重寄生车轮虫宿主新记录及种内分化研究

NEW HOST RECORD AND STUDY ON INTRASPECIFIC DIFFERENTIATION OF TRICHODINA HYPERPARASITIS CHEN & HSIEH, 1984

  • 摘要: 为探索重寄生车轮虫(Trichodina hyperparasitis Chen & Hsieh, 1984)种内分化的影响因素, 研究通过广泛采样分离获得寄生于乌鳢(Channa argus)与月鳢(Channa asiatica)鳃部的重寄生车轮虫3个地理株系, 即重庆沙坪坝乌鳢寄生株系(S株系)、重庆大足乌鳢寄生株系(D株系)与贵州凯里月鳢寄生株系(K株系), 其中贵州凯里为重寄生车轮虫的地理新记录, 月鳢为其宿主新记录。结合形态学与分子证据对重寄生车轮虫不同株系进行了比较研究, 基于附着盘形态学量化与主成分分析的研究结果显示: 三地理株系在虫体大小方面存在显著差异, 其中S株系是虫体最大的株系(P<0.05), 也是齿体最长的株系(P<0.05), K株系是齿体数最少的株系; S株系与K株系在附着盘整体结构与齿体形态方面存在一定的种内差异(P<0.05); 基于SSU rDNA序列的株系比较结果显示, K株系与其他2株系间存在10个碱基变异位点, 但3株系间序列相似度为99.45%—100%, 遗传距离为0.001—0.003; 基于SSU rDNA的系统发育分析显示, 重寄生车轮虫与近缘种之间形成了宿主种类特有的单系, 即“鲈形目Perciformes支系”与“鲇形目Siluriformes支系”; 同时在其种内也形成了宿主种群特有的单系, 即“乌鳢支系”与“月鳢支系”。综合研究结果表明, 重寄生车轮虫并非一定营“重寄生”生活, 且偏好寄生于鳢属(Channa)鱼类; 其中乌鳢寄生的两株系间较近缘, 与月鳢寄生的株系间则较远缘, 且各株系间已存在一定程度的遗传分化与形态分化; 推测对于外寄生车轮虫而言, 第一生境即宿主的类型可能是影响车轮虫种间或种群分化最直接的因素。

     

    Abstract: Trichodinid is regarded as one of microscopic parasitic ciliates with high diversity, which is mainly parasitic in fishes, mollusks, some tadpoles of amphibian, and minority of coelenterates in aquaculture. Some trichodinid infections can cause significant damage to their hosts. Trichodinids are diverse and distributed worldwide, with around 400 Trichodina species reported in different environments. However, despite advancements in molecular technology, the research on trichodinids lags behind other ciliate groups mainly due to insufficient or invalid molecular data in GenBank, which inhibited in depth studies. Trichodina hyperparasitis Chen & Hsieh, 1984, a freshwater trichodinid, parasitizes the crustacean Lampraglena chinensis, parasitizing on gills of Channa argus. Consequently, it was named T. hyperparasitis. Reports on T. hyperparasitis are fragmented, and molecular data are nearly blank, underscoring the need for additional valuable data to better understand this species, which is the focus of the present work. In order to explore the factors influencing population differentiation of T. hyperparasitis, three geographic strains were isolated from gills of Channa argus and Channa asiatica through extensive sampling. These strains include S strain from C. argus in Shapingba, Chongqing, D strain from C. argus in Dazu, Chongqing, and K strain from C. asiatica in Kaili, Guizhou. Among them, Guizhou represents a new geographic record, and C. asiatica is a new host record for T. hyperparasitis. Three SSU rDNA sequences from the three strains were sequenced and submitted to the GenBank, with further comparative study conducted based on morphological and molecular evidence. Morphological quantization of adhesive disc and PCA showed significant differences among the three geographic strains. The S strain was the largest in body size and denticle span (P<0.05), while K strain was the least one in denticle number (P<0.05). Intraspecific differences were also noted in adhesive disc structure and denticle morphology between both S and K strain (P<0.05). The comparative result of SSU rDNA sequences showed that ten base variant sites between K strain and the others, with a similarity range of 99.45% to 100% and genetic distance ranging from 0.001 to 0.003 among the three strains. The phylogenetic analysis based on SSU rDNA showed that T. hyperparasitis and its related species formed monophyletic lineages specific to host types, including the Perciformes and Siluriformes clades. Additionally, T. hyperparasitis formed host specific monophyletic lineages, viz. C. argus and C. asiatica clades. The comprehensive results indicate that T. hyperparasitis does not necessarily exhibit a hyperparasitic lifestyle and has a strong parasitic specificity to Channa species. Two strains from C. argus are closely related, while the strain from C. asiatica shows greater genetic and morphological divergence. This indicates that the host type, particularly initial habitat, may be the most direct factor influencing interspecific and intraspecific differentiation in ectoparasitic trichodinids.

     

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