Studies On The Mitochondrial DNA Diversity And MHC Class Ⅱ B Genes Diversity In Crested Ibis (Nipponia Nippon)

Crested Ibis (Nipponia nippon) is an Endangered species that is endemic to China. All living Crested Ibis are known to descent from two breeding pairs rediscovered in Yangxian county in 1981. Until the end of 2004, the total population has recovered to about 600 individuals, including the wild and the captive populations. In order to provide feasible strategies for its conservation, we collected samples from both the wild and the captive populations, selected mitochondrial DNA and major histocompatibility complex (MHC) as genetic makers, and did comprehensively research on genetic diversity of this species with both non-coding regions and functional loci. Our major results were:1) The results of analyses of mitochondrial DNA control region sequence variation indicated that the species demonstrated an extremely low level of genetic diversity. Only two haplotypes were found within the screened population, which differed from each other by only one variable site. The haplotype diversity and nucleotide diversity were 0.413±0.068 and 0.073% ±0.012% respectively.2) The two haplotypes were identified in both the wild and the captive populations. In the wild population screened, 60% were haplotype I and 40% were haplotype Ⅱ, and haplotype diversity and nucleotide diversity were 0.533±0.095 and 0.095%±0.017%, respectively. In the captive population screened, 76.9% were haplotype I and 23.1% were haplotype Ⅱ, and haplotype diversity and nucleotide diversity were 0.369±0.091 and 0.066% ±0.068%, respectively. The differences between the wild population and the captive population in haplotype distribution as well as the two genetic diversity parameters were not statistically significant, which indicated that there was no significant genetic differentiation occurred between the two populations.3) We successfully amplified the regions of the Crested Ibis MHC class ⅡB genes exon 2 with our own designed primers, and we found and named 5 new alleles. Comparatively lower level of divergence between MHC alleles was observed in the Crested Ibis than in other bottlenecked species. The average pairwise nucleotide difference and amino acid difference were only 7.4±1.9 nucleotides and 4.8±1.5 amino acids, respectively. This indicated that Crested Ibis population might be more vulnerable to infectious disease, and its reproductive fitness may be low.4) There were four overlaps in MHC alleles between the wild and the captive populations, yet allele Nini*0205 was detected only in one bird sampled in 1990 from the wild population. The disappearance of allele Nini*0205 in individuals from later sampling years might be a good evidence of allele loss by chance effect in small population, or at least the transition of rare allele frequencies to an extremely low level after generations.5) According to the results above, we provided advices for the conservation of Crested Ibis as listed below:? Special attention should be paid to individuals with haplotype II when considering captive breeding management, so that haplotype II might not be lost by chance in the captive population.? Since no significant genetic differentiation were observed between the captive population in Shaanxi Crested Ibis Protection and Breeding Centre and the wild population in Shaanxi Crested Ibis Natural Reserve, this captive population is one of the ideal source populations for reintroduction. Reintroduction projects should be conducted before significant genetic differentiation finally occurs.? A founder population for reintroduction should be selected based on the present genetic data to contain representative samples of individuals with most of the different MHC allele genotypes, which could possiblely maximize the chance for survival when the population are exposed to novel disease.