Comparative Mitogenomics And Phylogenetics Of Ichneumonidae(Hvmenoptera:Aculeata)

The family Ichneumonidae(Hymenoptera:Apocrita)is one of the largest families in the animal kingdom.More than 25,000 species have been described and they are divided into 42 existing subfamilies,more than 50 tribes and 1,500 genera.The larvae are either parasitoids or hyperparasitoids,and usually attack holometabolous insects and spiders.The ichneumonids,also named as "Darwin wasps",have multi-interpretable diverse morphological and biological characteristics,which have given rise to the controversy on the phylogeny of the subfamilies in Ichneumonidae.Mitochondrial genome has been widely used to the phylogeny in insects,and it is often regarded as phylogenetically relevant due to their frequent gene rearrangements in Hymenoptera.However,the mitochondrial genomes of Ichneumonidae have rarely been sequenced considering the size of the group,resulting in that their general features and phylogeny unclear.Our study sampled the representative species of different subfamilies of Ichneumonidae,and obtained 96 newly sequenced mitochondrial genomes.Combined with data from GenBank,the general and comparative features of mitochondrial genomes of 104 species from 88 genera and 33 subfamilies of Ichneumonidae are analysed,and the phylogeny of the subfamilies of Ichneumonidae based on mitochondrial protein-coding gene sequences are reconstructed.The main results are as follows:(1)For the majority strand of mitochondrial genomes in most ichneumonid species,the A+T contents are higher than 80%,and the GC-skew values are negative,that is,G is less than C.In terms of codon and amino acid usage bias,Leu is the most frequently used amino acid with occasional exceptions;the codon usage towards to NNA and NNU,and UUA which is encoding for Leu is the most frequently used codon.Most genes frequently used ATT and TAA as start and stop codons,respectively.Specifically,atp6 and nad4 used ATG more than ATT,cytb and nad3 used TAG more than other stop codons.All of tRNAs have the same anti-codons except for the trnK of Tersilochinae and Nesomesochorinae.Finally,there is little substitution saturation and a low evolutionary rate for the mitochondrial protein-coding genes.(2)The mitochondrial gene order of Ichneumonidae is more conservative than that of other species in Apocrita.There are 38 types of gene rearrangements in ichneumonid wasps,and almost all of the rearrangement events occurred on tRNA genes with a few exceptions.The most frequent type(46 times)included only two tRNA genes rearrangements:trnM is transposed from position between trnQ and nad2 to the front of trnI;trnC and trnY are shuffled and switched positions.This type is not found in the basal group Brachycyrtiformes,so it is inferred that the rearrangement type may occur after the division of this group.In addition,higher Ophioniformes,including Ophioninae,Nesomesochorinae,Campopleginae and Anomaloninae,share a trnL2 transposition where trnL2 is transposed from the position between coxl and cox2 into the cluster trnM-trnI-trnQ.It is implied that subfamilies Hybrizontinae and Cremastinae which have a similar rearrangement may be phylogenetically close to higher Ophioniformes.(3)The mitochondrial gene sequences are used to reconstruct the phylogeny of subfamilies in Icheneumonidae.Five high-level groupings are confirmed:Brachycyrtiformes,Ichneumoniformes,Ophioniformes,Pimpliformes and Xoridiformes,and their relationship is(((Pimpliformes+Ichneumoniformes)+Ophioniformes)+Xoridiformes)+Brachycyrtiformes);two formerly unplaced subfamilies,Eucerotinae and Microleptinae,are placed in Brachycyrtiformes and Ichneumoniformes,respectively.The basal subfamilies of the following high-level groupings are proposed that Acaenitinae is the sister group of other Pimpliformes,Agriotypinae was the sister group of other Ichneumoniformes,a part of Tryphoninae is sister to other Ophioniformes;finally,it is confirmed that the subfamilies Pimplinae,Orthocentrinae,Ctenopelmatinae,Metopiinae,Phygadeuontinae and Tryphoninae are paraphyletic groups.(4)Ichneumonidae originated approximately 135Mya,in the early Cretaceous.The rapid radiations resulting in the extant subfamilies occurred until the Paleogene.The ancestors of Ichneumonidae were inferred to be idiobiont ectoparasitoids.Within the Ichneumonidae,four changes likely took place from idiobiont to koinobiont parasitism,and nine transitions from ectoparasitism to endoparasitism may occur.