Evolutionary Relationship And Fragmented Mitochondrial Genome Of Parasitic Lice Of Eutherian Mammals

Objectives:The typical mitochondrial genome of insects is a single chromosome with37 genes.To date,the mitochondrial genomes of 23 species of parasitic lice of eutherian mammals have been studied and it was found that they deviated from the typical mitochondrial genome structure of bilatera1 animals and fragmented into multiple minichromosomes,the number of which ranged from 9 to 20,and each minicircle chromosome contained coding region and non-coding region.However,the fragmented pattern and extent of the mitochondrial genome are substantial variation among different parasitic lice.In order to understand fragmented mitochondrial genome organization and evolution of parasitic lice of eutherian mammals,Partial genes and the complete mitochondrial genome of parasitic lice of eutherian mammals were sequenced and analyzed evolution relationship based on cob,trn L_1(tag)and trn L_2(taa)gene sequences and the extent of mitochondrial genome of parasitic lice of eutherian mammals in the thesis.Based on these datasets,the structure and evolution of mitochondrial genome of 2 species of Polyplax lice of the dominant genus of parasitic lice of eutherian mammals were sequenced and analyzed,remedy traditional understanding deficiencies and limitations of the mitochondrial genome,in order to promote the research of insect mitochondrial genomics and vector insects-related field.The results provided further evidence for understanding mitochondrial genome fragmentation of parasitic lice of eutherian mammals and expanded our knowledge on the evolution of eukaryotes mitochondrial genome.Methods:Four species of parasitic lice,belonging to 3 genera and 3 families,were collected from Yunnan,China.Total DNA were extracted from 4 species of parasitic lice(Hoplopleura pacifica,Polyplax reclinata,Polyplax serrata,Ancistroplax crocidurae).The mitochondrial DNA of parasitic lice was amplified by PCR and purified with Wizard SV Gel and PCR clean-up system(Promega).Amplicons were sequenced with Illumina Miseq PE250.Illumina sequence reads were assembled in Geneious Prime 2021.0.1.The mitochondrial genome was identified by NCBI database,t RNAScan-SE and ARWEN online web pages.Results:1.Phylogeny of 22 species(6 genes only found in Damalinia meyeri,was not involved in the study)of parasitic lice in 11 genera,10 families of eutherian mammals were analyzed based on mitochondrial cob sequence and the extent of mitochondrial genome fragmentation.The results of phylogeny were consistent with the phylogeny from morphology.The numbers of fragmented minicircle in mitochondrial genome of parasitic lice of the same genus are similar,and the rate of mitochondrial genome fragmentation is similar,but the pattern of gene arrangement on mitochondrial minichromosomes has substantial variation.2.The trn L_1(tag)and trn L_2(taa)gene sequences of 17 species of sucking lice in 8 genera and8 families were used to explore the independent evolution and concerted evolution among genes.The results showed that sucking lice with longer identical sequences of trn L_1(tag)and trn L_2(taa)genes are prone to concerted evolution,while sucking lice with shorter identical sequences are prone to independent evolution.3.The mitochondrial genomes of 2 species(Polyplax reclinata and Polyplax serrata)of polyplax lice of the dominant genus of parasitic lice of eutherian mammals were sequenced entirely in this paper.Both had 37 mitochondrial genes of typical animals and fragmented into11 minichromosomes;each minichromosome was 2-4kb,and had 2-7 genes.Mitochondrial karyotypes of two species of(Polyplax reclinata and Polyplax serrate)Polyplax sequenced in this paper were compared with those of two species of Polyplax completely sequenced so far(Polyplax asiatica and Polyplax spinulosa),and deduced the ancestral mitochondrial karyotypes of the genus Polyplax.Conclusions:1.The analysis of the extent of mitochondrial genome fragmentation in 22species from 11 genera and 10 families shows that the 3 species of human lice(Pediculus humanus,Pediculus capitis and Pthirus pubis)have the most degree of fragmentation;3species of Haematopinus lice(Haematopinus suis,Haematopinus apri and Haematopinus asini)have the least degree of fragmentation;the remaining 16 species of parasitic lice were in the middle.2.Concerted evolution of sucking lice with trn L_1(tag)and trn L_2(taa)genes would be expected over long term or between distantly related species whereas independent evolution would be expected over short term(between two recombination events)or between closely related species.The fragmented pattern of the mitochondrial genome of Anoplura may influence the length of identical sequences of trn L_1(tag)and trn L_2(taa)genes.3.Using the genus Polyplax as a template,this paper studies how t RNA gene transfer affects mitochondrial karyotype changes.We concluded that the mitochondrial karyotype variation of the genus Polyplax is mainly attributed to the t RNA gene transfer.In addition,t RNA genes frequently transfer between different minichromosomes and move towards the control region(non-coding region),and similar t RNA gene transfer can be observed in other sucking lice that have genome fragmentation.In this paper,it is speculated that the frequent transfer of t RNA gene towards control region between minicircle chromosomes is the main reason for the high change of mitochondrial genome structure of sucking lice.