Tetrigoidea Insect Mitochondrial Cytochrome B Gene Sequences And Phylogenetic Study

Tetrigoids are the more basal caeliferan group of Orthoptera insects.There are argument for their taxonomic positions, and unclear for thephylogenetic relationships of each group within the tetrigoids. To knowthe phylogenetic relationships of the Tetrigoids, we selected themitochondrial cytochrome b gene as a genetic marker of the phylogeneticanalysis. Fragments of mitochondrial cytochrome b gene of 22 tetrigoidstaxa(representing four of the families) and two outgroupCaerlifera, collecting from Guangxi, Yunnan, Sichuan, Chongqing, andShannxi provinces, were sequenced. The results showed that: 1) The sequenceobtained is 432 bp in length and contains 67.0% A+T, among them thepercentages of variable sites in the gene is 56.9%, and the percentage ofparsimony informative polymorphic sites is 45.1%. The third codonpposition contains 76.7% A+T. A comparison of A+T content of each sequencesand the third codon revealed that, Scelimenidae is similar to Metrodoidea,and Discotettigidae is similar to Tetrigidae. 2)The translated proteincoding sequences of Tetrigoidea is composed of 19 amino acids, but is shortof cysteine, comparing with the homologous sequences of the Acridoidea. Itwas found that an increase in A+T content may have been accompanied byan increase in amino acid sequence divergence. 3) There are distinctgenetic divergences among the different populations of Tetrix japonica.The rate of synonymous substitution is higher than the rate ofnonsynonymous substitution. The each population is on the rapidlydivergent period. Whether T. Joponica has diverged into differentsubspecies wi11 be further studied and confirmed. 4)0ur studies re1ativeto the four families of Tetrigoidea indicated that Sce1imenidaerepresents a primitive pattern, and Tetrigidae a more evo1ved one.Tetrigidae comes c1oser to Acridoidea in a genera1 way. The re1ationshipbetween Sce1imenidae and Metrodoridae is c1ose. Discotettigidae comesc1oser to Tetrigidae. Simultaneous1y, we suggested that the currentTetrigidae cou1d be divided into two fami1ies. 5) We found that themitichondria1 cytochrome b gene was a more effective gene on the phylogenystudy of Tetrigoidea. However, the genetic informations provided by the432bp fragment of mtDNA sequences couldn' t sufficient to reconstruct thecorrect phylogenetic trees. 1t is very necessary for the phy1ogeneticanalysis that increasing the number of taxon, reinforcing therepresentat ively, and compari sing more gene sequences, inc1uding thenuclear gene sequences.