Studies On The Comparative Mitochondrial Genomics And Phylogeny Of Neuropterida

Neuroptera (lacewings) and allied orders Megaloptera (dobsonflies, alderflies) and Raphidioptera (snakeflies) are predatory insects and together make up the clade Neuropterida. The higher-level relationships within Neuropterida have historically been widely disputed with multiple competing hypotheses. Moreover, the evolution of important biological innovations among various Neuropterida families, such as the origin, timing and direction of transitions between aquatic and terrestrial life histories of larvae remains poorly understood.Mitochondrial (mt) genomes have been used as an effective marker to study phylogeny of different taxonomic levels in the past decades with the rapid development of DNA sequencing and analytical methods, because of advantages such as the gene conservation, generally unambiguous orthology of genes and the rarity of changes in the genome, including gene rearrangements, indels and mutations.To investigate the origin and diversification of Neuropterida, we conducted a large scale sequencing of Neuropteridan mt genomes, and determined the mt genomes of 25 specimens of Neuroptera,3specimens of Megaloptera as well as 3 specimens of Raphidioptera. The mt genomes of many key groups were firstly determined, such as Coniopterygidae, Nevrorthidae, Sisyridae, Berothidae, Rhachiberothidae, Rapisma Cryptunumatidae, Hemerobiidae, Dilaridae, Nemopteridae, Psychopsidae, Chauliodinae, Inocelliidae and so on. Based on these datasets, the structural traits and evolution of Neuropteridan mt genomes were analyzed using comparative genomic and bioinformatics methods. Besides, we reconstructed the phylogeny of Neuropterida using complete mt genomes. Conclusions were drawn as below:(1) There is some relevance between the gene overlaps of the Neuropteran mt genomes and specific genes. The most stable overlaps in the mt genomes of Neuropteran insects were located at ATP8-ATP6 and ND4-ND4L and most species had 7 bp overlaps between these two gene pairs, which are ATGATAA and TTAACAT, respectively.(2)Some mt genomes of Neuroperidan species had extremely large non-coding gaps between the gene cluster tRNAIle-tRNAGln-tRNAMet, such as the gap between tRNAIle-tRNAGln in Drepanepteryx phalaenoides was 106 bp, in Balmes birmanuswas 679 bp, while in Chasmoptera huttii even reached 883 bp. The reason why these large non-coding gaps except for control region appear and what are the functions of them still needs more studies to determine.(3)The gene arrangement of Neuropteran mt genomes is very conservative. Megaloptera, and Raphidioptera Only some families of Neuroptera have the translocation of trnCfrom its traditional downstream location to the upstream location of trnW (i.e., CWY),and is found here to be a synapomorphy for the derived clade including all neuropteran families except Coniopterygidae, Nevrorthidae,Sisyridae, and Osmylidae. Coniopterygidae, Nevrorthidae, Sisyridae and Osmylidae share the ancestral gene arrangement (WCY) with and Neuropteroidea.(4) The heterougous composition of Neuropteran mitochondrial genes and the distinctive diversity of this group contributed the systematic errors in the progress of phylogenetic reconstruction. Under the site-homogenous models, the phylogentic trees recovered using MP, BI (GTR) and ML all supported the paraphyletic Neuroptera with Coniopterygidae being the sister group of Raphidioptera. However, based on extensive morphological and molecular evidence for the monophyly of Neuroptera, we see the result recovering Coniopterygidae outside Neuroptera as extreamly implausible. Only under BI using the site-heterougous model (CAT-GTR) do we recover a monophyletic Nerouptera with Coniopterygidae as the sister to all the rest of the order, decreasing the systematic errors caused by the heterougous composition of mitochondrial genes.(5)The monophyly of Neuropterida, Neuroptera, Megaloptera and Raphidioptera as well as the sister relationship between Neuroptera and Megaloptera were confirmed in this study. The sister family of all other lacewings are the Coniopterygidae, diverged from early Permian. Nevrorthidae and Sisyridae are aquatic and diverged relative early in Neuroptera. Osmilidae were recovered to be the sister to all the families except Coniopterygidae, Nevrothidae and Sisyridae. The monophyly of all families except Coniopterygidae, Nevrothidae and Sisyridaeare confirmed and the tRNACysof these families translated from its traditional downstream location to the upstream location of tRNATrp. returned to their traditional position as sister-group of the spongilla-flies () and closely related to Osmylidae. Our divergence time analysis indicates that the Mesozoic was indeed a ’golden age’ for lacewings, with most families of Neuropterida diverging during the Triassic and Jurassic and all families present by the Early Cretaceous. Based on ancestral character state reconstructions of larval habitat we evaluate competing hypotheses regarding the life history of early Neuropterida as either aquatic or terrestrial. Dilaridae were the sister to all the rest families. The clade of Mantispidae, Berothidae and Rhachiberothidae was monophyly, diverged from early to middle Triassic. Berothidae was the sister to Mantispidae, together being the sister to Rhachiberothidae. The clade comprising Chrysopidae, Hemerobiidae, Ithonidae and those families included typically in Myrmeleontiformia was monophyly and originated during the Middle to Late Triassic and represent a major shift in larval head capsulesclerite architeture. Chrysopidae was confirmed to be the sister to Hemetobiidae, and diverged from it during late Triassic. Ithonidae was the sister to Myrmeleontiformia. The monophyly of the Myrmeleontiformia was confirmed. Psychopsidae was the sister to all the rest families of Myrmeleontiformi, followed sequentially by Nymphidae and Nemopteridae, with Myrmeleontidae sister to Ascalaphidae as the most derived grouping. Surprisingly, Myrmeleontidae are rendered paraphyletic with respect to Ascalaphidae here. As for the reason and whether Myrmeleontidae was paraphyletic still needs more samples of these two families to study and discuss.