长牡蛎(Crassostrea gigas)多代近交与自交家系遗传差异及生长性状比较

COMPARATION OF GENETIC DIVERSITY AND GROWTH OF PACIFIC OYSTER CRASSOSTREA GIGAS BETWEEN DIFFERENT INBREEDING SELECTION AND SELF FERTILIZATION SELECTION

在良种选育过程中,为了尽快得到稳定可遗传的优良性状,常采用近交方式进行纯系选育,而近交会导致群体的遗传多样性下降。为了解长牡蛎(Crassostrea gigas)多代近交和自交家系的遗传多样性、遗传结构和生长情况,本实验选用长牡蛎近交4代(F4代)、近交5代(F5代)家系和雌性同体自交1代(自交1代)家系,采用8对多态性高的微卫星序列进行分析,同时对其成体的三个时间点生长数据进行了显著性差异分析。实验结果表明,8对微卫星位点在野生对照组中表现出较高的多态性,F4代、F5代和自交1代3个家系的遗传多样性明显下降,平均等位基因数(Na)由17.00下降到2.00,平均观测杂合度(Ho)由0.538下降到0.449,平均多态信息含量(PIC)由0.826下降到0.297;哈迪-温伯格平衡(HWE)检验结果显示,8个位点在三个家系和野生对照组中均不同程度偏离HWE平衡(P<0.0062)。F4代、F5代、自交1代和野生对照的生长性状指标分析表明,和野生对照相比,三个家系生长指标明显提高,对于自交一代而言,与自交实验组亲本选择的偶然性有关。同时,三个家系三个时间点的壳长、壳宽生长性状没有显著性差异(除330日龄壳宽和630日龄壳长),F5代生长性状指标壳高和湿重均大于F4代和自交1代,且差异显著;但F4代和自交1代之间没有显著性差异。通过本研究发现,F5代可以继续用来进行生长性状新品系的选育,自交1代多样性降低程度相当于F5代,但多样性的降低对成体的生长性状影响不明显,仍可以用做相关实验材料。

To get stable and inheritable traits quickly, inbreeding is often used to obtain a pure line. However, this practice may cause a decline in the genetic diversity of the population. In this study we selected eight high-polymorphic microsatellite loci of oyster Crassostrea gigas to investigate the genetic diversity, genetic structure, and growth of the fourth breeding generation（F4）, the fifth breeding generation（F5） and the first selfing generation（selfing1）. The growth data were analyzed at three temporal points. The experimental results show that the eight microsatellite markers presented high polymorphism in the wild control group. All the indicators decreased significantly in the three inbreeding lines, and the average allele number（Na） descended from 12.25 to 2.00, the average observed heterozygosity declined（Ho） from 0.538 to 0.449, and the average polymorphism information content（PIC） of the eight microsatellite markers decreased from 0.826 to 0.297. The eight loci deviated from the Hardy-Weinberg equilibrium in three inbreeding lines and the wild control group. Analysis of growth traits showed that compared with wild control, the growth index of the three inbreeding increased significantly. On the other hand, there were no significant differences in shell length and shell width at the three temporal points（except for shell width at 330 days temporal point and shell length at 630 days temporal point）. However, the traits of shell height and wet weight of F5 generation were significantly higher than those of F4 generation were. Moreover, there was no significant difference between selfing 1 generation and F4 generation. Overall, the F5 generation inbreeding lines could be used continuously for growth traits（such as shell height and wet weight） selection, although the diversity may decline as a trade-off due to brother-sister self-fertilization.