Study On The Phylogeny Of The Basal Lineages In Hymenoptera Based On Genomes

The basal lineages of Hymenoptera is the former "Symphyta"(Insecta:Hymenoptera)and consists of 15 recognized families.At present,there are few species of the basal lineages to complete the whole genome sequencing,which has severely limited genome-level studies.In this study,we completed genome sequencing for 87 species from 58 genera across 14 families of the basal lineages of Hymenoptera and two species in two families of Apocrita.Combining the data downloaded from the Gen Bank database,we analyzed a total of 102 species from 61 genera across all families of the basal lineages of Hymenoptera and 63 species from 43 genera across 27 families of Apocrita.Based on the mitochondrial genome and nuclear genome sequence,we constructed the phylogenetic tree to study the phylogenetic relationship of the basal lineages of Hymenoptera with Maximum Likelihood(ML)and Bayesian Inference(BI).The main results are as follows:1.The length of the mitochondrial genome(Only complete genomes containing control regions are counted)in the basal lineages of Hymenoptera ranges from 14947bp(Ceraphron sp.)to 20393bp(Pachycephus Smyrnensis),with large variations within the Cephidae due to changes in the control region.The base composition of all mitochondrial genomes showed AT-biased.AT-biased is stable to A in Xyelidae and Tenthredinidae,T-biased is different in Pamphiliidae and Unicalcarida,GC-biased is C in all except Apocrita,and G-biased and C-biased exist in different degrees in Apocrita.Because most of the mitochondrial genomes are incomplete,the analysis of genome sequence characteristics is not enough to provide strong and available phylogenetic signals.2.In the 13 protein-coding genes,we observed the usage of start codons other than the common ATN,such as TTG and GTG,without clear regularity.However,we observed strong phylogenetic signals in the usage of stop codons,showing differences among genera within families.For example,the nad2 gene in the Blasticotomidae has a complete TAA stop codon in Runaria,but an incomplete TA stop codon in Blasticotoma.The cox1 gene in the Pleroneura and Macroxyela of the Xyelidae uses a complete TAA stop codon,while Megaxyela uses an incomplete TA stop codon,and Xyela uses an incomplete T stop codon.The phylogenetic trees constructed by Maximum Likelihood and Bayesian Inference for four mitochondrial genome datasets and single-copy orthologous genes dataset show the following results:All BI trees showed that the phylogenetic relationship among the main basal lineages of Hymenoptera was(Xyelidae,(Tenthredinoidea,(Pamphilioidea,Unicalcarida))),with support values ranging from 0.98 to 0.99.The monophyly of the Pamphilioidea in the results of the ML tree is controversial,but the support is not high(58%,60%,and 94%).Combined with the previous research results,it is considered that the inferred results of BI trees are closer to the true phylogenetic relationship of the basal lineages of Hymenoptera.Within Unicalcarida,all topologies support that the family Xiphydriidae is located at the base of Unicalcarida,with high support values(98%-100%).Siricidae and Cephidae form a monophyletic group with Vespina,but their relative position remains unclear.The support value of((Siricidae,Cephidae),Vespina)is between 67% and 92%.The support value of(Siricidae,Vespina)is 57%,and the support value of(Cephidae,Vespina)is 99%.Orussidae forms a monophyletic group with Apocrita with high support values(97%-99%),or it forms a monophyletic group with Stephanidae with support values(82%-94%).Therefore,in this study,the internal relationship of Unicalcarida is more supportive of(Xiphydriidae,(Siricidae,(Cephidae,(Orussidae,Apocrita)))).In Tenthredinoidea,the relationship(Athaliidae,((Cimbicidae,Diprionidae),(Tenthredinidae,Heptamelidae)))is very stable,and the family status of Tenthredinidae and Heptamelidae has been supported again.The sister group relationship between Argidae and Pergidae is also very stable.However,Blasticotomidae may form a sister group with(Argidae,Pergidae),and the support value of this relationship is range from93% to 98%.It is a traditional result to maintain the monophyly of Blasticotomidae,and the support value in the results of the mitochondrial genome and nuclear genome in this study reached 100% and 99% respectively.Therefore,the position of Blasticotomidae is more supportive of the traditional results in this study.Within Pamphilioidea,both BI and ML trees suggest that Pamphiliidae and Megalodontesidae form a monophyletic group with high support values(99%).However,the ML trees suggest a different topology of(Megalodontesidae,(Pamphiliidae,Unicalcarida)),with support values(59%-94%).The phylogenetic position of Pamphilioidea is stable and it forms a monophyletic group with Apocrita.Combined with the above results and previous studies,it is considered that the monophyly of the family Pamphilioidea is supported.Combined with the results of this study,according to the principle of monophyletic grouping,it is suggested that Hymenoptera be divided into eight clades: Xylomorpha,Tenthredinomorpha,Pamphiliomorpha,Xiphydriomorpha,Siricomorpha,Cephomorpha,Orussomorpha and Apocrita.