Complete mitochondrial genome of a hen harrier Circus cyaneus (Accipitriformes: Accipitridae) from South Korea

Abstract A hen harrier Circus cyaneus (Accipitriformes: Accipitridae), a migrant raptor having a wide breeding range from Europe to Northeast Asia, migrates to more southerly areas (Southern Europe, China, Korea and Japan) in winter. In this study, the complete mitochondrial genome of C. cyaneus was completely sequenced and characterized. It was 20,173 bp in length being composed of 13 protein-coding genes, 22 transfer RNA genes, two ribosomal RNA genes and two control regions. It has a base composition of A (32.2%), G (12.6%), C (30.5%) and T (24.7%). The phylogenetic tree reconstructed based on the maximum likelihood (ML) method confirms that C. cyaneus places within the clade of the family Accipitridae in the monophyletic avian order Accipitriformes.

A hen harrier Circus cyaneus (Linnaeus, 1766) is a representative winter migratory bird and an endangered species by the Ministry of Environment, South Korea, belonging to the avian family Accipitridae (Order Accipitriformes), which has a wide range of habitats from Europe and North Asia to Russian Far East. In winter season, it migrates from Europe and Northwest Africa through Turkey and Middle East to Southeast China, Korean peninsula and Japan (Ferguson-Lees and Christie 2006).
The specimen of C. cyaneus used in the present study was collected from Dalseong wetland, Daegu city,South Korea (35 49'02.4"N 128 29'26.9"E). The specimen was deposited under the voucher number GEIBGR0000289530 in the National Institute of Biological Resources (NIBR), South Korea. Total genomic DNA of C. cyaneus was extracted using QIAamp Tissue Kit (QIAGEN Co., Germany), and the mitochondrial genome was amplified by long range PCR method using Expand TM Long Template PCR System (Roche Co., Germany). 12S rRNA gene and four overlapping long fragments were amplified with specific primers shown in Table S1. Sequences were aligned and trimmed using the Clustal X2 program (Larkin et al. 2007) and BioEdit 7.0.9 program (Hall 1999). Protein-coding genes (PCGs), rRNAs, tRNAs and control region were characterized using NCBI Basic Local Alignment Search Tool (BLAST) and a program tRNAscan-SE (Chan and Lowe 2019).
The mitochondrial genome of C. cyaneus is 20,173 bp long (GenBank accession no. KU237286), which exhibits the same gene order with that of the order Accipitriformes. It contains total 37 genes including 13 PCGs (COX1-3, ND1-6, ND4L, CYTB, ATP6 and ATP8), 2 rRNAs (16S rRNA and 12S rRNA), 22 tRNAs and 2 control regions (CR and wCR), of which 28 genes places on the heavy strand (H-strand) and the remaining 9 genes are located on the light strand (L-strand). The overall genome components and gene orders are identical to those of C. cyaneus published with the specimens of Inner Mongolia (Gao et al. 2018). The overall A þ T content of C. cyaneus mitogenome is 56.9%: 53.7% for PCGs, 56.7% for tRNAs, 53.2% for rRNAs and 67.0% for CRs. In the PCGs (11,400bp long), 12 are encoded in the H-strand, and the only one (CYTB) is located in the L-strand. All PCGs use the conventional start codons ATN except for COX1 using GTG which was also employed as the initiation-codon in other avian species (Slack et al. 2003). CR (3,571bp long) locates between trnT and trnP, which is divided into three domains of Domain I, Central Conserved Domain II, and Domain III. Domain II exhibits only five conserved boxes of F, E, D, C and b, and B-box, generally existing in Aves, is not found.
The maximum likelihood (ML) tree was reconstructed with 13 PCGs among 27 accipitriform species (Figure 1). The best fitting model mtVer þ IþG4 was selected for the ML analysis. The ML tree confirms that C. cyaneus places within the clade of the family Accipitridae in the monophyletic avian order Accipitriformes. Within the family Accipitridae, there are found four different clades of Clade 1, 2, 3 and 4. In Clade 2, C. cyaneus from South Korea is grouped with C. cyaneus from Inner Mongolia within the monoclade of the genus Circus. Accipiter is a sister genus of Circus. The relationships of the four families of Accipitriformes are consistent with those of Burleigh et al. (2015) and Jiang et al. (2015).

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

Funding
This work was financially supported by the National Institute of Biological Resources (NIBR), the Ministry of Environment (MOE), Republic of Korea, granted to UWH [NIBR201503204].

Data availability statement
The data that support the findings of this study are openly available in NCBI at https://www.ncbi.nlm.nih.gov/nuccore/KU237286.