| Paphia undulata is an important economic bivalve, commonly known as "oil clam" in the southeast coast of China. The oil clam’s meat with high nutrition is very delicious. As its fast growth, less disease occuring and high economic returns, it has become an excellent mariculture species. But with wanton harvesting, wildlife resources are rapidly depleted. In recent years the process of artificial breeding begins, but it has never been able to achieve substantial breakthroughs. The seed still supply limitedly. It’s indeed necessary to study on early development stages. During our survey about P. undulata resource, we found that the seed market was mixed by several breeding areas along the coast and seed frequent exchanges cross regions, which may have an adverse effect on its germplasm and its genetic diversity need to be evaluated.In this thesis, combined with optical microscope scanning electron microscope, the embryonic development was observed with photographs showing the entire process of embryonic development and real-time monitoring of the growth and development of planktonic larva. Studies including bait density, heavy metal ions, temperature, salinity and pH decline caused by CO2 concentrations on early development stages were conducted. These would provide data for seed cultivation. Meanwhile five geographical groups were collected including Thailand (TH), Philippines (PH), Yunxiao Fujian (YX), Danzhou Hainan (HN), and Beihai (BH). Based on morphology, mitochondrial COI gene, micro-satellite DNA, the genetic diversity of P. undulate was researched and evaluated as to provide a theoretical basis for its germplasm resources protection and management. The main findings were as follows:1, under condition of 28.5 ℃, salinity 30, The fertilized egg diameter was 58.49 ± 2.16 μm, It came to be trochophore larvae after about 8 h of incubation, D-shaped larvae after 13 h of metamorphosis, metamorphosis after 11d when shell length was about 220 μm. The shell length and shell height showed a stable linear relationship during planktonic larval stage. Under suitable environmental conditions, the steady growth was no noticeable pause, the curve of shell length growth close to be a straight line.2,4 kinds of heavy metal ions (Cu, Zn, Cd, Pb) inhibited significantly on the embryonic development stages, with outcomes of embryonic malformations increasing and hatching rate declining. The order of toxicity was Cu> Zn> Cd> Pb, the EC50 values were 83.29,184.32,230.00,239.04 ppb.Under 4 different feeding density of Isochrysis galbana, larval growth differenciation was significant. The larval development was best with algae concentration of 3x104 cell/ml. The suitable water temperature for early development stages was between 24-30 ℃, the optimum was 27-30 ℃. The suitable water salinity for early development stages was 27-33, the optimum was 30, resulting above 80% hatching rate. Compared to the control seawater, CO2 concentrations exceeding 2000 ppm (pH7.60) began to have an adverse effect on embryonic development, the deformity rate exceed 80% as the result of 3000 ppm (pH7.50).800 ppm (pH7.90) and 1500 ppm (pH7.70) showed a promoting effect on planktonic larvae growth, while high CO2 concentrations (> 2000 ppm, pH7.60) were not conducive. SEM observation was used to observe shell surface and internal structure. The results showed that a change was occurring in 2000 ppm water of more blurred texture, the overall decreasing in density, the shell loosing of the internal structure, EDS analysis showed a decreasing of the relative quality percentage of Ca from shell umbo to edge with the increasing of CO2 concentration.3, the external and internal morphology of five populations collected from PH, TH, YX, HN, BH were studied. TH shell color was yellow-green which was distinct from others. Base on the morphological traits, five populations showed significant differences. Clustering results among groups displayed that YX and HN, BH clustered into one groups, PH and TH joined. Principal component analysis established two main components; the contribution rate was 38.114%,29.221% respectively. Discriminant function was constructed in five populations with P1 discriminant accuracy of 54.0-80.0%, discriminant accuracy was 65.0% for all individuals.4, Population genetic diversity analysis of 5 populations based on mitochondrial COI gene sequences revealed that, among the 154 individuals, exsited 104 haplotypes, Tahima’s D, Fu’s Fs statistic and mismatch distribution parameter estimates showed that there might have expansion events before 735000 years, there may be a second small expansion took place about 160000 years ago. AMOVA analysis showed that, there was a significant genetic structure; the estimate mean of gene flow between populations was large, significant genetic differentiations exsited between five populations (p< 0.05). The UPGMA tree was constructed, two main branches formed significantly, with XY as a single group and the remaining four groups together as one. This probably caused by the reasons as follows:the P.undulata lack long distance movement ability, but its larvae had a planktonic phase which lasts 2-3 days to spread over ocean current, and the clockwise circulation in summer in Beibu Gulf might play an important role. And the unique formation of YX might be subjected to the geographical barrier.5, genetic diversity analysis of five populations based on microsatellite DNA was conducted:at 8 microsatellite loci, average allele number was 7.5-12.25, average effective number of alleles was 3.17-3.59, average observed heterozygosity was 0.9628-0.9862, average expected heterozygosity was 0.6702-0.706, polymorphic information content was 0.9743-2.3696. All the data indicate that genetic diversity of these populations was high. Fst between groups showed significant genetic differentiation in addition to YX and BH. The results of AMOVA revealed that the 10.21% variations from inter-population and that gene flow estimation results revealed that widespread gene exchange among different populations exist, and the maximum value came from YX and BH. UPGMA tree was constructed according to genetic distance, separating the five populations into two groups, one of three domestic populations and another of other two foreign populations.The main causes might come from the artificial exchanging, while the research populations of samples numbers and number of micro-satellite may not big enough, could not reflect the actual situation of whole populations. |
PDF Full Text Request