Mitogenome Structure And Phylogenetic Analyses Of Exorista Sorbillans

Exorista sorbillans has been doing certain damage to sericulture for long terms, and the recognization of this species only focus on physiology, ecology and parasitic mechanism. The paper attempts to investigate the evolutionary status of Exorista sorbillans in phylogenetics by utilizing molecular strategies in order to support systematic knowledge regarding novel approaches of biological prevention. Mitochondrial DNA (mtDNA) fragments of Exorista sorbillans are amplified by PCR technology and taken into phylogenetic analyses. The above analyses are made up with mapping of phylogenetic relationship trees and comparison of mitochondrial gene orders. Neighbour joining (NJ), maximum parsimony analysis (MP), maximum likelihood (ML) and Bayesian analyses (BPP) are used to be main statistical approaches for evolutionary trees, and phylogenetic relationships in or between class are explored by means of comparison of mitochondrial gene orders. The primary results are as follows:1. Evolutionary relationships of Diptera in insectaExorista sorbillans, insect of genus Exorista, family Diptera order, leads to the multivoltine maggoty desease after parasiting silkworms. Understanding phylogenetic relationships of Exorista sorbillans will facilitate exploitation to its parasitic mechanism. A piece of mtDNA fragment of Exorista sorbillans was amplified by PCR technology. Sequence analysis showed that the cloned mtDNA fragment was of about 1.5 kb size, including a full-length cyto b gene and its flanking tRNA-Leu gene sequences. The structure of Exorista sorbillans mtDNA is generally consistent with the homologous fragments of 21 other insects, indicating convervatism on gene arrangement and gene structure of mtDNA. Besides, secondary structures of cyto b protein and tRNA-Leu gene had the typical spatial structure of functional macromolecules, having maintained certain conservatism during evolution. This high homology of mtDNA cyto b protein and tRNA-Leu gene in different flies of Diptera ensured the accuracy of the constructed phylogenetic tree for flies. Evolutionary analyses based on amino acids encoded by cyto b genes from 12 insect species in Diptera including Exorista sorbillans, 5 species in Lepidoptera, 4 species in Coleoptera, 1 species in Orthoptera indicated that the evolutionary order in flies were from Drosophilidae, Tachinidae, Muscidae, and to Calliphoridae. Tachinidae had relatively closer evolutionary distance with Muscidae and Drosophilidae. Species of Lepidoptera formed the root clade, an indication of their earliest origin, while those of Diptera lay at the most distant clade, an indication of their latest origin.2. Evolutionary relationships of insecta in arthropodThe first complete mitochondrial genome (mitogenome) of a representative of family Tachinidae Exorista sorbillans (arthropod: Insecta) is sequenced by PCR-based approach. Firstly, the introduction of its mitogenome refers to gene placement, nucleotide bias, and visual circular DNA molecule. In term of nucleotide compositions and bias, encoded genes on minor sense strand generally utilizes the majority of T+G (>50 %) in the third codon compositions, where they display higher T/C ratio. Secondly, the phylogenetic trees obviously point out the evolutionary position of Insecta adjacent to Crustacea, and the members of Crustacea are divided into two clades with the other branch closed to Diplopoda. Meanwhile, the conclusion involves in that Myriapoda are paraphyletic from the Limulus polyphemus as a putative arthropod ancestry. Lastly, a comparison of the listed Crustacea mitogenome orders exhibits huge divergence of the phylogenetic evolution, but Insecta covering Exorista sorbillans reveal a uniformity character with respect to mitogenome arrangement. The identical translocation of trnL between Insecta and Crustacea supports the assumption that Insecta evolved from Crustacea. In addition, Panulirus stimpsoni is supposed to combine Crustacea with Insecta in evolution. Subsequently, Myriapoda hold hardly a common event in the mitochondria rearrangement and likely arise in different lineages.This research is valueable to clarify the physical map and nucleotide bias of Exorista sorbillans, and analyze the evolutionary status and phylogenetics relationships of this species in insecta and arthropod.