Studies On Inbreeding Effects And Genetic Improvement Of Bay Scallop

The Bay scallop, Argopecten irradians (Lamarck), has served as a primary cultured speciesin north China since it was introduced from the United States in 1982 (Zhang FS et al., 1986).This species is a functional hermaphrodite. It can self-fertilize and cross-fertilize in nature.Self-fertilization can result in inbreeding depression by increasing the frequency of recessiveharmful gene. At the same time, self-fertilization can be seen as a useful tool to produce purelines and broadly used in breeding program. In this study, inbreeding effects was evaluated by comparing growth and survival of F1, F2with different effective population size. F1, F2, F3 families were obtained by self-fertilizing. Thegrowth and survival of families was observed, and combining ability were estimated. A basepopulation was produced by cross of two cultured populations of bay scallop, and the realizedheritability was estimated. A complete diallel cross between two bay scallop population,Argopecten irradians concentricus Say (M) and Argopecten irradians irradians Lamarck (C),was carried out, and heterosis and maternal effect were discussion. The main results of this study are listed as follows: 1. The experiment was designed to study the effect of effective population size (Ne) on thegrowth and survival of F1 and F2 bay scallop Argopecten irradians. To determine the magnitudeof these effects, six experimental groups were produced: Ne=1, 2, 10, 30, 50, control. At the firstgeneration, the shell length of Larvae for all experimental groups was not different from eachother at of 1th day D-larva. With the growth of the larvae, the growth and survival of Ne =1 groupwere gradually smaller than that of the others, while there was no significant difference amongNe=2, 10, 30, 50 and control groups. During grow-out stage, the growth of shell length, shell iii张海滨 海湾扇贝近交生物学效应和遗传改良研究 博士学位论文height, shell width and wet weight for Ne =1 group was lower than the others too. In winter,survival rate of Ne=1 is lower than that of others (P <0.05). At second generation, inbreedingdepression exists not only in Ne=1 group but also in Ne=2 group. The growth and survival ratesof the two groups are significantly lower than those of the other groups (Ne=10, 30, 50, control).There is no significant difference between the later (P>0.05). At the same time, the amount ofdepression in Ne=1 group is significantly higher than that of Ne=2 group (P<0.05). These resultsindicate that the low effective population size (Ne), which increases the possibility of inbreeding,can lead to some harmful effects to the offspring. So it is essential to maintain a high level of Nein commercial seed production. Furthermore, as the high fecundity of bay scallop might lead toincreased inbreeding, selecting broodstock from different growout sites is recommended. 2. A base population was produced by cross of two cultured populations of bay scallopArgopecten irradians irradians Lamarck. After 1 year rearing, truncation selection of the top10% (i=1.755) was carried out in the base population of about 1300 adults. A control parentalgroup with identical number to the select parental group was randomly selected from the entirepopulation before isolation of the select parental group. The result showed that, at larval stage,the growth rate of larvae in the selected line was significantly higher than that of control(P<0.05), and that the realized heritability was estimated to be 0.52±0.24. Due to the lowerdensity of control at spat stage, mean shell length of control line was larger than that of selectline at day 110. With the density was adjusted to the same between two lines in grow out stage(from day 110-160), daily growth rate of selected line was significantly higher than that ofcontrol line (P<0.05). Survival of se...