; 18S rDNA
; 28S rDNA
; ITS rDNA
|其他题名: ||phylogenetic study of parasitic copepods in the Ergasilidae and Lernaeidae on freshwater fish in China|
以18S、28S和18S-28S rDNA的联合片段为遗传标记研究鳋科4属共14种和锚头鳋科2属3种鳋之间的系统发育关系，支持鳋科和锚头鳋科为单系。在鳋科内部，中华鳋属与三指鳋属为单系，鳋属为复系，除了掘凿鳋和雅鲁藏布鳋的进化位置不十分明确外，所有的结果都支持将整个鳋科分为三个大类群，中华鳋属－鳋属类群为中华鳋属和鳋属的固着鳋，假鳋属－鳋属类群为假鳋属和部分鳋属的种类，三指鳋属－鳋属类群为三指鳋属和鳋属的奇异鳋。不同的是以18S rDNA为标记用最大似然法、邻接法和贝叶斯法建树的结果都支持中华鳋属－鳋属类群与假鳋属－鳋属类群的亲缘关系更近些，以28S rDNA为遗传标记支持假鳋属－鳋属类群与三指鳋属－鳋属类群的亲缘关系更近些，根据寄生桡足类的演化规律从半寄生到完全寄生状态，18S rDNA的建树结果更支持这一结论。Kishino-Hasegawa检验的结果支持将掘凿鳋和奇异鳋归为假鳋属－鳋属类群的假设，不支持将固着鳋归为假鳋属－鳋属类群的假设。在锚头鳋科内部，以28S rDNA为标记用最大似然法、邻接法和贝叶斯法建树的结果都支持狭腹鳋属为单系。
另外，在我国湖北省丹江口水库的鱼类寄生虫调查中从马口鱼和宽鳍鱲上获得了鳋属一新种丹江鳋。与我国鳋属其它鳋相比，丹江鳋形态上一个典型的特征就是第二触肢的第二节外缘呈明显的弧形，这与膨大鳋的第二触肢比较相似。以ITS和部分28S rDNA序列为标记进行进化分析，支持丹江鳋为一独立的新种，尽管变异分析表明丹江鳋与膨大鳋（ITS 为4.6%；28S为1.6%）和博氏鳋（ITS 为5.4%；28S为1.8%）之间的变异水平比较低。|
|英文摘要: ||Copepods in the Ergasilidae (Copepoda: Poecilostomatoida) and Lernaeidae (Copepoda: Cyclopoida) are two major groups of parasitic copepods on freshwater fish. The present study aimed to illustrate the phylogenetic relationship among species in the families Ergasilidae and Lernaeidae, and to understand the phylogenetic relationship among three species in the Sinergasilus (Ergasilidae) with the analysis of the Sinergasilus-host co-evolutionary relationship.
A total of 14 species belonging to 4 genera in the Ergasilidae and 3 species to 2 genera in the Lernaeidae were obtained from 24 species of fish in China, and the 18S, 28S rDNA sequences were cloned from the collected parasitic copepods. Phylogenetic analyses using partial 18S and partial 28S rDNA sequences and combined 18S-28S rDNA sequences suggested that both Ergasilidae and Lernaeidae are monophyletic. In the Ergasilidae, the genera Sinergasilus and Paraergasilus are monophyletic, and Ergasilus is paraphyletic. Except the uncertain position of E. scalaris and E. yaluzangbus, copepods in the Ergasilidae can be further separated into three main clades, i.e. the Sinergasilus-Eragsilus clade including species in the Sinergasilus and E. anchoratus in the Ergasilus, the Pseudergasilus-Ergasilus clade including P. parasiluri in the Pseudergasilus and some in the Ergasilus, and the Paraergasilus-Ergasilus clade including species of Paraergasilus and E. peregrinus in the Ergasilus. All the three trees generated by using maximum parsimony, neighbor-joinning and Bayesian inference methods support the Pseudergasilus-Ergasilus clade has a closer phylogenetic relationship with the Sinergasilus-Eragsilus clade based on 18S rDNA，and a closer relationship with the Paraergasilus-Ergasilus clade based on 28S rDNA sequences. The evolutionary rule of parasitic copepods always from half-parasitism to complete parasitism supported the results based on 18S rDNA. Kishino-Hasegawa tests based on either likelihood method or parsimony method supported the null hypotheses that E. scalaris and E. peregrinus were confined to group Pseudergasilus-Ergasilus, and rejected the hypothesis that E. anchoratus was confined to group Pseudergasilus-Ergasilus. In the Lernaeidae, the subfamily Lamprogleninae was monophyletic, as revealed by the maximum parsimony, neighbor-joining and Bayesian inference methods based on 28S rDNA sequences, which is consistent with the morphology taxonomy.
