The complete mitochondrial genome sequence of Sinopoppia nigroflagella Wei, 1997 (Hymenoptera: Tenthredinidae) reveals a new gene order

Abstract The complete mitochondrial genome of Sinopoppia nigroflagella Wei, 1997 was sequenced and assembled. The circular genome is 15,940 bp long, with an A + T content of 80.33%, 37 genes, and a 658-bp control region. Specifically, trnL1 was translocated into the MQI gene cluster, and the other tRNA cluster was arranged as ARENS1F. The two gene clusters were thus arranged as ML1QI and ARENS1F. The phylogenetic results indicated that S. nigroflagella forms a sister group with Blennocampinae and Fenusinae.

Sinopoppia nigroflagella is a peculiar sawfly species and its systematic position remains uncertain (Wei 1997). Wei and Nie (1998) placed S. nigroflagella into Caliroinae of Heterarthridae. Taeger et al. (2010) treated it as a member of Heterarthrinae of Tenthredinidae. Based on COI data S. nigroflagella seemed to be combined with the Dimorphopteryx species of Tenthredininae (Unpublished data). The phylogenetic position of S. nigroflagella remains to be determined. In this study, we sequenced the mitochondrial genome of S. nigroflagella to determine its phylogenetic position.
Phylogenetic analysis was performed, including only hymenopteran taxa, to avoid possible effects of long-branch attraction. The nucleotide sequences of 13 protein-coding genes (PCGs) of 50 other Symphytan and two Apocritan species were aligned using the MAFFT method in the TranslatorX server (Abascal et al. 2010). The phylogenetic tree was constructed using IQTREE (Jana et al. 2016) with default parameters. Based on the previous experience (Malm and Nyman 2015), to avoid the long-branch attraction, the outer group was excluded. Thus, Xyelidae was used for rooting the tree.
The sequence yield by MitoZ was 16,730 bp in length and contained 37 genes with an incomplete control region. We used the sequence flanking the control region as a reference sequence. One of the flanking regions contained trnM (120 bp) and the other included part of the rrnS (110 bp) gene. The results of the two assemblies were consistently showing them as a control region 658 bp in length. We then verified the 15,940 bp long genome using Endemyolia tibialis (unpublished) as the reference sequence and the mean depth of coverage across the contig sequence was 1180.
Compared to the ancestral insect mitochondrial genome (Boore 1999), three rare rearrangement events were detected in the mitochondrial genome of S. nigroflagella. The trnQ(À) and trnM(þ) genes were shuffled with trnL1(À) translocated downstream of trnM(þ). The rearrangement of trnL1(À) was verified using trnM(þ) and trnQ(À) as reference sequences, respectively. The last rearrangement event was trnE(þ) remote inversion to the downstream region of trnR(þ). The two gene clusters were thus arranged as ML1QI and ARENS1F.
Phylogenetic analysis indicated that S. nigroflagella is a sister group of the lineage of Blennocampinae and Fenusinae. The clade of S. nigroflagella þ (Blennocampinae and Fenusinae) forms a sister group of the clade combined by Tenthredininae and Allantinae. This study further clarified the phylogenetic position of Sinopoppia in the Tenthredinidae. However, considering the complexity of Tenthredinidae, dense sampling is essential to obtain a robust phylogeny ( Figure 1).

Disclosure statement
No potential conflict of interest was reported by the author(s).