ABSTRACT
The millipede Anaulaciulus koreanus (Verhoeff, 1937), belonging to the family Julidae, is an endemic species of the Korean fauna. In this study, we sequence and annotate the mitochondrial genome of A. koreanus. The complete mitochondrial genome of this species is 14,916 bp in length and contains 13 protein-coding genes, 22 transfer RNA genes, two ribosomal RNA genes (16S and 12S rRNA), and a large non-coding region. The genome has a very high A+T content (71.1%), less than of the species Brachycybe lecontii Wood, 1864 (order Platydesmida; 76.6%) and Sphaerotheriidae sp. (order Sphaerotheriida; 71.2%). In comparison with the mitochondrial gene arrangement of eight other millipede species, the whole mitochondrial gene arrangement of A. koreanus is most similar to the nemasomatid species, Antrokoreana gracilipes Verhoeff, 1938, but differs from those of the other diplopod orders. The absence of tRNACys between the ND2 and COI regions is unique to the order Polydesmida, whereas the translocation of tRNATyr to between ND2 and COI is exclusive to the Sphaerotheriida. It is also shown that the translocation of tRNAThr between ND4L and ND1 may be a synapomorphy to support a close relationship of two orders Spirobolida and Spirostreptida.
Subject(s)
Arthropods , Genome, Mitochondrial , Animals , Gene Order , Genes, Mitochondrial , RNA, Ribosomal , RNA, Transfer , Sequence Analysis, DNAABSTRACT
The complete mitochondrial genome of a troglobite millipede Antrokoreana gracilipes (Verhoeff, 1938) (Dipolopoda, Juliformia, Julida) was sequenced and characterized. The genome (14,747 bp) contains 37 genes (2 ribosomal RNA genes, 22 transfer RNA genes and 13 protein-encoding genes) and two large non-coding regions (225 bp and 31 bp), as previously reported for two diplopods, Narceus annularus (order Spirobolida) and Thyropygus sp. (order Spirostreptida). The A + T content of the genome is 62.1% and four tRNAs (tRNA(Ser(AGN)), tRNA(Cys), tRNA(Ile) and tRNA(Met)) have unusual and unstable secondary structures. Whereas Narceus and Thyropygus have identical gene arrangements, the tRNA(Thr) and tRNA(Trp) of Antrokoreana differ from them in their orientations and/or positions. This suggests that the Spirobolida and Spirostreptida are more closely related to each other than to the Dipolopoda. Three scenarios are proposed to account for the unique gene arrangement of Antrokoreana. The data also imply that the Duplication and Nonrandom Loss (DNL) model is applicable to the order Julida. Bayesian inference (BI) and maximum likelihood (ML) analyses using amino acid sequences deduced from the 12 mitochondrial protein-encoding genes (excluding ATP8) support the view that the three juliformian members are monophyletic (BI 100%; ML 100%), that Thyropygus (Spirostreptida) and Narceus (Spirobolida) are clustered together (BI 100%; ML 83%), and that Antrokoreana (Julida) is a sister of the two. However, due to conflict with previous reports using cladistic approaches based on morphological characteristics, further studies are needed to confirm the close relationship between Spirostreptida and Spirobolida.
