The Complete Mitochondrial Genomes Of Four Anseriformes Species And Implications For Their Phylogenetics

The sequence research of mtDNA and reconstruction of the phylogenetic relationship of animals are becoming more and more popular at present. The complete mitochondrional genomes have been widely used as powerful molecular markers to resolve the controversial Aves species. Anseriformes is a highly differentiated group with worldwide distribution, which is regarded as one of the best-studied groups of birds. The phylogenetic relationship among Anseriformes is rather complex and controversial, which has been affected by rearrangements for several times. Aix galericulata, Tadorna ferruginea, Mergus squamatus and Anser fabalis are typically waterbirds in Anseriformes, and their phylogenetic sites are controversially for a long time. In addition, the relationship of some important groups in Anseriformes are controversial widely, such as the stiff-tailed ducks, Anseranas semipalmata and the whistling ducks. Traditionally, most available phylogenetic data came from morphological, anatomical and behavioral analyses. As the development of genetic analysis and molecular biology, the mitochondrial genome has become a highly useful molecular marker for the reconstruction of phylogenetic relationships at different animal taxonomic levels. In mis study, in order to have an insight into the phylogenetic relationship among Anseriformes, we used PCR-based method to determine the complete mitochondrial genome sequences of Mergus squamatus, Anser fabalis, Aix galericulata and Tadorna ferruginea, and analyzed the structure of some published Anseriformes species mitochondrial genome. In order to clarify the phylogenetic position of these four species, the phylogenetic trees were based on the complete mtDNA among16Anseriformes species. In order to have an insight into the phylogenetic relationship among Anseriformes, phylogenetic trees are reconstructed by multiple sequence alignments of three mitogonome (Cyt b, ND2and COI) sequences among68typical Anseriformes species.The complete mtDNA nucleotide sequences of the four birds are circular molecule, which are16595bp,16688bp,16651bp and16639bp in size. The organization of the sequence encodes13protein genes (ATP6, ATP8, COI-Ⅲ, ND1-6, ND4L, and Cyt b),22tRNA genes,2rRNA genes (12S rRNA and16S rRNA) and the non-coding control region (D-loop). The same gene order and arrangement illustrate extremely conservative and similar to other Anseriformes birds. The length among them is similar and very conservative in the PCGs in the four Anseriformes species, the ATG as start codon is generally observed and TAA is the most frequent stop codon. All tRNAs could be folded into canonical cloverleaf secondary structures except for tRNASer(AGY) and tRNALeu(CUN)、which are missing the dihydrouridine (DHU) arm. Like other Anseriformes,12S rRNA and16S rRNA genes are located between tRNAPhe and tRNALeu, separated by tRNAVal.The phylogenetic relationship among16Anseriformes species based on the complete mtDNA shows that Aix galericulata and Tadorna ferruginea are in the lineage, Tadorninae. Mergus squamatus belongs to Anatidae, and Anser fabalis belongs to tribes Anserini of Anserinae. Anas formosa has no close relatives among living ducks, so it should be put in a distinct genus other than Anas.Molecular phylogenetic analysis based on concatenated sequences (Cyt b, ND2and COI) support the studied Anseriformes birds being divided into three families: Anhimidae, Anatidae and Anseranatidae. Anseranas semipalmata does not belong to Anatidae, but represents an independent family, Anseranatidae. The results suggest Anatidae birds being divided into five subfamilies:Anatinae, Tadorninae, Anserinae, Oxyurinae and Dendrocygninae. Stiff-tailed ducks (Oxyurinae) and whistling ducks (Dendrocygninae) should not belong to Anserinae, but represents an independent subfamily respectively. The Anatinae, includes species of tribes Mergini, Somaterini, Anatini and Aythyini. The subfamily Anserinae, which comprises tribes Anserini and Cygnini. The phylogentic relationship supports that the genus Somateria is an early-diverging lineage in Mergini which is sometimes classified as a separate tribe, Somaterini.