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The entomopathogenic Mermithidae is a class of valuable the insect predators resources, and comprehensive management of pests of agriculture, forestry and health, environmental protection, as well as to achieve farmland biological diversity, have important academic and practical value. Currently, domestic and outside the classification of Mermithidae main focus on the aspects of the morphological and biochemical still in its infancy, the use of molecular biology techniques to study the evolution of Mermithidae system. Xu Fen (2005) using RAPD technique of the kinship of 4 and 5 species Mermithidae reported; Blaxter (1998), and Vandergast (2003) on the nematode phylum 52 genera of 57 species of nematode 18S rDNA sequences analysis to explore the phylogenetic relationships between them, which includes only four kinds Saco the nematode (Mermis nigrecens and three undetermined species). This article was first selected from the nuclear DNA (rDNA) and mitochondrial DNA (mtDNA) molecular markers, more comprehensive coverage of the molecular phylogeny Mermithidae analysis of the part classification Mermithidae confuse the issue, in order to better phylogenetic tree constructed Mermithidae laid the theoretical foundation. Three pairs of specific primers amplified by extracting 18 Mermithidae total genomic DNA and determined the DNA sequence of 18S rRNA gene sequence fragment of about 750bp length COI and D genes were about 370bp and 300bp length sequence . Combined Xu Fen (2005) 6 and saved the 18S rDNA homologous sequences in GenBank Mermithidae use the phylogenetic ClustalX18.1, MEGA3.1, DNAsp4 analysis software base composition of the DNA sequence base substitutions, genetic distance, genetic analysis, the results showed that the determination of the sequence has a strong phylogenetic signal. The neighbor-joining (NJ) and maximum parsimony (MP) 3 gene data set of 18S rDNA data sets and COI and D relationship building Mermithidae system. Draw the following conclusions: 1.24 Mermithidae 18S rDNA sequences of A, T, G, C content, the average were 25.8%, 26.3%, 26.5% and 21.4%, respectively, which average AT content (52.1 %) with average CG content (47.9%) or less. Slave order level analysis, Mermithidae into two groups: the first groups including the Roseau genus (Romanomermis), two cord the genus (Amphimermis) and spider cable nematode genus (Aranimermis). The second largest category of group two sister group, the first sister group including stomach Sok the genus (Gastromermis), midges cable, case (Heleidomermis) and 施特克尔霍夫 cable nematode genus (Strelkovimermis), the second sister group Dosso case (Agamermis), the six cable genera (Hexamermis), the egg funiculus genus (Ovomermis), eight tendons, genus (Octomyomermis) Thaumamermis Sok genus (Mermis), different cable the case (Allomermis) and four kinds of undetermined species nematodes. 2.18 kinds Mermithidae COI gene sequences of A, T, G, C content, the average was 29.1%, 41.1%, 18.1% and 11.7%, which AT average content (70.2%) was significantly higher than that average CG content (29.8%), the sequence showed obvious A bias. Build two ways phylogenetic tree consistent results the 18 Mermithidae into two groups: the first groups including Roseau case, two cable genus, Thaumamermis, different cable case, 施特克尔霍夫 cable genera and stomach Sok nematode, including five kinds of the Mosquito Larvae parasitic Roseau is a nematode kinship recently, first together; second largest category of groups including Dosso case, six cable genera, genera, eight tendons in the case of egg funiculus and cable Division nematode of undetermined species AN-2007, of which six Sok genera the egg funiculus genera and Mermithidae of undetermined AN-2007 kinship closer together. From the genetic distance between the 18 cable nematodes are within interspecific genetic distance was significantly less than the genetic distance between the genus. 3.18 kinds Mermithidae D 3 gene sequences, A, T, G, C the content of an average value of 27.3%, 23.2%, 30.8% and 18.7%, respectively, which AT average content (50.5%) and the average CG content (49.5%) was essentially flat. 14 Mermithidae divided into two groups: the first groups including Roseau case, the two cable is undetermined species A-2007 (Amphimermis sp.-2007), gastric cable genus, different cable genera and 施特克尔霍Fusuo nematode which four-Chuan Luosuo nematodes (R.sichuanensis) and two cable case undetermined species A-2007 closest genetic relatives get together at a very significant level of confidence (100%); second largest category of groups, including eight tendon the two cable is a cable genera undetermined species B-2007 (Amphimermis sp.B-2007), Dosso is a case of six cable the egg funiculus genera and Mermithidae of undetermined species AN-2007, of which of Huazhong eight tendons nematodes (O. huazhongensis) and two cable is undetermined species B-2007 closest genetic relatives, first together. In this study, using 18S rDNA and COI gene D 3 three molecular markers of the part Mermithidae more comprehensive study of system evolution, and to explore the genetic relationship between them. The analysis results show that the selection of 18S rDNA and COI, 3 gene three different evolutionary rate of molecular markers the Mermithidae kinship analysis, to reflect the genetic relationship between the different species of Mermithidae status and system evolution. 18S rDNA contain a large number of highly conserved gene sequences, explore the evolution of biological high-level taxa system effective molecular markers and protein-coding genes in the mitochondrial DNA COI and D 3 belong to rapid evolutionary sequence in molecular systematics The study is mainly used for the comparative analysis between closely related species.
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