The phylogenetic relationship was also examined between parasitic copepods and free-living copepods from five orders in the subclass Copepoda based on partial 18S rDNA sequences. The cladistic analysis based on morphological characters showed that Siphonostomatoida formed a sister-lineage with Monstrilloida, then clustered with Poecilostomatoida, while Cyclopoida showed no closer relationship with any of the three orders, while the present study supported the sister-lineage of Poecilostomatoida and Cyclopoida, which then were clustered with Siponostomatoida. It is suggested that the Poecilostomatoida and Cyclopoida have a closer relationship, furthermore, Poecilostomatoida, Cyclopoida and Siphonostomatoida might have originated from a common ancestor. Phylogenetic study also showed that Lernaeidae and Caligiade should belong to Cyclopoida and Siponostomatoida, respectively.
In order to resolve the phylogenetic relationship among the three species in the Sinergasilus and the mechanisms involved in their speciation on their nine species of fish hosts, three species in the Sinergasilus species were obtained to construct the phylogenetic trees based on the internal transcribed spacer (ITS) sequences, i.e. S. polycolpus, S. major and S. undulatus, from two speices of host fish, i.e. Hypophthalmichthys molitrix, Aristichthys nobilis, five speices of fish, i.e. Ctenopharyngodon idellus, Mylopharyngodon piceus, Elopichthys bambusa, Squaliobarbus curriculus, Opsariichthys bidens, and two species Cyprinus carpio, Carassius auratus, respectively. All the trees generated showed that S. polycolpus and S. major had a closer relationship. Meanwhile, thirty specimens each for the three species in the Sinergasilus were obtained from C. idellus, H. molitrix and C. carpio in a same lake. It is revealed that the variation in the ITS sequences was among 0.28~0.51% for individuals within a given species, while the variation ranged among 9.65~10.81% at the species level based on the combined ITS1 and ITS2 sequences. Phylogenetic relationship of the 90 copepod individuals also supported that S. polycolpus and S. major had a closer relationship. The coevolutionary trees were constructed by using partial cyt b sequences for the nine species of fish and by using whole ITS sequences for the three species of copepods. It is demonstrated that S. undulatus might have cospeciated with their Cyprininae hosts earlier, and S. polycolpus and S. major, might cospeciate with their Hypophthalmichthyinae and Leuciscinae hosts, respectively later.
In addition, during the investigation of parasites in freshwater fish in Danjiangkou Reservoir, Hubei Province, China, a new species named as Ergasilus danjiangensis was found on gills of Opsariichthys bidens and Zacco platypus. Morphological observation shows that E. danjiangensis is characteristic of prominent arc outer edge on the second segment of antenna, which is similar to E. tumidus. Molecular studies based on ITS and 28S rDNA sequences also support that E. danjiangensis is an independent and new species, although the divergence level between E. danjiangensis and E. braini (4.6% for ITS; 1.6% for 28S rDNA) is not high, nor between E. danjiangensis and E. tumidus (5.4% for ITS; 1.8% for 28S rDNA).|
|Appears in Collections:||中科院水生所知识产出（2009年前）_学位论文|
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