Abstract
The complete mitogenome sequence of Anser cygnoides was determined and compared with those previously released. The whole mitogenome was 16,740 bp, with 13 protein-coding genes, 22 transfer RNA genes, 2 ribosomal RNA genes, and 1 putative non-coding region (1178 bp). The overall nucleotide composition was 30.2%, 32.0%, 15.1%, and 22.7% for A, C, G, and T, respectively. Phylogenetic analyses strongly supported two clades in Anserini and demonstrated that A. cygnoides is not monophylogenetic. This division of A. cygnoides indicates that more research is necessary to clarify phylogenetic relationships for A. cygnoides and determine how they relate to morphological traits.
The swan goose, Anser cygnoides (order Anseriformes, family Anatidae) is one of the rare large geese. It is distributed from central Asia to Mongolia and northern China and winters in South/North Korea and central and eastern China (Carboneras & Kirwan Citation2017). Considerable population decline has been observed in some parts of its breeding and wintering areas (BirdLife International Citation2016). This species is labelled as Vulnerable on the IUCN Red List. It was classified as an Endangered species II by the Ministry of Environment of Korea and designated a Natural Monument (No. 325-1) by the Cultural Heritage Administration of Korea. Here, we provide the mitogenome sequence of A. cygnoides from South Korea and compare it with those previously published (Dai et al. Citation2015; Liu et al. Citation2015; Ren et al. Citation2016; Zhu et al. Citation2016).
As part of an ecological study to investigate migration patterns between breeding and wintering sites and with a permit from the Cultural Heritage Administration of Korea, a blood sample (IN717) of A. cygnoides was collected from Seocheon-gun, Chungcheongnam-do, South Korea and was deposited in the National Institute of Biological Resources at Incheon, South Korea. The complete mitochondrial genome of A. cygnoides was determined using a primer walking approach and has been deposited in GenBank (KY767671). The circular mitogenome of A. cygnoides was 16,740 bp in length and contained 13 typical vertebrate protein-coding genes, 22 transfer RNA genes (tRNA), two ribosomal RNA genes (rRNA), and one putative non-coding region (D-loop region). The overall nucleotide composition of the mitogenome was 30.2%, 32.0%, 15.1%, and 22.7% for A, C, G, and T, respectively. The D-loop (1178 bp) was located between tRNA-Phe and tRNA-Glu and does not include tandem repeats. Mindell et al. (Citation1998) found a single extra nucleotide ‘C’ at position 174 in some birds and turtles, which also occurs in the ND3 of the individual of A. cygnoides examined in this study. When examining close relatives, this nucleotide also was observed in A. albifrons (NC_004539) and A. anser (NC_011196) but not in A. fabalis (HQ890328).
To perform phylogenetic analyses, all 13 of the protein-coding genes (11,457 bp) were concatenated from 19 mitogenomes. Along with the individual sampled by this study, 10 additional individuals of A. cygnoides and individuals from eight other species of the Anserinae were sampled from GenBank. A neighbour-joining (NJ) tree was constructed by MEGA 6.0 (Tamura et al. Citation2013). The phylogenetic tree revealed that tribe Anserini consisted of two clades; one including A. cygnoides (9 of the 11 sampled individuals) and A. albifrons and the other containing A. cygnoides (individuals KJ124555, KP238480), A. fabalis, and A. anser (). Thus, A. cygnoides did not form a monophyletic group in this study. This shows the need for more research on possible connections between separate lineages of A. cygnoides and potential morphological or biogeographical differences.
Figure 1. Neighbour-joining tree of four species of Anserini based on the concatenated nucleotide sequences of the 13 protein-coding genes of their mitochondrial genomes. Bootstrap values are shown at the nodes. GenBank accession numbers for the sequences are indicated next to species designations.
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The authors report no conflicts of interest.
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References
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