Studies On Genetic Diversity Of Two Wild Populations Of Pearl Oyster Pinctada Martensi

Genetic diversity refers to the full genetic information in living things.It does not only indicate how richness the gene variation is, but also refersto how genotypes distribute within populations, that is population geneticstructure. Studies on genetic diversity helps to know origination andevolution of biodiversity; and to provide valuable references forresearching into differentiation and evolution of plants and animals; andfurther more to set up a background knowledge for breeding and geneticimproving. Pearl oyster Pinctada martensi, which mainly distribute alongthe coasts of Guangdong, Guangxi and Hainan, is one of the importanteconomic marine species for pearl farming. Since 1970, with the rapidincreasing of pearl farming in China, pearl oysters were over fished, andwhat make it goes from bad to worse is that their habitat deteriorated withhuman activities. The genetic resources of pearl oysters are witheringgradually, and now it is difficult to find wild species along the coasts ofFujian and Taiwan, which were good habitat for pearl oysters. Hundredsand millions of pearl oysters used in pearl farming for almost 20 years aredescendents of a small amount of parent shellfishes, the detrimental effectsof inbreeding depression leads to the variety degeneration, e.g. earlysex-maturity and small body-size. And in turn it leads to inferior quality ofcultured pearls and a great decrease in quantity of pearls. Therefore, athorough and systematic study on genetic resource and breeding of pearloysters is necessarily to carry out as soon as possible. Thus, it helps tomake corresponding measures for resource conservation and continuesusing, and to guarantee a sound and stable development of pearl farming.This paper reports the studies on genetic diversity of wild pear oysterPinctada martensi, which comes from Beibu Bay and Daya Bay in China,by comparing their morphological characters and ultrastructure ofspermatozoa, analyzing their polyacrylamide gel electrophoretic patternsfor proteins or isozymes, using random amplified polymorphic DNAmarkers. The results suggest that (1) Morphologically, (a) the Beibu Bay population (BBP) display ayellowish-brown shell color and shell surface radial lines are verypronounced. In the Daya Bay population (DBP), shell color isyellowish-green with dim radial lines. (b) The shell length of BBP rangesmainly (90%) in 50-80mm, its mean value is 69.4mm; And that of DBP(92%), in 50-70mm, the mean value, 60.3mm, which means that BBP has alonger shell-length than DBP. (c) The majority shell-height value of boththe populations distributed in 50-80mm, the average value of BBP is70.3mm, and that of DBP, 64.9mm. Therefore, BBP has a highershell-length than DBP. Regression analysis indicates that the relationship ofshell-height and shell-length can be described in a power function. (d) Theaverage shell-width of BBP is 22.2mm, with a shell-width index of 0.1369;and that of DBP, 24.9mm and 0.1653, which means that DBP has moreswelled shells than BBP. The relationship of shell-width and shell-lengthcomes to a logarithmic function. (e) The shell-weight index of BBP is22.6268, and that of DBP, 27.9615, therefor, BBP has thinker valves thanDBP. (f) The value of condition factor for BBP is 7.8053, and that for DBP,13.9580, which means that BBP has a lighter soft body than DBP. (g) Thehinge-length of the majority in BBP is shorter than shell-length; however,about more than a half of shellfishes in DBP have a longer hinge-lengththan shell-length. (h) The rate of female/male in BBP is 26/24, which isnear to 1/1; and that in DBP, 21/29, which is about 3/4. (2) The ultrastructure of spermatozoa in both the populations does notshow any distinguishable differences, except that there are much morespermatozoa with 5 mitochondria in BBP than those in DBP. (3) Karyotype analysis indicate that both the populations has the samekaryotype which is 2N=28=16m+6sm+4st+2t, NF=50. The chromosomeorder, however, shows obvious distinction between the two populations, i.e.the telocentric chromosome in DBP occupies the 6-8th places, but that inBBP, the 9-11th places. (4) Polyacrylamid gel electrophoresis for soluble proteins inextrapallial fluid indicates different proportions of protein band betweenthe two populations. (5) Electrophoretic analysis of 15 isozymes at 26 loci in both thepopulations shows significant variation, among which band 89 of ALP andband 100 are characteristic bands in DBP. The heterozygosity value of BBPis 0.0999, of DBP, 0.1243; The rate of polymorphic locus is 38.46% in BBPand 46.15% in DBP. And the genetic identity and distance between the twopopulations is 0.9842 and 0.0159, respectively. (6) RAPD markers used in the study suggest a higher gene diversity inboth the populations than that gained by isozyme electrophoresis. Among220 random primers screened, there are 77 primers found to be positive; atleast 14 primers revealed clear and stable polymorphisms. The 2027, 1904and 250 bp DNA bands amplified by T-06 primer and A 1904 bp DNA bandamplified by E-17 primer were absent in Daya Bay population. Similarly,the 1375 and 564 bp DNA bands amplified by T-18 primer and a 564 DNAbp band amplified by O-01 primer were absent in Beibu Bay population.Calculating result indicate that at DNA level the gene diversity is 0.2594 inBBP and 0.2721 in DBP. The rate of polymorphic locus is 83.8% in BBPand 87.7% in DBP. The genetic identity and distance between the two...