| Among avian orders, the Anseriformes (screamers and waterfowls ) are a morphologically and biologically diverse group containing ca. 150 species distributed worldwide except Antarctica. This paper will review the phylogeny of Anseriformes firstly and then discuss the molecular phylogeny of Anseriformes based on the genetic variation of mitochondrial 12S rRNA gene and cytochrome b gene respectively.1. Because the taxonomic division is rather complex and has been much disputed and revised, in this part, we will review the classification and phylogeny of families, subfamilies and tribes of Anseriformes based on morphology, ethology, osteology, mitochondrial and nuclear DNA restriction fragment length polymorphism, single-copy nuclear DNA hybridization and the sequences of mitochondrial gene analysis referring to the different definition, classification and phylogenetic relationships of the families, subfamilies and tribes of Anseriformes. The controversial questions and deficiency in the systematic studies of Anseriformes were pointed out.2. The sequences variation of mitochondrial 12S rRNA gene and phylogenetic relationships of Anseriformes were studied based on the complete 12S rRNA gene sequences of 36 living species of which 19 species were sequenced and other related data obtained from Genbank. Total of 1030 aligned sites were obtained, including 346 variable and 259 parsimony informative sites. The pairwise comparisons show higher number of insertions and deletions ininthe 12S rRNA gene of Anseriformes, and the number of transitions is much more than that of transversions. Phylogenetic analysis surports that Anseranas should be placed in monotypic family Anseranatidae, and the whistling ducks and the white-backed duck should be separated from subfamily Anserinae and placed them into family Dendrocygnidae. The family Anatidae could be classified into two subfamilies, Anserinae and Anatinae. The results approve that the swans should be put into the tribe Cygnini of subfamily Anserinae as suggested by Livezey ( 1996, 1997b ) and the shelducks should be placed in the tribe Tadornini of subfamily Anatinae, therefore, our results do not support Sibley and Ahlquist's (1990) establishment of the subfamily Cygninae and placing the shelducks in the tribe Anserini. Phylogenetic analysis also shows that the tribe Aythyini cleavaged early during the evolution of Anatinae, and there is a closer relationship among tribes of Tadornini, Mergini and Cairinini. The tribe Anatini was a monophyletic group which formed a separate clade during the evolution of Anatinae.3. The sequence variation of mitochondria! cytochrome b gene and phylogenetic relationships of Anseriformes were studied based on the complete cytochrome b gene sequences of 19 species combined with 4 species got from Genbank. Analysis of the sequence variation of cytochrome b gene indicated that there is no evidence of insertions or deletions, i.e., they are all of identical length of 1143 bp in all the sequences of cytochrome b gene. Further, the sequences can be fully translated into amino acid using chicken mitochondrial codon without nonsense mutations or intervening stop codons. The 1143 bp cytochrome b alignment contained 416 variable sites, of which 306 were parsimony informative sites with the strongest variable in third codon positions and less variable in first and second codon positions. Sequence variation analysis exhibits high transition to transversion substitution ratios, and transitions and transversions are unsaturated in the sequence of cytochorme b gene. The base composition of the cytochrome b sequences was highly biased. Using a structural model of the cytochrome b protein as a template, we divided cyt b sequence data for species within Anserifomes into three functional domains. Saturation of substitutions of sequences within these regions was assessed graphically. These results demonstrate that saturation of substitutions is correlated with functional regions of cytochrome b. Phylogenetic anal...
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