Population Genetics And Phylogeny Of Panorpidae Based On Mitochondrial DNA

The Panorpidae is the largest family in Mecoptera,and currently consists of eight genera.Adult scorpionflies are adapted to cool and humid climatic conditions.They usually live in cool mountainous areas above 1200 m.Adults are very weak in flight and dispersal ability,and usually form sky-island-like distributions at mountaintops.These cold-adapted montane species are good materials to study population dispersal and migration and evolutionary biology during climate changes.The Qinling-Bashan Mountain region is one of the biodiversity centers in the world.Clarifying the population genetic structure and the impact of the glacial period on the distribution pattern of the organisms in this region is of great significance to the study of biodiversity and the protection of animal resources.The large two-horned scorpionfly Dicerapanorpa magna is mainly distributed in the high-elevated Minshan Mountains and the Qinling-Bashan Mountains,and is a good material for population genetics research.We used the mitochondrial cox1 gene to study the population genetics and evolutionary history of D.magna.Panorpidae currently consists of more than 470 species,which are assigned into eight genera.However,the phylogenetic relationship between the genera of Panorpidae has not been satisfactorily resolved,especially the paraphyly of the genus Panorpa.Mitochondrial genomes play an important role in reconstructing phylogenetic relationships and revealing the molecular evolution of insects.Previous studies on population genetics and species delimitation of Panorpidae mainly focused on the mitochondrial cytochrome c oxidase subunit I(the gene cox1),and there are still many phylogenetic questions which are not resolved.Therefore,it is necessary to use mitochondrial genomes that contains more genetic information for further intensive analysis.However,only two species of Panorpidae have been documented for mitochondrial genomes in Mecoptera to date.Here,we analyzed complete mitochondrial genomes of 17 species of Panorpidae,and attempted to reconstruct the phylogenetic relationship of Panorpidae from the perspective of the mitochondrial genome.The main results are as follows:(1)We reconstructed the population demographic dynamics and evolutionary history of D.magna with phylogeographic approaches based on cox1 sequences.We predicted the potential refugia under the Last Glacial Maximum(LGM),and verified the species' suitable habitats of D.magna between the two periods using the ecological niche modeling.The results show that D.magna can be divided into three distinct lineages,such as the Qinling,Minshan,and Bashan Lineages.The formation of these three lineages was affected by the glacial period in the late Pleistocene.When the glacial period came,the three lineages were isolated,and experienced a certain degree of differentiation in their respective glacial refugia in the Qinling and Bashan Mountains under LGM,and spread after the end of the glacial period.The Liping area,as a crossing point for population migration or a glacial refugia,occurred a strong gene exchange.The glacial refuges in the Bashan Mountains may be in the areas of Liping and Shennongjia-Hualongshan Mountains.Among them,the refugia in Liping mainly received populations from the Minshan Mountains in the southwest and the Tongtianhe-Jialing River in the north;the refugis in the Shennongjia-Hualongshan Mountains mainly received populations from the Micang and Nangong mountains in the northwest.There are a large number of micro-glacial refugia in the Qinling Mountains,such as Taibai Mountain and Huoditang.The Liping area,as a crossing point of population migration or a glacial refugia,generates a large amount of gene exchange.(2)Starting from the Shennongjia,via the Hualong Mountains(including Nangong Mountain),and then to the Micang Mountains,the nucleotide diversity of cox1 is gradually decreasing.After the end of the ice age,the population expanded northwest along the mountainside or ridge,and the genetic diversity gradually decreased under the effect of the founder effect.The population in the Minshan Mountains experienced a bottleneck effect,and expanded twice after the end of the ice age.(3)We obtained complete mitochondrial genomes from 17 species of Panorpidae.The complete mitochondrial genome sequences of Panorpidae all contain 37 genes,including 13 protein-coding genes,22 tRNAs,two rRNAs,and one control region.The mitochondrial genomes exhibit a strong AT bias.The AT-skew can either be slightly positive or slightly negative,while the GC-skew is usually negative.The 22 tRNA genes can fold into a common cloverleaf secondary structure except trn S1.The sliding window and genetic distance analyses demonstrate highly variable nucleotide diversity among the 13 protein-coding genes,with comparatively low evolutionary rate of cox1,cox2 and nad1,and high variability of nad2 and nad6.Our analyses indicate that the genes nad2 and nad6 can be regarded as potential markers for population genetics and species delimitation in Panorpidae.(4)Based on the mitochondrial genome analysis,the phylogenetic relationship of Panorpidae can be presented as follows:(Neopanorpa + Furcatopanorpa)+(Dicerapanorpa +(Panorpa debilis +(Sinopanorpa +(Cerapanorpa + Panorpa)))).The genus Panorpa is reconfirmed to be a paraphyletic group,which may need further subsplit.