Phylogeny Of Partial Species Of Aquatic Beetles Based On MtDNA Sequences

A 485 base pair region of the mitochondrial cytochrome b gene was sequenced for nine species of aquatic beetles,representing four families.All sequences were aligned using Clustalx1.8 software and molecular phylogenetic trees were constructed using Mega2.1 software and PHYLIP software package.First from the molecular level,the phylogenetic relationships of the nine aquatic species were discussed in this research.1. There were total eleven sequences:four of them belongs to Dytiscidae three species (R.suturalis Macleay, H.grammicus Cermar, A.japonicus Sharp); three belongs to Hydrophilidae(A mater Sharp, B. elogatulus Jorden , H. acuminatus Motschulsky); two is P.chinensis Falkenstroem and H.chinensis Falkenstroem representing Haliplidae; one is Oretochilus. sp(Gyrinidae),and the last sequence is from the outgroup: G.stercorarius Linnaeus.2.Processing and analysing all sequences with ContigExpress , Clustalxl .8 , Megalign and Mega2.1 softwares and PHYLIP software package.Through Mega2.1 software ,some useful statistical data set could be obtained and the phylogenetic trees were constructed by three distance-matrix methods(UPGMA, N-J, ME).Meantime,maximum parsimony(MP) and maximum likelihood(ML) methods were also used in PHYLIP.3.Compared with the divergence of mtDNA Cytb 485bp sequences in interspecies,the nucleotide variation of intraspecies is lower .The average content of A, T, C, G of Dytiscidae three species is 38.6%,33.1%, 12.0% and 16.3% respectively.From the data , it could be inferred that the average A+T content(A+T%=71.7%) is higher than that of G+C(G+C%=28.3%).As far as each amino acid codon is concerned,the third codon site has the highest A+T content,arriving at 90.6%.4.Phylogenetic relationships in the Hydrophilidae three species was determined by the sequence of the Cytb gene. The result indicated that the nucleotide variation of these three species is higher than that of Dytiscidae three species.Thereby,the conclusion was drawn that the relationship among Hydrophilidae three species is not so close as Dytiscidae three species.5.On the whole,the mean A+T content of the nine aquatic beetles are all higher .As to each amino acid codon ,the highest A+T content lies in the third site .Meanwhile, the study also showed that most tranversion is higher than transition and the transition between A and G happens more frequently than others;the tranversion of A and T is also more frequent.6.In general.the molecular phylogenetic trees constructed by three ways are consistent except for P.chinensis Falkenstroem(IVA), H.chinensis Falkenstroem (CKS3). So,it was necessary to have more investigation on the phylogenetic relationship of P.chinensis Falkenstroem(IVA) and H. chinensis Falkenstroem (CKS3).The relationships in the nine species drawn from the phylogenetic trees are also essentially identical with the traditional morphological taxonomy.7.This research provided the phyligenetic relationships of nine aquatic species,representing four families.The conclusions were as follows:1)Haliplidae is basal to Dytiscidae and Gryrinidae which two belong to sister group. 2)A.japonicus Sharp diverges first from another three individuals (Dytiscidae) that aremonophyletic and closely related to each other .3)Among Hydrophilidae three species,H .acuminatus Motschulsky separates first from another two species,so it is less closely related to them . In total,the present study provided the phylogeny of partial families and species ofaquatic beetles from molecular level.