Comparative Mitochondrial Genomes And High Altitude Adaptation Of Six Cordyceps Host Of Hepialidae

The Hepialidae is a relatively primitive group in the Lepidopera insects,with a wide variety of species,some of which can be infected by fungi to form Cordyceps（such as Ophiocordyceps sinensis）,which has important economic and medicinal value.Due to the difficulty of sampling,the phylogenetic and ecological adaptation mechanisms of the Hepialidae insects are still insufficiently understood.The comparative analysis of the mitochondrial genome is an important tool to study the evolution of insects,and it may also help to understand the adaptability of insects to high altitude.This study collected six Hepialidae insects,Thitarodes renzhiensis,T.xiaojinensis,Ahamus luquensis,T.sp.GS1,Napialus hunanensis,Endoclita davidi,respectively.The mitochondrial genomes sequencing,and combining previous published seven Hepialidae species of mitochondrial genome comparative analysis.By comparing the composition and arrangement of mitochondrial genes,the evolutionary regular of Hepialidae species were explored,and the phylogenetic relationship of Hepidiaceae insects was analyzed by combining 13 protein-coding genes and 2ribosomal RNAs.Meanwhile,the Paml selection pressure analysis was carried out based on the reported data of Hepidiaceae mitochondrial genome.By calculating the positive selection of high-altitude species（Thitarodes and Ahamus）were compared with low-altitude species（Napialus and Endoclita）.Meanwhile,the Paml selection pressure analysis was carried out based on the reported data of Hepidiaceae mitochondrial genome.By calculating the positive selection of high-altitude species（Thitarodes and Ahamus）were compared with low-altitude species（Napialus and Endoclita）.To explore the adaptation mechanism of Hepidiaceae insects to high altitude habitats from the mitochondrial level.The main conclusions are as follows:（1）Mitochondrial genomes of Hepidiaceae contain 37 genes including 22 t RNA,13 PCGs,2 r RNA and 1 A+T rich region.The gene arrangement is similar to that of Drosophila diptera but different from that of most genes in Lepidoptera.The content of AT in mt DNA sequences was very high,showing obvious AT skew.The AT content of r RNA was generally higher than that of mt DNA and t RNA in all types of insect genes.The mitochondrial genome size of Hepidiaceae ranges from 15,249 bp to 16,280 bp,among which Thitarodes Altaiensis was the largest mitochondrial genome of Lepidoptera.In this study,the lengths of the T.renzhiensis,T.xiaojinensis,Ahamus luquensis,N.hunanensis,E.davidi and T.sp.GS1 was15,627 bp,15,249 bp,16,065 bp,15,946 bp,15,929 bp and 15,319 bp,respectively.（2）The phylogenetic analysis showed that the phylogenetic tree of Hepidata was mainly divided into three branches,Thitarodes,Ahamus,Napialus and Endoclita.Among them,the genus Thitarodes is mainly the host of O.sinensis living at high altitude,while the genera Napialus and Endoclita include the low altitude species such as N.hunanensis,E.davidi.Notably,the combination of ML and BI trees showed that the genus Thitarodes and the genus Ahamus formed a union,which supported the establishment of Ahamus.In addition,the T.dumxungensis with the Ahamus cluster together,so the T.dumxungensis should probably be revised into the Ahamus.In addition,T.sp.GS1 reported in this study has a close genetic distance with T.gonggaensis and forms separate branches.Combined with current literature reports and single gene molecular data,this species may be a potential new species of Hepidiaceae,and morphological data of this species should be supplemented for verification in the following work.The phylogenetic tree of 13 PCG and 2 r RNA single genes was verified,and cox1,cox2,cob and atp6 genes were selected as potential molecular markers of Hepidiaceae.（3）Mitochondrial genomes were compared and found by dividing the species into two groups of high and low altitude: The AT skew of all species at high altitude was positive,while the AT skew of other species living at lower altitude was negative,indicating that base proportion of A to T were higher in species at high altitude,while base proportion of T to A were higher in species at low altitude.The high-altitude species were set as the background branches of the Codeml model,and 30 positive selection sites were found by combining the selection pressure analysis between different altitudes.Among them,nad1: 5,cox3 : 2,cob: 6,nad4L: 15 and nad2:2.When p< 0.01,cox1 and cox3 are significantly affected by positive selection,and cox1 is under greater positive selection pressure.When p< 0.05,cox1,cox3 and nad3 significantly received positive selection,and nad3 had the least positive selection pressure.Therefore,these mitochondrial genes may have contributed to the adaptation of Hepidiaceae to high altitudes during their evolution from low to high altitudes.In summary,the mitochondrial genomes of six species of Hepidiaceae were reported in this study.Among them,the mitochondrial genomes of A.luquensis,E.davidi and T.sp.GS1 were reported for the first time,which supplemented the molecular database of Hepidiaceae and laid a foundation for future studies.There is little difference in the mitochondrial genome of Hepidiaceae,but the variation rate of D-loop region is fast,and the structures of various microsatellites are different among different species.Phylogenetic analysis showed that the formed an independent branch,which supported the establishment of the Ahamus,and suggested that the T.dumxunensis should be revised into the Ahamus.Based on mitochondrial genes,we found that high altitude species of O.sinensis were significantly positive selected.Therefore,these genes may play a positive role in the adaptive evolution of O.sinensis hosts in the uplift process of Tibet Plateau and Hengduan Mountains.