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The Complete Mitochondrial Genomes of the Tobacco cutworm, Spodoptera litura (Lepidoptera: Noctuoidea) and the Rice Leaf Roller, Cnaphalocrocis medinalis (Lepidoptera: Pyralidae), and Reconstruction of Phylogenetic Relationships among Lepidoptera
Two complete mitochondrial genomes of the tobacco cutworm, Spodoptera litura (Lepidoptera: Noctuoidea) and the rice leaf roller, Cnaphalocrocis medinalis (Lepidoptera: Pyralidae), were sequenced. Each 15,388 bp and 15,368 bp-long genome contained both the lepidopteran specific gene arrangement that differ from the most common arrangement of insects by the movement of tRNAMet to a position 5’-upstream of tRNAIle. Neither of the species have typical COI start codon. Instead, the CGA (arginine) sequence that is commonly present in other lepidopterans was also found both in S. litura and C. medinalis. The evolutionary rates among 13 protein-coding genes (PCGs) in Lepidoptera showed ATP8 the highest, whereas COI the lowest. The high A+T-content, which is characteristic of mitochondrial genome was well reflected in the two lepidopteran mitochondrial genomes: higher frequency of A/T-rich codons, severe A/T bias in 3rd codon position, and extremely high A/T content in the A+T-rich region. Because insect mitochondrial genomes harbor biased nucleotide and resultantly biased amino acid sequences, phylogenetic inference is often misled by them. Although each recoded and unrecoded datasets for nucleotide sequences and amino acid sequences of PCGs provided overall identical topology, regardless of recoded scheme, each nucleotide and amino acid dataset provided difference in the status of Macrolepidoptera, providing a monophyletic group by amino acid dataset, whereas non-monophyletic group by nucleotide dataset.
