Study On The Phylogeny Of Coccinellidae Based On Comparative Mitochondrial Genomics

Family Coccinellidae is subordinate to a diverse superfamily of beetles,Coccinelloidea(Coleoptera,Ployphaga).There are about 6000 species in over 400 genera all over the world.Currently,the classification system of Coccinellidae is still not satisfied.Different subfamilies of the ladybird beetles are recognized.At present,systematics of Coccinellidae lags behinds and needs a detailed revision.Characters of subfamilies and tribes in this family are poorly understood and the taxonomic system is not suitable.Moreover,relationships among tribes are still poorly understood.In order to restablish a rational systematic system of the family Coccinellidae,the phylogeny and character evolution were analyzed in this study based on mitochondrial genome with the characteristics of short genome size,stable gene content,uniparental inheritance and lack of extensive recombination.The results of this study will be of great significance in tracking the origin and evolution of ladybird,and will provide important theoretical basis for the study of Coccinellidae.In this thesis,263 species belong to 89 genera within 25 tribes of Coccinelllidae were collected from 14 countries in Asia,Europe,Australia,North America,South America and Africa.With the method of genomic sequencing for PCR(Polymerase chain reaction)amplification products,the sequence of protein coding region was obtained.Mitochondrial genome of other 24 species within 18 genera under 7 tribes of Coccinellidae and 6 species in3 families and 3 superfamilies of outgroups were downloaded from Gene Bank.In addition,10 morphological characteristics and food habits were selected and analyzed.Main results are summerized as follows:(1)The completed coding region of 214 species in 81 genera under 25 tribes were obtained.Among them,59 species of completed mitochondrial genome were obtained.This study used gene annotation on MITOS webserver for each genome,and gene content of each genome,intergenic region,and codon usage were analyzed.The structure characteristics of mitochondrial genomes were closed circular double stranded DNA,length of 14-19 kbs.Mitochondrial genomes contain 13 protein-coding genes(PCGs),22 transporter RNA(t RNAs)and 2 ribosomal RNAs(r RNAs),that is a typical set of 37 genes and A+T rich regions.The mitochondrial genome of Coccinelllidae is compact in structure,but the length of non-coding region varies from 3 to 3500 bp.The structure of protein coding was relatively stable,but the transporter RNA and ribosomal RNA had some variation.Distance between trn I and trn Q of Chilocorini,Coccinellini,and Psylloborini was from 663 to 3017 bp.Tandem repeat sequences of 6 genes occurred in the trn C of Scymnus(Pullus)tenius,namely 28 t RNAs.The trns of Acarinus aretusis occurred repeatedly,namely 23 t RNAs.Whereas Parexochomus oligotrichus,Platynaspis tricolor,Vibidia duodecimguttata and Illeis confusa were lacking in t RNA.(2)Using the methods of maximum likelihood,Bayesian and maximum parsimony,the phylogenetic tree was constructed based on 15 genes in 244(Gen Bank 30)specimens with RAx ML,Mrbayes,and PAUP software,respectively.It was confirmed that Coccinellidae was monophyletic and sister group with Endomychidae.The phylogenetic relationship at the tribe-level confirmed that the tribes Ccccinellini,Epilachini,Sticholotidini,Coccidulini,Argentipilosini and Scymnini were not monophyletic.On the contrary,the tribes Psylloborini,Singhikalinini,Stethorini,Chilocorini,Shiirozuellini,Plotinini,Ortaliini,Aspidimerini,Hyperaspini(Hypersaspis),Platynaspini(Platynaspis),Crytognathini,Serangiini,Noviini(Rodolia),Telsimini(Telsimia),Monocorynini,Subcoccinellini and Epivertini were monophyletic.(3)In order to elucidate the phylogenetic relationship of Coccinellidae,the ML and BI trees were constructed based on 15 genes of mitochondrial genome.The result suggested that Coccinellidae can be divided into 5 subfamilies including 27 tribes: Subfamily Microweiseinae Leng,1920(comprise of tribes Microweiseini Leng,Serangiini Pope,Carinodulini Gordon et al.and Sukunnahikonini Kamiya);Subfamily Monocoryninae subfam.nov.(Tribe Monocorynini);Subfamily Noviinae subfam.nov.(comprise of tribes Noviini Gangelbauer,Tesiminni Casey,Horniolini trib.nov.and Axinoscymnini trib.nov.);Subfamily Scymninae Mulsant,1846(comprise of tribes Scymnini Costa,Cryptolaemini trib.nov.,Platynaspini Mulsant,Hyperaspini Costa,Aspidimerini Mulsant,Argentipilosini Gordon & Almeida,Ortaliini Mulsant and Epilachnini Mulsant);Subfamily Coccinellinae Mulsant,1850(comprise of tribes Coccinellini Latreille,Coccidulini Kugelann,Shirozuelolini Sasaji,Stethorini Dobzhansky,Chaetolotisini trib.nov.,Boschalini trib.nov.,Sticholotidini Weise,Plotinini Miyatake,Sumnini trib.nov.and Chilocorini Mulsant).(4)Based on 10 morphological characteristics and food preference of 238 species in 87 genera under 26 tribes,character evolution of Coccinellidae was analyzed using Mesquite(3.2 version)software with the method of Bayesian tree.The following ancestor characters of Coccinellidae are recongnized: dorsum with apparent setae at least on pronotum or elytra,clypeus without expanded laterally,eyes emarginate absent,protarsus 4-segmented,abdominal postcoxal line incomplete and predaceous.The characteristics of dorsum apparently glabrous,clypeus with expanded laterally,eye emargination present,hind tibia with spur,protarsus 3-segmented,abdominal postcoxal line complete,herbivorous and fungivorous were convergent evolution.These morphological characters are key diagnostic characteristics used as the classification evidences,but they do not have the significant importance of systematics.In addition,these morphological characters including;mandible,maxillary terminal palpomere,antennae segments and prosternal carina were not confirmed as the ancestral characters.