Sequence Variability At Four Nuclear Introns Of The Finless Porpoise And Adaptive Evolution Of Digestive RNASE1 Gene In Cetaceans

This thesis includes three chapters:1. Some advances in the studies of cetaceans in Chinese waters were reviewed.2. Intraspecific genetic variation and phylogeographic pattern can provide insights into the population-level process responsible for differentiation and speciation and yield information useful for conservation purposes. In the present study, sequence variation at four nuclear introns which are respectively from the parathyroid hormone-like (PTH) gene, isolate Pdalzl692 interferon (IFN) gene, peripherin-like (RDS) gene, and tyrosine kinase receptor-like (KIT) gene, were examined to analyse genetic diversity and population, structure of the finless porpoise (Neophocaena phocaenoides) in Chinese waters. High among-population differentiation was revealed, with the analysis of molecular variance (AMOVA) showing a significant genetic structure between populations (PTH:FST=0.29, P< 0.001; IFN1@:FST=0.23, P<0.001; RDS:FST=0.12, P<0.001; KIT:FST=0.16, P<0.001). Although the common haplotypes accounted for more than one half of all samples examined, many haplotypes were found,to be restricted to specific population. The mismatch distributions, Tajima's D and Fu's test all suggested a recent colonization and population expansion in finless porpoises in Chinese waters. Some conservation considerations, with special reference to the conservation priority of the unique Yangtze freshwater population, were discussed.3. Pancreatic ribonuclease (RNASEl) is a digestive enzyme that has been recognized to be one of the most attractive model systems for molecular evolutionary studies. The contribution of RNASE1 gene duplication to the functional adaptation of digestive physiology in foregut-fermenting herbivores, mostly in ruminants, has been well documented. However, no one has ever done a comprehensive study on the cetacean, which are sister to the artiodactyls. Here, we sequenced this gene from 5 species of the cetacea, seal, hippopotamus,which all have a relatively simple digestive system and lack the microbial digestion in rumen or cecum, except hippopotamus. In contrast to our initial expectation bursts of positive selection have been shown to contribute the enigmatic diversification of these RNASE 1 genes in cetacean. The finding of the adaptive evolution of RNASE1 in animals without foregut fermentation provides another opportunity for further studies of the structure, function, and evolution of this gene, raising the possibility that new tissue specificity or other functions of RNASE1 genes might have developed in these species.