A Study On The Cetacean Phylogeny And The BDNF Gene Of Baiji

This thesis includes three chapters:1. Some developments in the studies of river dolphin phylogeny based on morphology, paleontology, and molecular biology were reviewed.2. Using the primers cited from previous studies, and the primers for ND3 gene, which were designed based on the conservative flanking sequences of the ND3 gene in some of the cetacean mitochondrial genomics, two nuclear genes BDNF, c-mos and one mtDNA gene ND3 from cetaceans were amplified and sequenced. The sequence lengths for BDNF, c-mos, and ND3 genes are 527 bp, 546 bp and 318 bp, respectively. In combination with some relevant sequences from GenBank, 22 individuals of cetaceans including 13 species of seven families from toothed whales and one species of one family from baleen whales were included in the present analysis. The phylogenetic reconstruction supported Delphinidae and Phocoenidae respective monophyletic groups, and proposed a sister relationship between these two families. The inclusion of Physeteridae in toothed whales is also supported in this study. No direct affinities among the three river dophins (Lipotes vexillifer, Platanista gangetica, Pontoporia blainvillei), and the most divergent position of Platanista in river dolphins were found, which can be regarded the new evidence supporting the non-monophyletic origin of river dolphins and the family status for all river dolphin genera.3. The full coding region of the brain - derived neurontrophic factor (BDNF) gene from the Baiji (Lipotes vexillifer) was amplified by polymerase chain reaction (PCR). The nucleotide sequences that we had cloned showed an open reading frame (ORF) of 747 bpwithout any introns, which encoded a protein of 248 amino acids. The nucleotide sequences in the BDNF coding region of the Baiji had a high level of similarity (>90%) with those of other mammalians, especially with pig (Sus scrofa) (95%) and cow (Bos taurus) (94.7%). The amino acids sequence comparison showed that the BDNF precursor proteins of the Baiji had a 94.5-99.5% of similarity with other mammalians, indicating the high level of gene conservation. In the phylogenetic tree, species from Order Cetacea and Order Carnivora constituted respective monophyletic clades. Further, species of cetaceans had a relatively closer affinity with those of ungulates rather than with other mammalians. This suggests BDNF an appropriate candidate in the phylogenetic reconstruction at order or lower level.