Phylogeny And Diversification Of The Tenthredo Linné Based On Mitochondrial Genomes

Tenthredo Linné,1758 is the largest,most complex,and diverse genus in the Tenthredininae(Insecta: Hymenoptera: Tenthredinidae).Individuals within the genus exhibit significant differences in size and coloration.Larger species can reach lengths exceeding 20 mm,while smaller species only 3-4 mm in length.The predominant colors of the insect body include black,yellowish-red,green,metallic blue or green,and variegated patterns,with great variation observed between species.The taxonomy and classification of this genus have been the subject of more than 260 years of research,yet there remains significant controversy among scholars regarding its boundaries and classification status,with differing viewpoints and approaches taken.This study used high-throughput sequencing to obtain 189 mitochondrial genomes as samples,of which 32 were used as outgroups.A total of 157 data of Tenthredo and closely related genera whose taxonomic status is significantly disputed were used as ingroups.The mitochondrial genome features of the ingroups were analyzed,including gene length,base composition,use of start and stop codons,use of synonymous codons,and gene arrangement.Phylogenetic relationship reconstruction by Maximum Likelihood(ML)and Bayesian Inference(BI)based on 13 protein-coding genes,and calculated the genetic distances between each clade and both the outgroups and the each clade within the ingroup.The main findings of the study are as follows.1.The mitochondrial genome of Tenthredo and its close relatives exhibit a clear AT bias in base composition in all species,with a bias towards A in AT bias and towards C in GC bias.Among the protein-coding genes,the start codons are mainly ATA,ATG,ATT,and TTG,and the stop codons are mainly TAA and T.Compared with ancestral species,there are two rearrangement patterns: “trn M-trn Q-CR-trn I” and “trn M-trn QCR-trn I”,with “trn M-trn Q-CR-trn I” being the main arrangement pattern.The rearrangement of t RNA genes supports the phylogenetic relationship.2.The phylogenetic tree constructed based on 13 protein-coding genes showed that the closely related genera Jermakia Jakowlew,Propodea Malaise,Casipteryx Taeger,and Metallopeus Malaise as monophyletic groups within Tenthredo s.str.,the relationships within these genera were well-supported and stable.Rhogogaster Konow includes R.allovirescens,R.nr.psudokaszabi,and R.brevilabrina,which are also classified within Tenthredo s.str.,this is consistent with previous research,which has identified these three species as belonging to the Tenthredo.Other species within Rhogogaster form a monophyletic group and are not part of Tenthredo s.str..Therefore,the monophyly of Tenthredo s.str.was supported in this study,including Tenthredo,Jermakia,Propodea,Casipteryx,Metallopeus,and Rhogogaster with R.allovirescens,R.nr.psudokaszabi,R.brevilabrina.Two species of Peus Konow were included in this study,and Peus pannulosus and Tenthredo aliana form a sister group within Tenthredo s.str..Peus priva,as an outgroup,therefore,the relationship between Peus and Tenthredo s.str.requires further study with additional Peus samples.The sister group of the closely related genera is unstable,additionally,the low support for the clade,the position of these closely related genera within Tenthredo s.str.is not stable.Within the original Tenthredo,the monophyly of Tenthredo cestanella group,Tenthredo jozana group,and Tenthredo pompilina group are all supported.Tenthredo grahami group and Tenthredo mesomelas group are intermixed in one clade,and based on their morphological characteristics,these two groups are merged.Tenthredo lagidina group and Tenthredo potanini group are large species clusters with about 150 species.The phylogenetic results show that the main species in the two groups are clustered into one clade respectively,and the two groups were basically established.Tenthredo olivacea group and Tenthredo trunca are closely related and can be merged into a single group.Based on morphological characteristics,Tenthredo genitalis group and Tenthredo sinensis group are closely related to each other.This study does not support this view,only two species of Tenthredo genitalis group,and additional samples are necessary for further study.The monophyly of Tenthredo cyanata group,Tenthredo issiki group,Tenthredo fortunei group,Tenthredo nigropilosa group,and Tenthredo ichneumonia group did not receive support.Abe & Smith(1991)and Taeger et al.(2010)divided Tenthredo into different subgenera based on morphological studies.This study involved subgenera such as Cephaledo,Maculedo,Olivacedo,Temuledo,Zonuledo,Eurogaster,Tenthredella,and Tenthredina.The phylogenetic relationships do not support the monophyly of the subgenera mentioned above.Therefore,the taxonomic status of the above subgenera may not be valid,and it is more reasonable to divide the species of Tenthredo into groups for the time being.3.The phylogenetic tree constructed by Maximum Likelihood will be sorted from top to bottom according to the branching pattern,resulting in 39 branches.Calculation of genetic distance(P-distance)within each clade and between clade and outgroup Rhogogaster nigrospina.Among the 39 branches,the genetic distances obtained within each branch were compared,and they were found to vary greatly,ranging from 0.007 to 0.137.The genetic distance between each clade and the outgroup Rhogogaster nigrospina ranged from 0.163 to 0.203,with an average of 0.179.This value is significantly higher than the genetic distances observed among genera-level taxa in Tenthredinidae.This indicates that the differentiation distance between various clades within Tenthredo s.str.is already quite large.The comparison of the genetic distance between each clade and the outgroup reveals a small difference,which is consistent with the hypothesis of rapid and widespread differentiation of the genus Tenthredo.