| Cheyletus malaccensis (Oudemans)(Acari:Cheyletidae), is a predatory mite widely distributed in nature as well as in agriculture fields and storages. It has been regarded as an important biological control species for pest mites, such as acarid mites, spider mites and gall mites, and therefore has important economic values. The aim of this study was to assess the phylogeographic structure of C. malaccensis using mitochondrial COI sequence as molecular marker, to investigate what had influenced C. malaccensis phylogeographic structure and to provide some theoretical basis for the control of pest mites in grain storages.The main results of this study are as follows:(1)116C. malaccensis individuals of14different geographic populations were sampled from grain storages in Southeastern China. The mitochondrial COI fragments were amplified and sequenced from all samples. As a result,39different COI haplotypes were detected, of which11were shared haplotypes from75%individuals. The aligned consensus COI fragment was709bases long. The number of variable sites was62, which accounted for8.74%of the total sites. Among the116COI sequences, the overall nucleotide diversity (pi) was1.987%, and haplotype diversity (Hd) was0.939. In each population, the nucleotide diversity ranged from0.094%to2.160%and haplotype diversity from0.600to1.000. In general, the genetic diversity was relatively high for all sampled populations.(2) The analysis of haplotype network revealed three well-supported clades:the A clade included13populations with19haplotypes belonging to69individuals; the B clade contained13populations with18haplotypes of38individuals; the C clade represented only3populations with2haplotypes from9individuals. The distribution of haplotypes in the haplotype network did not show clear correlation with geographical distribution. Both of the Bayesian and MP consensus trees showed three clades with the same topological structure and haplotype composition as revealed by the haplotype network. Moreover, in the Bayesian and NJ trees based on individuals, individuals from different geographical populations were mixed together without a clear geographical pattern. The results of haplotype network and phylogenetic trees indicated that there was no obvious phylogeographic structure for C. malaccensis.(3) In agreement with the above haplotype analyses, the AMOVA showed a significant differentiation between haplotype phylogenetic clades, in which89.01%of the total variation was among clades. The NJ tree based on population genetic distance revealed2big clades, with different geographical populations randomly distributed in different clades. In addition to the topological structure of the NJ tree, paired-wide genetic distance between populations in different clades was mostly larger than those within the same clade; among all the paired-wide Fst between populations,30.8%was significant and they mostly occurred between populations from different clades. These results suggested that, for C. malaccensis, significant genetic differentiation occurred among individuals, and most of the genetic differentiation occurred within populations.(4) Spatial structure analysis showed no significant correlation between genetic and geographical distance.During Pleistocene, individuals of C. malaccensis in different regions might have significantly genetic differentiation because of dramatic climate change, habitat heterogeneity and barriers to gene flow during a very long time period in geologic time scale. That may explain the clear genetic structure revealed by the haplotype network and haplotype phylogenetic trees. But recent anthropogenic disturbance may strongly change the historical genetic structure. The C. malaccensis individuals were sampled from grain storage in our study. The grain trade activities of human beings might promote the dispersal of C. malaccensis among different geographic populations, leading to increasing shared haplotypes among populations. The newly added haplotypes, may increase the genetic differentiation within populations and decrease that between populations, therefore the original phylogeographic structure was altered. So, the phylogeographic structure of C. malaccensis obtained in this study might be the results from both long period of natural historical and geographical effects and the recent human disturbance. |
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