罗非鱼鳃寄生非洲拟车轮虫群体分化及遗传多样性

POPULATION DIFFERENTIATION AND DENETIC DIVERSITY OF PARATRICHODINA AFRICANA PARASITIC ON GILLS OF TILAPIA

  • 摘要: 本研究聚集于罗非鱼的鳃寄生非洲拟车轮虫(Paratrichodina africana El-Tantawy & Kazubski, 1986), 基于附着盘形态量化与SSU rDNA分子数据对采自重庆与广东两地的罗非鱼鳃寄生非洲拟车轮虫进行了群体分化与遗传多样性研究。基于附着盘形态量化研究结果表明: 重庆与广东两种群除了在齿体形态(齿体纵长、齿长、齿钩长)和齿体比方面具显著性差异( P<0.05)外, 其他方面均无差异; PCA分析结果显示广东种群的散点图分布包含于重庆种群之中, 表明两种群的形态相似度极高。遗传多样性研究结果: 28个SSU rDNA分子序列共计检测到10个单倍型, 含7个特有单倍型和3个共享单倍型, 其中Hap 3是最大的共享单倍型, 且重庆、广东两地均有分布; 广东种群(高HdPi型)的遗传多样性高于重庆种群(高HdPi型), 推测水温与地理分布可能是影响非洲拟车轮虫遗传多样性的重要因素。分子系统发育分析结果显示: 来自广东的Hap5位于系统树底部, 且广东样本遍布于每个分支; 而遗传分化指数(Fst)和基因流(Nm)结果显示两群体间的基因交流不频繁, 具有中等程度的遗传分化, 以此推测重庆种群起源于广东种群, 且分子变异分析(AMOVA)结果进一步证明其种群变异主要来源于群体内(变异率为92.18%)。中性检验(Tajima’s D和Fu’s Fs )和核苷酸错配分析结果认为, 非洲拟车轮虫整个群体可能经历过早期的种群扩张, 但近期未发生; 而不同地理群体(广东种群与重庆种群)均未经历过种群扩张事件。该工作为后续车轮虫的群体遗传及谱系地理学研究奠定基础, 同时为水产养殖的车轮虫病害防控提供参考资料。

     

    Abstract: This study focused on Paratrichodina africana El-Tantawy & Kazubski, 1986 from gills of tilapia, aiming to investigate population differentiation and genetic diversity based on the morphometric quantization of adhesive disc and molecular evidence of SSU rDNA in Chongqing and Guangdong populations. Morphometric analysis of the adhesive disc revealed significant differences ( P<0.05) in denticle morphology, including denticle span, denticle length, blade length, and denticle ratio, while no significant differences were observed in other aspects. Principal component analysis (PCA) indicated that the scatter plot distribution of Guangdong population was nearly contained within that of Chongqing population, suggesting a high degree of morphological similarity between the two populations. Genetic diversity analysis identified 10haplotypes among 28 SSU rDNA samples, including seven unique haplotypes and three shared haplotypes. Hap3 was the largest haplotype, present in both Chongqing and Guangdong population. The genetic diversity of Guangdong population (high Hd, high Pi) was higher than that of Chongqing population (high Hd, low Pi), implying that water temperature and geographic distribution may influence the genetic diversity of P. africana. Molecular phylogenetic analysis placed Hap5 from Guangdong at the basal position of phylogenetic tree, with Guangdong samples distributed across all branches. The genetic differentiation index (Fst) and gene flow (Nm) indicated moderate genetic differentiation with limited gene exchange between the two populations. The above results suggested that the Chongqing population probably originated from the Guangdong population. Analysis of molecular variance (AMOVA) study further confirmed that the majority of genetic variation (92.18%) originated within populations. Neutrality tests (Tajima’s D and Fu’s Fs) and nucleotide mismatch analysis indicated that the whole population of P. africana (CQ+GD) might have undergone a population expansion event in the early stage but not recently, however the different geographic populations (Guangdong and Chongqing populations) had not undergone any population expansion events. The present study has laid a foundation for the future research on population genetics and phylogeography of trichodinids, which could provide reference data for the prevention and control of trichodinasis in aquaculture.

     

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