Phylogenetic Analysis Of Cynipoidea Based On Mitochondrial Genomes

The Cynipoidea is a large superfamily with plenty of species distributed in all biogeographical regions.The biological habits are complex and diverse,Characterized by their parasitic,phytophagous and inquiline traits.It is an ideal group for the study of the evolution of biological traits of Hymenoptera.The phylogenetic relationships within Cynipoidea have always been controversial.The mitochondrial genome is considered to be an ideal molecular marker for phylogenetic research due to its stable gene composition,relatively conservative gene rearrangement,and maternal inheritance.At present,there are only six known mitochondrial genomes of this superfamily,so the sequencing and analysis of the mitochondrial genome of the superfamily is of great significance for revealing the evolution of mitochondrial genomes of the superfamily and its phylogenetic relationships.With the advancement of next-generation sequencing,the mitochondrial genomes of 26 species of the superfamily were sequenced and annotated.By combining four known mitochondrial genomes of other species in the superfamily,the characteristics of mitochondrial genomes,phylogenetic relationships and divergence time of the Cynipoidea were analysed.The main findings are as follows:(1)The lengths of the mitochondrial genomes of the superfamily Cynipoidea are14361-20386 bp,the longest is Anacharis sp.1,and the shortest is Ceroptres sp.All the mitochondrial genomes are tightly structured,and the genes ATP6-ATP8 and nad4-nad4 L have a 7-bp overlapping.Most of the protein-coding genes use ATN as the start codon,but nad1 of Ganaspini sp.,cox1 of Leptopilina heterotoma,nad4 L of Saphonecrus sp.,and ATP6 of Prosaspicera validispina use TTG as the start codon,which is rare in the protein-coding genes of other groups of Hymenoptera.Most of them use TAA or TAG as the stop codons,and a few ends with incomplete stop codons TA or T.(2)The AT contents in the mitochondrial genomes of the Cynipoidea are 79.3%?87.9%.The lowest is Trybliographa sp.,and the highest is Kiefferiella sp.Unlike the mitochondrial genomes of most insects that exhibit AT-skew and CG-skew,most of the mitochondrial genomes of Cynipoidea show TA-skew and CG-skew.The protein-coding genes,tRNA genes and rRNA genes of the mitochondrial genomes of the Cynipoidea all have rearrangements to some extent.The rearrangements of protein-coding genes are characterized by inversion,and the rearrangement hot spots are nad2,nad1 and nad5-nad4-nad4L-nad6-cob regions.The hot spots regions of tRNA gene rearrangements are concentrated in trnI-trnQ-trnM,trnA-trnR-trnN-trnS1-trnE-trnF,and the rearrangements occur randomly.rather than the rearrangement probability of tRNA genes between the protein coding genes in the non-hot spot regions is low.The rRNA gene rearrangements are also very frequent,and both translocation or remote inversion occurs.The Ka/Ks values of all species are greater than one,indicating that their protein-coding genes have been subjected to positive selection during the history of evolution.(3)The phylogenetic relationships within Cynipoidea were analyzed based on mitochondrial genomes.The results showed that Figitidae was recovered as a polyphyletic group while Ibaliidae,Cynipidae and Liopteridae were robustly recovered as monophyly in all analyses.(4)We estimated that the origin of Cynipoidea was 219.46 Mya;the diverging time of phytophagous and inquiline cynipid wasp were 84.47 Mya.