不同年龄段大连群体菲律宾蛤仔EST-SSR多样性

为查明年龄结构对菲律宾蛤仔同一群体内遗传多样的影响,采用14个SSR分子标记对大连石河不同年龄段的野生蛤仔进行了检测。结果表明:不同年龄段(1龄-Age1、2龄-Age2、3龄-Age3)蛤仔均维持着较高的遗传多样性。根据POPGENE 1.31和SPSS16.0统计分析显示,位点Rp-11、Rp-12、Rp-19对3个年龄段蛤仔的等位基因数差异极显著(P<0.01);位点Rp-20、Rp-24、Rp-27、Rp-30对其差异显著(P<0.05);剩余7个位点表现为差异不显著(P>0.05)。在平均水平上,每位点等位基因数目Na为4.3095,有效等位基因数目Ne为2.3729,多态位点百分数P(%)为14。观察杂合度和期望杂合度都比较高,观察杂合度平均为Ho=0.2335,期望杂合度平均为He=0.5140。而且,Ne和He随年龄的变化表现出Age2>Age3>Age1的趋势。各年龄段蛤仔——Age1、Age2、Age3的平均观察杂合度(Ho)和平均期望杂合度(He)分别为0.2357、0.2546、0.2159和0.4951、0.5286、0.5184。Age2的遗传多样性指数高于Age1及Age3,遗传分化相对较低。其中,Age1与Age3蛤仔遗传距离最小,D为0.0195,即变异很小;而Age1与Age2遗传距离较大,D为0.0437,变化范围不大(0.0195—0.0437)。从遗传一致度的数值上看了3个年龄段蛤仔的遗传相似程度很大,平均为0.9655。Age1与Age3遗传相似程度高达0.9807,而Age1与Age2相似程度较小为0.9572。说明不同年龄段蛤仔相似程度非常高。根据不同年龄段蛤仔的遗传距离,采用UPGMA平均聚类方法对其进行聚类可知,Age3与Age1蛤仔间遗传距离较小,与Age2蛤仔差异较大。通过对等位基因频率进行卡方检验发现,随着年龄结构的变化,部分基因基因频率减小;同时随着年龄的增长,有部分等位基因得到了纯化。大连群体蛤仔总的遗传分化较低,其遗传分化指数Fst为0.0248(Fst<0.05),遗传分化系数为0.02,说明总的遗传变异中有2%来自于不同年龄段的蛤仔之间。遗传距离和遗传一致度均值分别为0.035和0.9655,基因流(Nm=9.8238)相对流畅,进一步表明年龄结构对蛤仔种群内遗传分化的影响较小。

Genetic diversity analysis of different age of a Dalian population of the Manila clam Ruditapes philippinarum by EST-SSR

The genetic diversity and population structure of a Dalian (shihe) population of the wild Manila clam Ruditapes philippinarum with different ages were examined using SSR markers. The genetic diversity of the different ages (1 age, Age1; 2 age, Age2; and 3 age, Age3) was relatively high. Statistical analyses using POPGENE 1.31 and SPSS16.0 showed that the sites of Rp-11, Rp-12, and Rp-19, was well as the number of alleles significantly differed among the three ages (P < 0.01); the sites of Rp-20, Rp-24, Rp-27, and Rp-30 also significantly differed (P < 0.05); and the remaining seven sites had no significant difference (P > 0.05). The average number of alleles per locus was 4.3095, the effective number of alleles was 2.3729, and the polymorphic loci percentage P (%) was 14. The observed heterozygosity and expected heterozygosity were high; the average observed heterozygosity was 0.2335 and the average expected heterozygosity was 0.514. The changes in the Ne and He age followed the trend Age2 > Age3 > Age1. The observed and expected heterozygosity for each age were 0.2357, 0.2546, and 0.2159, as well as 0.4951, 0.5286, and 0.5184, respectively. The Age2 genetic diversity index was higher than Age1 and Age3, whereas genetic differentiation was relatively low among the three groups. Among them, the minimum Age1- and Age3-clam genetic distance was 0.0195, which was a small variation. In contrast, the genetic distance between Age1 and Age2 was 0.0437, indicating a small range (0.0195-0.0437). From a numerical point of view, there was great genetic similarity among the three ages of clams, with an average genetic identity of 0.9655. Age1 and Age3 have a genetic similarity of up to 0.9807, whereas the degree of similarity between Age1 and Age2 was small (0.9572). The clams with different ages had a very high degree of similarity. The calculated average genetic distances using the UPGMA clustering method revealed a smaller genetic distance between Age3 and Age1 clams than between Age3 and Age2 clams. Allele frequencies, calculated by the chi-square test, showed changes in the population structure with age, changes in parts of the gene, decreased allele frequency, and some alleles becoming fixed. The overall genetic differentiation was low, with an F_st values of 0.0248 (P < 0.05) for the Manila clam population of Dalian. The coefficient of gene differentiation in the different ages was 0.02, which showed that 2% of the total arose from differences among age groups. The genetic distance and genetic identity average between age classes were 0.035 and 0.9655, respectively. The mean gene flow (N_m=9.8238) was relatively smooth, and the age classes of genetic differentiation within a population of clams were less affected.