Phylogenetic Relationships among Nematodes of Strongylidae Based on Mitochondrial cox1,nad1 and rrnL Sequences
To explore the relations among the Strongylidae nematodes(Strongylinae and Cyathostominae)in equine,the mitochondrial cox1,nad1 and rrnL genes of six species of nematodes including Cylicostephanus longibursatum,Coronocyclus coronatus,Cylicoc-yclus leptostomus,Poteriostomum ratzii,Parapoteriostomum mettami and Strongylus edentatus were amplified,and a comparative analysis was performed with the related nematodes in the same family.Then,the phylogenetic relationships among the Strongylidae nematodes was explored based on the mitochondrial cox1,nad1 and rrnL tandem genes using Bayesian inference(BI)method.The results showed that the length of cox1 sequence of six nematodes in this study was 1578 bp,the length of nad1 was 873 bp,except for S.edentatus,which was 879 bp,and the length of rrnL was different,ranging from 959 bp to 980 bp.The AT contents of cox1,nad1 and rrnL of six nematodes were 67.55%to 69.71%,71.36%-73.83%and 80.88%-82.59%,respectively.The similarity of cox1,nad1 and rrnL among the Strongylidae nematodes were 83.4%-97.9%,79.0%-98.4%and 78.8%-98.9%,respectively.Significantly,compared to the Strongylus sepcies of Strongylinae,Triodontophorus species had higher similarity with Cyathostominae nematodes.The phylogenetic analysis showed that Triodontophorus nematodes of Strongylinae did not form a single branch,but formed a group with the Cyathostominae nematodes.In the branch of Cyathostominae,not each genus formed a group singly,and Coronocyclus and Cylico-cyclus were the most obvious which were polyphyletic.Based on the sequence and phylogenetic analysis of the mitochondrial cox1,nad1 and rrnL of equine strongyles,the results indicated that Triodontophorus species were more closer with Cyathostominae than with Strongylinae,which supported the hypothesis that Triodontophorus species belonged to Cyathostominae.
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