三种胡子鲶的遗传变异及其系统分类的研究

为确定三种胡子鲶(胡子鲶Clarias fuscus、两栖胡子鲶C.batrachus和革胡子鲶C.lazera)的遗传变异及系统分类关系,采用淀粉凝胶电泳技术比较了三种胡子鲶4个样本的30—31个基因座位。每个座位观测到的平均等位基因数(Na)为1.01—1.39;多态座位百分比P_(0.99)为3.33—16.13％,平均杂合度观测值(Ho)为0.004—0.072;期望值(He)为0.004—0.064。3个种的遗传变异均较小,其中以革胡子鲶的遗传变异较其它两种大。两栖胡子鲶因采样的限制和养殖群体的奠基者效应而引起多态基因座位减少。4个样本的遗传相似性(I)和遗传距离(D)的比较,表现了3个水平的进化趋异;1)胡子鲶的两个没有生殖隔离的群体间的比较,彼此具有高度的遗传相似性(I=0.999);2)胡子鲶和两栖胡子鲶这对姐妹种间的比较,尽管它们在形态上难以分辨,但在遗传上仍有11个基因座位各具种的特异性;3)外表区别明显的种间比较,彼此表现了很大的遗传分异(D=0.999和0.818)。可见胡子鲶与两栖胡子鲶之间的系统分类关系较它们与革胡子鲶间的关系更密切。

GENETIC VARIATION AND SYSTEMATIC RELATIONSHIPS IN THREE SPECIES OF GENUS Clarias

30-31 loci in four samples of three Clarias species were compared, with starch gel electrophorosis, in order to determine their genetic variation and systematic relationships. The mean number of alleles per locus (Na) ranges 1.01-1.39; percentage of polymorphic loci (P0.99) 3.33-16. 13%; mean heterozygosity observed 9Ho) 0.004-0. 072; expected (He) 0. 004-0. 064. All three species express a very low level of genetic variation ,among them Clarias lazera expresses a higher level. The polymorphic loci of Clarias batrachus appear to have been reduced as the result of limitation of sample collection and founder effect of cultivated population.The comparison of genetic similarities (I) and genetic distances (D) among the four samples represents three levels of evolutionary divergence: 1) Comparison between two populations of Clarias fuscus without any reproductive isolation between them, indicate a very high degree of genetic similarity (I = 0.999). 2) Comparison between sibling species (C. fuscus and C. batrachus), despite their morphological similarity, they are genetically quite different, eleven loci are virtually fixed for different alleles. 3) Comparisons between morphologically different species (C. lazera and C. fuscus; C. lazera and C. batrachus), exhibit a very high degree of genetic differentiation (D = 0.999 and 0. 818). The systematic relationship between C. fuscus and C. batrachus are closer than compared to C. lazera.