Evolutionary trend of the small subunit nuclear ribosomal DNAs (SSU rDNAs) of wood-feeding Cryptocercus cockroaches (Blattaria: Cryptocercus)

The objective of this study is to elucidate the evolutionary rate of Cryptocercus SSU rDNAs based on the relative rate test (RRT) and comparative analysis of the primary sequences. In the RRTs, the evolutionary rate differences (dKs) of the Cryptocercus SSU rDNAs were not statistically significant (0.107 <P<0.996) in all cases, although an Asian Cryptocercus appeared to evolve more slowly than a North American Cryptocercus as indicated by the negative signs of dKs. Contrary to the RRT, the comparative analysis of SSU rDNA sequences revealed some interesting aspects in the evolutionary rates of Cryptocercus SSU rDNAs. In comparison with those of closely (Mastotermes darwiniensis and Tenodera aridifolia) or more distantly related taxa (Locusta migratoria), the SSU rDNAs of the genus Cryptocercus showed that insertions are progressing in a variable region (HV2). The SSU rDNA of Calymmaderus punctulatus species complex (Mountain Lake Biological Station, VA), a North American species, was unusually more elongated in the HV2 than those of the reference taxa or the other congeneric species.