基于SSU rDNA序列的网状车轮虫群体遗传结构及多样性研究

基于SSU rDNA序列对当前分布于我国的网状车轮虫(Trichodina reticulata Hirschman&Partsch,1955)的群体遗传结构与多样性进行了研究。遗传结构研究结果表明:20个样本共检测到9个单倍型,含4个共享单倍型与5个特有单倍型,其中鲫来源的Hap3是最大的共享单倍型;草鱼来源的Hap8和小黄黝鱼来源的Hap9暂被视为湖北武汉和西藏地区各自特有的单倍型;同时推测鲫来源的单倍型Hap1为祖先单倍型。结合ML系统发育树分析推测,在多宿主的进化历程中,鲫寄生的网状车轮虫可能是分化最早的群体,且草鱼寄生的网状车轮虫在起源上来自于鲫。遗传多样性结果显示,所有群体均呈现较高的单倍型多样性(Hd≥0.5)与较低的核苷酸多样性(Pi<0.005),且鲫来源的单倍型多样性显著高于草鱼来源,但核苷酸多样性(Pi)明显低于后者。遗传分化(Fst)与基因流(Nm)研究结果表明, Group A(鲫来源)与Group B(草鱼来源)群体间相对独立且已经达到了极度分化程度,群体内基因层面的交流较少。综合中性检验与核苷酸单倍型错配分析认为, Group A(鲫来源)未...

GENETIC STRUCTURE AND DIVERSITY OF TRICHODINA RETICULATA HIRSCHMAN & PARTSCH, 1955 POPULATIONS BASED ON SSU rDNA SEQUENCE

Trichodinid ciliates are well known as ectoparasites of fishes, mollusks, amphibians, as well as crustaceans, sometimes they can cause serious diseases for the maricultured and freshwater animals. They are diverse and widely distributed in the world, and about 400 nominal Trichodina species have been reported in different environments. So far, the shortage of molecular data of trichodinids in GenBank has inhibited the development of those studies on their population genetic structure and population evolutionary history, which resulted in very little valuable information of the genetic diversity about this special group. So, in order to learn about more genetic knowledge about trichodinids, the present work was carried out. Based on the SSU rDNA sequences, the population genetic structure and genetic diversity of Trichodina reticulata Hirschman & Partsch, 1955 in China were explored. The research results of genetic structure indicated that totally nine haplotypes were detected from twenty samples, including four shared haplotypes (Hap1, Hap2, Hap3 and Hap7) and five peculiar haplotypes (Hap4, Hap5, Hap6, Hap8 and Hap9). Among them, the Hap3 from Carassius auratus was the largest shared haplotype. The Hap8 from Ctenopharyngodon idellus and Hap9 from Micropercops swinhonis were temporarily regarded as the peculiar haplotype in Wuhan and Tibet Autonomous Region, respectively. At the same time, the Hap1 from Carassius auratus was supposed to be the ancestral haplotype. Combining with the ML phylogenetic tree, Trichoina reticulata from Carassius auratus was probably the first differentiated group during the multi-host evolutionary progress, and maybe Trichoina reticulata parasitic on Ctenopharyngodon idellus was originated from Carassius auratus. The research results of genetic diversity indicated that all populations showed high haplotype diversity (H_d≥0.5) and low nucleotide diversity (P_i＜0.005), and the H_d of Carassius auratus source was significantly higher than that of Ctenopharyngodon idellus source, but the nucleotide diversity of Carassius auratus source was significantly lower than the latter. The research results of genetic differentiation (F_st) and gene flow (N_m) revealed that the group A (from Carassius auratus) and the group B (from Ctenopharyngodon idellus) were relatively independent and reached the extremely differentiated extent because of the lesser genetic communication within the group. Combining the neutral test with the nucleotide mismatch analysis, it was concluded that the group A (from Carassius auratus) has never gone through the population expansion, whereas the population expansion has probably existed during the early history of the group B (from Ctenopharyngodon idellus).