Structure and variation of the Anseriformes mitochondrial DNA control region
The control region is the major non-coding segment of animal mitochondrial DNA. To infer the structure and variation of Anseriformes mitochondrial DNA control region, the control region sequences of 52 species were analyzed. The length of the control region sequences ranged from 968 bp (Chenonetta jubata) to 1335 bp (Anseranas semipalmata) and can be separated into three domains. There is a deletion of 100–130 bp in Anatinae, compared to other groups of Anserinae. The average genetic distances among the species within the genera varied from 4.14% (Anser) to 10.58% (Cygnus). The average genetic distances showed insignificantly negative correlation with ts/tv. Domain I is the most variable among the three domains among all the genera. Five conserved sequence boxes in the domain II of Anseriformes sequences were identified. The alignment of the Anseriformes five boxes sequences showed considerable sequence variation. CSB-1, -2 and 3 were not found in the Anseriformes. Maximum-likelihood method was used to construct a phylogenetic tree, which grouped all of the genera into four divergent clades. Anseranas + Chauna and Dendrocygna were identified as early offshoots of the Anatidae. All the remaining taxa fell into two clades that correspond to the two subfamilies Anserinae and Anatiane.