but closely related to the Dictyoptera. Stick-insects were closely related to the Dictyoptera and grylloblattids, not to crickets. Locusts and crickets formed a monophyletic group. Earwigs were only distantly related to the Dictyoptera. Within the Dictyoptera, cockroaches and termites constituted a monophyletic group, with mantids as a sister group to that complex.