| The complete mitochondrial genome sequences of three subterranean termites, Reticulitermes aculabialis Tsai et Hwang, R. labralis Hsia and R. chinensis Snyder, were determined in this research. Based on PCGs、 rRNAs and PCGs & rRNAs data sets of the results of assembling and annotation in these three species, together with mitochondrial genome of other termite species deposited in GenBank database, the phylogenetic relationship of Isoptera were reconstructed by using Maximum parsimony (MP), Maximum likelihood (ML) and Neighbor joining(NJ) methods. In addition, genetic diversity within populations, breeding systems, reproductive strategies in 15 colonies of R. aculabialis in Xi’an were estimated. These informations provided academic reference for control and utilizeition of R. aculabialis. The results were as follows:(1) The mitochondrial genome size of R. aculabialis, R. labralis and R. chinensis were 16475 bp,16113 bp and 15925 bp, respectively. They encoded 13 protein-coding genes (PCGs),2 ribosomal RNA genes (rRNAs),22 transfer RNA genes (tRNAs) and a control region (CR). The base size of CR was different.(2) The nucleotide compositions of mitochondrial genomes of R. aculabialis, R. labralis and R. chinensis were biased toward adenine and thymine, and the A+T omposition of mitochondrial genomes were 65.8%,65.1% and 65.3%, respectively. Coding genes (PCGs, tRNAs & rRNAs) of R. aculabialis, R. labralis and R. chinensis were 14688 bp,14689 bp and 14687 bp accordingly, which accounted for 89.15%,91.16% and 92.23% of the whole mitochondrial genomes, respectively.(3) The majority of the control region (CR) was consisted of 2 sets of repeat units (A and B). The gene lengths of CR were 1679 bp,1311 bp and 1125bp in R. aculabialis, R. labralis and R. chinensis, respectively. The A+T omposition of CR accounted for 69.8%, 65.98% and 67.02%, respectively. The A+T-rich control region located between srRNA and tRNAIle. The CR of R. aculabialis was consisted of 2 full and 1 partial copies of A and B, while R. labralis was 3 full and 1 partial copies of A,1 full and 1 partial copies of B, and R. chinensis was 2 full and 1 partial copies of A,1 full and 1 partial copies of B.(4) The determined mitochondrial genome sequences of the three species all contained overlap regions and intergenic spacers. R. aculabialis contained 6 overlap regions spinning 24 bp and 17 intergenic spacers spanning 108 bp. And, there were 6 overlap regions spinning 23 bp, and 17 intergenic spacers spanning 113 bp both in R. labralis and R. chinensis.(5) Except for tRNASer(AGN) which lacked a DHU arm, and had a highly expanded extra arm, tRNATyrwhich had a nonstandard TψC arm, tRNASer(UCN) which had a nonstandard DHU arm, all of the tRNAs gene of R. aculabialis, R. labralis and R. chinensis had typical clever-leaf structures. There were some unmatched base pairs in all tRNAs secondary structure in the three species, and the main unmatched base pairs were GU.(6) Phylogenetic relationship of Isoptera were reconstructed using the ML, NJ and MP methods based on the combined dataset of nucleotide sequences of 13 protein coding genes, rRNA genes (srRNA and lrRNA) and PCGs & rRNAs. The results showed that Termitidae, Rhinotermitidae and Serritermitidae had a closer relationship. This produced an inconsistent conclusion with Engel et al. (2009), which believed that Termitidae had a closer relationship with Serritermitidae by morphological analysis, In the phylogenetic tree, some rhinotermitid species mixed with Serritermitidae, indicating that these species might have different taxonomic status. As for 3 local Reticulitermes species, all the 9 phylogenetic trees constructured by three methods showed that R. labralis and R. chinensis have a closer relationship; R. aculabialis had a farther relationship to R. labralis and R. chinensis.(7) 6 microsatellite markers suited for R. aculabialis were selected from 26 microsatellite markers and used to analyze the genetic diversity of 15 R. aculabialis populations.17 alleles were found in 6 microsatellite markers, and 2.833±0.753 average alleles in each locus were detected. The effective number of alleles was 1.421-3.318. The average value of gene expected heterozygosity and observed heterozygosity of 6 microsatellite loci was 0.504±0.163 and 0.468±0.206, respectively. There were no obvious differences between the observed heterozygosity and expected heterozygosity (t11=7.35, P=0.268), but there was a linear relationship between observed heterozygosity and expected heterozygosity (r=0.954, P=0.003<0.01).(8)Analysis of worker genotypes within 15 colonies of R. aculabialis in Xi’an indicated that 11 colonies were simple (Mendelian) families. The remaining four colonies were consistent with being extended families, there was not mixed family.(9) Colony and population genetic structure were investigated by estimating F-statistics. We found that observed F-values were not consistent with expected F-values. This situation was likely to arise when colonies were represented by a mixture of breeding systems, with no single type of colonies predominating. There were only 4 extended families in the 15 colonies, indicating that an AQS system might existed in R. aculabialis. Although there were multiple neotenic (secondary) reproductives descended from the original king and queen, genotype of neotenic reproductives were all homozygotes, so we cannot determine the number of neotenic reproductives. |
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